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
Step 2 Check to see whether the Call Agent can reach the terminating MTA—that is, are repeated attempts to
create the connection (CRCX messages) seen at the terminating side? This may indicate a problem
communicating with the terminating MTA.
Note This failure should normally cause the Call Agent to route the originator to an announcement.
Verify L3 connectivity between the Call Agent and the terminating MTA.
Step 3 If the MGCP messaging looks correct, check to see whether the originator can dial another on-net test
phone. If the originator can call the test phone and talk successfully, the problem could be with the
terminating MTA. Use the test phone to originate a call to the terminating MTA. If the test phone cannot
terminate to the MTA, the problem may be in the terminating MTA.
Step 4 If the CRCX messages are not sent to the originating and terminating MTAs, the Call Agent may not be
responding correctly—that is the Call Agent may provide dial tone, but may not continue with the call
flow. Contact Cisco technical support.
No Post-Dial Cut-Through (No Ringback)—On-Net to Off-Net
This scenario is similar to the previous one, except that this call is attempting to reach the PSTN, so SS7
messaging is required. The symptom is the same: the caller receives dial tone and can dial digits, but
then receives “dead air.” The call flow is between an originating MTA, the Call Agent, and a trunking
gateway (TGW). The call flow is very similar to the previous case, with the following exceptions:
• The CRCX messages to the TGW do not request power ring (ring signal), or ringback tone. These
signals are normally generated by the terminating PSTN switch, carried over TDM facilities to the
TGW, which digitizes the tone for transport over the VoIP over cable network.
Note The ringback and ring signals may be included in the TGW CRCX, but are ignored by the TGW.
See the reference call flow below.
• The call flow includes SS7 messaging to the PSTN switch.