This error applies to the IGX broadband trunk module (BTM) with T3, E3,
and E1 backcards.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware
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The Blue Signal, also known as an Alarm Indication Signal (AIS),
indicates one of two problems:
Equipment upstream from the trunk interface is in alarm.
Equipment upstream from the trunk interface is functional, but an
intermediate device is in alarm.
The term upstream refers to the relative position of a piece of
transmission equipment in the network. The BTM is:
The T3 or DS3 Blue Signal or AIS is generated on all DS3 outputs of a
higher order transmission system during a complete system failure. A Blue
Signal triggers to prevent unnecessary tributary alarms. A DS3 Blue Signal
(AIS) is a signal with the following:
Transmission equipment generates an AIS in the downstream direction if
it cannot recover from a problem that occurs with the upstream signal.
Transmission equipment includes multiplexers, channel service units (CSUs), and
digital cross-connect systems (DCS).
Error conditions such as a loss of signal (LoS) or loss of frame (LoF)
prevent the trunk from delivering the signal received from the equipment
upstream to the downstream equipment.
The likely location of equipment errors is highlighted in yellow.
The following troubleshooting activities are intrusive. Perform these
steps in a maintenance window only if user traffic is affected or if
dsptrks indicates an error condition still persists
such as when the trunk is not in Clear-OK.
Both ends of the trunk must be active during troubleshooting. Issue
the dsptrks command to verify that the trunk is
active. If the trunk number is not displayed in the
dsptrks screen, the trunk is not active. To activate
a trunk, issue the uptrk command.
If the remote end of the trunk is in Yellow alarm in the
dsptrks screen, verify that the cabling is correct
between the remote IGX and the remote end of the trunk.
The local trunk end will be in an AIS
(BLUE) alarm if the transmit direction of the remote IGX trunk
cable is not connected. Therefore, the remote Network Termination (NT) would
have an LoS.
Verify the remote cabling.
Leave the remote cabling connected to the remote trunk card but
remove it from the remote NT.
Place a hardware loop on the BTM backcard. For E1, use a loopback
plug. For T3/E3, use an appropriate BNC connector.
As an alternative to the hardware loop on the BTM backcard, place
the remote NT into the loop toward the customer premises equipment (CPE). The
CPE is the BTM at the remote site.
Issue the clrtrkerrs command and then
the dsptrkerrs command.
If errors have stopped incrementing, the cabling and the BTM card
set at the remote IGX are working properly.
Monitor dsptrkerrs for at least five
minutes before proceeding.
Restore the cabling at the remote IGX.
Ask your Telco to trace the source of the AIS. The problem could
exist on an intermediate device.
If the problem persists after performing the troubleshooting steps,
please contact the Cisco Systems Technical Assistance Center (TAC) at (800)
553-24HR, (408) 526-7209, the Cisco
Technical Support Website, or send e-mail to