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H.248 User's Manual
7
Standard Control Protocols
7.1
General
MG 3200 can be controlled from a Media Gateway Controller (MGC) / Call Agent using
standard H.238 (MEGACO Media Gateway Control).
7.2
H.248 (Media Gateway Control) Protocol
7.2.1
H.238 Overview
H.238 (MEGACO Media Gateway Control) Protocol is a standards-based network control
protocol (based on IETF RFC 3015 and ITU-T H.248 V1). H.248 assumes a call control
architecture where the call control intelligence is outside the MG 3200 and handled by an
external Media Gateway Controller (MGC). H.248 is a master/slave protocol, where the MG
3200 is expected to execute commands sent by the Call Agent (another name for MGC).
The connection is handled using two elements: Terminations and Contexts. Termination
is the basic element of the call. There is a physical Termination representing a physical
entity (e.g., B-channel), and an ephemeral Termination representing the generated stream.
To create a connection, a Context is used. A Context contains one or more Terminations,
and describes the topology between the Terminations. A typical connection creation
command creates a new Context and adds into it one physical Termination and one new
(ephemeral) Termination. The ephemeral Termination parameters describe the media type
and the stream direction (SendReceive, SendOnly or ReceiveOnly).
Since this is a standards-based control protocol, no special software library to enable users
to construct their own Call Agent is provided. (Users can choose any of many such stacks
are available in the market.)
7.2.2
Operation
7.2.2.1
Executing H.248 Commands
H.248 commands, received from an external Call Agent through the IP network, are
decoded and executed in the MG 3200. Both text encoding and binary encoding are
supported. Commands can create new connections, delete connections, or modify the
connection parameters.
Several commands that support the basic operations required to control a MG 3200:
Status change command - The command ServiceChange allows changing the status
of one or more Terminations. When used with a special Termination, called the ROOT
Termination, it affects the entire MG 3200.
Connection commands - The commands Add, Move, Modify and Subtract allow the
creation and deletion of a call connection inside the MG 3200. These commands allow
the application to create new connections, delete existing connections, and modify the
connection parameters.
Version SN09
87
7. Standard Control Protocols
October 2006
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