oint are critical components of a circuit order. If the location does not have phone service, in most cases, it won't exist to telco. The port speed The port speed is the size of the physical circuit you will deliver to each end. These physical links do not have to be the same size or type, but they must both be able to support the CIR requested for the frame-relay link. The port speed can be anything from a 56 Kbps DDS circuit up to and exceeding a DS3. These days, the most common frame-relay handoff is a full T1, though fractional T1s are still used as well. It all depends on the cost of the physical circuit. Chapter 22: Frame Relay The committed information rate (CIR) The CIR is the rate of transfer that you want the carrier to provide. When requesting frame-relay service, you specify the amount of bandwidth you want to be available, and the provider guarantees that up to this level, all frames that are sent over this virtual circuit 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 virtual circuit. The burst rate The burst rate is the maximum speed of the frame-relay virtual circuit. 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 virtual circuit with zero burst. A burst rate is required for each virtual circuit. Figure 22-4 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 link has been provision