How to configure Remote Assistance Step By Step Guide

Remote assistance is a cool feature of XP to get help from other. You could generate a help request and send it to your network administrator for assistance. In this article we would generate a help request and get assistance.

Sending a remote assistance request

Remote Assistance feature enable users to call for help. This is especially helpful when your client is living in remote area.

Before an administrator can render assistance, the end user must send a Remote Assistance request to the administrator.

Clients should follow these steps to send a Remote Assistance request:

• Click Start.
• Click Help and Support.

Select the Invite A Friend To Connect To Your Computer With Remote Assistance link (found beneath the Ask For Assistance heading). The Remote Assistance menu appears.

Click the Invite Someone To Help You link.

users seeking for help can either send an invitation through Windows Messenger or Microsoft Outlook or save invitation .

Click on save invitation as a file (Advance)

You should enter your name and set the invitation's expiration period and click Continue.

Specify a location for the remote assistance file and click Save.

Windows will save the remote connection file (named RAInvitation.msrcincident by default) to the location the end user specify;

you will have to forward it to the administrator or support technician.

login from your e-mail account

Aattach invitation and send mail

Administrator should login from his e-mail account

Open the mail contaning invation

Now download the invitation

Once the remote assistance invitation is downloaded, administrators can follow these steps to render assistance:

• To accept the Remote Assistance invitation, the administrator should double-click the attachment. Before doing so, it's a good idea for the administrator to confirm the user, in fact, sent the request. When doing so, the administrator can learn the password the client entered for the remote assistance request.
• Upon double-clicking the attachment, the administrator will have to supply the password and click OK

The client will receive a dialog box stating that the administrator wishes to connect to the user's desktop. The client must click Yes to enable the connection.

Now administrator can provide text base help

• If the administrator wishes to take control of the user's system, the administrator can click the Take Control icon that appears at the top of the Remote Assistance window.
• Once the administrator or support technician has clicked Take Control, the end user will see a dialog box stating that the user providing the assistance would like to share control of the computer to solve the problem. The user must click Yes to permit the support tech with access. When the remote user clicks Yes, the staff member providing support will receive a confirmation message stating the helper is now in control of the user's desktop. To surrender desktop control, the administrator need only press the Esc key; the end user can terminate the administrator's control at any time byPressing the Esc key (or disconnecting the session using the Disconnect button from the Remote Assistance menu).

Having the ability to view or actually control a remote user's desktop drastically simplifies troubleshooting and repair operations. All the end user must do is send the Remote Assistance request to an administrator. The administrator or support tech needs only to connect to the remote system and perform diagnostic actions and repairs. The user and support tech can exchange chat messages with one another using the provided window.

Confirming proper firewall configuration

Occasionally Remote Assistance connections fail to connect. A typical culprit, ironically, is Windows' own firewall. Note that the Windows Firewall (installed by default with Windows XP Service Pack 2) must be properly configured to enable connectivity.

Follow these steps to confirm Windows Firewall isn't blocking Remote Assistance connections:

• Click Start.
• Click Control Panel.
• Click Windows Firewall.
• Select the Exceptions tab.
• Ensure the Remote Assistance box is checked.

How to configure Gmail With Microsoft outlook Express

Outlook express is the most popular e-mail client. It is inbuilt mail client on all window operating system. In this article we would configure Gmail with outlook.

Enable POP in Gmail

You can retrieve your Gmail messages with a client or device that supports POP, like Microsoft Outlook or Netscape Mail. For this you need to enable POP in your gmail account.
To enable POP in Gmail:

• Sign in to Gmail.
• Click Settings

Click Forwarding and POP/IMAP 

• Select Enable POP for all mail or Enable POP for mail that arrives from now on.
• Choose the action you would like Gmail to take after they are accessed with POP.

Configure your POP client* and click Save Changes

Set up Outlook Express to work with Gmail:

• Open Outlook or Outlook Express.
• Click the Tools menu, and select Accounts...
• Click Add and then click Mail...

• Enter your name in the Display name: field, and click Next.
• Enter your full Gmail email address (username@gmail.com) in the Email address: field, and click Next.

Enter pop.gmail.com in the Incoming mail (POP3, IMAP or HTTP) server: field. Enter smtp.gmail.com in the Outgoing mail (SMTP) server: field.

• Click Next.
• Enter your Gmail username (including '@gmail.com') in the Account name: field. Enter your Gmail password in the Password field:, and click Next

• Click Finish.
• Highlight pop.gmail.com under Account, and click Properties.

• Click the Advanced tab.
• Fill in the following information:

• Check the box next toThis server requires a secure connection (SSL) under Outgoing Mail (SMTP).
• Enter 465 in the Outgoing mail (SMTP): field.
• Under Outgoing Mail (SMTP), check the box next toThis server requires a secure connection (SSL).
• Under Incoming mail (POP3), check the box next to This server requires a secure connection (SSL). The port will change to 995.

Return to the Servers tab, and check the box next to My server requires authentication. 
Click OK.

Repeatedly prompted for your username and password or 'invalid credentials' error.

Enable POP in Gmail. Clear the captcha. If you're a Google Apps user, visit 
https://www.google.com/a/yourdomain.com/UnlockCaptcha. 
Be sure to replace 'yourdomain.com' with your actual domain name.

Gmail Error Message

The connection to the server has failed. Account: 'Gmail', Server: 'pop.gmail.com', Protocol: POP3, Port: 110, Secure(SSL): Yes, Socket Error: 10060, Error Number: 0x800CCC0E.

On the Advanced tab of your POP client, set Incoming mail (POP3): to 995.

Gmail Error Message

The message could not be sent because the server rejected the sender's e-mail address. The sender's e-mail address was 'example@gmail.com'. Subject 'example', Account: 'pop.gmail.com', Server: 'smtp.gmail.com', Protocol: SMTP, Server Response: '530 5.5.1 Authentication Required f45sm8616pyh', Port: 25, Secure(SSL): Yes, Server Error: 530, Error Number: 0x800CCC78.

On the Servers tab of your POP client, Enable My server requires authentication beneath Outgoing Mail Server.

Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'pop.gmail.com', Server: 'pop.gmail.com', Protocol: POP3, Port: 995, Secure(SSL): No, Error Number: 0x800CCC0F.

On the Advanced tab of your POP client, enable This server requires an encrypted connection (SSL) for the POP server.

Gmail Error Message

Your SMTP server has not responded in 60 seconds. Would you like to wait another 60 seconds for the server to respond? A time-out occurred while communicating with the server. Account: ' pop.gmail.com', Server: 'smtp.gmail.com', Protocol: SMTP, Port: 465, Secure(SSL): No, Error Number: 0x800CCC19.

On the Advanced tab of your POP client, enable This server requires an encrypted connection (SSL) for the SMTP server.

Gmail Error Message

The host 'smpt.gmail.com' could not be found. Please verify that you have entered the server name correctly. Account: 'pop.gmail.com', Server: 'smpt.gmail.com', Protocol: SMTP, Port: 465, Secure(SSL): Yes, Socket Error: 11001, Error Number: 0x800CCC0D.

On the Servers tab, change smpt.gmail.com to smtp.gmail.com.

Gmail Error Message

An unknown error has occurred. Account: 'Gmail', Server: 'pop.gmail.com', Protocol: POP3, Port: 995, Secure(SSL): Yes, Error Number: 0x800C0133.

In your POP client, click File > Folder > Compress All Folders.

How to configure Microsoft Outlook Express step by step guides

Microsoft Outlook Express is delivered with windows. With Outlook Express you could create, get, send email directly from window. It allows you to store email in local system so you could read them even while you are offline. You could compose messages in offline mode. Messages which created in offline mode would automatically be sent while you become online.

Microsoft Hotmail no longer allows you to configure Outlook Express with its free account. You have two options to resolve this.

• Use Method 1 for Outlook Express.
• Use Method 2 for Outlook 2003 and for Outlook 2007.

Method 1: Use Windows Live Mail instead of Outlook Express

Window Live Mail is a nice and free e-mail program offered from Microsoft. It works in the same way of Microsoft Outlook Express. Use following link to download and configure Window Live Mail.

http://windows.microsoft.com/en-US/windows-live/essentials-other-programs

Method 2: Use Outlook 2003 and Outlook 2007 together with the Outlook Connector

• Close Outlook if it is opened.
• Download and install the Outlook Connector
• When prompted to open or save the file, click Open.
• When prompted to run the software, click Run.

 
You may see a security prompt, depending on which operating system or Web browser you use. If you see such a dialog box, you must click the option to continue with the installation.

Follow the instructions on your screen to complete the installation.
The next time when you start Outlook, you are prompted to configure the Outlook Connector. Enter the following information:
and Click OK.

• Your e-mail address
• Your password
• Your name as you want it to appear in the receiver's Inbox

Outlook main window would appear once you entered all necessary information. On main window by default you have two panes. In left pane you would see the shortcuts of mail folders, calendar, contacts and tasks. In right panes you would see the details of mail.

To Synchronize mail Click on send/receive

To view the status of account click on Server status

Add an additional Windows Live Hotmail account

• On the Outlook Connector menu, click Add a New Account.
  ( Note:- The Outlook Connector menu only appears if the Outlook Connector is installed.)
• Enter the following information:

• Your e-mail address
• Your password
• Your name as you want it to appear in the receiver's Inbox

• Click OK.
• A dialog box appears to notify you that you must exit and restart Outlook to see the new account. Click OK.

Remove a Windows Live Hotmail account

Office Outlook 2007

• On the Tools menu, click Account Settings. 
  On the E-mail tab, click the Windows Live Hotmail account which you want to remove.
• Click Remove.
• Click Yes to confirm that you want to remove the account.
• Click Close.

Office Outlook 2003

• On the Tools menu, click E-mail Accounts.
• Select View or change existing e-mail accounts, and than click Next.
• On the E-mail tab, click the Windows Live Hotmail account, and than click on Remove.
• Click Yes to confirm that you want to remove the account.
• Click Finish.

Update a Windows Live Hotmail account password

If you change Windows Live Hotmail account password, you must have to update the information in Outlook. 
Follow the instructions for the version of Office Outlook you are using.

Office Outlook 2007

• On the Tools menu, click Account Settings.
• On the E-mail tab, click the Windows Live Hotmail account you want to update.
• Click Change.
• On the E-mail tab, click the Windows Live Hotmail account, and than click Change.
• In the Password box, type your new password.
• Click OK.
• On the Account Settings dialog box, click Close.

Office Outlook 2003

• On the Tools menu, click E-mail Accounts.
• Select View or change existing e-mail accounts, and than click Next.
• On the E-mail tab, click the Windows Live Hotmail account, and then click Change.
• In the Password box, type your new password.
• Click OK.
• On the E-mail Accounts dialog box, click Finish.

To remove Outlookconnector:

• On the Start menu, point to Settings and then click Control Panel.
• Double-click Add/Remove Programs.
• In the list of currently installed programs, select Microsoft Office Outlook Connector and click Remove or Add/Remove.
• If a dialog box appears, follow the instructions to remove the program.
• Click Yes or OK to confirm that you want to remove the program.

Peer to Peer Workgroup Network Error Description Solutions

In our previous articles we have configured our workgroup network. We have also listed most common errors with their possible solutions those might have occured during the workgroup configuration.

In this article we would use a step by step approach for troubleshooting workgroup.

For troubleshooting workgroup windows xp network we would use inbuilt tool of xp. To use inbuilt Networking Troubleshooter follow these steps:

• Click Start, and then click Help and Support.
• Under Pick a Help Topic, click Networking and the Web.
• Under Networking and the Web, click Fixing networking or Web problems, and then click Home and Small Office Networking Troubleshooter.
• Answer the questions in the troubleshooter to try to find a solution.

If the troubleshooter resolves the issue, you are finished. 
If the troubleshooter does not resolve the issue, than go through the process given below

Home-network structures and their configurations

Before you troubleshoot home networking issues, first determine the network structure you are using. The network structure is the arrangement or mapping of network elements such as links and nodes, and the physical connections between them. There are several common home-network structures:

Computers that are connected to a NAT device

The computers are connected to a NAT device that provides a single, shared Internet connection. A hardware network address translation (NAT) device is a broadband or satellite modem that enables the computers to obtain and share a single connection. In this configuration, computers generally receive an IP address from the NAT device. Typically, the NAT device uses the address 192.168.1.1 and assigns addresses to other computers in the range 192.168.1.x, where x is a number between 2 and 254.

Computers that are connected to a network hub

A network hub receives data through one port, and then makes it available to all ports. This enables data sharing or Internet connection between all computers that are connected to the hub. Computers that are connected to a network hub can have many configurations:

The computers have no Internet connection.

In this configuration, the computers are generally assigned IP addresses in the range of 169.254.x.y, where x and y are numbers between 1 and 254.

The computers are connected to a hub,

Where only one computer has Internet connection shared by using Internet Connection Sharing.

This connection can be a dial-up connection or a broadband connection (typically xDSL or a cable modem). 
In this configuration, the computer that shares the connection generally assigns IP addresses to other computers on the home network. The computer that is sharing the connection will have IP address 192.168.1.1 configured for the adapter that is connected to the home network. Other computers on the network will have addresses in the range 192.168.1.x, where x is a number between 2 and 254.

The computers are connected to the Internet through a broadband connection.

This configuration is also known as an edgeless network. In this configuration, the computers on the home network each have an IP address that is provided by the Internet service provider (ISP). The addresses that are used vary, depending on the ISP. The computers each have a separate dial-up connection or broadband connection to the Internet.In this configuration, the computers generally use automatically assigned IP addresses for their home network adapters.
Typically, the network adapters assign IP addresses in the range of 169.254.x.y, where x and y are numbers between 1 and 254. The computers use ISP-provided addresses for their Internet connections.

Troubleshoot basic connectivity issues

To troubleshoot basic connectivity issues and verify name resolution between computers, follow these steps in the order in which they are provided until you isolate and resolve the issue.

Step 1: Verify the physical connection between computers

The back of each network adapter in a desktop computer has visible lights. These lights indicate a good connection. If you are using a network hub, or a switch to connect the computers, make sure that the network hub or the switch is turned on and that the lights are illuminated for each client connection. This indicates a good link.

Step 2: Make sure that all computers have TCP/IP installed

This step is especially important with Microsoft Windows 95-based computers. By default, Windows 95-based computers do not have TCP/IP installed. If you are using computers that run Windows 95, Microsoft Windows 98, or Microsoft Windows Millennium Edition on the network, you can look for TCP/IP by using the Network item in Control Panel. If TCP/IP is not installed, you must install it to communicate with Windows XP-based computers on the network. TCP/IP is always installed in Windows XP.

Step 3: Make sure that the network configuration includes the IP addresses

Collect network configuration information from at least two computers on the network by using the adapter status. Then, make sure that the assigned IP addresses match the home-network configurations described above in the "Home-network structures and their configurations" section. Follow these steps:

• Click Start, click Run, type ncpa.cpl and then click OK.
• Locate and right-click the icon that represents this computer's connection to the home network, and then click Status.
• Click the Support tab, and then under Connection status, locate the IP addresses.

If the assigned IP addresses do not match the topology that this article described in the "Home-network structures and their configurations" section, the computer that is assigning the addresses may not be available. This is likely to be true if 169.254.x.y addresses are in a configuration where you expect a different address range.

To change the configuration so that the addresses on the home network adapter for each computer are in the same range, determine which address is correct based on the network topology. To do this, check whether one computer receives an address in the range 192.168.0.x, and another receives an address in the range 169.254.x.y. When you isolate which computer has the incorrect address, troubleshoot the computer that has the incorrect address.

Note:- For Windows 95-based computers in a network that uses 169.254.x.y addressing, you must configure IP addresses manually. For information about how to do this, see the online Help for Windows 95.

