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 * *