The H.248 connection model uses contexts, terminations, and streams, which are logical entities that the PGC controls. In the router, the MultiServices PIC creates a context. The software then adds terminations to the context and adds streams to the terminations. Figure 17 shows a context, termination, and stream.
Figure 17: Context, Termination, and Stream
A termination can be a source and sink for media and control streams, and the parameters of the streams are encapsulated within the termination. A termination is characterized by properties that are grouped in a set of descriptors that are included in add, subtract, modify, or audit commands. Terminations have unique identifiers (TerminationIDs) that the packet gateway assigns when it creates the termination.
Each termination is the source and destination of a gate. A termination exists only as long as a call. It is removed when the call is removed.
A context is an association between a collection of terminations. The VPG instructs a MultiServices PIC to create a context for each voice session and each signaling session. Using instructions from the VPG, the PIC then applies policies such as DSCP, NAT, rate limiting, and inactivity timers to the gates within a context. If the VPG does not specify an existing context to which the termination is to be added, the PIC creates a new context.
A stream is one bidirectional flow within a context.
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