VC will be forwarded through the Frame Relay cloud to their intended destinations (additional frames may be dropped). The higher the CIR, the more the service will cost. A CIR is required for each VC. The burst rate The burst rate is the maximum speed of the Frame Relay VC. Frames that exceed the CIR-but not the burst rate-are marked discard-eligible (DE). DE frames will be forwarded by the switches in the Frame Relay cloud as long as there is sufficient bandwidth to do so, but may be dropped at the discretion of the Frame Relay provider. Having a high burst rate is an inexpensive way to get more bandwidth for a lower cost. The burst rate is often a multiple of the CIR; you may hear the burst rate referred to as a "2x burst," which means the burst rate is twice the CIR. You can also order a VC with zero burst. A burst rate is required for each VC. Figure 23-4 shows a bandwidth utilization graph for a Frame Relay link. The link is running locally over a T1 with a port speed of 1.5 Mbps. The CIR is 512 Kbps, and the Chapter 23: Frame Relay Port speed 1536 kbps All Frames in this Burst 1024 kbps range are discard-eligible 512 kbps 0 Mbps Figure 23-4. Frame Relay CIR and DE frames link has been provisioned with a 2x burst. As you can see in the graph, as traffic exceeds the 2x burst threshold, it is discarded. This type of graph indicates that the link is saturated and needs to be upgraded. A good rule of thumb is to order more bandwidth when your link reaches 70 percent utilization. This circuit should have been upgraded long ago. Frame Relay has fallen out of favor with many enterprises. Aggressive MPLS pricing by the major carriers along with features like Ethernet handoff have made MPLS more economical and therefore more popular. Frame Relay is still out there, though, SO even if your job is to replace it with MPLS, you'll still need to understand how it works. Frame Relay Network Design Frame Relay links are more flexible than point-to-point links, because multiple links can be terminated at a single interface i