ZyXEL Communications MSC1024G Series User Manual page 548

Chapter 18 VoIP
• Signals are instructions applied to Terminations by the MG when requested to do so by the
MGC. The type and content of signals depends on the type of Termination (switched
circuit network channel, RTP stream, etc.). Signals include media streams such as DTMF
tones and audio messages.
• Statistics are information related to a Termination's activity in a Context, and are sent to
the MGC on request, or when the Termination is removed from the Context.
18.1.4.2 H.248 Commands
In an H.248 network, the MGC controls calls by issuing commands to the Media Gateways. In
turn, the media gateways can issue reports to the MGC. The commands allow control of
Terminations and Contexts. For example, the MGC can specify what events a Termination
should log and report, which Terminations should exist in which Contexts, and which signals
the MG should apply to a Termination.
Commands and reports are grouped into Transactions. Each Transaction consists of a number
of actions, which must all refer to the same Context. To verify that Transactions have been
correctly sent and received, each Transaction must be preceded by a TransactionRequest
message and concluded with a TransactionReply message. In addition, a TransactionPending
message indicates that a Transaction has been initiated, and is being processed, but is not
complete.
The following table lists the H.248 commands.
Table 288 H.248/MEGACO Commands
COMMAND
Add
Modify
Subtract
Move
AuditValue
AuditCapabilities
Notify
ServiceChange
18.1.4.3 H.248/MEGACO Call Progression Example
The following figure shows two analog telephones (A and B) connected to two media
gateways (MG1 and MG2). MG1 and MG2 are connected to one another via an IP network.
MG1 and MG2 are controlled by the media gateway controller MGC.
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DESCRIPTION
Adds a Termination to a Context. If a Termination does not already exist, it
is created by this command.
Alters a Termination's events, properties and signals.
Removes a Termination from a Context and sends statistics to the MGC on
the Termination's activities in the Context. Ephemeral Terminations are
destroyed by this command.
Moves a Termination from one Context to another.
Sends information on a Termination's current events, properties and
signals.
Sends information on all possible properties, events and signals permitted
by the MG.
Sent by the MG to the MGC to inform the MGC of events.
Sent by the MG to the MGC, or vice versa, indicating that one or more
Terminations is about to be removed from service, or has been returned to
service.
MSC1000G/1024G/1224G Series User's Guide