[Sip] Question about Q-SIP

[maria.a.cuevas@bt.com]

Dear all,

I have a couple of questions regarding the internet draft: "SIP extensions
for QoS support" (draft-veltri-sip-qsip-01.txt) and I was wondering if
somebody in the mailing list could answer them.

Question 1:
I am trying to understand the requirements for a UA to implement the Q-SIP
"QoS assured" mode of operation. I know that the draft explicitly says that
no enhancements/modifications are  needed in the SIP UA applications to
implement these mechanisms. But it also mentions (Appendix A) that, a UA
must be "preconfigured" to rely on the Q-SIP proxy for QoS handling. I would
like to understand what that "pre-configuration" means in terms of the UA's
SIP behaviour. 

Is there any difference in the way that an UA interprets the precondition
parameters for the Q-SIP QoS-assured mode and the mechanisms described in
RFC 3312 ?

In the Q-SIP example A.1.1, the UA seems to interpret the curr:qos e2e
sendrecv in the 183 message (SDP 4) as the result of the reservation for its
own side of the network (UA(A)) (because it is assuming that the Q-SIP
server reserved it on its behalf) and it responds with an UPDATE to confirm
to the other end that the reservation in UA(A)'s send direction was
successful (confirmation was requested by the UA(B) in SDP 2, 3 and 4 :
conf:recv).

But according to RFC 3312, any curr: header in a message recevied should be
interpreted as the current QoS reserved by the other end of the network. It
seems to me that the two interpretations of SDP preconditions at the UA are
different. 

I would appreciate if somebody could comment on this, maybe I am wrong, the
two interpretations are exactly the same and I just can't see it.

Question 2.

My second question is much shorter: Is the QoS-Info header needed in the
scenario described in A.1.1 ? 
It seems to me that the information carried in the SDP is enough to convey
the QoS mechanisms required when using preconditions and unidirectional QoS
reservation (using RSVP end-to-end for example) for e2e bidirectional
reservation.

Thank you very much in advance
Regards
Maria 


Maria Cuevas                                                       
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