Subject: [PCN] What does "reservation" mean?

From: "Osama Aboul-Magd" <[email-masked]>
Date: Thu, 17 Aug 2006 09:57:17 -0400

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
P.O. Box 3511, Station C
Ottawa, ONT, Canada
K1Y-4H7
e.mail: [email-masked]
Phone: +1 613 763-5827
Fax: +1 613 763-2697

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From: <[email-masked]>
Date: Mon, 21 Aug 2006 10:56:13 +0100

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:[email-masked]] 
Sent: 17 August 2006 14:57
To: [email-masked]
Subject: [PCN] What does "reservation" mean?

Regards; 

Osama Aboul-Magd 
CTO Strategic Standards 

Nortel Networks 
P.O. Box 3511, Station C 
Ottawa, ONT, Canada 
K1Y-4H7 
e.mail: [email-masked] 
Phone: +1 613 763-5827 
Fax: +1 613 763-2697