[SR-Users] Need help understanding/separating signaling from media

[Alex Balashov]

Hi Grant,

On 01/28/2013 11:03 AM, Grant Bagdasarian wrote:

> I think that the RTP Proxy module does precisely this, but what I
> still don’t understand is how the rtp stream is passed between these
> two agents for each call.

The Kamailio 'rtpproxy' module goes out to the rtpproxy service[1] and 
asks it to engage the call, saying: "Can you please allocate and provide 
me with a pair of ports for each end of this call?"  The rtpproxy 
process answers, and Kamailio then writes the IP and ports provided by 
rtpproxy into the SDP of both the requests and replies involved in 
setting up the call.

The result is that as far as both UAs are concerned, rtpproxy is their 
endpoint, and they will send media to it.  Kamailio instructs rtpproxy 
to bridge both streams.

When the call is torn down, Kamailio tells rtpproxy to disengage and 
deallocate the bridge mapping for those streams.

-- Alex

[1] Which may be running on the same host, or may be running on another 
host, in a distributed fashion.  Kamailio talks to rtpproxy through 
rtpproxy's UDP control socket, and more than one rtpproxy may be used, 
both for failover and round-robin load distribution.  This is readily 
baked into the rtpproxy module.

-- 
Alex Balashov - Principal
Evariste Systems LLC
235 E Ponce de Leon Ave
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Tel: +1-678-954-0670
Web: http://www.evaristesys.com/, http://www.alexbalashov.com/