1/5/2007
EAG Gateway Series Administration Guidelines
MAG-06007 Rev. A
networks. Echo cancellation involves first recognizing the originally transmitted signal that re-appears,
with some delay, in the transmitted or received signal. Once the echo is recognized, it can be removed
by 'subtracting' it from the transmitted or received signal.
This technique is generally implemented using a digital signal processor (DSP), but can also be
implemented in software. Echo cancellation is done using either echo suppressors or echo cancellers.
MGCP (Media Gateway Control Protocol)
Media Gateway Control Protocol (MGCP) is used for controlling telephony gateways from external call
control elements called media gateway controllers or call agents. A telephony gateway is a network
element that provides conversion between the audio signals carried on telephone circuits and data
packets carried over the Internet or over other packet networks.
MGCP assumes a call control architecture where the call control intelligence is outside the gateways
and handled by external call control elements. The MGCP assumes that these call control elements, or
Call Agents, will synchronize with each other to send coherent commands to the gateways under their
control. MGCP is, in essence, a master/slave protocol, where the gateways are expected to execute
commands sent by the Call Agents.
The MGCP implements the media gateway control interface as a set of transactions. The transactions
are composed of a command and a mandatory response. There are nine types of commands:
MGCP Commands (MGC=Media Gateway Controller; MG=Media Gateway)
MGC --> MG CreateConnection: Creates a connection between two endpoints; uses SDP to
define the receive capabilities of the participating endpoints.
MGC --> MG ModifyConnection: Modifies the properties of a connection; has nearly the same
parameters as the CreateConnection command.
MGC <--> MG DeleteConnection: Terminates a connection and collects statistics on the
execution of the connection.
MGC --> MG NotificationRequest: Requests the media gateway to send notifications on the
occurrence of specified events in an endpoint.
MGC <-- MG Notify: Informs the media gateway controller when observed events occur.
MGC --> MG AuditEndpoint: Determines the status of an endpoint.
MGC --> MG AuditConnection: Retrieves the parameters related to a connection.
MGC <-- MG RestartInProgress: Signals that an endpoint or group of endpoints is taking in or out
of service.
MGC --> MG: Endpoint Configuration
The first four commands are sent by the Call Agent to a gateway. The Notify command is sent by the
gateway to the Call Agent. The gateway may also send a DeleteConnection. The Call Agent may send
either of the Audit commands to the gateway. The Gateway may send a RestartInProgress command
to the Call Agent.
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