Step 4: Make sure that firewall features are not enabled on the home network adapters

Verify that the Internet Connection Firewall (ICF) or Windows Firewall (WF) feature is not enabled on the adapters that you use to connect the computers to the home network. If these features are enabled on these adapters, you cannot connect to shared resources on other computers in the network. 
Note:-Edgeless networks are the exception. You can use ICF with edgeless networks if you take additional measures to enable connectivity in the home network.

Step 5: Test connectivity between computers by using the "ping" command

Use the ping command to test connectivity between two computers on the network, 
On one of the computers, click Start, click Run, type command and then click OK. 
At the command prompt, type ping x.x.x.x (where x.x.x.x is the IP address of the other computer), and then press ENTER. If the ping command is successful, and the computers can connect correctly 
After you have verified connectivity and name resolution between computers, you can troubleshoot the connectivity for file and printer sharing.

Troubleshoot file sharing and printer sharing

After the computers are connected, you can share files and printers between computers through the home network. To troubleshoot file sharing and printer sharing, follow these steps in the order in which they are provided until you isolate and resolve the issue.

Step 1: Run the Network Setup Wizard to configure each computer in the network

To configure file and printer sharing, run the Network Setup Wizard on each computer in the network. When you are finished , go to step 2.

Step 2: Make sure that the Guest account is set up for network access

All network access to either a Windows XP Home Edition-based computer in a workgroup or to a Windows XP Professional-based computer in a workgroup uses the Guest account. Before you continue to troubleshoot, make sure that the Guest account is set up for network access.Follow these steps:

• Click Start, click Run, type command, and then click OK.
• Type the net user guest and then press ENTER.
• If the account is active, a line appears in the output of the command that has the following format:
  Account active Yes
• If the account is not active,
• type net user guest /active:yes and then press ENTER to give the Guest account network access. The following text returns after the command:
  The command completed successfully.

If you receive any other response, make sure that you are logged on as an administrator, and than confirm that you typed the command correctly before you try again. When you are finished setting up the Guest account for network access, go to step 3.

Step 3: Make sure that folder for the computer name is shared

After you have verified the file-sharing configuration and set up the Guest account for network access, make sure that the folder for each computer is shared. Follow these steps:

• To locate the computer name for each computer, click Start, click Run, type sysdm.cpl, and then click OK.
• On the Computer Name tab, under Full computer name, locate the computer name.
• To determine whether a folder is shared, click Start, click Run, type fsmgmt.msc, and then click OK.
• In the left navigation pane, click Shares. A list of shared folders is displayed in the right navigation pane.
• Locate the share folder for each computer.
• If all computer names are listed, go to step 4.

Step 4: Test the connection between computers

To test the connection from one computer to another, follow these steps:

• Click Start, click Run, type \\computername (where computername is the name of another computer on the network), and then press ENTER. A window opens that contains an icon for each shared folder on the other computer.
• Try to open one of the shared folders to confirm that the connection is working.
• If you can open a shared folder, the computers are connected. Go to step 5.
• If you cannot open a shared folder, go to step 2.
• Test the connection from the opposite direction. To do this, go to the other computer on the network and repeat steps 1 and 2 to try to open a shared folder between the computers, or between other computers to make sure that the problem is not with a particular computer on the network.
• If you can open a shared folder from each computer, the computers are connected. Go to step 5.
• If you can open a shared folder from one computer but not the other, the problem may be that the other computer cannot access the folder. Go to step 3 to troubleshoot the connection for the other computer.
• If you cannot open a shared folder from either computer, there may be a problem with the connection. Go to the "Troubleshoot basic connectivity" section and see step 5.
• If you still cannot open a shared folder, try again to test the connection with the computer name as the name of the local computer. This tests the connection locally. A window is displayed with an icon for each shared folder on the computer. Try to open one of the shared folders to make sure that you have access.
• If you can open a shared folder, the computers are connected. Go to step 5.

Step 5: Check the Network Setup Wizard log file for errors

Check the Network Setup Wizard log file for errors in any events that are not followed by successful operations. To open the log and check for errors, follow these steps: 
Click Start, click Run, type %SystemRoot%\nsw.log and then press ENTER. 
If you find errors in the log, search the computernetworkingnotes.com for more information about how to manually configure the computer to have the correct settings. When you are finished checking the Network Setup Wizard log file for errors, you should have connectivity for file and printer sharing.

Peer to Peer Workgroup Network Error Description Solutions

In this article I have listed more common problems with their possible solutions for workgroup network.

Error Message:
No more connections can be made to this remote computer at this time because there are already as many connections as the computer can accept.

Description: 
Windows XP Home Edition allows a maximum of 5 other computers to access its shared disks and folders simultaneously. Windows XP Professional allows a maximum of 10. This message appears when the maximum has been reached and another computer requests access.

Possible Solutions:
There's no way to change the limit. A computer that's already connected must close its connection before another can have access.

Error Message:
An error has occurred while trying to share >filename>. The Server service is not started. The shared resource was not created at this time.

Possible Solutions: 
To start the Server service: 
* Right click My Computer and select Manage. 
* Double click Services and Applications. 
* Double click Services. 
* Scroll down the list of services and double click Server. 
* Click the Start button. 
* Set the Startup type to Automatic.

Error Message: Can browse the Internet but not LAN

Description:
In a mixed OS network including Win9x, ME, NT, W2K and XP, the computers can still obtain IP addresses that are assigned by a DHCP server, but they cannot see each other in Network Neighborhood or in My Network Places. You can browse the Internet, but you cannot browse your local area connection. You are able to ping your loopback address (127.0.0.1), but you cannot ping another computer on the same network.

Possible Solutions:
The problem may occur if your hardware router has a built-in firewall or software firewall like ICF that has closed ports. Open the ports or for the test, disable firewall.

Error Message:
Can't enable Client for MS Networks and File and Printer Sharing

Description:
When trying to enable Client for MS Networks and File and Printer Sharing, you may get warning that Client for MS Network and File and Printer Sharing will be disabled.

Possible Solutions:

Go to Network Connection ==> Advanced ==> Advanced Settings, make sure Client for MS Networks and File and Printer Sharing are checked.

Error Message:
Error Message: Can't see one of the shared folders

Description:
your peer network with one Win 98SE and some Win 2000 Pro systems on the LAN operates fines except the W98SE machine sees all W2kPro machines but not one of shared folders on one w2k computer. Other W2kPro machines can sees the folder. You have set necessary permissions, users, passwords.

Possible Solutions:

make sure the folder's name is shorter then 15 characters.

Error Message:
Error Message: Can ping but can't see other computers

Description:
If W2k machine is multi homed, you may be able to ping other computers but can't see them on My Network Places.

Possible Solutions:

change the Connection order. To do this, open Network Connection>Advanced (Menu)>Advanced Settings>Adapters & Bindings, reorder the Connections

Error Message:
Can't net view computer name - error 52

Description:
you can ping a host but not net view it. When using net view \\hostname, you get system error 52 - a duplicate name exists on the network.

Possible Solutions:

there are two host names or alias name (cname) are pointed to the same IP. 

* Check the WINS records. 
* Check DNS records. 
* Go to System in the Control Panel to change the computer name and try again.

Error Message:
Can't ping or net view computer name - error 53

Description:
if you can ping IP but not computer name, or if you can net view \\IP but not \\computername (error 53). You have name resolution problem.

Possible Solutions:

Make sue all computers are in the same group or logon the same username. Or need to cache credential: logon the same username and password on both computers or use net net use \\computername /user:username command.

Error Message:
How can I restore IPC$

Description: 
IPC$ is a resource that shares the named pipes that are essential for communication between programs. You use IPC$ during remote administration of a computer and when you view a computer's shared resources. You should not delete this resource.

Possible Solutions:

If IPC$ share is missing, restore it by using command net share ipc$.

Step by Step Troubleshooting of peer to peer workgroup network

• 
This article is the extension for our previous article. In this section we would list most common errors with their possible solutions. Use this guide for Troubleshooting workgroup window xp network.
Error Message:
Windows XP takes a long time to open a shared disk or folder on a computer running Windows 95, 98, or Me
Description:
This is a different problem than My Network Places taking a long time to open. This problem occurs after you double click a shared disk or folder.
Possible Solutions:

Disable searching for scheduled tasks by deleting this registry key: 
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\ 
CurrentVersion\Explorer\RemoteComputer\NameSpace\ 
{D6277990-4C6A-11CF-8D87-00AA0060F5BF}
Error Message:
Network Connection Has IP Address 169.254.x.x
Description: 
The network card is configured to obtain an IP address automatically, and it's connected to a network with a DHCP server: hardware router, another computer running Internet Connection Sharing, cable modem, DSL modem, etc. But it gets a 169.254.x.x IP address, which indicates that it can't communicate with the DHCP server:
Possible Solutions:

• Connect the computer using a different Ethernet cable or hub/switch/router port.
• Download and install the latest firmware for the hardware router.
• Disable XP's Internet Connection Firewall on the local area network connection.
• The card is configured to automatically sense network speed and duplex mode, but auto-sensing is failing. Configure the speed and duplex mode manually. For example, most switches and routers use 100 Mb speed and full duplex. To make the settings, right click the network connection and click Properties | Configure | Advanced.
• Un-install the network card and move it to a different slot.
• If you have a cable modem connection, turn off the computer, turn off the cable modem, and wait a few minutes. Turn on the cable modem, and then turn on the computer
• Error Message:
  Renewing a DHCP lease fails, with error message "An error occurred while renewing interface The system cannot find the file specified."
  Description: 
  Network connection configured to obtain an IP address automatically has IP address 0.0.0.0
  Possible Solutions:
  Make sure that the DHCP Client service is running: 
  1. Right click My Computer, and click Manage. 
  2. Double click Services and Applications. 
  3. Double click Services. 
  4. Double click DHCP Client. If the Service status is Stopped, click Start. 
  5. Set the Startup type to Automatic.
  Error Message:
  Computers can ping each other by IP address, but not by name.
  Description: 
  An attempt to ping a computer by name gets the message Ping request could not find host >computer name<. Please check the name and try again.
  Possible Solutions:
  Make sure that NetBIOS Over TCP/IP is enabled.
  Error Message:
  Network Cable Unplugged
  Description: 
  Don't take this message literally - there are many causes besides not having a cable physically plugged into the network card. The message really means that the network card doesn't detect a live link to another device on the other end of the cable.
  Possible Solutions:
  1. Download and install the latest network card driver program. 
  2. Check the cabling - a bad cable will prevent link detection. Substitute a cable that's known to be good. 
  3. Check the link lights on the device on the other end of the cable, whether it's a hub, switch, router, or a NIC in another computer. It should show a live link to the NIC. If it doesn't, try a different port. 
  4. Auto-detecting speed and duplex mode can be unreliable. Set them manually. Most routers and switches use 100Mb, full duplex. Hubs can only use half duplex
  Error Message:
  The list of servers for this workgroup is not currently available.
  Possible Solutions:
  Make sure that the Computer Browser service is running on at least one Windows XP computer on the network: 
  * Right click My Computer, and click Manage. 
  * Double click Services and Applications. 
  * Double click Services. 
  * Double click Computer Browser. If the Service status is Stopped, click Start. 
  * Set the Startup type to Automatic.
  Error Message:
  Unable to browse the network. The network is not accessible.
  Description:
  This error message appears on a computer running Windows 95/98/Me.
  Possible Solutions:
  Make sure that: 
  * The user is logged on. Click Start | Log Off >user name< and log back on. 
  * The Computer Browser service is running on at least one Windows XP computer on the network.
  Error Message:
  Computer A Can Ping Computer B, but not Vice Versa
  Possible Solutions:
  This is almost always caused by an improperly configured firewall on Computer A.
  Error Message:
  XP's Network Setup Wizard Says That No Network Card Is Installed
  Possible Solutions:
  XP's Network Setup Wizard sometimes fails to recognize an installed and working network card. This is because the NIC's driver program doesn't respond correctly to all of the queries that the Wizard makes when it's looking for a NIC. Configure the card's TCP/IP properties manually.
  Error Message:
  One Computer Can't Access Some Web Sites, but Other Computers Can
  Possible Solutions:
  Look for the Windows Hosts file on the problem computer: 
  * Windows 95/98/Me: C:\Windows\Hosts 
  * Windows 2000: C:\WinNT\System32\Drivers\Etc\Hosts 
  * Windows XP: C:\Windows\System32\Drivers\Etc\Hosts 
  Open it with a text editor and you'll probably find lines with the names of the sites that you can't access. Delete those lines, save the file, and try again. If those are the only lines in the file, delete the file. Be sure to save it with a file name of just Hosts, with no file type. If your editor saves it as Hosts.txt, rename it to just Hosts. The Hosts file can be created by "web accelerator" programs that store name-to-IP address translations. This might speed up access by a tiny amount, but it causes problems when a site's IP address changes.
  Error Message:
  PING: transmit failed, error code 65
  Description:
  This error message occurs when you try to ping any IP address.
  Possible Solutions:
  A firewall program has been incompletely removed. Re-install it, then remove it.
  Error Message:
  A shared disk or folder doesn't appear in My Network Places
  Description:
  The disk or folder is shared correctly on another computer, but it doesn't appear.
  Possible Solutions:
  * Click Add a network place and follow the prompts to add it. Browse to it through Entire Network, or specify the path name using the form \\computer\share. 
  * Click View workgroup computers, then click the computer that has the shared disk or folder.

  Error Description Solutions of Peer to Peer Workgroup

  • 

  Continuing from our last article in this article we would list more errors with their possible solutions for workgroup network.

  Error Message:
  I have enable NetBIOS over TCP/IP but ipconfig /all shows NetBIOS over TCP/IP disable.

  Description: 
  For some reasons, you have enabled NetBIOS over TCP/IP on W2K/XP but using ipconfig /all still shows NetBIOS over TCP/IP disable.

  Possible Solutions: 
  The alternative solution will be installing NetBEUI to all computers.

  Error Message:
  I can't see a computer even I can ping \\computername

  Description: 
  Sometimes, you may be able to ping or net view \\computer, but can't see it in My Network Places.

  Possible Solutions: 
  If this is a case, you may want to check the workgroup or domain, make sure they are in the same group or domain. Also check the computer browser issue. In the most cases, you may be able to use the computer resources if it enable file and printer sharing and logon the same logon.

  
  

  Error Message:
  Loading NetBEUI works but not NetBIOS over TCP/IP

  Possible Solutions: 
  In general, computer browser performance improves with fewer protocols or network cards on a computer. This is one of reasons why NetBEUI is not loaded WinXP by default. If loading NetBEUI make the workgroup to see each but not enabling NetBIOS over TCP/IP, this is not name resolution issue. This is because of some reasons such as a firewall running.

  Error Message:
  Logon ID works on win9x but not W2K/XP

  Description:
  You can logon all workstations with different OS such as win9x, w2k and xp. If logon win9x, you can access any network resources; but if you logon w2k/xp, you will get access denied fro accessing any network resources.

  Possible Solutions: 
  have your administrator to re-set your password.

  Error Message:
  One computer cannot access the Internet

  Description:
  you have a network with a router connecting to the Internet. All computers except one can't access the Internet. That computer can ping most other computers' IPs except the router's LAN IP.

  Possible Solutions: 
  Check the router settings and make sure MAC Address Control doesn't deny that computer.

  Error Message:
  
  * Unable to browse the network". The network is not present or not stated when click MS Windows Network under Entire Network. 
  * "The service has not been started" when using net view or net send. 
  * You may not be able to logon.

