THE INTERACTIVE NETWORK DESIGN MANUAL

Building a Frame Relay Network

An Example Network

Let's say that you wanted to connect five campus locations across the country. After studying your applications, you determine that your connection needs are as follows:

In this configuration, traffic flows from Site "A" to Site "B" require a maximum speed of 256 Kbps; Connections between sites "C," "D" and "E" to Site B require a maximum speed of 48 Kbps; and Site E exchanges a small amount of traffic with Site A, at 12 Kbps.

This would require a leased-line network design like this:

In addition to being costly, this design wastes bandwidth in the following areas:

• Of the 24 T1 channels (DSOs) available at Site A and B, only five and seven are utilized, respectively.
  
• Because Site E requires access to both Sites A and B, 2 costly access lines must be installed.
  
• None of the DS0s in the core of the network will be used to full capacity. For example, the link between Site A and Site E is projected to be used at only 21 percent of its installed rate.

The leased-line design also limits flexibility:

• If a need arises to connect sites C and E, new circuit installations will likely take weeks or even months to complete.
  
• Fault tolerance using spare or standby circuits and ports is very costly to implement

These requirements could be met with a frame relay network design like this:

A cost comparison shows that the frame relay network saves between $26,872 and $37,192 in the first year, and $31,872 and $42,192 per ongoing year, as compared to the leased-line alternative.

Why the savings range? If you're willing to let the carrier throw away your traffic when its network gets congested, you can elect for a "0 CIR" link. Using 0 CIR, link costs were reduced by as much as $6,000 for a single link in this example. It's a little more risky to the customer, but carriers are now backing up their 0 CIR service with performance guarantees.