RE: [RPRWG] Frame reordering for medium priority traffic in Ganda lf?
Mike, Anoop, Jim,
Unfortunately, the revised text still says:
"However the priority class on the ring transit
path will be different depending on whether the
particular frame is in or out of its agreed
CIR/EIR/BIR profile."
This would still lead to misordering.
Looking at other parts of the proposal, in particular
the flowchart of Fig. 12 on page 39 I think the profile
conformance only affects access to the ring: during
the time of conformance Med packets are added just
behind Hi packets in priority, but during the time of
nonconformance they are added subject to the
fairness algorithm, just ahead of Lo traffic.
Once on the ring Med traffic always occupies the Lo
transit queue.
Is this correct?
Thanks,
Gary Turner
> ----------
> From: Anoop Ghanwani[SMTP:anoop@xxxxxxxxxxxxxx]
> Sent: Friday, December 07, 2001 1:01 AM
> To: 'Mike Takefman '; Anoop Ghanwani
> Cc: 'stds-802-17@xxxxxxxx '
> Subject: RE: [RPRWG] Frame reordering for medium priority traffic in
> Ganda lf?
>
>
>
> Mike,
>
> And in fact the pre-Gandalf proposal did actually state
> things the way you explain below. That's what confused
> me. Thanks for the clarification.
>
> -Anoop
>
> -----Original Message-----
> From: Mike Takefman
> To: Anoop Ghanwani
> Cc: stds-802-17@xxxxxxxx
> Sent: 12/6/01 8:24 PM
> Subject: Re: [RPRWG] Frame reordering for medium priority traffic in
> Gandalf?
>
> Anoop,
>
> We discovered this error in the document soon after the meeting.
> Our presentations have consistently stated that the medium
> priority class is treated as high priority only from the
> perspective of admission, not transit. Clearly, we missed it
> in our review of the document prior to the meeting.
>
> thank you for raising the issue,
>
> mike
>
> Anoop Ghanwani wrote:
> >
> > In Section 2.2.2 of the Gandalf proposal, we have the following
> > statement:
> > "However the priority class on the ring transit path will be
> > different depending on whether the particular frame is in or
> > out of its agreed CIR/EIR/BIR profile. In-profile frame will
> > be delivered on the high priority low-delay transit path while
> > out-of-profile traffic will transit on the low-priority,
> > best-effort path."
> >
> > This seems to suggest that frames belonging to the medium
> > priority class of traffic can get reordered since a later
> > frame that is determined to be in-profile may get to
> > the destination node before an earlier one that was
> > determined to be out-of-profile.
> >
> > It's well known that protocols such as TCP will suffer
> > throughput degradation if packets are reordered, and
> > therefore most protocols (such as, for example, 802.3ad
> > link aggregation) make every effort to ensure that frames
> > are delivered to the destination in order. Is there a
> > reason why re-ordering has been considered acceptable in
> > this case?
> >
> > This issue may have already been brought up at the meeting,
> > but if it was then I missed it. (I must've been at one
> > of them bridging sessions. :-)).
> >
> > -Anoop
>
> --
> Michael Takefman tak@xxxxxxxxx
> Manager of Engineering, Cisco Systems
> Chair IEEE 802.17 Stds WG
> 2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> voice: 613-254-3399 fax: 613-254-4867
>