  Possible Solutions: 
  Problems with workstation service you may need to check workstation service and make sure it is running on the computer. 
  Control panel ==> administrative tools ==> services ==> workstation ( This service should start)

  Error Message:
  
  * You may receive "System error 53 has occurred. The network path was not found" when using net view \\computername from a remote computer. 
  * The service has not been started when using net share. 
  * You may receive "\\computername is not accessible. Then network path was not found" when trying to browse the computer from My Network Places. 
  * You may receive "System error 51 has occurred. The remote computer is not available" when using net use to map the computer drive.

  Possible Solutions: 
  Problems with server service you may need to check server service and make sure it is running on the computer. 
  Control panel ==> administrative tools ==> services ==> server ( This service should start)

  Error Message:
  Win9x can't see Win2000/XP

  Description:
  By default, Win2000/XP disables NetBIOS over TCP/IP (NetBuI) for selected clients. In a peer-to-peer network without WINS, Win9x will be unable to browse, locate, or create file and print share connections to a Windows 2000 computer with NetBIOS disabled.

  Possible Solutions: 
  you must setup the Win2000/XP to uses NetBIOS over TCP/IP to communicate with prior versions of Windows NT and other clients, such as Microsoft Windows 95. Alternatively, you may want to add NetBEUI on all workstations in the peer-to-peer network.

  Error Message:
  Zone Alarm may disable file sharing

  Description:
  You setup a peer-to-peer network correctly but no one can see one of the networking computers and the computer can't see others. Later you find that Installing ZA prevents file sharing because Zone Alarm will consider all other machines on the network as entrusted and will not allow them to communicate with the machine ZA is installed on.

  Possible Solutions: 
  Disabling Zone Alarm. 
  To fix this, in the firewall section "ZONE" tab use the ADD button to specify which Ip's or range of ip's are local, it would also be a good idea to specify which NIC is local on a multi-homed machine. To do that, 
  Go to Security >> Advance button and select the "local zone contents" tab then click Add and specify which ip or range of ip are local also specify local interface on multi-homed machine.

  NETWORK TECHNOLOGIES

  This section covers the different protocols used on a network. In this section you will learn about MAC addresses, the OSI model, and the common network protocols such as TCP/IP, FTP, SMTP, and TFTP, for example. This section also covers TCP/UDP port functionality, network services such as DHCP, DNS, WINS, and SNMP. IP Addressing is also covered in this part along with understanding public and private networks, WAN technologies, remote access, and security protocols.

  
  

  Dhcp Server

  Computers on a IP networks need some essentials information before it can communicate with other hosts. This information include an IP address, and a default route and routing prefix. Configuring IP addressing on a large TCP/IP-based network can be a nightmare, especially if machines are moved from one network to another frequently. DHCP eliminates the manual task by a network administrator. The Dynamic Host Configuration Protocol (DHCP) can help with the workload of configuring systems on a network by assigning addresses to systems on boot-up automatically. It also provides a central database of devices that are connected to the network and eliminates duplicate resource assignments.

  DHCP server may have three methods of allocating IP-addresses:

  static allocation: The DHCP server allocates an IP address based on a table with MAC address/IP address pairs, which are manually filled Only requesting clients with a MAC address listed in this table will be allocated an IP address.

  dynamic allocation: A network administrator assigns a range of IP addresses to DHCP, and each client computer on the LAN is configured to request an IP address from the DHCP server during network initialization.

  automatic allocation: The DHCP server permanently assigns a free IP address to a requesting client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had.

  Among these three method static and dynamic method are the most popular implementation.

  How DHCP work

  DHCP provides an automated way to distribute and update IP addresses and other configuration information on a network. A DHCP server provides this information to a DHCP client through the exchange of a series of messages, known as the DHCPconversation or the DHCP transaction.

  DHCP discovery

  The client computers broadcasts messages on the physical subnet to discover available DHCP servers. This client-computers creates a User Datagram Protocol (UDP) packet with the default broadcast destination of 255.255.255.255 or the specific subnet broadcast address if any configured.

  DHCP offer

  When a DHCP server receives an IP lease request from a client, it reserves an IP address for the client and extends an IP lease offer by sending a DHCPOFFER message to the client. This message contains the client's MAC address, the IP address that the server is offering, the subnet mask, the lease duration, and the IP address of the DHCP server making the offer.

  DHCP request

  In most companies, two DHCP servers provide fault tolerance of IP addressing if one server fails or must be taken offline for maintenance. So client could receive DHCP offers from multiple servers, but it will accept only one DHCP offer. In response to the offer Client requests the server. The client replies DHCP Request, unicast to the server, requesting the offeredaddress. Based on the Transaction ID field in the request, servers are informed whose offer the client has accepted. When other DHCP servers receive this message, they withdraw any offers that they might have made to the client and return the offered address to the pool of available addresses. In some cases DHCP request message is broadcast, instead of being unicast to a particular DHCP server, because the DHCP client has still not received an IP address. Also, this way one message can let all other DHCP servers know that another server will be supplying the IP address without missing any of the servers with a series of unicast messages.

  DHCP acknowledgement

  When the DHCP server receives the DHCPREQUEST message from the client, the configuration process enters its final phase. The acknowledgement phase involves sending a DHCPACK packet to the client. This packet includes the lease duration and any other configuration information that the client might have requested. At this point, the IP configuration process is completed.

  

  
  

  
  

  Function of TCP UDP protocols DNS NAT ICS WINS SNMP NFS SMB AFP ISDN FDDI

  
  

  The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) are used to transmit network data to and from server and client applications. The main difference between the two protocols is that TCP uses a connection-oriented transport, while UDP uses a connectionless type of communication. When the TCP protocol is used, a special connection is opened up between two network devices, and the channel remains open to transmit data until it is closed.

  On the other hand, a UDP transmission does not make a proper connection and merely broadcasts its data to the specified network address without any verification of receipt. For certain types of applications and services, a TCP connection makes more sense, while other types are more efficiently provided by UDP communication. The advantage of TCP is that the transmission is much more reliable because it uses acknowledgement packets to ensure delivery. The advantage of UDP is that there is no connection, so it is much faster without all the checks and acknowledgements going on, but is also less reliable. In Table some common TCP/IP applications are shown with the type of protocol they use.

  Protocol	Common Port
  FTP (File Transfer Protocol)	20, 21
  SSH (Secure Shell)	22
  Telnet	23
  SMTP (Simple Mail Transfer Protocol)	25
  DNS (Domain Name Service)	53
  TFTP (Trivial File Transfer Protocol)	69
  HTTP (Hypertext Transfer Protocol)	80
  POP3 (Post Office Protocol version 3)	110
  NNTP (Network News Transport Protocol)	119
  NTP (Network Time Protocol)	123
  IMAP4 (Internet Message Access Protocol version 4)	143
  HTTPS (Hypertext Transfer Protocol Secure)	443

  
  

  DNS

  TCP/IP networks communicate with hosts using their IP addresses. It would be very difficult for someone to have to memorize the different IP addresses for the hosts they want to connect to on the network. A Domain Name Service (DNS) makes it easier toidentify a host by a domain name. A domain name uses words rather than numbers to identify Internet hosts. Suppose you want to connect to the CompTIA Web site by using your Web browser. You would enter

  http://www.comptia.org
  

  In the address bar to go to the Comp TIA Web page. www.comptia.org would be a common name used for a numerical IP address. You could use 216.119.103.72 instead, but www.comptia.org is easier to remember. A DNS server translates these addresses. Your Web browser asks the TCP/IP protocol to ask the DNS server for the IP address of www.comptia.org. When the browser receives the address, it connects to the Web site. Remember that DNS stands for Domain Name System (or Domain Name Service) and that a DNS server translates domain names into their IP addresses.

  NAT (Network Address Translation)

  NAT translates one IP address to another. This can be a source address or a destination address. Two basic implementations of NAT can be used: static and dynamic

  Static NAT

  With static NAT, a manual translation is performed by an address translation device, translating one IP address to a different one. Typically, static NAT is used to translate destination IP addresses in packets as they come into your network, but you can translate source addresses also.

  Dynamic NAT

  With static address translation, you need to build the translations manually. If you have 1000 devices, you need to create 1000 static entries in the address translation table, which is a lot of work. Typically, static translation is done for inside resources that outside people want to access. When inside users access outside resources, dynamic translation is typically used. In this situation, the global address assigned to the internal user isn’t that important, since outside devices don’t directly connect to your internal users—they just return traffic to them that the inside user requested.

  ICS (Internet Connection Sharing)

  ICS (Internet Connection Sharing) is a built-in feature of Windows 98 Second Edition, Windows 2000, Windows Me, and Windows Xp. ICS provides networked computers with the capability to share a single connection to the Internet. Multiple users can use ICS to gain access to the Internet through a single connection by using Dial-Up Networking or local networking.

  WINS (Windows Internet Name Service)

  While DNS resolves host names to IP addresses, WINS resolves NetBIOS names to IP addresses. Windows Internet Name Service provides a dynamic database of IP address to NetBIOS name resolution mappings. WINS, determines the IP address associated with a particular network computer. This is called name resolution. WINS supports network client and server computers running Windows. WINS uses a distributed database that is automatically updated with the names of computers currently available and the IP address assigned to each one. DNS is an alternative for name resolution suitable for network computers with fixed IP addresses.

  SNMP (Simple Network Management Protocol)

  Simple Network Management Protocol, is a TCP/IP protocol for monitoring networks and network components. SNMP uses small utility programs called agents to monitor behavior and traffic on the network, in order to gather statistical data. These agents can be loaded onto managed devices such as hubs, NIC's, servers, routers, and bridges. The gathered data is stored in a MIB (management information base). To collect the information in a usable form, a management program console polls these agents and downloads the information from their MIB's, which then can be displayed as graphs, charts and sent to a database program to be analyzed.

  NFS (Network File System)

  Network File System (NFS) is a distributed file system that allows users to access files and directories located on remote computers and treat those files and directories as if they were local.

  Zeroconf (Zero configuration)

  Zero Configuration Networking is a set of techniques that automatically create a usable IP network without configuration or special servers. This allows unknowledgeable users to connect computers, networked printers, and other items together and expect them to work automatically. Without Zeroconf or something similar, a knowledgeable user must either set up special servers, like DHCP and DNS, or set up each computer's network settings manualy.
  Zeroconf currently solves three problems :

  • Choose numeric network addresses for networked items
  • Figure out which computer has a certain name
  • Figure out where to get services, like printing.

  SMB (Server Message Block)

  A file-sharing protocol designed to allow networked computers to transparently access files that reside on remote systems over a variety of networks. The SMB protocol defines a series of commands that pass information between computers. SMB uses four message types: session control, file, printer, and message. It is mainly used by Microsoft Windows equipped computers. SMB works through a client-server approach, where a client makes specific requests and the server responds accordingly. One section of the SMB protocol is specifically for filesystem access, such that clients may make requests to a file server. The SMB protocol was optimised for local subnet usage, but one could use it to access different subnets across the Internet on which MS Windows file-and-print sharing exploits usually focus. Client computers may have their own hard disks, which are not publicly shared, yet also want access to the shared file systems and printers on the server, and it is for this primary purpose that SMB is best known and most heavily used.

  AFP (Apple File Protocol)

  The file sharing protocol used in an AppleTalk network. In order for non-Apple networks to access data in an AppleShare server, their protocols must translate into the AFP language. AFP versions 3.0 and greater rely exclusively on TCP/IP (port 548 or 427) for establishing communication, supporting AppleTalk only as a service discovery protocol. The AFP 2.x family supports both TCP/IP and AppleTalk for communication and service discovery.

  LPD (Line Printer Daemon) and Samba)

  LPD is the primary UNIX printing protocol used to submit jobs to the printer. The LPR component initiates commands such as "print waiting jobs," "receive job," and "send queue state," and the LPD component in the print server responds to them. The most common implementations of LPD are in the official BSD UNIX operating system and the LPRng project. The Common Unix Printing System (or CUPS), which is more common on modern Linux distributions, borrows heavily from LPD. Unix and Mac OS X Servers use the Open Source SAMBA to provide Windows users with Server Message Block (SMB) file sharing.

  WAN (Wide Area Networks) technologies:

  Circuit-switched

  services provide a temporary connection across a phone circuit. In networking, these are typically used for backup of primary circuits and for temporary boosts of bandwidth.

  dedicated circuit

  dedicated circuit is a permanent connection between two sites in which the bandwidth is dedicated to that company’s use. These circuits are common when a variety of services, such as voice, video, and data, must traverse the connection and you are concerned about delay issues with the traffic and guaranteed bandwidth.

  Cell-switched

  cell-switched services can provide the same features that dedicated circuits offer. Their advantage over dedicated circuits is that a single device can connect to multiple devices on the same interface. The downside of these services is that they are not available at all locations, they are difficult to set up and troubleshoot, and the equipment is expensive when compared to equipment used for dedicated circuits.

  Packet switching

  Packet-switched services are similar to cell-switched services. Whereas cell-switched services switch fixed-length packets called cells, packet-switched services switch variable-length packets. This feature makes them better suited for data services, but they can nonetheless provide some of the QoS features that cell-switched services provide. Packet switching offers more efficient use of a telecommunication provider's network bandwidth. With packet switching, the switching mechanisms on the network route each data packet from switch to switch individually over the network using the best-available path. Any one physical link in a packet-switched network can carry packets from many different senders and for many different destinations. Where as in a circuit switched connection, the bandwidth is dedicated to one sender and receiver only.

  ISDN (Integrated Services Digital Network)

  Integrated Services Digital Network adapters can be used to send voice, data, audio, or video over standard telephone cabling. ISDN adapters must be connected directly to a digital telephone network. ISDN adapters are not actually modems, since they neither modulate nor demodulate the digital ISDN signal. Like standard modems, ISDN adapters are available both as internal devices that connect directly to a computer's expansion bus and as external devices that connect to one of a computer's serial or parallel ports. ISDN can provide data throughput rates from 56 Kbps to 1.544 Mbps using a T1 service. ISDN hardware requires a NT (network termination) device, which converts network data signals into the signaling protocols used by ISDN. Some times, the NT interface is included, or integrated, with ISDN adapters and ISDN-compatible routers. In other cases, an NT device separate from the adapter or router must be implemented. ISDN works at the physical, data link, network, and transport layers of the OSI Model.

  FDDI (Fiber Distributed Data Interface)

  Fiber Distributed Data Interface, shares many of the same features as token ring, such as a token passing, and the continuous network loop configuration. But FDDI has better fault tolerance because of its use of a dual, counter-rotating ring that enables the ring to reconfigure itself in case of a link failure. FDDI also has higher transfer speeds, 100 Mbps for FDDI, compared to 4 - 16 Mbps for Token Ring. Unlike Token Ring, which uses a star topology, FDDI uses a physical ring. Each device in the ring attaches to the adjacent device using a two stranded fiber optic cable. Data travels in one direction on the outer strand and in the other direction on the inner strand. When all devices attached to the dual ring are functioning properly, data travels on only one ring. FDDI transmits data on the second ring only in the event of a link failure.

  Media	MAC Method	Signal Propagation Method	Speed	Topologies	Maximum Connections
  Fiber-optic	Token passing	Forwarded from device to device (or port to port on a hub) in a closed loop	100 Mbps	Double ring Star	500 nodes

  T1 (T Carrier level 1)

  A 1.544 Mbps point to point dedicated, digital circuit provided by the telephone companies. T1 lines are widely used for private networks as well as interconnections between an organizations LAN and the telco. A T1 line uses two pairs of wire one to transmit, and one to receive. and time division multiplexing (TDM) to interleave 24 64-Kbps voice or data channels. The standard T1 frame is 193 bits long, which holds 24 8-bit voice samples and one synchronization bit with 8,000 frames transmitted per second. T1 is not restricted to digital voice or to 64 Kbps data streams. Channels may be combined and the total 1.544 Mbps capacity can be broken up as required.

