Information Technology Reference
In-Depth Information
Media gateways can be classified depending on the connectivity they provide. For example, a media gateway that terminates
trunks connecting to the telephone network can be referred to as a
trunking gateway
, and a media gateway that provides
analog connections to phones can be referred to as a
residential gateway
.
MGCP specifies a connection model involving endpoints and connections:
■
Endpoint:
MGCP media gateways contain endpoints, which are sources/destinations for data. Endpoints can be physical,
such as interfaces terminating trunks connecting to a PSTN or interfaces terminating plain old telephone service (POTS)
connections to PBXs, key systems, or telephones. Endpoints can also be virtual endpoints, such as audio content sourced from
a server.
■
Connection:
This is an association between endpoints for the purpose of transmitting data and can be either point-to-point or
multipoint in nature.
MGCs/call agents and MGs use several commands and responses (or verbs) to communicate with each other:
■
EndpointConfiguration (EPCF):
A call agent sends this message to a gateway to specify signal encoding that will be
received by an endpoint. This message could, for example, be used to specify whether audio calls will be encoded using mu-
law or a-law.
■
CreateConnection (CRCX):
This creates a connection between two endpoints. The connection is created based on
parameters included with the command, such as codec, allowable bandwidth, use of echo cancellation, silence suppression,
gain control, and so on.
■
ModifyConnection (MDCX):
This modifies the parameters associated with a connection that was previously created.
■
DeleteConnection (DLCX):
The call agent can send this command to inform a gateway that it should terminate a
connection, and a gateway can send this command to indicate that a connection can no longer be sustained. In response to a
DeleteConnection
command, a media gateway sends statistics associated with the connection.
■
NotificationRequest (RQNT):
This is sent by a call agent to instruct a gateway to inform it when specific events occur in an
endpoint. These events could, for example, be on-hook/off-hook status changes or the reception of certain tones.
■
Notify (NTFY):
A media gateway uses this command to inform a Call Agent when requested events occur.
