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 5 The first CRCX to the MTA contains the Call ID parameter. The Call ID parameter is used to link
connection control messages (CRCXs, MDCXs, and DLCXs) at both ingress and egress endpoints. This
is important if the call is off-net, since you do not know from the facts gathered so far which trunk
gateway is used to egress the call.
Search the LAN analyzer trace for messages that contains the same Call ID used in the first CRCX to
the MTA. This trace enables you to locate the other MGCP messages going to the egress trunk gateway,
since they use the same call ID. By noting the transaction ID and destination IP address in the CRCXs
to the TGW, you can determine the associated gateway ACKs.
Step 6 The connection control messages to the egress trunk gateway contain endpoint IDs, which correspond to
the voice gateway port being used. This corresponds to a specific PSTN trunk, which is identified by an
SS7 Circuit Identification Code (or CIC). Analysis of the dialed digits in the NTFY message from the
MTA should indicate the target SS7 node for the call (that is, the SS7 destination point code, or DPC).
Provisioning records should show the relationship of a trunk gateway endpoint ID with the PSTN trunk
group identifier and CIC that are provisioned to the DPC. This allows you to follow the call flow into
the SS7 network.
For example, endpointID DS0-1/[e-mail] may correspond to CIC 4015 between SS7 point
codes 229-151-023 (the VoIP virtual switch) and 229-151-024 (an adjacent Lucent 5ESS switch). To
trace the SS7 messaging associated with this call, the SS7 messaging must first be captured on an SS7
protocol test tool. You must locate all SS7 messaging between the two point codes which have the CIC
code 4015. This corresponds to SS7 messaging related to call setup on trunk gateway endpointID
DS0-1/[e-mail].
At this point, there is sufficient information to identify all messages associated with the call flow.
Call Flow Problems
Configuration errors or lack of resources may be revealed in signaling messages to and from the Call
Agent. The following sections list the problems encountered in call flows, and some guidelines for
diagnosing the causes. For additional information about troubleshooting call flows, see Chapter 4,
“Troubleshooting with Call Flows”.
No Dial Tone
In this scenario, the customer cannot get a dial tone after going off-hook. Normally, in order to get dial
tone, the following sequence of messages must be exchanged between the Call Agent and the MTA:
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NTFY - off-hook, xsactionID-001
ACK - xsactionID=002
RQNT - play dial tone, collect digits
with map, xsactionID=002
ACK - xsactionID=001
Call Agent
MTA