  T3 (T Carrier level 3)

  A T3 line is a super high-speed connection capable of transmitting data at a rate of 45 Mbps. A T3 line represents a bandwidth equal to about 672 regular voice-grade telephone lines, which is wide enough to transmit real time video, and very large databases over a busy network. A T3 line is typically installed as a major networking artery for large corporations, universities with high-volume network traffic and for the backbones of the major Internet service providers.

  OCx (Optical Carrier)

  Optical Carrier, designations are used to specify the speed of fiber optic networks that conforms to the SONET standard.

  Level	Speed
  OC-1	51.85 Mbps
  OC-3	155.52 Mbps
  OC-12	622.08 Mbps
  OC-24	1.244 Gbps
  OC-48	2.488 Gbps

  X.25

  X.25 is a network layer protocol that runs across both synchronous and asynchronous physical circuits, providing a lot of flexibility for your connection options. X.25 was actually developed to run across unreliable medium. It provides error detection and correction, as well as flow control, at both the data link layer (by LAPB) and the network layer (by X.25). In this sense, it performs a function similar to what TCP, at the transport layer, provides for IP. Because of its overhead, X.25 is best delegated to asynchronous, unreliable connections. If you have a synchronous digital connection, another protocol, such as Frame Relay or ATM, is much more efficient. An X.25 network transmits data with a packet-switching protocol, bypassing noisy telephone lines. This protocol relies on an elaborate worldwide network of packet-forwarding nodes that can participate in delivering an X.25 packet to its designated address.

  Internet access technologies:

  xDSL (Digital Subscriber Line)

  xDSL is a term referring to a variety of new Digital Subscriber Line technologies. Some of these varieties are asymmetric with different data rates in the downstream and upstream directions. Others are symmetric. Downstream speeds range from 384 Kbps (or "SDSL") to 1.5-8 Mbps (or "ADSL").

  Asymmetric Digital Subscriber Line (ADSL)

  A high-bandwidth digital transmission technology that uses existing phone lines and also allows voice transmissions over the same lines. Most of the traffic is transmitted downstream to the user, generally at rates of 512 Kbps to about 6 Mbps.

  Broadband Cable (Cable modem)

  Cable modems use a broadband connection to the Internet through cable television infrastructure. These modems use frequencies that do not interfere with television transmission.

  POTS / PSTN

  (Plain Old Telephone Service / Public Switched Telephone Network) POTS / PSTN use modem's, which is a device that makes it possible for computers to communicate over telephone lines. The word modem comes from Modulate and Demodulate. Because standard telephone lines use analog signals, and computers digital signals, a sending modem must modulate its digital signals into analog signals. The computers modem on the receiving end must then demodulate the analog signals into digital signals. Modems can be external, connected to the computers serial port by an RS-232 cable or internal in one of the computers expansion slots. Modems connect to the phone line using standard telephone RJ-11 connectors.

  Wireless

  A wireless network consists of wireless NICs and access points. NICs come in different models including PC Card, ISA, PCI, etc. Access points act as wireless hubs to link multiple wireless NICs into a single subnet. Access points also have at least one fixed Ethernet port to allow the wireless network to be bridged to a traditional wired Ethernet network, such as the organization’s network infrastructure. Wireless and wired devices can coexist on the same network.

  • WLAN (Wireless Local Area Network) A group of computers and associated devices that communicate with each other wirelessly.
  • WPA (Wi-Fi Protected Access) A security protocol for wireless networks that builds on the basic foundations of WEP. It secures wireless data transmission by using a key similar to WEP, but the added strength of WPA is that the key changes dynamically. The changing key makes it much more difficult for a hacker to learn the key and gain access to the network.
  • WPA2 (Wi-Fi Protected Access 2) WPA2 is the second generation of WPA security and provides a stronger encryption mechanism through Advanced Encryption Standard (AES), which is a requirement for some government users.
  • WPA-Personal A version of WPA that uses long and constantly changing encryption keys to make them difficult to decode.
  • WPA-Enterprise A version of WPA that uses the same dynamic keys as WPA-Personal and also requires each wireless device to be authorized according to a master list held in a special authentication server.

  Tcp ip udp ftp smtp HTTPs POP3 IMAP4 telnet SSH ICMP ARP RARP NTP SNMP SCP LDAP LPR

  TCP (Transmission Control Protocol)

  Transmission Control Protocol uses a reliable delivery system to deliver layer 4 segments to the destination. This would be analogous to using a certified, priority, or next-day service with the Indian Speed Post;Service.

  For example, with a certified letter, the receiver must sign for it, indicating the destination actually received the letter: proof of the delivery is provided. TCP operates under a similar premise: it can detect whether or not the destination received a sent segment. With the postal example, if the certified letter got lost, it would be up to you to resend it; with TCP, you don’t have to worry about what was or wasn’t received—TCP will take care of all the tracking and any necessary resending of lost data for you.

  TCP’s main responsibility is to provide a reliable full-duplex, connection-oriented, logical service between two devices.

  TCP goes through a three-way handshake to establish a session before data can be sent. Both the source and destination can simultaneously send data across the session. It uses windowing to implement flow control so that a source device doesn't overwhelm a destination with too many segments. It supports data recovery, where any missed or corrupted information can be re-sent by the source. Any packets that arrive out of order, because the segments traveled different paths to reach the destination, can easily be reordered, since segments use sequence numbers to keep track of the ordering.

  UDP (User Datagram Protocol)

  UDP uses a best-effort delivery system, similar to how first class and lower postal services of the Indian Postal Service work. With a first class letter (post card), you place the destination address and put it in your mailbox, and hope that it arrives at the destination.

  With this type of service, nothing guarantees that the letter will actually arrive at the destination, but in most instances, it does. If, however, the letter doesn’t arrive at the destination, it’s up to you, the letter writer, to resend the letter: the postoffice isn’t going to perform this task for you.

  UDP operates under the same premise: it does not guarantee the delivery of the transport layer segments. While TCPprovides a reliable connection, UDP provides an unreliable connection.

  UDP doesn’t go through a three-way handshake to set up a connection—it simply begins sending the data. Likewise, UDP doesn’t check to see whether sent segments were received by a destination; in other words, it doesn’t use an acknowledgment

  Some commonly used ports

  Port Number	Service
  80	HTTP
  21	FTP
  110	POP3
  25	SMTP
  23	Telnet

  FTP (File Transfer Protocol)

  One of the earliest uses of the Internet, long before Web browsing came along, was transferring files between computers. The File Transfer Protocol (FTP) is used to connect to remote computers, list shared files, and either upload or download files between local and remote computers.

  FTP runs over TCP, which provides a connection-oriented, guaranteed data-delivery service. FTP is a character-based command interface, although many FTP applications have graphical interfaces. FTP is still used for file transfer purposes, most commonly as a central FTP server with files available for download. Web browsers can make FTP requests to download programs from links selected on a Web page.

  You should become familiar with the basic commands available in an FTP session. To begin a characterbased command session on a Windows computer, follow these steps.

  • Open a Command prompt window, type ftp at the prompt, and press Enter.
  • This will begin an FTP session on the local machine but will not initialize a connection to another machine.
  • Without a connection to another machine, you will not be able to do anything. To connect, type open example.comor open 10.10.10.1, in which exmple.com or 10.10.10.1 is the name or IP address of a host that is available as an FTP server. Most FTP servers require a logon id and password, or they will accept anonymous connections. At this point you will be prompted for a logon ID and password.
  • Once you are connected, you can list the files on the remote server by typing dir.
  • If you have create privileges on the remote server, you can create a new directory by typing mkdir.
  • To download a file, type get filename.txt where filename.txt is the name of the file you are downloading. 
    To upload a file, typeput filename.txt.

  SFTP (Secure File Transfer Protocol)

  SSH File Transfer Protocol or SFTP is a network protocol that provides file transfer and manipulation functionality over any reliable data stream.

  TFTP (Trivial File Transfer Protocol)

  TFTP is used when a file transfer does not require an acknowledgment packet during file transfer. TFTP is used often in router configuration. TFTP is similar in operation to FTP. TFTP is also a command-line-based utility.

  One of the two primary differences between TFTP and FTP is speed and authentication. Because TFTP is used without acknowledgment packets, it is usually faster than FTP. TFTP does not provide user authentication like FTP and therefore the user must be logged on to the client and the files on the remote computer must be writable. TFTP supports only unidirectional data transfer (unlike FTP, which supports bi-directional transfer). TFTP is operated over port 69.

  SMTP (Simple Mail Transfer Protocol)

  SMTP is a standard electronic-mail protocol that handles the sending of mail from one SMTP to another SMTP server. To accomplish the transport, the SMTP server has its own MX (mail exchanger) record in the DNS database that corresponds to the domain for which it is configured to receive mail.

  When equipped for two-way communication, mail clients are configured with the address of a POP3 server to receive mail and the address of an SMTP server to send mail. The clients can configure server parameters in the properties sheets of the mail client, basing the choices on an FQDN or an IP address.

  SMTP uses TCP for communication and operates on port 25. Simple Mail Transfer Protocol (SMTP) is the application-layer protocol used for transmitting e-mail messages. SMTP is capable of receiving e-mail messages, but it's limited in its capabilities. The most common implementations of SMTP are in conjunction with either POP3 or IMAP4. For example, users download an e-mail message from a POP3 server, and then transmit messages via an SMTP server

  HTTP (Hypertext Transfer Protocol)

  HTTP is often called the protocol of the Internet. HTTP received this designation because most Internet traffic is based on HTTP. When a user requests a Web resource, it is requested using HTTP. The following is a Web request:

  http://www.example.com

  When a client enters this address into a Web browser, DNS is called to resolve the Fully Qualified Domain Name (FQDN) to an IP address. When the address is resolved, an HTTP get request is sent to the Web server. The Web server responds with an HTTP send response. Such communication is done several times throughout a single session to a Web site. HTTP uses TCP for communication between clients and servers. HTTP operates on port 80.

  HTTPS (Hypertext Transfer Protocol Secure)

  HTTP is for Web sites using additional security features such as certificates. HTTPS is used when Web transactions are required to be secure. HTTPS uses a certificatebased technology such as VeriSign.

  Certificate-based transactions offer a mutual authentication between the client and the server. Mutual authentication ensures the server of the client identity, and ensures the client of the server identity. HTTPS, in addition to using certificate-based authentication, encrypts all data packets sent during a session.

  Because of the encryption, confidential user information cannot be compromised. To use HTTPS, a Web site must purchase a certificate from a third-party vendor such as VeriSign, CertCo, United States Postal Service, or other certificate providers. When the certificate is issued to a Web site from a third-party vendor, the Web site is using trusted communication with the client. The communication is trusted because the third party is not biased toward either the Web site or the client. To view a certificate during a HTTPS session, simply double-click the lock icon in the lower-right area of the Web browser. HTTPS operates on port 443 and uses TCP for communication.

  POP3 / IMAP4 (Post Office Protocol version 3 / Internet Message Access Protocol version 4)

  Post Office Protocol 3 (POP3) and Internet Message Access Protocol 4 (IMAP4) are two application-layer protocols used for electronic messaging across the Internet. POP3 is a protocol that involves both a server and a client. A POP3 server receives an e-mail message and holds it for the user. A POP3 client application periodically checks the mailbox on the server to download mail. POP3 does not allow a client to send mail, only to receive it. POP3 transfers e-mail messages over TCP port 110.

  IMAP4 is an alternate e-mail protocol. IMAP4 works in the same way as POP3, in that an e-mail message is held on a server and then downloaded to an e-mail client application. Users can read their e-mail message locally in their e-mail client application, but they can't send an e-mail message using IMAP4. When users access e-mail messages via IMAP4, they have the option to view just the message header, including its title and the sender's name, before downloading the body of the message. Users can create, change, or delete folders on the server, as well as search for messages and delete them from the server.

  To perform these functions, users must have continued access to the IMAP server while they are working with e-mail messages. With IMAP4, an e-mail message is copied from the server to the e-mail client. When a user deletes a message in the e-mail client, the message remains on the server until it is deleted on the server. POP3 works differently in that an e-mail message is downloaded and not maintained on the server, unless configured otherwise. Therefore, the difference between POP3 and IMAP4 is that IMAP4 acts like a remote file server, while POP3 acts in a store-and-forward manner in its default configuration. (You can configure POP3 clients to leave copies of messages on the server, if you prefer.)

  Both Microsoft and Netscape Web browsers have incorporated POP3. In addition, the Eudora and Microsoft Outlook Express e-mail client applications support both POP3 and IMAP4.

  Telnet

  Short for Telecommunication Network, a virtual terminal protocol allowing a user logged on to one TCP/IP host to access other hosts on the network. Many people use remote control applications to access computers at their workplace from outside the network. In remote control, a session appears in which the user is able to manage the files on the remote computer, although the session appears to be functioning locally. Telnet is an early version of a remote control application.

  Telnet is very basic; it offers solely character-based access to another computer. If you want to see a person's graphical desktop, you would need a different type of protocol, such as Remote Desktop Protocol (RDP), Independent Computing Architecture (ICA), or X Windows. Telnet acts as a user command with an underlying Transmission Control Protocol/Internet Protocol (TCP/IP) protocol that handles the establishment, maintenance, and termination of a remote session. The difference between using Telnet and a protocol such as File Transfer Protocol (FTP), is that Telnet logs you directly on to the remote host, and you see a window into that session on your local computer. A typical Telnet command might be as follows:

   telnet example.com

  Because this particular host is invalid, this command will have no result. However, if it were a valid host the remote computer would ask you to log on with a user ID and password. A correct ID and password would allow you to log on and execute Telnet commands.

  You can often use Telnet to manage equipment that lacks a monitor. For example, most routers have Telnet enabled so that the administrator can log in and manage the router. Telnet also provides a quick check to make certain that network connectivity is functioning. Because Telnet sits at the application layer, if it can connect to a remote host, you can be certain that network connectivity between the two hosts is operational, as well as all lower-layer protocols.

  SSH (Secure Shell)

  is a program for logging in to and executing commands on a remote machine. It provides secure encrypted communications between two untrusted hosts over an insecure network. X11 connections and arbitrary TCP/IP ports can also be forwarded over the secure channel. When SSH connects and logs in to a specified computer, the user must prove his/her identity to the remote machine which is transmitted across the connection using one of three forms of data encryption. This process makes SSH impervious to Internet eavesdroppers who might otherwise steal account information.

  ICMP (Internet Control Message Protocol)

  ICMP provides network diagnostic functions and error reporting. One of the most used IP commands is the Packet Internet Grouper (PING) command. When a host PINGS another client, it sends an ICMP ECHO request, and the receiving host responds with an ICMP ECHO REPLY. PING checks network connectivity on clients and routers. ICMP also provides a little network help for routers. When a router is being overloaded with route requests, the router sends a source quench message to all clients on the network, instructing them to slow their data requests to the router.

  ARP / RARP (Address Resolution Protocol / Reverse Address Resolution Protocol)

  The Address Resolution Protocol (ARP) is an Internet layer protocol that helps TCP/IP network components find other devices in the same broadcast domain. ARP uses a local broadcast (255.255.255.255) at layer 3 and FF:FF:FF:FF:FF:FF at layer 2 to discover neighboring devices. Basically stated, you have the IP address you want to reach, but you need a physical (MAC) address to send the frame to the destination at layer 2.

  ARP resolves an IP address of a destination to the MAC address of the destination on the same data link layer medium, such as Ethernet. Remember that for two devices to talk to each other in Ethernet (as with most layer 2 technologies), the data link layer uses a physical address (MAC) to differentiate the machines on the segment. When Ethernet devices talk to each other at the data link layer, they need to know each other’s MAC addresses.

