CUCM Call Flow

[fayiz husain]

What are the things that will happen when IP phoneA calls Ip phoneB?

[Chris Deren]

In a nutshell signaling from/to call agent (i.e. CUCM or CME) establishes the call between the 2 phones and RTP packets (voice stream) flows between the phones directly. Call agent is in charge of the call tracking the state, etc.

For more details it depends on protocol being used i.e. SIP, SCCP, etc. Here is similar thread:

https://supportforums.cisco.com/message/3544970#3544970

HTH, please rate all useful posts!

Chris

[fayiz husain]

Thanks for your reply

Can you explain me what are the signallings(consider SCCP) involved and how the media path is established between two IP phones under same device pool.

Does the phones communicate through the same RTP port?

[Chris Deren]

Signaling is between phones and call agent, the link I provided has a link to doc that shows ladder diagram for ATA, but the concept is the same for phones:

http://www.cisco.com/en/US/docs/voice_ip_comm/cata/186_188/2_15_ms/english/administration/guide/sccp/sccpaaph.html

The RTP is established on negoriated UDP port, so yes all packets for the stream go through the same port.

HTH,

Chris