Call Set Up Flow on WAN

[Grant Curell]

I'm looking to confirm my understanding of the call set up process. Let's say you have a multi site WAN with one centralized call processor at the main site. So would someone at a branch office dial a number and then that number would be sent across the WAN via SIP or something to the CUCM (or equivalent) and then the resulting data be sent back to the originating IP phone after which they would then connect directly to the other IP/analog phone with RTP. Holy run on sentence batman... sorry about that.

[George Thomas · Accepted solution]

Thats correct to an extent. If you have CUCM, the signaling from phones go directly to CUCM. CUCM sits in the middle and acts as a proxy between the two endpoints. As soon as both phones are ready to send voice (ie. callee picks up, caller still wants to talk), the media (voice packets) is sent directly between the phones similar to any other data traffic in your network. Media doesnt flow through CUCM in most cases. The protocol used for signaling between phones and CUCM depends on the model of the phone and the configuration. It could be SCCP or SIP. However, there are no SIP trunks in the mix. SIP trunks are used to connect to other systems or the provider but not to phones. 

HTH

[Grant Curell]

Sweet, that's how I imagined it working. Thanks for your response.