  RARP is sort of the reverse of an ARP. In an ARP, the device knows the layer 3 address, but not the data link layer address. With a RARP, the device doesn’t have an IP address and wants to acquire one. The only address that this device has is a MAC address. Common protocols that use RARP are BOOTP and DHCP

  NTP (Network Time Protocol)

  The Network Time Protocol is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides accuracy's typically within a millisecond on LANs and up to a few tens of milliseconds on WANs.

  SNMP

  SNMP is a two-way network management protocol. SNMP consists of two components, the SNMP Agent, and the SNMP Management Console. The SNMP Management Console is the server side for SNMP. The management console sends requests to the SNMP Agents as get commands that call for information about the client.

  The SNMP Agent responds to the Management Console’s get request with a trap message. The trap message has the requested information for the Management Console to evaluate. Security can be provided in many ways with SNMP; however, the most common form of security for SNMP is the use of community names, associations that link SNMP Agents to their Management Consoles:

  • Agents, by default, respond only to Management Consoles that are part of the same community name.
  • If an SNMP Agent receives a request from a Management Console that is not part of the same community name, then the request for information is denied.

  Because SNMP is an industry-standard protocol, heterogeneous environments are common. Many vendors provide versions of SNMP Management Consoles. Hewlett Packard, for example provides HP Open View (one of the most popular Management Consoles on the market); Microsoft provides SNMP Server with the Windows NT and 2000 Resource Kits and Systems Management Server. SNMP Management Consoles request information according to a Management Information Base (MIB) format. An MIB is a numeric value that specifies the type of request, and to which layer of the OSI model the request is being sent.

  SCP (Secure Copy Protocol)

  Secure Copy or SCP is a means of securely transferring computer files between a local and a remote host or between two remote hosts, using the Secure Shell (SSH) protocol. The protocol itself does not provide authentication and security; it expects the underlying protocol, SSH, to secure this.

  The SCP protocol implements file transfers only. It does so by connecting to the host using SSH and there executes an SCP server (scp). The SCP server program is typically the very same program as the SCP client.

  LDAP (Lightweight Directory Access Protocol)

  Lightweight Directory Access Protocol, or LDAP, is a networking protocol for querying and modifying directory services running over TCP/IP.

  A directory is a set of information with similar attributes organized in a logical and hierarchical manner. The most common example is the telephone directory, which consists of a series of names organized alphabetically, with an address and phone number attached.

  An LDAP directory often reflects various political, geographic, and/or organizational boundaries, depending on the model chosen. LDAP deployments today tend to use Domain Name System (DNS) names for structuring the topmost levels of the hierarchy. Deeper inside the directory might appear entries representing people, organizational units, printers, documents, groups of people or anything else which represents a given tree entry.

  IGMP (Internet Group Multicast Protocol)

  The Internet Group Management Protocol is a communications protocol used to manage the membership of Internet Protocol multicast groups. IGMP is used by IP hosts and adjacent multicast routers to establish multicast group memberships. It is an integral part of the IP multicast specification, like ICMP for unicast connections. IGMP can be used for online video and gaming, and allows more efficient use of resources when supporting these uses.

  LPR (Line Printer Remote)

  The Line Printer Daemon protocol/Line Printer Remote protocol (or LPD, LPR) also known as the Berkeley printing system, is a set of programs that provide printer spooling and network print server functionality for Unix-like systems.

  The most common implementations of LPD are the official BSD UNIX operating system and the LPRng project. The Common Unix Printing System (or CUPS), which is more common on modern Linux distributions, borrows heavily from LPD.

  A printer that supports LPD/LPR is sometimes referred to as a "TCP/IP printer" (TCP/IP is used to establish connections between printers and workstations on a network), although that term seems equally applicable to a printer that supports CUPS.

  Ip address IPv4 IPv6 public ip private ip APIPA Static Dynamic ip classes

  Systems that have interfaces to more than one network require a unique IP address for each network interface. The first part of an Internet address identifies the network on which the host resides, while the second part identifies the particular host on the given network. This creates the two-level addressing hierarchy.

  The leading portion of each IP address identifies the network prefix. All hosts on a given network share the same network prefix but must have a unique host number. Similarly, any two hosts on different networks must have different network prefixes but may have the same host number.

  An IP is a 32-bit number comprised of a host number and a network prefix, both of which are used to uniquely identify each node within a network. A shortage of available IP addresses has prompted the creation of an addressing scheme known asClassless Inter-Domain Routing (CIDR). Among other capabilities, CIDR allows one IP address to designate many unique IP addresses within a network. In addition, the current version of the IP address, IPv4, is being upgraded to IPv6. The latter uses a 128-bit address, allowing for 2128 total IP addresses, as opposed to IPv4's 232.

  Internet Protocol version 4

  IPv4 addresses are 32 bits in length. To make these addresses more readable, they are broken up into 4 bytes, or octets, where any 2 bytes are separated by a period. This is commonly referred to as dotted decimal notation.

  Here’s a simple example of an IP address: 10.1.1.1

  An additional value, called a subnet mask, determines the boundary between the network and host components of an address. When comparing IP addresses to other protocols’ addressing schemes, TCP/IP addressing seems the most complicated.

  Internet Protocol version 6 (IPv6)

  Whereas IPv4 addresses use a dotted-decimal format, where each byte ranges from 0 to 255. 
  IPv6 addresses use eight sets of four hexadecimal addresses (16 bits in each set), separated by a colon (:),

  like this: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx (x would be a hexadecimal value). 
  This notation is commonly called string notation.

  • Hexadecimal values can be displayed in either lower- or upper-case for the numbers A–F.
  • A leading zero in a set of numbers can be omitted; for example, you could either enter 0012 or 12 in one of the eight fields—both are correct.
  • If you have successive fields of zeroes in an IPv6 address, you can represent them as two colons (::). For example,0:0:0:0:0:0:0:5 could be represented as ::5; and ABC:567:0:0:8888:9999:1111:0 could be represented asABC:567::8888:9999:1111:0. However, you can only do this once in the address: ABC::567::891::00 would be invalid since :: appears more than once in the address. The reason for this limitation is that if you had two or more repetitions, you wouldn't know how many sets of zeroes were being omitted from each part.
  • An unspecified address is represented as ::, since it contains all zeroes.

  Classful IP (Internet Protocol) Ranges and Their Subnet Masks

  When dealing with IP addresses, the address is broken into two components:

  Network component Defines on what segment, in the network, a device is located

  Host component Defines the specific device on a particular network segment

  The network number uniquely identifies a segment in the network and a host number uniquely identifies a device on a segment. The combination of these two numbers must be unique throughout the entire network. TCP/IP uses the same two components for addressing, but it adds a twist by breaking up network numbers into five classes: A, B, C, D, and E. Each of these classes has a predefined network and host boundary:

  • Class A address,The first byte is a network number (8 bits) and the last 3 bytes are for host numbers (24 bits).
  • Class B address ,The first 2 bytes are a network number (16 bits) and the last 2 bytes are for host numbers (16 bits).
  • Class C address ,The first 3 bytes are a network number (24 bits) and the last 1 byte is for host numbers (8 bits).
  • Class D and E ,addresses Class D Used for multicasting and Class E addresses are reserved.

  What distinguishes the different classes of addresses are the settings to which the first bit to 5 bits are set:

  • Class A addresses always begin with a 0 in the highest order bit.
  • Class B addresses always begin with 10 in the highest order bits.
  • Class C addresses always begin with 110 in the highest order bits.
  • Class D addresses always begin with 1110 in the highest order bits.
  • Class E addresses always begin with 11110 in the highest order bits.

  When talking about the highest order bit or bits, this includes all 32 bits. Therefore, this would be the very first bit on the left of the address (the most significant bit). If the first octet contains 1000001, this represents 129 in decimal, which would be a Class B address. Given these distinctions with the assigned high order bit values, it is easy to predict, for a given address, to what class of network numbers it belongs:

  Class A addresses range from  1-126:   00000001-01111111
  Class B addresses range from 128-191:  10000000-10111111
  Class C addresses range from 192-223:  11000000-11011111
  Class D addresses range from 224-239:  11100000-11101111
  Class E addresses range from 240-254:
  
  0 is reserved and represents all IP addresses;
  127 is a reserved address and is used for loop back tasting:
  255 is a reserved address and is used for broadcasting purposes.
  

  Given these restrictions with beginning bit values, it is fairly easy to predict what address belongs to what class. Simply look at the first number in the dotted-decimal notation and see which range it falls into.

  When you are dealing with IP addresses, two numbers are always reserved for each network number:

  The first address in the network represents the network's address, and the last address in the network represents the broadcast address for this network,called directed broadcast.

  When you look at IP itself, two IP addresses are reserved: 0.0.0.0 (the very first address), which represents all IP addresses, and 255.255.255.255 (the very last address), which is the local broadcast address.

  Purpose of subnetting.

  Subnetting allows you to break up and use an addressing space more efficiently. Basically, subnetting steals the higher-order bit or bits from the host component and uses these bits to create more subnets with a smaller number of host addresses in each of these subnets.

  Subnet masks are 32 bits long and are typically represented in dotted-decimal (such as 255.255.255.0) or the number of networking bits (such as /24). The networking bits in a mask must be contiguous and the host bits in the subnet mask must be contiguous. 255.0.255.0 is an invalid mask. A subnet mask is used to mask a portion of the IP address, so that TCP/IP can tell the difference between the network ID and the host ID. TCP/IP uses the subnet mask to determine whether the destination is on a local or remote network.

  Advantages of subnetting a network include the following:

  • Reducing network colision by limiting the range of broadcasts using routers
  • Enabling different networking architectures to be joined

  Differences between private and public network addressing schemes.

  As to assigning addresses to devices, two general types of addresses can be used: public and private.

  Public addresses

  Public addresses are Class A, B, and C addresses that can be used to access devices in other public networks, such as the Internet. The Internet Assigned Numbers Authority (IANA) is ultimately responsible for handing out and managing public addresses. Normally you get public addresses directly from your ISP, which, in turn, requests them from one of five upstream address registries:

  • American Registry for Internet Numbers (ARIN)
  • Reseaux IP Europeans Network Coordination Center (RIPE NCC)
  • Asia Pacific Registry for Internet Numbers (APNIC)
  • Latin American and Caribbean Internet Address Registry (LACNIC)
  • African Network Information Centre (AfriNIC)

  Private Addresses

  Within the range of addresses for Class A, B, and C addresses are some reserved addresses, commonly called private addresses. Anyone can use private addresses; however, this creates a problem if you want to access the Internet. Remember that each device in the network (in this case, this includes the Internet) must have a unique IP address. If two networks are using the same private addresses, you would run into reachability issues. To access the Internet, your source IP addresses must have a unique Internet public address. This can be accomplished through address translation. Here is a list of private addresses that are assigned in RFC 1918:

  • Class A: 10.0.0.0–10.255.255.255 (1 Class A network)
  • Class B: 172.16.0.0–172.31.255.255 (16 Class B networks)
  • Class C: 192.168.0.0–192.168.255.255 (256 Class C networks)

  IP (Internet Protocol) addressing methods:

  Static /Dynamic

  Each device in an IP network is either assigned a permanent address (static) by the network administrator or is assigned a temporary address (dynamic) via DHCP software. Routers, firewalls and proxy servers use static addresses as do most servers and printers that serve multiple users. Client machines may use static or dynamic IP addresses. The IP address assigned to your service by your cable or DSL Internet provider is typically dynamic IP. In routers and operating systems, the default configuration for clients is dynamic IP.

  DHCP

  DHCP stands for Dynamic Host Configuration Protocol. This protocol assigns network IP addresses to clients on the network at startup. With DHCP, each client workstation does not need to be set up with a static IP address. DHCP is recommended on large networks. It would be very time consuming to manually assign a static IP address to every workstation on your network.

  With static IP addressing, the IP address that you assign to a device never changes. A DHCP server contains a pool of IP addresses that it can draw from to assign to devices that are connecting to the network. Other TCP/IP properties, such as default gateways, DNS servers, and subnet masks can also be assigned automatically.

  Self-assigned (APIPA (Automatic Private Internet Protocol Addressing))

  Automatic Private IP Addressing (APIPA) is a feature of Windows-based operating systems (included in Windows 98, ME, 2000, and XP) that enables a computer to automatically assign itself an IP address when there is no Dynamic Host Configuration Protocol (DHCP) server available to perform that function.

  Using APIPA, a Windows based client assigns itself an IP address from a range reserved for authorized private class B network addresses (169.254.0.1 through 169.254.255.254), with a subnet mask of 255.255.0.0. A computer with an authorized private address cannot directly communicate with hosts outside its subnet, including Internet hosts.

  APIPA is most suitable for small, single-subnet networks, such as a home or small office. APIPA is enabled by default if no DHCP servers are available on the network.

  Note APIPA assigns only an IP address and subnet mask; it does not assign a default gateway, nor does it assign the IP addresses of DNS or WINS servers. Use APIPA only on a single-subnet network that contains no routers. If your small office or home office network is connected to the Internet or a private intranet, do not use APIPA.

  
  

  Network security protocols CHAP MS-CHAP PAP RADIUS RAS PPP SLIP PPPoE PPTP RDP

  Security protocols protect a computer from attacks. To understand how security protocols work, you must first understand what types of attacks they protect against. Networks and data are vulnerable to both active attacks, in which information is altered or destroyed, and passive attacks, in which information is monitored. Attacks that you might encounter include thefollowing:

  Altering data

  This active attack takes place when data is interrupted in transit and modified before it reaches its destination, or when stored data is altered. This passive attack takes advantage of network traffic that is transmitted across the wire in clear text. The attacker simply uses a device that monitors traffic and "listens in" to discover information. You'll hear this term referred to as sniffing the wire, and sometimes as snooping.

  IP address spoofing

  One way to authenticate data is to check the IP address in data packets. If the IP address is valid, that data is allowed to pass into the private network. IP address spoofing is the process of changing the IP address so that data packets will be accepted. IP address spoofing can be used to modify or delete data, or to perpetuate an additional type of attack.

  Password pilfering

  A hacker will obtain user IDs and passwords, or even encryption keys, to gain access to network data, which can then be altered, deleted, or even used to create another attack. This type of attack is usually done by asking unsuspecting users, reading sticky notes containing passwords that are posted next to computers, or sniffing the wire for password information. Sometimes a hacker will attempt to get hired at a company merely to obtain an ID and password with access rights to the network.

  Denial of service

  This active attack is intended to cause full or partial network outages so that people will not be able to use network resources and productivity will be affected. The attacker floods so many packets through the network or through specific resources that other users can't access those resources. The denial-of-service attack can also serve as a diversion while the hacker alters information or damages systems.

  Virus

  A virus is an attack on a system. It is a piece of software code that is buried inside a trusted application (or even an e-mail message) that invokes some action to wreak havoc on the computer or other network resources.

  Security Method	Type of Attack	Notes
  Authentication	Password guessing attacks	Verifies the user's identity
  Access control	Password pilfering	Protects sensitive data from access by the average user
  Encryption	Data alteration	Prevents the content of the packets from being tampered with
  Certificates	Eavesdropping	Transmits identity information securely
  Firewalls	Denial of service (as well as others)	When configured correctly, can prevent many denial-of-service attacks
  Signatures	Data alteration	Protects stored data from tampering
  Public key infrastructure	Spoofing	Ensures that data received is from correct sender
  Code authentication	Virus and other code attacks	Protects the computer from altered executables
  Physical security	Password pilfering	Protects unauthorized persons from having access to authorized users and their IDs and passwords
  Password policies	Password pilfering	Ensures that passwords are difficult to guess or otherwise decipher

  IPSec (Internet Protocol Security)

  IPSec Is a set of protocols used to support secure exchange of packets at the IP layer. IPsec supports two encryption modes: Transport and Tunnel.

  Transport mode encrypts only the data portion of each packet, but leaves the header untouched.

