This document explains standby Pseudo-Random Bit Sequence (PRBS) errors
on the Cisco BPX and provides an approach to resolve the errors.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
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The Cisco BPX has redundant buses for point-to-point links. When a
standby Broadband Controller Card (BCC) is present and you have fully updated
the BCC, the Serial Interface Unit (SIU) generates a test pattern on the
inactive bus transmitter. The SIU receives the same pattern on the SIU receiver
on the inactive bus. The standby BCC provides the loopback of the
Standby PRBS errors indicate the failure of a background test of the
standby bus. This test sends and receives a PRBS over the standby circuitry.
The test failure can indicate a problem with the reporting card, the backplane,
or the standby BCC. The errors warn that, if a BCC switchover takes place, the
card may not be able to transmit or receive data properly on the
The resolution of standby PRBS errors is a process of elimination. If
multiple cards report the error, the error can mean that the BCC crosspoint
switch is faulty or the configuration was poor. When a single card has counts
that increment, you should either switch the card or switch the standby BCC.
(You can try to reset each card first, but this reset is not likely to resolve
the problem.) If possible, use a flashlight to inspect the backplane pins while
you remove the cards for replacement. Look for any bent pins. As a final
option, you can replace the backplane.
The report of a failure on the card can be the result of a bad SIU
chip, failure of the report mechanism, or poor workmanship on any of the
associated components. These are important failures to correct because the
failures indicate that the card has problems with the transmission of data to
other cards when you issue a switchcc