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How do you get SDP in the SIP invite?

I have a 3825 that's a CUBE device. IOS is c3825-ipvoice_ivs-mz.124-15.T8.bin. The SIP invites going out from the CUBE to an 800 number do not contain SDP and therefore, the call is not being setup properly, it rings for several minutes before being connected. This only happens to one specific 800 number. All other calls, even to other 800 numbers, work fine.

The CallManager sends the call the 3825, which is an H323 device in CM. There are no SIP trunks. I tried checking the outbound fast start on the h323 configuration page in CM, but it didn't help.

I tried to force early-offer in the voip dialpeer on the CUBE router but that option was not available in the voice-class sip.

Does forcing early-offer cause the SDP to go out as part of the invite? And, can I configure this globally without affecting other calls? Or, what else do I need to do to force the SDP in the SIP invite? Thanks.


Re: How do you get SDP in the SIP invite?

First off, i would recommend upgrading your CUBE code to 12.4.20 or above. It has more sip functionality.

early-offer forced & g729 annexb-all are not located under voice-class sip. You put these commands under

Voice Service Voip


early-offer forced

You need to ensure you have software mtp resources configured in the CUBE to be used by UCM.

Re: How do you get SDP in the SIP invite?

A few things here:

Delayed-offer to early offer is a SIP-SIP feature only. It won't do anything (except interfere) in a H323-SIP call.

The only way to get early media in an outgoing H323-SIP call is via MTP on CUCM. If you checked it and you didn't get an SDP it is because:

1) No available MTPs (all in use)

2) No available MTPs for the codec you're trying to use

3) The MRGL under your device pool or on the gateway does not contain a MRGL

4) You didn't reset the gateway after the change



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Re: How do you get SDP in the SIP invite?

Thanks for the reply. So several points here:

1. Is this an H323-SIP call were're dealing with, being that the CUBE is an H323 device in CM?

2. In CM, the CUBE router has an MRGL (and a Device Pool which contains the same MRGL). That MRGL contains three groups:

A. 3825-Hdw-Trans which has two software resources: MTP_2 and MTP_3 (publisher and subscriber respectively)

B. 3825-Sft-MTP which has only one resource: 3825MTP (which is a hardware resource on the router HDV2)

C. Sft-MTP which contains two resources: MTP_2 and MTP_3

3. There is a 3825swMTP (IOS) resource available but not used. the description says software (IOS) but the icon next to it is the same, MTP/HDV2, as the 3825MTP resource above.

Can I just move the 3825-Sft-MTP group up one in the MRG List order? Would this affect other calls?

Should I add the 3825swMTP resource into one of the groups? Thanks again.

Re: How do you get SDP in the SIP invite?

What is the calling going out as, G.729, G.711, etc? Make sure your router MTP has this defined in the profile otherwise it won't allocate. The MRGL should check each of the MRGs for an available MTP.

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Re: How do you get SDP in the SIP invite?

The calls are going out as G729. The router has a MRGL that includes a MRG which has the PVDM on the 3825 as an MTP resource. I changed the order of the resources but it didn't help. Here are two questions:

1. Would it help to upgrade the IOS to 12.2.20 as suggested in the above post?

2. Why is it that only calls to a particular call center are affected (call center has an auto attendant)?


Re: How do you get SDP in the SIP invite?

On the 3825 in the dspfarm profile, does it have codec g729?

If you're using SIP at all I suggest 12.4(20)T or later.

Sometimes for certain calls to autoattendants, they don't return a 200 OK, and it's only a 183 with SDP. If we didn't send them media, it's never established and this causes problems.

Your other option is to use H323 or in CUCM under SIP service parameters enable "Rel1xx Enabled".


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