  The more secure Tunnel mode encrypts both the header and the data portion.

  For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley, which allows the receiver to obtain a public key and authenticate the sender using digital certificates. IPsec protocols operate at the network layer, layer 3 of the OSI model. Other Internet security protocols in widespread use, such as SSL and TLS, operate from the transport layer up (OSI layers 4 - 7). This makes IPsec more flexible, as it can be used for protecting both TCP and UDP based protocols

  L2TP (Layer 2 Tunneling Protocol)

  Layer 2 Tunneling Protocol is a tunneling protocol used to support virtual private networks VPNs. L2TP is an extension to the PPP protocol that enables ISPs to operate Virtual Private Networks. L2TP combines the best features of two other tunneling protocols:PPTP from Microsoft and L2F from Cisco Systems.

  SSL (Secure Sockets Layer)

  Secure Sockets Layer is a protocol that supplies secure data communication through data encryption and decryption. SSL enables communications privacy over networks by using a combination of public key, and bulk data encryption.

  WEP (Wired Equivalent Privacy)

  Wired Equivalent Privacy is a scheme that is part of the IEEE 802.11 wireless networking standard to secure IEEE 802.11 wireless networks. Because a wireless network broadcasts messages using radio, it is particularly susceptible to eavesdropping.
  WEP was intended to provide comparable confidentiality to a traditional wired network and thus it does not protect users of the network from each other.

  WPA (Wi-Fi Protected Access)

  A security protocol for wireless networks that builds on the basic foundations of WEP. It secures wireless data transmission by using a key similar to WEP, but the added strength of WPA is that the key changes dynamically. The changing key makes it much more difficult for a hacker to learn the key and gain access to the network.

  WPA2 (Wi-Fi Protected Access 2)

  WPA2 is the second generation of WPA security and provides a stronger encryption mechanism through Advanced Encryption Standard (AES), which is a requirement for some government users.

  802.11x

  IEEE 802.11 also known by the brand Wi-Fi, denotes a set of Wireless LAN/WLAN standards developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802). The term 802.11x is also used to denote this set of standards and is not to be mistaken for any one of its elements. There is no single 802.11x standard.

  Protocol	Release Date	Op. Frequency	Data Rate (Typ)	Data Rate (Max)	Range (Indoor)	Range (Outdoor)
  802.11a	1999	5.15-5.35/5.47-5.725/5.725-5.875 GHz	25 Mbit/s	54 Mbit/s	~25 meters	~75 meters
  802.11b	1999	2.4-2.5 GHz	6.5 Mbit/s	11 Mbit/s	~35 meters	~100 meters
  802.11g	2003	2.4-2.5 GHz	25 Mbit/s	54 Mbit/s	~25 meters	~75 meters
  802.11n	2007	2.4 GHz or 5 GHz bands	200 Mbit/s	540 Mbit/s	~50 meters	~125 meters

  Identify authentication protocols:

  CHAP (Challenge Handshake Authentication Protocol)

  Challenge Handshake Authentication Protocol is a challenge-response authentication protocol that uses the industry-standard Message Digest 5 (MD5) hashing scheme to encrypt the response. CHAP is used by various vendors of network access servers and clients.

  MS-CHAP (Microsoft Challenge Handshake Authentication Protocol)

  MS-CHAP Microsoft Challenge Handshake Authentication Protocol. MS-CHAP is a nonreversible, encrypted password authentication protocol. The challenge handshake process works as follows:

  • The remote access server or the IAS server sends a challenge to the remote access client that consists of a session identifier and an arbitrary challenge string.
  • The remote access client sends a response that contains the user name and a nonreversible encryption of the challenge string, the session identifier, and the password.
  • The authenticator checks the response and, if valid, the user's credentials are authenticated.

  PAP (Password Authentication Protocol)

  Password Authentication Protocol uses plaintext passwords and is the least sophisticated authentication protocol. It is typically negotiated if the remote access client and remote access server cannot negotiate a more secure form of validation.

  RADIUS (Remote Authentication Dial-In User Service)

  Is an AAA (authentication, authorization and accounting) protocol for applications such as network access or IP mobility. It is intended to work in both local and roaming situations.

  Some ISPs (commonly modem, DSL, or wireless 802.11 services) require you to enter a username and password in order to connect on to the Internet. Before access to the network is granted, this information is passed to a Network Access Server (NAS) device over the Point-to-Point Protocol (PPP), then to a RADIUS server over the RADIUS protocol. The RADIUS server checks that the information is correct using authentication schemes like PAP, CHAP or EAP.

  If accepted, the server will then authorize access to the ISP system and select an IP address. RADIUS is also widely used by VoIP service providers.

  Kerberos and EAP (Extensible Authentication Protocol)).

  An authentication system, Kerberos is designed to enable two parties to exchange private information across an open network. It works by assigning a unique key, called a ticket, to each user that logs on to the network. The ticket is then embedded in messages to identify the sender of the message.

  Extensible Authentication Protocol, or EAP, is a universal authentication framework frequently used in wireless networks and Point-to-Point connections. Although the EAP protocol is not limited to wireless LANs and can be used for wired LAN authentication, it is most often used in wireless LANs. Recently, the WPA and WPA2 standard has officially adopted five EAP types as its official authentication mechanisms.

  Smart Cards

  Smart cards are gaining in popularity as a way to ensure secure authentication using a physical key. Smart cards are able to provide an interactive logon, secure e-mail messages, and authenticate access to network services.

  Smart cards contain chips to store a user's private key and can also store logon information; public key certificates; and other information, depending on the smart card's usage. When a user needs to access a resource, the user inserts the smart card into a reader attached to the network. After typing in the user's personal identification number (PIN), the user is authenticated and can access network resources. The private key is automatically available for transparent access to encrypted information.

  Smart cards require Public Key Infrastructure (PKI), a method of distributing encryption keys and certificates. In addition, each protected resource will require a smart-card reader. Some implementations of smart cards combine the smart card with employee badges so that employees need a single card for building and network access.

  Remote access protocols and services:

  RAS (Remote Access Service)

  Remote Access Service A service that provides remote networking for telecommuters, mobile workers, and system administrators who monitor and manage servers at multiple branch offices. Users with RAS can dial in to remotely access their networks for services such as file and printer sharing, electronic mail, scheduling, and SQL database access.

  PPP (Point-to-Point Protocol)

  PPP is based on an open standard defined in RFCs 1332, 1661, and 2153. PPP works with asynchronous and synchronous serial connections as well as High-Speed Serial Interfaces (HSSI) and ISDN interfaces (BRI and PRI).

  PPP Components 
  PPP has many more features than HDLC. Like HDLC, PPP defines a frame type and how two PPP devices communicate with each other, including the multiplexing of network and data link layer protocols across the same link. However, PPP also does the following:

  • Performs dynamic configuration of links
  • Allows for authentication
  • Compresses packet headers
  • Tests the quality of links
  • Performs error detection and correction
  • Allows multiple PPP physical connections to be bound together as a single logical connection (referred to as multilink)

  PPP has three main components:

  • Frame format (encapsulation)
  • Link Control Protocol (LCP)
  • Network Control Protocol (NCP)

  Each of these three components plays an important role in the setup, configuration, and transfer of information across a PPP connection.

  SLIP (Serial Line Internet Protocol)

  An older industry standard that is part of Windows remote access client to ensure interoperability with other remote access software.

  PPPoE (Point-to-Point Protocol over Ethernet)

  Point-to-Point Protocol over Ethernet encapsulates PPP frames in Ethernet frames and is usually used in conjunction with ADSL services.

  It gives you a lot of the familiar PPP features like authentication, encryption, and compression, but there’s a downside—it has a lower maximum transmission unit (MTU) than standard Ethernet does, and if your firewall isn’t solidly configured, this little attribute can really give you some grief! Still somewhat popular in the United States, PPPoE on Ethernet’s.

  main feature is that it adds a direct connection to Ethernet interfaces while providing DSL support as well. It’s often used by many hosts on a shared Ethernet interface for opening PPP sessions to various destinations via at least one bridging modem.

  PPTP (Point-to-Point Tunneling Protocol)

  Networking technology that supports multiprotocol virtual private networks (VPNs), enabling remote users to access corporate networks securely across the Internet or other networks by dialing into an Internet service provider (ISP) or by connecting directly to the Internet. The Point-to-Point Tunneling Protocol (PPTP) tunnels, or encapsulates, IP, IPX, or NetBEUI traffic inside of IP packets. This means that users can remotely run applications that are dependent upon particular network protocols.

  VPN (Virtual Private Network)

  Virtual private network A remote LAN that can be accessed through the Internet by using PPTP (see above)

  RDP (Remote Desktop Protocol)

  Remote Desktop Protocol (RDP) is a multi-channel protocol that allows a user to connect to a computer running Microsoft Terminal Services. Clients exist for most versions of Windows (including handheld versions), and other operating systems such as Linux, FreeBSD, Solaris Operating System and Mac OS X. The server listens by default on TCP port 3389.

  • Version 4.0 was introduced with Terminal Services in Windows NT 4.0 Server, Terminal Server Edition.
  • Version 5.0, introduced with Windows 2000 Server, added support for a number of features, including printing to local printers, and aimed to improve network bandwidth usage.
  • Version 5.1, introduced with Windows XP Professional, included support for 24-bit color and sound.
  • Version 5.2, introduced with Windows Server 2003, included support for console mode connections, a session directory, and local resource mapping.
  • Version, 6.0, introduced with Windows Vista and Windows Server includes a significant number of new features, most notably being able to remotely access a single application instead of the entire desktop, and support for 32 bit color.

  Star Topology ring Topology bus Topology Logical Physical mesh Topology

  Topologies

  The first thing to consider about a network is its physical shape, or the design layout, which will be extremely important when you select a wiring scheme and design the wiring for a new installation.

  Network really has two shapes, or two types of topology; one is physical and the other is logical. The physical topology is the shape you can see, and the logical topology is the shape that the data travels in.

  Physical Topologies

  Physical topology is further divided in two section

  • Point-to-point connections
  • Multipoint connections

  Point-to-point connections

  Only two devices are involved in a point-to-point connection, with one wire (or air, in the case of wireless) sitting between them. A point-to-point link is typified by two devices monopolizing the media-similar to two teenagers talking on the telephone with one another, not allowing anyone else to use the phone on either side.

  Multipoint connections

  In a multipoint connection, multiple machines share the cabling. Multipoint connections might be a group of computers strung together in a long line on an old-fashioned ThinNet (10Base2) cable, or it could be a party line of telephones, all sharing a common phone connection. In fact, even your local cable TV provider uses a multipoint system to get every person in the neighborhood hooked up. In every multipoint connection, each device must be able to identify itself. This is where addressing at the hardware level starts. The device's address must be unique on the channel that it shares with those other devices, or else confusion reigns. Just ask any network administrator who has accidentally assigned the same logical address to two computers. It's not fun dealing with any type of addressing conflict.

  logical topology

  A logical topology describes how components communicate across the physical topology. The physical and logical topologies are independent of each other. For example, any variety of Ethernet uses a logical bus topology when components communicate, regardless of the physical layout of the cabling. This means that in Ethernet, you might be using 10BaseT with a physical star topology to connect components together; however, these components are using a logical bus topology to communicate.

  Media Type	Physical Topology	Logical Topology
  Ethernet	Bus, star, or point-to-point	Bus
  FDDI	Ring	Ring
  Token Ring	Star	Ring

  Token Ring is another good example of a communication protocol that has a different physical topology from its logical one. Physically, Token Ring uses a star topology, similar to 10BaseT Ethernet. Logically, however, Token Ring components use a ring topology to communicate between devices. This can create confusion when you are trying to determine how components are connected together and how they communicate. FDDI, on the other hand, is straightforward. FDDI’s physical and logical topologies are the same: a ring.

  Ethernet Networks

  In late 1978, the first experimental network system was created to interconnect the Xerox Altos PCs to one another and to servers and laser printers. This first experimental network was called the Alto Aloha Network.

  In 1979 the name was changed to Ethernet, to make it clear that the system could support any computer not just Altos and to point out that the new network mechanisms had evolved well beyond the Aloha system.

  The base word ether was chosen as a way of describing an essential feature of the system; the physical medium (a cable) carries bits to all stations

  In the diagram you can see two ethernet configurations. On the left the computers are connected together with a single cable coming from the router/switch, this is called a bus or thin ethernet configuration. On the right side of the diagram each computer connects directly to the router/switch. this is how most ethernets are configured today. In this topology management of the network is made much easier (such as adding and removing devices), because of the central point. If computers are connected in a row, along a single cable this is called a bus topology, if they branch out from a single junction or hub this is known as a star topology. When computers are connected to a cable that forms a continuous loop this is called a ring topology. We will go trough all of these topologies in coming section.

  Star Topology

  A star configuration is simple: Each of several devices has its own cable that connects to a central hub, or sometimes a switch, multipoint repeater, or even a Multistation Access Unit (MAU). Data passes through the hub to reach other devices on the network. Ethernet over unshielded twisted pair (UTP), whether it is 10BaseT, 100BaseT, or Gigabit, all use a star topology.

  Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer which acts as a router to transmit messages. If the central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time (i.e. to and from the central node) plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems.

  The star topology reduces the chance of network failure by connecting all of the systems to a central node. When applied to a bus-based network, this central hub rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the rest of the systems will be unaffected.

  

  You will find that a star topology is most common in networks. This is mainly because of the ease of configuring and troubleshooting it. If a wire or a single port on the hub or switch goes bad, only one network node goes down, which prevents a huge impact on productivity overall (unless the entire hub or switch fails-in which case, the whole LAN goes down). However, because a star topology involves a central hub or switch as well as a lot more cabling, it costs more to implement.

  Disadvantages of a Star Network

  • Twisted pair cables typically used in star topologies are not as immune to interferences as coxiale cable
  • Expensive because of additional cabling and central hub require
  • If the centralize device fails the entire system is affected.

  Advantages of Star Network

  • Easy to Install: Each device on network simply requires a cable run between it and the concentrator device.
  • Flexible: Devices can be added or removed without affecting the other devices on the network.
  • A single device or cable failure will not bring down the network
  • Easy to set up and to expand.as each device on the network simply requires a cable run between it and the concentrator device
  • Any non-centralised failure will have very little effect on the network, whereas on a ring network it would all fail with one fault.
  • Data Packets are sent quickly as they do not have to travel through any unnecessary nodes.
  • Performance is greater with speeds capable of 10mbps to 100mbps or more
  • The ability to isolate individual devices in troubleshooting An intelligent central hub or switch that can help diagnose and manage the network Adjusting traffic levels so that computers that place heavy loads on the network are moved to separate hubs

  Hierarchical Topology (also known as Tree)

  The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy - the hierarchy of the tree is symmetrical, each node in the network having a specific fixed number, f, of nodes connected to it at the next lower level in the hierarchy, the number, f, being referred to as the 'branching factor' of the hierarchical tree.

  

  
  Notes:

  • A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star.
  • A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology.
  • The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large - this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible.
  • The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less that the total number of nodes in the network.
  • If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes that are lower in the hierarchy.

  Bus Topology

  In bus topologies, all computers are connected to a single cable or "trunk or backbone", by a transceiver either directly or by using a short drop cable. All ends of the cable must be terminated, that is plugged into a device such as a computer or terminator. Most bus topologies use coax cables.

