Introduction
This document discusses very high level and brief over view of H.323 Call Flow in CVP Comprehensive Deployment Model.
The PSTN call could arrive using a traditional T1/E1 PRI trunk or using some IP based trunk potentially a SIP trunk. The PSTN call will be terminated on a Cisco voice gateway in case of T1/E1 PRI trunk for example. And from the voice gateway it could be sent to a H.323 gatekeeper or directly to the CVP depending on the deployment.
PSTN----T1/E1-----VGW----GK----->CVP
OR
PSTN----T1/E1-----VGW----------->CVP
In case of SIP trunk, it will be terminated on a Cisco Unified Border Element (also called Session Border Controller). From here it could be sent to a Cisco Unified Presence Server (CUPS) SIP Proxy Server or directly to the CVP depending on the deployment.
PSTN----SIP------CUBE----CUPS-SIPProxy----->CVP
OR
PSTN----SIP------CUBE---------------------->CVP
Call Flow
1. Public switched telephone network (PSTN) call arrives at the ingress voice gateway (VGW).
2. Ingress VGW delivers the call to CVP (with H.323).
3. CVP informs ICM of the new call. This leg is the switch leg of the call. ICM routing script instructs CVP to perform queuing or self-service application (using CVP studio).
CVP-----Switch-Leg----->CUICM
4. CVP transfers the call to the Voice Extensible Markup Language (VoiceXML) gateway for VRU leg operation to perform prompt/queuing or self-service. VoiceXML gateway fetches VoiceXML pages from the CVP Call Server and/or CVP VoiceXML Server.
CVP-----VRU-Leg-------->VXML-GW
5. After the self-service session or queuing, eventually ICM sends an agent label (directory number) to CVP to transfer the call to the agent.
CUICM-----agent-label------>CVP
6. CVP tears down the VRU leg towards the VoiceXML gateway and transfers the call to the agent through IP switching by performing the call setup (H.323) to the destination IP device (egress VGW or Communications Manager, etc.) and redirecting the switch leg media stream to the agent destination. CVP remains in the call signaling path for subsequent transfers as needed and the media flows from the ingress VGW to the destination IP endpoint.
