CUCM 8.6.2 Hunt group to SIP phones; showing hunt group number in TO field

[Ruud van Strijp]

Hi,

We have an environment where we have Ascom IP DECT phones attached to a CUCM 8.6.2 platform. The Ascom IP DECT phones register as SIP clients. The Ascom phones register with DECT on an Ascom station (call it a PBX if you want), which then registers each individual number in the Cisco PBX as SIP phone.

They seem to work fine, they can call and be called normally. However, if we try to call them through a huntgroup, they won't pick up. I did a SIP trace, and this is the SIP Invite:

INVITE sip:30175@x.x.x.235:2074;transport=UDP SIP/2.0

Via: SIP/2.0/UDP x.x.x.1:5060;branch=z9hG4bK32c46c4b47f4

From: <sip:00653xxxxxx@xxxxxx>;tag=670276~daf58153-2252-4da2-af1b-66831969dab3-21573927

To: <sip:30197@x.x.x.235>

Date: Thu, 13 Sep 2012 18:02:12 GMT

Call-ID: 23432f80-5211fa4-13be-101000a@x.x.x.1

Supported: timer,resource-priority,replaces

Min-SE:  1800

User-Agent: Cisco-CUCM8.6

Allow: INVITE, OPTIONS, INFO, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY

CSeq: 101 INVITE

Expires: 180

Allow-Events: presence

Send-Info: conference, x-cisco-conference

Alert-Info: <file://Bellcore-dr2/>

Contact: <sip:00653xxxxxxx@x.x.x.1:5060>

Remote-Party-ID: <sip:00653xxxxxxx@sip.kreuze.nl;x-cisco-callback-number=00653xxxxxx>;party=calling;screen=yes;privacy=off

Max-Forwards: 67

Content-Length: 0

After this Invite, the Ascom PBX where the phones are connected to replies with a 404 Not Found. I think this is because the TO field shows the huntgroup number (30197) instead of the SIP phone's number (30175). If I dial 30175 directly this number is in the INVITE and TO fields, and the call gets routed to the phone properly.

Is there a way to change this behaviour?

Regards,

Ruud van Strijp

[Ruud van Strijp]

I contacted TAC for this, their final reply was:

I was doing some further research in to the same, and Cisco would always route/receive calls on the basis of SIP-URI, which would be the invite field.

The “TO” header field first and foremost specifies the desired  "logical" recipient of the request, or the address-of-record of the user or resource that is the target of this request.  This may or may not be the ultimate recipient of the request.

So, in our case from the Invite filed we can see that the call is being re-directed to

INVITE sip:30175@x.x.x.235:2074;transport=UDP SIP/2.0

The “TO” field specifies the originating Called number which is the hunt pilot number.

So, in CUCM we would not be able to modify the “TO” field.

Ascom device should be able to receive requests on basis of “Invite” message. If they are not, I feel that they are violating the Sip RFC.