ZyXEL Communications MSC1000G Series, User Manual

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Chapter 16 VoIP
Management Switch Card User’s Guide
606
Figure 410
H.248 Interface, SCs and MCs
• The active SC uses the IP address of the H.248 interface to communicate with the MGC.
• Each SC has an IP address for communicating with the MCs (the active SC has one IP address
and the backup SC has a different IP address).
• Each MC has one IP address it uses to communicate with the SC.
16.1.4.1 Media Gateway Terminology
Communication in an H.248 network depends on two concepts contained in the MG: “Terminations”
and “Contexts”.
• A Termination is a logical entity representing a connection to a media stream. A Termination
sources and/or sinks connections to the media stream. Every connection to the MG is uniquely
represented by a Termination.
A Termination may represent either a physical connections (such as an analog phone connection)
or an ephemeral connection (such as an RTP stream). Generally, ephemeral Terminations exist
for only as long as they are in use. In contrast, physical Terminations exist for as long as they are
provisioned in the gateway.
Each Termination is assigned a unique identity at the moment of its creation by the MG.
• A Context is a grouping of Terminations. Terminations within the same Context can
intercommunicate. A Termination can belong to only one Context at a time, and Contexts cannot
intercommunicate. Contexts connect two or more Terminations, with the exception of one - the
Null Context. The Null Context contains all physical Terminations not currently belonging to
another Context. Terminations in the Null Context cannot intercommunicate.
A Context is created when the MGC adds the first Termination to the Context. A Context is
destroyed when the last Termination is removed from the Context.
Standby SC
Media Gateway
Active SC
MC
MC
MC
MC
MGC
H.248 signaling
RTP payload
IP NETWORK
Interface
Backup Media Gateway