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This figure shows the call flow messages between, from right to left, a Client Application, Signaling Engine, a SIP Proxy, and a SIP Phone. The message include:
Client to Signaling Engine: handshake.
Signaling Engine to Client: handshake response.
Client to Signaling Engine: connect.
Signaling Engine to SIP Proxy: register.
SIP Proxy to Signaling Engine: 200/OK.
Signaling Engine to Client: connect response.
Signaling Engine to SIP Proxy: REGISTER.
SIP Proxy to Signaling Engine: 200/OK.
Signaling Engine to Client: connect/response.
SIP Phone to SIP Proxy: INVITE.
The SIP Proxy starts a SIP session by sending an INVITE to Signaling Engine.
Signaling Engine to Client: start which starts a subsession.
Signaling Engine to SIP Proxy: 100/trying.
Client to Signaling Engine: start/initial response.
Signaling Engine to SIP Proxy: 180/Calling.
Client to Signaling Engine: start/final response.
Signaling Engine to SIP Proxy: 200/OK.
SIP Proxy to Signaling Engine: ACK.
Signaling Engine to Client: complete.
The media session then opens between the Client and the SIP Proxy.
SIP Proxy to Signaling Engine: BYE.
Signaling Engine to Client: shutdown which shuts down the subsession and WebSocket.
Signaling Engine to SIP Proxy: 200/OK, which ends the SIP session.