Troubleshooting guide

4-4
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 4 Troubleshooting with Call Flows
Understanding MGCP
Call Identifier (C)
The call ID identifies the call (or session) to which this connection belongs. This parameter is unique
within the network of gateways; however, connections that belong to the same call share the same call
ID. The call ID can be used to identify calls for reporting and billing purposes.
Connection Identifier (I)
The connection ID identifies the connection within the call.
Request Identifier (X)
The request ID is used to correlate the request with the notifications that it triggers.
Notified Entity (N)
The notified entity is an optional parameter that specifies where the notification should be sent. An
example of notification is a disconnect request from the gateway.
Local Connection Options (L)
The local connection options describe the operational parameters that the call agent suggests to the
gateway. These parameters are:
• The length in time in milliseconds, encoded as the keyword p, followed by a colon and a decimal
number. If the call agent specifies a range of values, the range is specified as two decimal numbers
separated by a hyphen.
• The preferred type of compression algorithm, encoded as the keyword a, followed by a character
string. If the call agent specifies a list of values, these values are separated by a semicolon.
This is the parameter that specifies the codec. Should the Call Agent request the wrong codec, or
should the endpoint be configured incorrectly and respond that it cannot support the correct
requested codec, voice quality will be affected (or the call may not succeed, triggering a NAK).
G.711 is specified in the case of fax, mode, and when connecting to the voice-mail system. G.711
samples the analog signal 8000 times/sec, producing an 8-bit pulse code modulation. Thus, G.711
requires 64 kbps of continuous transmission. G.711 provides extremely high-quality speech
transmission (often referred to as toll quality), but can tolerate little delay or variation.
• The bandwidth in kilobits per second, encoded as the keyword b, followed by a colon and a decimal
number. If the call agent specifies a range of values, the range is specified as two decimal numbers
separated by an hyphen.
• The echo cancellation parameter, encoded as the keyword e, followed by a colon and the value on
or off. By default, telephony gateways always perform echo cancellation. However, for some calls
it is necessary to turn it off.
Each of the parameters is optional. When several parameters are present, the values are separated by a
comma.
Examples:
L: p:10, a:G.711
L: p:10, a:G.711;G.726-32
L: p:10-20, b: 64
L: b:32-64, e:off