What is the use case of "Out of Dialog Refer CSS" on SIP Trunk?

[Meddane]

What is the use case of "Out of Dialog Refer CSS" on SIP Trunk?

[b.winter]

Similar question here:
https://community.cisco.com/t5/ip-telephony-and-phones/what-is-the-difference-between-reouting-css-and-out-of-dialog/td-p/4437609

[Meddane]

I already seen the CUCM Help Page but not really clear.

[b.winter]

And which part is not clear? What's an "out of dialog refer"? If yes, probably google helps.
The only scenario where I configure it, is in conjunction with Unity. Then this CSS is used, if Unity transfers the call back to CUCM.
In conjunction with CMS, the "Rerouting CSS" is used.

[Meddane]

I googled and I didnt find clear explanation. I seen example that puts a CSS in the Out of dialog refer css field but without giving the reason.

For Unity Connection Transfer Rules, the Rerouting CSS must be used to allow the transfer but I dont think the Out-Of-Dialog CSS is needed in this case because I configured Unity Transfer Rules without it and it works.

[Jonathan Schulenberg]

This allows the SIP server on the other end of the trunk to issue a REFER for a call that it is not involved in, ie out of dialog. The most common (legitimate) example is CUC MWI. Treat this as sensitive; the CSS probably should be limited to on-net destinations.

[Meddane]

But MWI is sent with the SIP NOTIFY message.

[Roger Kallberg]

It does use Notify, but it is sent out of dialogue.

https://community.cisco.com/t5/collaboration-knowledge-base/understanding-troubleshooting-mwi-on-unity-connection/tac-p/3162952

[aalejo]

Hey Jonathan

On traces for Unity MWI for SIP integration i don't see SIP REFER  messages, only NOTIFY messages:
Example (This was from another post but very similar to my traces):

NOTIFY sip:216181@10.106.117.132 SIP/2.0
From: sip:10.106.117.132;tag=185be2450fa4498f9ad928a998f4cc11
To: sip:216181@10.106.117.132
Via: SIP/2.0/TCP 10.106.117.133:5060;branch=z9hG4bK83d91e663e4d47768465116b5a37666c
Max-Forwards: 70
Contact: sip:10.106.117.133:5060
Call-ID: faa6de08ae424acc8dda1cc260e732ed@10.106.117.132
CSeq: 300 NOTIFY
Event: message-summary
Content-Length: 73
Content-Type: application/simple-message-summary

Messages-Waiting: yes
Voice-Message: 4/0 (0/0)
Fax-Message: 0/0 (0/0)

https://community.cisco.com/t5/collaboration-knowledge-base/understanding-troubleshooting-mwi-on-unity-connection/ta-p/3162948

[Jonathan Schulenberg]

SIP MWI is an unsolicited notify. For CUCM to accept it, the SIP Trunk Security Profile must be configured to allow it and the DN must be in a Partition of the Out-of-Dialog Refer CSS. In hindsight, Cisco should have named it differently.

SIP Refer is used by CUC for unsupervised transfers and is subject to the rerouting CSS. IIRC Outlook ViewMail and the CUC admin prompt player both use an out-of-dialog replaces to initiate the play via phone behavior. It’s been a long time since I have looked at those traces though and I can’t recall whether that uses rerouting or out-of-dialog CSS.

[aalejo]

Indeed not the best name and nice explanation, REFER messages not used only that SIP NOTITY (for MWI)  uses a CUCM CSS that has refer on it.