9500 MXC User Manual
3DB 23063 ADAA - Rev 004 July 2007 Vol. II-2-31
• The guard time halves after each period of guard time during which no
switching occurs (down to the minimum).
• When the guard time decays to its minimum, subsequent switch requests are
actioned immediately.
• There are two independent guard timers for each protection context, one
associated with TX switching and one associated with RX switching.
• The switch guard time has a minimum period of 5 seconds and a maximum
period of 320 seconds (5 x 26 events).
• The guard time mechanism is disabled in protection diagnostic modes.
Switch Conditions: IDU 20x and IDU 155o
This data is applicable to hot-standby and space diversity.
• Tx switching is not hitless.
• Rx switching between the two receive paths is hitless (errorless) for Rx path
alarm events - except for IDU 20x when operated in the Hot-standby:
Non-protected Tributary mode.
• Receiver voting is used between the two receiving IDUs such that the least
errored data stream is selected on a frame-by-frame basis within the online
Rx IDU. This voting action is hitless (errorless).
• The online Rx IDU controls the Rx protection switch function (Rx diversity
bus), and is default assigned to be with the online Tx IDU (the primary IDU
of the protected pair is default online for Tx and Rx).
• An Rx path alarm will not cause an Rx online switch (Rx path alarms are not
included in the IDU 20x and IDU 155o switch conditions).
• For the IDU 20x in Hot-standby: Non-protected Tributary mode, switching
on a failed path is not hitless; the 20/16 tribs assigned on the failed path are
restored from the remaining path (via the IDU-IDU expansion cable) within
200 ms, the 20/16 tribs assigned on remaining path are not affected.
• When a Tx online switch occurs, the Rx online function is switched to be with
the new Tx online providing there is no blocking condition on the partner Rx
path, and providing there are no System/Controls locks in place. This switching
of the Rx online function, as for a Tx switch, is not hitless.
• In the event of a switch of Rx online function, the Tx online will not be
switched, meaning one IDU will be online receiving, the other online
transmitting. Such a switch of online Rx function is not hitless and should only
occur when forced by an Rx lock command in the Systems/Controls screen.
• Protection switch oscillation is prevented by the guard time mechanism. It
applies to Tx and Rx online switch events.
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