  

  The number of computers on a bus network will affect network performance, since only one computer at a time can send data, the more computers you have on the network the more computers there will be waiting send data. A line break at any point along the trunk cable will result in total network failure. Computers on a bus only listen for data being sent they do not move data from one computer to the next, this is called passive topology. 
  Disadvantages

  • Entire network shuts down if there is a break in the main cable.
  • Difficult to identify the problem if the entire network shuts down.
  • Performance: Coax technology is usually limited to a maximum of 10mbs.
  • Not intended for use as a standalone solution in a large building.
  • Coax technology is usually limited to a maximum of 10mbs.
  • Limited cable length and number of stations.
  • Not intended for use as a standalone solution in a large building.
  • If there is a problem with the cable, the entire network goes down.
  • Performance degrades as additional computers are added or on heavy traffic.
  • Low security (all computers on the bus can see all data transmissions).
  • If one node fails, the whole network will shut down.
  • You are limited with the number of devices that you can have on a single segment.

  Advantages

  • Inexpensive: Does not require additional hardware to interconnect the attached devices.
  • Easy to Install: Coax cable is durable and performs well in harsh environments.
  • Flexible: New devices can be added by simply installing a new ‘T’ connector.
  • Well suited for temporary or small networks not requiring high speeds(quick setup)
  • Initially less expensive than other topologies.
  • Requires less cable length than a star topology

  MeshTopology

  A Mesh topology Provides each device with a point-to-point connection to every other device in the network. These are most commonly used in WAN's, which connect networks over telecommunication links. Mesh topologies use routers to determine the best path. Mesh networks provide redundancy, in the event of a link failure, meshed networks enable data to be routed through any other site connected to the network. Because each device has a point-to-point connection to every other device, mesh topologies are the most expensive and difficult to maintain.

  

  Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile. Mobile ad-hoc networking (MANET), featured in many consumer devices, is a subsection of mesh networking. Mesh networks are self-healing: the network can still operate even when a node breaks down or a connection goes bad. As a result, a very reliable network is formed.

  This concept is applicable to wireless networks, wired networks, and software interaction. There are three distinct generations of wireless mesh architectures. In the first generation one radio provides both backhaul (packet relaying) and client services (access to a laptop). In the second generation, one radio relayed packets over multiple hops while another provided client access. This significantly improved backhaul bandwidth and latency. Third generation wireless mesh products use two or more radios for the backhaul for higher bandwidth and low latency. Third generation mesh products are replacing previous generation products as more demanding applications like voice and video need to be relayed wirelessly over many hops of the mesh network.

  Advantages of Mesh topology

  • Extremely reliable. Data has access to fastest paths and can load balance.
  • Provides redundancy and fault tolerance between devices and ensures the best possibility that the network is always available.

  Diadvantage of Mesh

  • Uses the most cabling to implement.
  • Has a high administrative overhead.

  Ring

  In a ring topology network computers are connected by a single loop of cable, the data signals travel around the loop in one direction, passing through each computer. Ring topology is an active topology because each computer repeats (boosts) the signal before passing it on to the next computer. One method of transmitting data around a ring is called token passing. The token is passed from computer to computer until it gets to a computer that has data to send.

  

  If there is a line break, or if you are adding or removing a device anywhere in the ring this will bring down the network. In an effort to provide a solution to this problem, some network implementations (such as FDDI) support the use of a double-ring. If the primary ring breaks, or a device fails, the secondary ring can be used as a backup.

  Advantages

  • Data is quickly transferred without a 'bottle neck'
  • The transmission of data is relatively simple as packets travel in one direction only.
  • Adding additional nodes has very little impact on bandwidth
  • It prevents network collisions because of the media access method or architecture required.
  • All devices have equal access.

  Disadvantages

  • Because all stations are wired together, to add a station you must shut down the network temporarily.
  • It is difficult to troubleshoot the ring.
  • Data packets must pass through every computer between the sender and recipient Therefore this makes it slower.
  • If any of the nodes fail then the ring is broken and data cannot be transmitted successfully.

  Wireless

  A wireless network consists of wireless NICs and access points. NICs come in different models including PC Card, ISA, PCI, etc. Access points act as wireless hubs to link multiple wireless NICs into a single subnet. Access points also have at least one fixed Ethernet port to allow the wireless network to be bridged to a traditional wired Ethernet network, such as the organization's network infrastructure. Wireless and wired devices can coexist on the same network.

  Wireless topologies seem odd at first because there are no physical wires to guide you to the actual topology shapes that they use. In fact, wireless topologies are implemented in a star, a mesh, or a cellular configuration.

  BSS wireless topology

  In the star configuration, the wireless topology is called a Basic Service Set (BSS). It consists of a wireless access point connected to a wired network, and it enables each wireless device to connect to the access point and through it to all other devices.

  

  Independent Basic Service Set (IBSS)

  In the case of the mesh configuration, the wireless network, the Independent Basic Service Set (IBSS), enables each wireless device to connect to any other wireless device within range.

  

  Extended Service Set (ESS)

  In the cellular topology, the wireless network, referred to as an Extended Service Set (ESS),

  

  consists of a series of overlapping wireless cells, each with its own WAP. Devices can actually move among cells and continue working seamlessly, regardless of which cell they happen to be in. It's easiest to think of this as a radio station. Imagine you're driving down a long road and you have your radio tuned to 95.5 FM. As you go along, you eventually fade out of 95.5 FM for one area, but you fade into 95.5 FM for the next area. If these two stations were playing the exact same program, you wouldn't even know that you had changed from one to another.

  The ESS cascades wireless access points, enabling seamless access to data as a mobile wireless device moves along the network.

  Factors which affect Wireless Network Range Speed Infrared Bluetooth FHSS DSSS OFDM MIMO

  Infrared

  Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of microwave radiation. The name means "below red" (from the Latin infra, "below"), red being the color of visible light of longestwavelength.

  Bluetooth

  Is an industrial specification for wireless personal area networks (PANs). Bluetooth provides a way to connect and exchange information between devices like personal digital assistants (PDAs), mobile phones, laptops, PCs, printers and digitalcameras via a secure, low-cost, globally available short range radio frequency.

  FHSS

  Frequency-hopping spread spectrum is a spread-spectrum method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. Spread-spectrum transmission offers these advantages over a fixed-frequency transmission:

  • Highly resistant to noise and interference.
  • Signals are difficult to intercept. A Frequency-Hop spread-spectrum signal sounds like a momentary noise burst or simply an increase in the background noise for short Frequency-Hop codes on any narrowband receiver except a Frequency-Hop spread-spectrum receiver using the exact same channel sequence as was used by the transmitter.
  • Transmissions can share a frequency band with many types of conventional transmissions with minimal interference. As a result, bandwidth can be utilized more efficiently.

  DSSS

  direct-sequence spread spectrum is a modulation technique where the transmitted signal takes up more bandwidth than the information signal that is being modulated, which is the reason that it is called spread spectrum. Direct Sequence Spread Spectrum (DSSS) uses one channel to send data across all frequencies within that channel. Complementary Code Keying (CCK) is a method for encoding transmissions for higher data rates, such as 5.5 and 11 Mbps, but it still allows backward compatibility with the original 802.11 standard, which supports only 1 and 2 Mbps speeds. 802.11b and 802.11g support this transmission method.

  
  

  Comparison of DSSS and Frequency Hopped SS

  DSSS Flexible support of variable data rates High capacity is possible with enhancements (interference cancellation, adaptive antenna, etc.) Suffers from near-far effect

  FHSS Suitable for ad hoc networks (no near-far problem) Robust to interference Limited data rate

  OFDM

  Orthogonal frequency-division multiplexing, also called discrete multitone modulation (DMT), is a transmission technique based upon the idea of frequency-division multiplexing (FDM). OFDM (Orthogonal Frequency Division Multiplexing)increases data rates by using a spread spectrum: modulation. 802.11a and 802.11g support this transmission method.

  • Used in some wireless LAN applications, including WiMAX and IEEE 802.11a/g
  • Used in many communications systems such as: ADSL, Wireless LAN, Digital audio broadcasting.

  MIMO (Multiple Input Multiple Output)

  MIMO (Multiple Input Multiple Output) transmission, which uses DSSS and/or OFDM by spreading its signal across 14 overlapping channels at 5 MHz intervals. 802.11n uses it. Use of 802.11n requires multiple antennas.

  
  

  
  

  	802.11a	802.11b	802.11g	802.11n
  Data Rate	54 Mbps	11 Mbps	54 Mbps	248 Mbps (with 2×2 antennas)
  Throughput	23 Mbps	4.3 Mbps	19 Mbps	74 Mbps
  Frequency	5 GHz	2.4 GHz	2.4 GHz	2.4 and/or 5 GHz
  Compatibility	None	With 802.11g and the original 802.11	With 802.11b	802.11a, b, and g
  Range (meters)	35–120	38–140	38–140	70–250
  Number of Channels	3	Up to 23	3	14
  Transmission	OFDM	DSSS	DSSS/OFDM	MIMO

  Radio Frequency Transmission Factors

  Radio frequencies (RF) are generated by antennas that propagate the waves into the air. Antennas fall under two different categories:

  • Directional
  • Omni-directional

  Directional Directional antennas are commonly used in point-to-point configurations (connecting two distant buildings), and sometimes point-to-multipoint (connecting two WLANs). An example of a directional antenna is a Yagi antenna: this antenna allows you to adjust the direction and focus of the signal to intensify your range/reach.

  Omni-directional Omni-directional antennas are used in point-to-multipoint configurations, where they distribute the wireless signal to other computers or devices in your WLAN. An access point would use an omni-directional antenna. These antennas can also be used for point-to-point connections, but they lack the distance that directional antennas supply

  Three main factors influence signal distortion:

  • Absorption Objects that absorb the RF waves, such as walls, ceilings, and floors
  • Scattering Objects that disperse the RF waves, such as rough plaster on a wall, carpet on the floor, or drop-down ceiling tiles
  • Reflection Objects that reflect the RF waves, such as metal and glass

  Responsible body

  The International Telecommunication Union-Radio Communication Sector (ITU-R) is responsible for managing the radio frequency (RF) spectrum and satellite orbits for wireless communications: its main purpose is to provide for cooperation and coexistence of standards and implementations across country boundaries. 
  Two standards bodies are primarily responsible for implementing WLANs:

  • The Institute of Electrical and Electronic Engineers (IEEE)
  • The Wi-Fi Alliance.

  IEEE Defines the mechanical process of how WLANs are implemented in the 802.11 standards so that vendors can create compatible products.

  The Wi-Fi Alliance Basically certifies companies by ensuring that their products follow the 802.11 standards, thus allowing customers to buy WLAN products from different vendors without having to be concerned about any compatibility issues.

  Frequencies bands:

  WLANs use three unlicensed bands:

  • 900 MHz Used by older cordless phones
  • 2.4 GHz Used by newer cordless phones, WLANs, Bluetooth, microwaves, and other devices
  • 5 GHz Used by the newest models of cordless phones and WLAN devices

  900 MHz and 2.4 GHz frequencies are referred to as the Industrial, Scientific, and Medical (ISM) bands.

  5 GHz frequency the Unlicensed National Information Infrastructure (UNII) band.

  Unlicensed bands are still regulated by governments, which might define restrictions in their usage.

  A hertz (Hz) is a unit of frequency that measures the change in a state or cycle in a wave (sound or radio) or alternating current (electricity) during 1 second.

  802.11g

  Suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones. Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points; it also means that 802.11a cannot penetrate as far as 802.11b since it is absorbed more readily, other things (such as power) being equal.

  802.11a

  Transmits radio signals in the frequency range above 5 GHz. This range is "regulated," meaning that 802.11a gear utilizes frequencies not used by other commercial wireless products like cordless phones. In contrast, 802.11b utilizes frequencies in the unregulated 2.4 GHz range and encounters much more radio interference from other devices.

  IEEE 802.11a / IEEE 802.11h

  This is also a physical layer enhancement. IEEE 802.11a provides significantly higher performance than 802.11b, at 54 Mbps. Unlike 802.11b, the 802.11a standard operates within the frequency range of 5.47 to 5.725 GHz and is not subject to the same interference from other commercial electronic products. This higher frequency band allows significantly higher speeds of communication over the 2.4 GHz range.

  802.11g APs are backward compatible with 802.11b APs. This backward compatibility with 802.11b is handled through the MAC layer, not the physical layer. On the negative side, because 802.11g operates at the same frequency as 802.11b, it is subject to the same interferences from electronic devices such as cordless phones. Since the standard’s approval in June 2003, 802.11g products are gaining momentum and will most likely become as widespread as 802.11b products. Table II-1 displays basic 802.11b/a/g characteristics.

  The common range of operation for 802.11b is 150 feet for a floor divided into individual offices by concrete or sheet-rock, about 300 feet in semi-open indoor spaces such as offices partitioned into individual workspaces, and about 1000 feet in large open indoor areas. Disadvantages of 802.11b include interference from electronic products such as cordless phones and microwave ovens.

  Range

  The layout of your building can reduce the range.

  • A lot of concrete walls can reduce your range.
  • The size of the antenna and the placement greatly affect the range of their signals
  • The weather and amount of water vapor in the air can affect your signals strength

  Speed

  • The layout of your building can reduce the speed
  • The size of the antenna and its signal can affect your speed
  • The weather and amount of water vapor can weaken the signal and affect your speed

  Main features of 802.2 Logical Link Control 802.3 Ethernet 802.5 token ring 802.11

  • Access method
  • CSMA / CD (Carrier Sense Multiple Access / Collision Detection)
  • CSMA / CA (Carrier Sense Multiple Access/Collision Avoidance)
  • Topology
  • Media
  • Speed

  Gaining Access to the Media

  Media access methods are independent of the physical and logical topologies. You will find that there are usually just a few combinations that seem to work well, however. Media access methods are simply the rules that govern how a device can submit data to the network. Each access method will have a different effect on network traffic.

  Contention as a Method of Media Access

  Contention, often called random access, is the media access method that acts as an open door to anyone who wants to walk in. Two types of contention methods exist for media access; they are similar, but a single difference between themchanges how efficiently they operate. They are:

  • CSMA/CD (Carrier Sense Multiple Access / Collision Detection)
  • CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance)

  CSMA/CD

  In a traditional, or hub-based, Ethernet environment, only one NIC can successfully send a frame at a time. All NICs, however, can simultaneously listen to information on the wire. Before an Ethernet NIC puts a frame on the wire, it will first sense the wire to ensure that no other frame is currently on the wire. If the cable uses copper, the NIC can detect this by examining the voltage levels on the wire. If the cable is fiber, the NIC can detect this by examining the light frequencies on the wire. The NIC must go through this sensing process, since the Ethernet medium supports

  multiple access

  another NIC might already have a frame on the wire. If the NIC doesn't sense a frame on the wire, it will transmit its own frame; otherwise, if a frame is found on the wire, the NIC will wait for the completion of the transmission of the frame and then transmit its own frame.

  Collision Detection

  If two or more devices simultaneously sense the wire and see no frame, and each places its frame on the wire, a collision will occur. In this situation, the voltage levels on a copper wire or the light frequencies on a piece of fiber get messed up. For example, if two NICs attempt to put the same voltage on an electrical piece of wire, the voltage level will be different from that of only one device. Basically, the two original frames become unintelligible (or indecipherable). The NICs, when they place a frame on the wire, examine the status of the wire to ensure that a collision does not occur: this is the collision detection mechanism of CSMA/CD.

  If the NICs see a collision for their transmitted frames, they have to resend the frames. In this instance, each NIC that was transmitting a frame when a collision occurred creates a special signal, called a jam signal on the wire. It then waits a small random time period, and senses the wire again. If no frame is currently on the wire, the NIC will then retransmit its original frame. The time period that the NIC waits is measured in microseconds, a delay that can't be detected by a human. Likewise, the time period the NICs wait is random to help ensure a collision won't occur again when these NICs retransmit their frames. The more devices you place on an Ethernet segment, the more likely you will experience collisions. If you put too many devices on the segment, too many collisions will occur, seriously affecting your throughput. Therefore, you need to monitor the number of collisions on each of your network segments. The more collisions you experience, the less throughput you will get.

