[SIPForum-discussion] Expires and Contact; expires for Microsoft SIP client compatibility

[Steve]

Hi group,

This is my first message, so I hope I'm all good with this....

My question is the validity and repercussions of implementing the
'Expires' header field.

The RFC3261 to me implies that Expires covers all Contact
(per-binding) addresses are the same time-out. Would it be acceptable
to have both 'expires' and 'Expires' in the same response to cover any
incompatibilities?

Steve

Background:
I'm integrating our office PBX with GSM + WiFi handsets. In this
particular case the Windows Mobile 6 handsets which use the Microsoft
RTC 1.5.

I have found that the PBX cuts off calls after the SIP registration
times out because of the incompatibility in negotiation.

The Windows RTC client used in WM6 reacts to the 'Expires header
field' value and not the 'Contact; expires=' value. E.g.

Real response (;expires=52):
Message Header
Contact: <sip:258 at 192.168.1.90:5060>;expires=52
From: <sip:258 at 192.168.1.146>;tag=f7c498be3c;epid=877e4564ac
To: <sip:258 at 192.168.1.146>;tag=329214850
Call-ID: 000070c4000018188079efd4ed25c801
CSeq: 2 REGISTER
Server: AspireML-GE 07.02/2.1
Via: SIP/2.0/UDP 192.168.1.90:5060;branch=z9hG4bK23b877d934-1
Content-Length: 0

My Emulated response that the device honours (Expires: 52):
Message Header
Contact: <sip:258 at 192.168.1.90:5060>
From: <sip:258 at 192.168.1.146>;tag=f7c498be3c;epid=877e4564ac
To: <sip:258 at 192.168.1.146>;tag=329214850
Call-ID: 000070c4000018188079efd4ed25c801
Expires: 52
CSeq: 2 REGISTER
Server: AspireML-GE 07.02/2.1
Via: SIP/2.0/UDP 192.168.1.90:5060;branch=z9hG4bK23b877d934-1
Content-Length: 0