Cisco OL-4015-08 Guide de dépannage télécharger pdf (Page 139)

4-13

Cisco Broadband Local Integrated Services Solution Troubleshooting Guide

OL-5169-01

Chapter 4 Troubleshooting with Call Flows

Call Flow Analysis

The following sections discuss how to use MGCP and SS7 messages in troubleshooting problems.

MGCP Key Fields

The first problem in call flow analysis is to identify which messages are associated with a single call

attempt. A modest amount of call activity on the network produces a relatively large volume of MGCP

messages. You must be able to extract a small subset of messages for analysis, those related to the failed

call. Several fields can be used to identify related MGCP messages. Table 4-8 lists the key fields, which

are described in more detail in the “Understanding MGCP” section on page 4-2

Every MGCP command associated with call setup (RQNT, NTFY, CRCX, MDCX, DLCX) contains the

endpoint ID of the gateway voice port and a transaction ID that uniquely identify the instance of a

transmitted MGCP message, called an MGCP transaction. A node that receives an MGCP command

must respond to the sender with an ACK (or NAK) message. The ACK message does not contain an

endpoint ID, making it more difficult to correlate the ACK with its associated MGCP command.

However, the ACK message does contain a transaction ID that can be correlated to the original command

and the destination IP address, which is the original sender of the MGCP command. It is the combination

of both the destination IP address and transaction ID in the ACK that associates it with an MGCP

command. The transaction ID by itself is not required to be unique in the network; it is only required to

be unique between the Call Agent and a specific gateway.

MGCP Message Correlation

A major obstacle to tracing call flows in a production network is the sheer volume of MGCP messages

that flow through the network at any time. In order to extract a call, you must find a way of linking all

the messages in a call setup together. This section on correlation assumes the following:

• All the MGCP traffic has been captured and fully decoded, and is available to you.

• The call is made from an MTA to an off-net location (that is, SS7 messaging is involved).

Table 4-8 Key MGCP Fields Used to Identify Messages Related to a Single Call

Parameter Purpose OSI Layer

endpoint ID Identifies the endpoint involved in the call. Application

transaction ID Links an MGCP verb (NTFY, RQNT, CRCX,

MDCX, DLCX) with the its associated ACK.

For example, CRCX xsactionID=001, with

ACK xsactionID=001

Application

call ID Identifies the group of connection

management messages (CRCX, MDCX,

DLCX) associated with a call instance.

Note: you can have multiple call instances

associated with a single endpoint.

Application

IP address Indicates the source/destination IP address of

the gateway and/or call agent node

Network

1 2 ... 134 135 136 137 138 139 140 141 142 143 144 ... 369 370

Commentaires sur ces manuels

Pas de commentaire

Cisco OL-4015-08 Guide de dépannage Page 139

Commentaires sur ces manuels

Produits connexes et manuels pour Mise en réseau Cisco OL-4015-08