A condition may occur where a single slave continues to send data to the master after the normal response period has expired. This condition locks up the bridge so that no other slave can transmit data back to the master. To resolve this condition, the squelch command can be enabled on a bridge or on an individual slave or master branch. Squelch is enabled by configuring a timeout period that, once expired, raises an alarm and triggers the squelching function. A normal quiescent traffic pattern (all 1s for MDDB and low volume for PCM multidrop) is inserted towards the bridge. This blocks the problematic slave so that other slaves can continue to use the bridge.
In order to put the bridge into the normal state, it must be reset. This can be manually initiated by the operator with the squelch reset command, or it can occur automatically after a configured time if the squelch-recovery command is set to auto.
For MDDB, because different algorithms are needed to detect squelch conditions at low-speed and high-speed rates, interface speed selection is required. The interface speed is set at the bridge level.