Several times this year, we have discussed benchmarks for determining the maximum number of permanent virtual circuits you should deploy per port. In response a couple of those newsletters, we recently received some interesting insight from Dan Kosek, vice president of marketing at American Technology, a WAN-access router company. Kosek points out that the Local Management Interface update status that must fit in a frame limits you to 317 Data Link Connection Identifier status updates. So, only 317 of the approximately 1,000 theoretical addresses available per port are actually available.
Some people prefer to overbook the CIRs on their ports.
That is, the sum of the CIRs for each of the PVCs may exceed the port speed. In this case, you are still guaranteed that you will get your PVC through a WAN backbone if and when you need it. However, you have also assumed that the likelihood of all PVCs being active at the same time is low. This means that you are willing to take a chance that the egress port queue at the last switch in the carrier network occasionally will have more data offered to it than it can handle. Steven Taylor, consultant and broadband packet evangelist, and Joanie Wexler, an independent networking technology editor and writer, team up to bring you this analysis and commentary.