Vendors such as Fore are starting to offer OC-3c/12/c and OC-48c (future) interfaces on their ATM switches. Using these interfaces, the switches can be connected together in a ringlike fashion. A service offered when connected in a ring is called Fast Failover Recovery, or something along that line. This service provides functionality that is identical to SONET protection-switching. Basically, bandwidth is reserved around the ring for protection scenarios. When the ATM switches detect failure (fiber cut, node failure, etc.), they recreate the VP around the opposite direction of the ring using the reserved bandwidth. This is done at the ATM level, versus the physical level for SONET. As expected, the switchover time is in seconds versus the milliseconds for SONET.

For networks that carry data that is not sensitive to this increased switchover time, does it make sense to use SONET at all? The question comes down to why do you need a SONET ring when then same functionality and speed is provided by the ATM ring?

mm mm sssss nnnnnn * Bharat Ranjan * m m m s nnnnnnn * Network Engineer * m m m sssss nn nn * MSN Network Services * m m s nn nn * (206)-936-0471 * m m sssss nn nn * bharatr@microsoft.com * ******************************************************* * The opinions/ideas in this memo are not necessarily * * those of Microsoft Corp. * *******************************************************