Alcatel-Lucent 9500 MXC User Manual page 190

Chapter 3. 9500 MXC Nodes
Receiver Switching
Vol. II-3-96
Receiver path switching (voting) between the two receiving RACs is hitless for
hot-standby and diversity configurations. The least errored data stream is
selected on a frame-by-frame basis within the online, bus-driving, RAC.
The online Rx RAC manages the Rx protection switch function, and is
transferred between RACs to always be with the online Rx RAC.
The RAC assigned as the secondary RAC in a protected primary/secondary
pairing is the default online RAC. Refer to Protected and Diversity Operation on
page F-10, Appendix F.
In the event of RAC/ODU receive equipment failure:
• If the designated offline RAC/ODU (default primary) receiver fails or is
removed, the receive data stream will not be errored as the RAC designated as
online is controlling the switching and driving the TDM bus.
• If the designated online RAC/ODU (default secondary) receiver fails, the
receive data stream will not be errored if the failure occurs prior to the RAC Rx
diversity bus (between ODU antenna input and the RAC Rx diversity bus).
• If the designated online RAC/ODU (default secondary) receiver fails after the
diversity bus (between RAC Rx diversity bus and the TDM bus) or is removed,
the offline (primary) RAC/ODU is switched to become the online bus-driving
RAC. This switching is not hitless, and the primary RAC remains as the online
bus-driving RAC until changed within 9500 MXC CT, or a subsequent
bus-drive switch event.
• Switching from the online to offline Rx RAC will not be initiated if the offline
Rx RAC has failed, or the offline Rx RAC has been removed or replaced by an
incorrect plug-in. Similarly, a switch will not be initiated if the ODU associated
with the offline RAC has failed or is disconnected.
One gate-array is employed between the Rx diversity bus and the TDM bus. It
provides a function that is directly equivalent to a receive protection switch.
Correct operation is monitored, and in the event of an alarm (software corruption)
a RAC switch command is initiated. A software auto-reload to the alarmed gate
array (from the embedded software set held in the NCC CompactFlash) is also
initiated to attempt to clear the alarm.
RAC Rx Online Switching Criteria
An online RAC switch is triggered by one or more of the following conditions:
• RAC plug-in is missing
• RAC plug-in is incorrect
• RAC FPGA software load failure
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