Frame Relay Traps for the Unwary

On the surface, Frame Relay is a marvelous technology for lowering ones' leased line network costs. However, there are traps for the unwary hiding in the very structure of the service.


The theory is nice:

The most attractive thing about Frame Relay is that if one or more of your PVCs needs to "burst" faster than the CIR (i.e. consume more bandwidth than the CIR allows), well, then it can do so, provided that there is available bandwidth in the network (from your access pipe on out). Nothing additional is required - you just start blatting more data through the PVCs. If the bandwidth is available in the network, your extra frames will arrive at their destination, and if not, they will be dropped by the Frame Relay switches.

The Underlying Assumption

The basic assumption in this network design is that no one will be using their full CIR on every PVC all the time (or even at the same time), so that there should always be "excess" bandwidth available for "bursting" above the CIR on any given PVC.

The Traps

Unfortunately, this design also has some potentially nasty side effects given the economic structure of the offering:

The end result of this clash of incentives is a network that cannot burst above CIR on any PVC. There are only two forces that mitigate against this dire outcome:

One Additional "Gotcha!"

Telephone companies, whose principle business is voice, have consistently failed to provide data services with the same reliability, care and regard as their voice networks. Anecdotal evidence suggests that for any "intelligent" switched data service (e.g. Frame Relay, SMDS, ATM), whenever the switch configuration is touched by the TelCo (e.g. to add or delete a customer) one or more existing customers are adversely affected (i.e. lose service).

As is often said, "They Just Don't ``Get It.''"

The one data service that the TelCos seem to be able to get right with some consistency is leased circuits with no switching on them at all.

Erik Fair <>
October 20, 1997