Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 4 Troubleshooting with Call Flows
Call Flow Analysis
To troubleshoot the problems in this scenario, perform the following steps:
Step 1 Trap the message exchange between the Call Agent, the originating MTA and trunk gateway, and verify
it against the reference call flow.
Determine whether CRCX or MDCX messages are receiving return NAK messages. The MTAs or trunk
gateway may NAK for the following reasons:
• The Call Agent is attempting to create a connection (CRCX) for a line or trunk that already has an
RTP session active. This can happen if the Call Agent and MTA/trunk gateway get out of sync.
Somehow, an RTP session from a previous call was not torn down, though the Call Agent thinks the
line or trunk endpoint is idle.
From the trunk gateway, use the show mgcp command to compare the channels that the SS7 gateway
and the trunk gateway both view as available. If they are out of sync, use the Circuit Group Block
feature of Maintenance Block to instruct the SS7 gateway not to route calls to the problem trunk.
Wait until all active calls are complete, then delete idle calls, and bring the trunk up again.
• The SDP parameters are not understood by the TGW. Check the SDP parameters in the trapped
message against the reference call flow.
Step 2 Check to see whether the Call Agent can reach the terminating MTA and ingress trunk gateway—that is,
can you see repeated attempts to create (CRCX) the MTA or trunk gateway connection? This may
indicate a problem communicating with the gateways.
Note In this case the Call Agent should send a REL message to the PSTN switch, and route the caller
to an announcement.
Call Agent
Originating MTA
CRCX, full duplex, ringback, ring,
SDP params B, xsaction ID=004
ACK - xsactionID=004, SDP params A
MDCX, half duplex, SDP params A,
xsactionsID=006
ACK - xsactionID=006
CRCX, full duplex, xsactionID=006
ACK - xsactionID=005, SDP params B
Terminating MTA
PSTN Switch
104552
RTP Session Establishment
Ringbacktone
SS7 Initial Address
Message (IAM)
SS7 Address Complete
Message (ACM)