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Re: [8023-CMSG] Questions



Matt,

Thanks.  I understand the structure a bit better now.  Is it also your
belief that 802.3 should throw out PAUSE?  That was added for some
QoS/CoS functionality, but it would obviously break your paradigm.

Thanks,
Brad

-----Original Message-----
From: Matt Squire [mailto:MSquire@HatterasNetworks.com]
Sent: Sunday, May 16, 2004 10:24 PM
To: Booth, Bradley; STDS-802-3-CM@LISTSERV.IEEE.ORG
Subject: RE: [8023-CMSG] Questions



I'll throw some opinions out, may or may not agree with Norm.

>
> Norm,
>
> Thanks for the response.  Two follow-up questions:
> 1) Is it understood or implied that Ethernet knows how to
> direct frames
> to and from these 8 queues?

802.1 knows how to direct frames to those queues.  The queues are above
the MAC and therefore Ethernet knows nothing about it.

> 2) What if the device does not use a bridge as in an adapter?
>

A device, even a host adapter, can use 802.1 rules if it wishes to apply
layer two prioritization.  Alternatively, a device could use layer 3
rules to perform prioritization.

I would argue that the main point is that there are a large number of
prioritization and scheduling options available above the MAC to ensure
a wide variety of services are possible, and that all of these operate
best when Ethernet remains a single pipe with no inherent QoS/CoS.

>
> -----Original Message-----
> From: owner-stds-802-3-cm@LISTSERV.IEEE.ORG
> [mailto:owner-stds-802-3-cm@LISTSERV.IEEE.ORG] On Behalf Of
> Norman Finn
> Sent: Sunday, May 16, 2004 11:11 AM
> To: STDS-802-3-CM@LISTSERV.IEEE.ORG
> Subject: Re: [8023-CMSG] Questions
>
>
> Brad,
>
> I think you did miss the mark, particularly with:
>
>   "Considering that Ethernet doesn't know in advance about the
> provisioning
>    of the network and does not care about which packets it delays or
> drops,
>    then it is likely that 802.1 and the upper layers can do all the
>    priorities or differentiated services that they want but will see
>    diminishing returns as the load on the network increases."
>
> I would agree with, "Ethernet doesn't know in advance about the
> provisioning
> of the network", but 802.1D bridges certainly do care about
> which frames
> are
> delayed or dropped.  Bridges define the use of 8 queues per
> output port,
> and
> frames are marked with 8 levels of priority.  Although strict priority
> scheduling is the only queue draining algorithm specified in the
> standard,
> others are explicitly allowed, and most vendors implement
> varieties that
> provide very good latency and bandwidth guarantees.  Furthermore, a
> great
> many bridges are able to assign priorities to 802.3 frames based on
> criteria
> such as IP DSCP code points.
>
> In short, ethernet is *far* from "best effort".
>
> -- Norm
>
>