Lesson 6: WAN Basics

WAN Basics | Transmission Options | WAN Requirements & Solutions

Wide-Area Network Requirements

 - Minimize bandwidth costs
 - Maximize efficiency
 - Maximize performance
 - Support new/emerging applications
 - Maximize availability
 - Minimize management and maintenance

Manage Bandwidth to Control Cost

Because transmission costs are by far the largest portion of a network’s cost, there are a number of bandwidth optimization features you should be aware of that enable the cost-effective use of WAN links. These include dial-on-demand routing, bandwidth-on-demand, snapshot routing, IPX protocol spoofing, and compression.
Dial-on-demand ensures that you’re only paying for bandwidth when it’s needed for switched services such as ISDN and asynchronous modem (and switched 56Kb in the U.S. and Canada only).
Bandwidth-on-demand gives you the flexibility to add additional WAN bandwidth when it’s needed to accommodate heavy network loads such as file transfers. Snapshot routing prevents unnecessary transmissions. It inhibits your switched network from being dialed solely for the purpose of exchanging routing updates at short intervals (e.g.: 30 seconds). Many of you are familiar with compression, which is also a good method of optimization.

Lets take a close look at a few features that will keep your WAN costs down.

 - Dial-on-Demand Routing

Dial-on-demand routing allows a router to automatically initiate and close a circuit-switched session.
With dial-on-demand routing, the router dials up the WAN link only when it senses “interesting” traffic. Interesting traffic might be defined as any traffic destined for the remote network, or only traffic related to a specific host address or service.
Equally important, dial-on-demand routing enables the router to take down the connection when it is no longer needed, ensuring that the user will not have unnecessary WAN usage charges.

 - Bandwidth-on-Demand

Bandwidth-on-demand works in a similar way.
When the router senses that the traffic level on the primary link has reached a certain threshold—say, when a user starts a large file transfer—it automatically dials up additional bandwidth through the PSTN to accommodate the increased load.
For example, if you’re using ISDN, you may decide that when the first B channel reaches 75% saturation for more than one minute, your router will automatically dial up a second B channel. When the traffic load on the second B channel falls below 40%, the channel is automatically dropped.

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