Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 4 Troubleshooting with Call Flows
Voice Quality Problems
Step 3 If the MGCP messaging looks correct, check to see if the Call Agent sent an ACM to the PSTN switch.
If the Call Agent appears to have sent the MGCP messaging correctly, but there is no ACM, check L3
connectivity between the connection manager and SS7 gateway. If there is L3 connectivity, the
connection manager is not communicating with the SS7 gateway. Contact Cisco technical support.
Step 4 If the CRCX messages are not seen by the originating MTA and trunk gateway, and the Call Agent did
not send a REL message, the Call Agent may be having a problem. Contact Cisco technical support.
Test Tools
Even in a lightly loaded network, it can be difficult to extract MGCP messages associated with a single
call. It is desirable, from an operational perspective, to have test tools capable of automatically
correlating the messages in the fashion described above.
Network monitoring provides visibility into the internal operation of the VoIP network. This allows
maintenance personnel to understand how well the network is performing and to understand what is
happening when a network element fails. Almost all network elements keep information about their
current status, which can be reported to a centralized network management system using SNMP. Another
method of monitoring is to capture MGCP protocol messages as they traverse the VoIP network. Protocol
message capture is the starting point for call flow analysis. A protocol analyzer is an invaluable tool in
tracking down the causes of problems in a network.
Remember to keep reference call flows up-to-date. If there are changes to the network or updates to
software, update your working call flow references. When you encounter problems, you need to compare
problem call flows to the reference call flows.
Note In general, errors, packet or cell loss, and latency increase with load. Therefore, you should take your
sample of performance during peak load, as well as during normal periods.
Voice Quality Problems
This section describes several types of voice quality problems and troubleshooting strategies for them.
Voice quality problems include lost or distorted audio during phone calls. Common problems include
breaks in the sound that cause the audio to be intermittent (like broken words), the presence of odd noises
that distort the audio, echo, or effects that cause spoken words to sound watery or robotic.
Note One-way audio, that is, a conversation between two people where only one person can hear anything, is
not considered a voice quality problem. A protocol analyzer can help you verify that the phone or
gateway is actually sending or receiving packets.
One or more of the following components can cause audio problems:
• Telephone
• Gateway
• Network
To troubleshoot voice quality problems, you must examine the infrastructure and all devices for drops
and delays. You may find that all individual devices are working fine, but that you have address sizing
and scaling problems (which are discussed in a later chapter).