March 28, 2011, 5:28 p.m.
posted by who
The call-flows outlined in this section demonstrate ways the H.323 family of protocols provides call setup between two endpoints. Assume these are speech calls and that all endpoints already completed registration with the appropriate gatekeeper. The call setup examples include two different gatekeeper implementations as well as two different call signaling methods.
The examples in Figures 11-10 and 11-11 detail call setup procedures for single gatekeeper implementations. Figure illustrates call-flows using direct endpoint signaling between two endpoints sharing the gatekeeper.
Direct Endpoint SignalingSame Gatekeeper
Gatekeeper-Routed Call SignalingSame Gatekeeper
Figure illustrates call-flows using gatekeeper call routed signaling between two endpoints sharing the gatekeeper. Note that the H.245 procedure is handled directly between the endpoints and is not gatekeeper-routed.
The examples in Figures 11-12 and 11-13 detail call setup procedures for dual-gatekeeper implementations. Specifically, Figure illustrates call-flows using direct endpoint signaling between two endpoints that have different gatekeepers. The main difference between GKRCS and Directed Call Signaling is that in GKRCS the setup message is directed to the gatekeeper, and in Directed Call Signaling it is directed to the terminating endpoint.
Direct Endpoint SignalingTwo Gatekeepers
Gatekeeper Routed Call SignalingTwo Gatekeepers
The final H.323 call-flow example demonstrates call setup procedures for the GKRCS method, whereby each endpoint has a different gatekeeper. This enables LRQs and LCFs to be sent between the two gatekeepers, which enables control of billing records at the gatekeeper as all the setup and control messages pass through the gatekeeper.