Call processing
Figure 47: Discovery and registration process to the gatekeeper
Call signaling
Communication Manager implements the gatekeeper routed call model of H.323. The registration process that is described above allows the endpoint and the Communication Manager gatekeeper to exchange addresses to establish a TCP connection for a “call signaling” channel (the H.323/H.225 channel). Once the TCP connection is established for call signaling, the H.225.0/Q.931 signaling protocol is used over that connection to route the call and exchange addresses necessary to establish a second TCP connection. This second TCP connection is used for “media control” (the H.245 channel).
When Communication Manager chooses to route the media flow streams through the switch, it selects and allocates available media processor resources, and sets the corresponding circuit packs up to receive and send the media stream or streams from/to the endpoints using the negotiated capabilities for each terminal. Each terminal is told to send its media stream or streams to the appropriate Media Processor circuit pack. The switch connects the two media streams, and thus completes the bearer path between the terminals.
