CUCM 7.x SIP Trunk - Invite with SDP without using MTP?

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Jan 8th, 2010
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Does anyone know if CUCM 7.x is able to send SDP in SIP invites for outbound calls via a SIP trunk without using a MTP resource?

Topology is SCCP Endpoint --> CUCM 7.x  --SIP Trunk--> SBC --> SIP Proxy --> SIP Endpoint.

I would like to see the RTP stream established directly between the SCCP endpoint and the SBC instead of going via a MTP resource. SDP is mandatory in any SIP invites sent to the SIP endpoint.



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shell99102 Fri, 01/08/2010 - 08:03
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From my understanding UCM can only due Delayed Offer or an Early Offer with an MTP. Delayed offer does not send an invite with SDP, which is why it's referred to a Delayed offer.

This is from the UCM 7.1 SRND;

In a Delayed Offer, the session initiator does not send its capabilities in the initial Invite but waits for the called device to send its capabilities first (for example, the list of codecs supported by the called device, thus allowing the calling device to choose the codec to be used for the session).

Media Termination Points (MTPs) are generally not required for Delayed Offer calls from Unified CM SIP trunks. For this reason, Cisco recommends Delayed Offer as the call setup method for outbound calls from Unified CM SIP trunks. For outbound Early Offer calls from Unified CM, MTP resources are required (SIP Trunk

MTP required box is checked and the desired codec to be offered is selected) and remain in the media path for the duration of the call.

Hope this helps.

We use the Cisco CUBE for our SIP Trunks to SIP Providers so that we have better control of Codecs, Call Flow, SIP Messages, Etc...

Mike Shelley


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