[Serusers] Session-Timer at proxy level?

[Jamie Yukes]

UAC -> SER -> ProxyWithTimer -> UAS

Both UAC and UAS do not support session timers, or session refresh requests.
However, ProxyWithTimer is losing call state after 30 minutes.  

The only thing I can control is SER.  The piece I read
"draft-ietf-sip-session-timer-13.html" suggests that it should only be
implemented at UAC or UAS.  So am I restricted to using SER as B2BUA,
or would it be theoretically possible to implement this in stateful
proxy mode, without the UAC's cooperation?  (The CSeq will be out of
sync, which gets kludgey)

Jamie Yukes