What does "reservation" mean?

Osama,

Thanks very much for your = comments.

You’re right, there’s = no reservation of a physical circuit in the CL-region (which is the region = of the internet enabled with PCN).

What we wanted to do in this = deployment model draft was show one possible “big picture” where QoS is operating end-to-end: PCN as the QoS mechanism in the CL-region, and = IntServ in the access networks between the end hosts and the CL-region. In these = access networks RSVP signalling sets up an IntServ reservation. In the = CL-region, as you rightly say, there’s no reservation – instead our measurement-based admission control scheme is used to decide whether or = not to accept the new flow request.

Also, as I think you suggest, the = ingress gateway of the CL-region will store RSVP signalling state and could also = do policing (to make sure a source isn’t sending more traffic into = the CL-region than it’s paying for).

The draft shouldn’t use = “reservation” to imply there’s a reservation of capacity in the CL-region. Will = try and make this clearer in the next version. Would appreciate it if you could = point out the bits of text that were misleading.

I’m not sure I’d say = our PCN mechanism delivers “soft” QoS. We believe that the admission control / flow pre-emption mechanisms mean you achieve Controlled Load = QoS (under the assumptions given in Section 2.2).

Re section 1.1.3 - Yes, personally = I believe it would be possible to implement only the flow pre-emption mechanism of = PCN – perhaps relying for admission control on the static traffic conditioning agreements of the DiffServ architecture [RFC2475]. But we think = it’s a good idea for us to develop both the admission control & flow = pre-emption mechanisms of PCN.

Thanks

Philip Eardley

-----Original Message-----
From: Osama Aboul-Magd [mailto:osama@nortel.com]
Sent: 17 August 2006 = 14:57
To: pcn@ietf.org
Subject: [PCN] What does "reservation" mean?

I read the draft "draft-briscoe-tsvwg-cl-architecture-03.txt". In various palces of the draft there is the use of the word "reservation" and I am struggling with what does it mean in = this context. Admission control and reservation in PSTN meant the reservation = of a physical circuit for a call. In ATM it meant the reservation of some = equivalent bandwidth (virtual circuit) for the request. In the context of this = draft it is not clear to me what is the "quantity" that is got reserved. =

I tend to believe = that the admission control presented in this draft is kind of a "soft" admission control with no associated reservation of any kind, except = perhaps at the ingress. Had there been any reservation a problem like flash crowd = would have never arised.

In section 1.1.3 it = is stated that an operator may want to implement only one(admission control = and/or preemption). The discussion that follows focuses on admission control = examples. Would it be possible to implement preemption only?

Regards;

Osama = Aboul-Magd
CTO Strategic Standards

Nortel Networks
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