CUCM 8.5 and initial delay on SIP trunk

[pjiracek]

Hi there,

We have Cucm 8.5 over several sites using local gateways to PSTN calls. On a gateway connected to CUCM over a SIP trunk and then connected to provider through another SIP trunk, we get an initial delay of 0.5 - 2s on an outbound call (usually initial "Hello?" is missed or first few words of a recorded message). Then the call proceeds without any problems - no delay, no drop offs.

At sites where we have a gateway connected to CUCM via H.323 and then ISDN link to PSTN, or QSIG to a legacy PBX, this delay doesn't happen.

I've tried to check "Disable early media on 180" for the internal SIP trunk profile, which I think helped a bit, but there is still a short delay. Any thoughts?

Thanks

[Jonathan Schulenberg]

Questions:

• Is the provider doing Early or Delayed Offer?
• Is the provider doing Early Media?
• Is CUCM configured to do Early Offer on the SIP Trunk?
• What device is being called on CUCM (e.g. 7975 IP phone or CTI Port)?

If you don't know the answers for the first two questions please enable 'debug ccsip messages' and post an example of the problem.

Also, please post a copy of your dial-peers from the router.

[pjiracek]

Thanks.

I've fixed the problem by checking the following 2 (seemingly contradictory) options on the SIP trunk between CUCM and the CUBE:

1. Disable Early Media on 180

2. Send PRACK if 1xx contains SDP

No delay any more for outbound calls, but why these settings work I don't know.