Call Control

SIP is peer-to-peer -- thus a proxy cannot issue a BYE, only end devices (UAs) can. To methods for third party call control:

A proxy passes an invite on, but stays in the signaling path
Use REFER to initial third party control (the third party is no longer in the signaling path).

Useful for:

click-to-call
Automatic Call Distribution (ACD)
web call center

Transcript

[slide162] Call control, things like click to dial, or automatic call distribution, or web call centers. So now the proxy, instead of just forwarding the message, stays in the SIP session, so now we can do additional signaling and provide other functionality for it.