  CSMA/CA

  WLANs use a mechanism called Carrier Sense, Multiple Access/Collision Avoidance (CSMA/CA). Unlike Ethernet, it is impossible to detect collisions in a wireless medium. In a WLAN, a device cannot simultaneously send or receive and thus cannot detect a collision: it can only do one or the other. To avoid collisions, a device will use Ready-to-Send (RTS) and Clear-to-Send (CTS) signals. When a device is ready to transmit, it first senses the airwaves for a current signal. If there is none, it generates an RTS signal, indicating that data is about to send. It then sends its data and finishes by sending a CTS signal, indicating that another 

  Ethernet (802.3) and LLC (802.2)

  There are two ways that specifications become standards. One is through standardized development, and the other is through common usage of a proprietary specification, where the usage becomes so prevalent that the specification is adopted as a standard. Ethernet is the latter. The IEEE was not the first to develop Ethernet. That honor goes to the research and development efforts of three companies in the 1970s: Digital, Intel, and Xerox, which were known collectively as DIX. Later on, the IEEE based its 802.3 standard on the DIX specification. In return, DIX updated its implementation to match the small changes made by the IEEE.

  Nowadays, Ethernet is used for these and several other specifications. Ethernet 802.3 is generally implemented in conjunction with 802.2. The system uses the CSMA/CD media access method, with a logical bus topology. Physically, Ethernet can be either a star or a bus. It can use copper coaxial cabling, UTP, and fiber optics. Since Ethernet uses the broadcast system of a bus topology, each node receives every data message and examines the frame header to see whether the message is meant to be received by it. If not, the frames are discarded; if so, the frames are passed on to upper layer protocols so that the receiving application can act on them.

  Data Link Layer	Name	IEEE Standard	Description
  Top part	Logical Link Control (LLC)	802.2	Defines how to multiplex multiple network layer protocols in the data link layer frame, which doesn't have to be Ethernet. LLC is performed in software.
  Bottom part	Media Access Control (MAC)	802.3	Defines how information is transmitted in an Ethernet environment and defines the framing, MAC addressing, and mechanics as to how Ethernet works. MAC is performed in hardware.

  10BaseT 10BaseF 10Base2 5-4-3 rule 10Base5 100BaseFX 100BaseT4 100BaseTX

  IEEE shorthand identifiers, such as 10Base5, 10Base2, 10BaseT, and 10BaseF include three pieces of information:
  • The number 10: At the front of each identifier, 10 denotes the standard data transfer speed over these media - ten megabits per second (10Mbps).
  • The word Base: Short for Baseband, this part of the identifier signifies a type of network that uses only one carrier frequency for signaling and requires all network stations to share its use.
  • The segment type or segment length: This part of the identifier can be a digit or a letter:
  • Digit - shorthand for how long (in meters) a cable segment may be before attenuation sets in. For example, a 10Base5 segment can be no more than 500 meters long.
  • Letter - identifies a specific physical type of cable. For example, the
  • T at the end of 10BaseT stands for twisted-pair.
  10BaseT
  One of the most common types of Ethernet in use today is 10BaseT. This particular implementation uses four-pair UTP wiring (Cat3 or higher, but most commonly you will see Cat5) using RJ-45 connectors. Each cable is connected from each network device to a central hub in a physical star topology. Within the hub, the signals are repeated and forwarded to all other nodes on the network because it is a logical bus topology. Older network interface cards are configured with jumpersto set addresses and interrupts.
  Today's network interface cards can be managed through a diagnostic program, or automatically configure themselves through plug and play technology. There is a limit of 1024 devices on an Ethernet segment, plus you can have a maximum of 1024 network segments. A UTP cable has a maximum distance of 100 meters, which is equivalent to 328 feet.
  10BaseF
  10BaseF is an implementation of Ethernet 802.3 over fiber optic cabling. 10BaseF offers only 10 Mbps, even though the fiber optic media has the capacity for much faster data rates. One of the implementations of 10BaseF is to connect two hubs as well as connecting hubs to workstations. The best time to use 10BaseF is in the rewiring of a network from copper to fiber optic, when you need an intermediate protocol using the new wiring. 10BaseF is not often a permanent solution because the data rate is so low and the cabling so expensive in comparison to using UTP.
  10Base2
  10Base2, also called ThinNet, is one of the two Ethernet specifications that use coaxial cable. (One of the best ways to remember that 10Base2 is ThinNet, and 2 is smaller than 10Base5, which is ThickNet.) One of the most important issues to remember in an Ethernet coax wiring scheme is the 5-4-3 rule,
  5-4-3 rule
  which states that you can have up to five cable segments, connected by four repeaters, with no more than three of these segments being mixing segments. In the days of coaxial cable networks, this meant that you could have up to three mixing segments of 500 or 185 meters each (for 10Base5 and 10Base2, respectively) populated with multiple computers and connected by two repeaters. You could also add two additional repeaters to extend the network with another two cable segments of 500 or 185 meters each, as long as these were link segments connected directly to the next repeater in line, with no intervening computers,
  A 10Base2 network could therefore span up to 925 meters and a 10Base5 network up to 2,500 meters which states that there can only be 5 segments in a series and 4 repeaters between these 5 segments, although only 3 of the segments can be populated with devices. 10Base2 uses BNC connectors and is implemented as both a physical and logical bus topology using RG-58 cabling.
  The minimum distance for cables between workstations must be at least a half-meter. Drop cables should not be used to connect a BNC connector to the network interface card (NIC) because this will cause signaling problems unless the NIC is terminated. 10Base2 ThinNet segments cannot be longer than 185 meters, although it is often exaggerated to 200 meters, and you can't put more than 30 devices on each populated segment. The entire cabling scheme, including all five segments, can't be longer than 925 meters.
  10Base5
  10Base5 is nearly identical to 10Base2, except that it uses a different type of cabling and media connector. 10Base5 is known as ThickNet because it uses the RG-8 coaxial cable. It requires an external transceiver to attach to the network interface card on each device. The transceiver is a device that translates the workstation's digital signal to a baseband cabling format. ThinNet and UTP network interface cards have built-in transceivers. Only 10Base5 ThickNet network interfaces use external transceivers. In the 10Base5 configuration, the NIC attaches to the external transceiver using an AUI connector. The transceiver then clamps into the ThickNet cabling, which is why it is usually called a vampire tap. 10Base5 can also use BNC connectors. For 10Base5, the following rules apply: First the 5-4-3 rule applies to ThickNet just as it did to ThinNet. In addition, the minimum cable distance between each transceiver is 2.5 meters. The maximum network segment length is 500 meters, which is where 10Base5 gets the "5" in its name. The entire set of five segments cannot exceed 2,500 meters. You can have 100 devices on a 10Base5 network segment.
  100BaseFX
  100BaseFX is simply Fast Ethernet over fiber. Originally, the specification was known as 100Base-X over CDDI (Copper Data Digital Interface) or FDDI (Fiber Data Digital Interface). Because the signaling is so vastly different, these two technologies were split into 100BaseFX and 100BaseTX. 100BaseFX runs over multimode fiber. There are two types of fiber in use. Multimode fiber optic cables use LEDs to transmit data and are thick enough that the light signals bounce off the walls of the fiber. The dispersion of the signal limits the length of multimode fiber. Single mode fiber optic cables use injected lasers to transmit the data along fiber optic cable with an extremely small diameter. Because the laser signal can travel straight without bouncing and dispersing, the signal can travel much farther than multimode.
  100BaseT4
  100BaseT4 was the specification created to upgrade 10BaseT networks over Cat3 wiring to 100 Mbps without having to replace the wiring. Using four pairs of twisted pair wiring, two of the four pairs are configured for half-duplex transmission (data can move in only one direction at a time). The other two pairs are configured as simplex transmission, which means data moves only in one direction on a pair all the time.
  100BaseTX
  100BaseTX, Fast Ethernet, transmits data at 100 Mbps. Leveraging the existing IEEE 802.3u standard rules, Fast Ethernet works nearly identically to 10BaseT, including that it has a physical star topology using a logical bus. 100BaseTX requires Cat5 UTP.
  Gigabit Ethernet
  The fastest form of Ethernet is currently Gigabit Ethernet, also known as 1000BaseT over Cat5 or highergrade cable, using all four pairs of the cable. It uses a physical star topology with logical bus. There is also 1000BaseF, which runs over multimode fiber optic cabling. Data transmission is full-duplex, but half-duplex is also supported.
  1.3 Specify the characteristics (For example: speed, length, topology, and cable type) of the following cable standards:
  • 10BASE-T and 10BASE-FL
  • 100BASE-TX and 100BASE-FX
  • 1000BASE-T, 1000BASE-CX, 1000BASE-SX and 1000BASE-LX
  • 10 GBASE-SR, 10 GBASE-LR and 10 GBASE-ER
  Designation	Supported Media	Maximum Segment Length	Transfer Speed	Topology
  10Base-5	Coaxial	500m	10Mbps	Bus
  10Base-2	ThinCoaxial (RG-58 A/U)	185m	10Mbps	Bus
  10Base-T	Category3 or above unshielded twisted-pair (UTP)	100m	10Mbps	Star,using either simple repeater hubs or Ethernet switches
  1Base-5	Category3 UTP, or above	100m	1Mbps	Star,using simple repeater hubs
  10Broad-36	Coaxial(RG-58 A/U CATV type)	3600m	10Mbps	Bus(often only point-to-point)
  10Base-FL	Fiber-optic- two strands of multimode 62.5/125 fiber	2000m (full-duplex)	10Mbps	Star(often only point-to-point)
  100Base-TX	Category5 UTP	100m	100Mbps	Star,using either simple repeater hubs or Ethernet switches
  100Base-FX	Fiber-optic- two strands of multimode 62.5/125 fiber	412 meters (Half-Duplex) 2000 m (full-duplex)	100 Mbps (200 Mb/s full-duplex mode)	Star(often only point-to-point)
  1000Base-SX	Fiber-optic- two strands of multimode 62.5/125 fiber	260m	1Gbps	Star,using buffered distributor hub (or point-to-point)
  1000Base-LX	Fiber-optic- two strands of multimode 62.5/125 fiber or monomode fiber	440m (multimode) 5000 m (singlemode)	1Gbps	Star,using buffered distributor hub (or point-to-point)
  1000Base-CX	Twinax,150-Ohm-balanced, shielded, specialty cable	25m	1Gbps	Star(or point-to-point)
  1000Base-T	Category5	100m	1Gbps	Star
  802.5 (token ring)
  The IEEE 802.5 Token Ring standards define services for the OSI physical layer and the MAC sublayer of the data link layer. Token Ring computers are situated on a continuous network loop. A Token Ring controls access to the network by passing a token, from one computer to the next. Before they can transmit data they must wait for a free token, thus token passing does not allow two or more computers to begin transmitting at the same time.
  • Token Ring has some major advantages over Ethernet:
  • The maximum frame size for Token Ring is 4k, which is much more efficient that the small Ethernet maximum.
  • Token Ring has long-distance capability.
  • Every station in the ring is guaranteed access to the token at some point; thus, every station can transmit data.
  • Error detection and recovery techniques are also enhanced in a Token Ring environment by using a monitor function normally controlled by a server. For example, if the token is lost or corrupted, the protocol provides a mechanism to generate a new token after a specified time interval has elapsed.
  Media	MAC Method	Signal Propagation Method	Speed	Topologies	Maximum Connections
  Twisted-pair(various types)	Token passing	Forwarded from device to device (or port to port on a hub) in a closed loop	4Mbps 16 Mbps	Ring Star-using Token Ring repeater hubs	255nodes per segment
  802.11b (wireless)
  802.11b is a wireless Ethernet technology operating at 11MB. 802.11b devices use Direct Sequence Spread Spectrum (DSSS) radio technology operating in the 2.4GHz frequency band. An 802.11b wireless network consists of wireless NICs and access points. Access points act as wireless hubs to link multiple wireless NICs into a single subnet. Access points also have at least one fixed Ethernet port to allow the wireless network to be bridged to a traditional wired Ethernet network.. Wireless and wired devices can coexist on the same network. 802.11b devices can communicate across a maximum range of 50-300 feet from each other.
  FDDI networking technologies
  Fiber Distributed Data Interface, shares many of the same features as token ring, such as a token passing, and the continuous network loop configuration. But FDDI has better fault tolerance because of its use of a dual, counter-rotating ring that enables the ring to reconfigure itself in case of a link failure. FDDI also has higher transfer speeds, 100 Mbps for FDDI, compared to 4 - 16 Mbps for Token Ring. Unlike Token Ring, which uses a star topology, FDDI uses a physical ring. Each device in the ring attaches to the adjacent device using a two stranded fiber optic cable. Data travels in one direction on the outer strand and in the other direction on the inner strand. When all devices attached to the dual ring are functioning properly, data travels on only one ring. FDDI transmits data on the second ring only in the event of a link failure.
  Media	MAC Method	Signal Propagation Method	Speed	Topologies	Maximum Connections
  Fiber-optic	Token passing	Forwardedfrom device to device (or port to port on a hub) in a closed loop	100 Mbps	Double ringStar	500 nodes
  Types of Networks LAN MAN WAN CN VPN SAN Internet Extranet Intranet
  A network is basically all of the components (hardware and software) involved in connecting computers across small and large distances. Networks are used to provide easy access to information, thus increasing productivity for users.
  benefits of networking
  There are lots of advantages from build up a network, but the three big facts are- 
  File Sharing 
  From sharing files you can view, modify, and copy files stored on a different computer on the network just as easily as if they were stored on your computer. 
  Resource Sharing 
  Resources such as printers, fax machines, Storage Devices (HDD, FDD and CD Drives), Webcam, Scanners, Modem and many more devices can be shared.
  Program Sharing 
  Just as you can share files on a network, you can often also share program on a network. For example, if you have the right type of software license, you can have a shared copy of Microsoft Office, or some other program, and keep it on the networkserver, from where it is also run
  Types of Networks
  Local Area Networks
  Local area networks (LANs) are used to connect networking devices that are in a very close geographic area, such as a floor of a building, a building itself, or a campus environment.
  Wide Area Networks
  Wide area networks (WANs) are used to connect LANs together. Typically, WANs are used when the LANs that must be connected are separated by a large distance.
  Metropolitan Area Networks
  A metropolitan area network (MAN) is a hybrid between a LAN and a WAN.
  Storage Area Networks
  Storage area networks (SANs) provide a high-speed infrastructure to move data between storage devices and file servers. 
  Advantage
  • Performance is fast.
  • Availability is high because of the redundancy features available.
  • Distances can span up to 10 kilometers.
  • Management is easy because of the centralization of data resources.
  • Overhead is low (uses a thin protocol).
  Disadvantage of SANs is their cost.
  
  
  Content Networks
  Content networks (CNs) were developed to ease users' access to Internet resources. 
  Companies deploy basically two types of CNs:
  • caching downloaded Internet information
  • Distributing Internet traffic loads across multiple servers
  Intranet
  An intranet is basically a network that is local to a company. In other words, users from within this company can find all of their resources without having to go outside of the company. An intranet can include LANs, private WANs and MANs,
  Extranet
  An extranet is an extended intranet, where certain internal services are made available to known external users or external business partners at remote locations.
  Internet
  An internet is used when unknown external users need to access internal resources in your network. In other words, your company might have a web site that sells various products, and you want any external user to be able to access this service.
  VPN
  A virtual private network (VPN) is a special type of secured network. A VPN is used to provide a secure connection across a public network, such as an internet. Extranets typically use a VPN to provide a secure connection between a company and its known external users or offices.
  Authentication is provided to validate the identities of the two peers.
  Confidentiality provides encryption of the data to keep it private from prying eyes.
  Integrity is used to ensure that the data sent between the two devices or sites has not been tampered with.