Subject: comments on draft-ietf-policy-qos-device-info-model-02.txt

From: "Yoram Bernet" <[email-masked]>
Date: Mon, 11 Dec 2000 12:37:36 -0800

Here are a couple of high level comments on the above draft:

Distinction between IntServ and DiffServ
Introductory sections distinguish between IntServ and DiffServ, but on
shaky grounds. Fore example, section 2.1states that IntServ differs from
DiffServ because it forwards based on 5-tuples, whereas DiffServ
(mostly) forwards based on DSCP. It also states that IntServ is much
more dynamic than DiffServ. It also states that DiffServ operates
exclusively in the forwarding plane. None of these strike me as true.
Many associate IntServ with 5-tuple classification, but this is not
necessarily the case. IntServ can be applied to aggregates (just see
1633). Also - IntServ can be invoked dynamically, when used with RSVP,
but nothing dictates that it be used with RSVP. Further, nothing says
that DiffServ should be static -- especially, when considering using
DiffServ at ingress routers to mark based on MF criteria, DiffServ will
have to be quite dynamic. Finally, DiffServ operates quite significantly
at ingress nodes in classifying, marking, policing, none of which are
really 'forwarding' functions. So - I see the distinction between
IntServ and DiffServ, with respect to classification, scheduling,
buffering and policing (all types of traffic handling), to be quite
arbitrary.

I think that a much more useful distinction is between the configuration
of traffic handling components (which are common to IntServ and
DiffServ) on the one hand and the mechanisms used to configure these
(such as COPS, SNMP, RSVP, etc) on the other hand. I think that this
draft is mostly about traffic handling, which is common to both IntServ
and DiffServ. In other words - the traffic handling is mostly forwarding
path or data path stuff. The other stuff is control-plane stuff.

Use of the term 'service'
Probably because of the cim background, the term 'services' is used
quite liberally in this draft, and I ifnd it very confusing. In section
3.6, it states that: QoS
   is a set of services that can be controlled using policy.  These
services are represented as device mechanisms. Device mechanism are not
services nor do they represent services. Services in DiffServ are much
more than device mechanisms - they are combinations of device mechanisms
coupled with policing and related criteria. The use of the term
'services' throughout the draft should be significantly scaled back. In
addition, the usage should be defined up front. 

More as I read further.

Yoram