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Jeff,
I am
perfectly fine with NOT having such an objective if you think we can get
away with it. I'm not sure we can ignore how, what we propose to do at L2, will
affect the operation of the upper layers.
On the
subject of DiffServ, I would simply propose that, within the limited scope of
the high speed, short range, L2 interconnects we are trying to enhance, we leave
the discard decisions up to the upper layers while maintaining the desired
latency and traffic differentiation qualities within layer 2. We have shown
through simulations that layer 2 rate control mechanisms can eliminate (or
significantly reduce frame) discards within layer 2 (effectively pushing the
discard decision up to L3). We have also shown that rate control combined with
prioritization in layer 2 can maintain excellent latency and traffic
differentiation qualities.
Maybe
you can explain to us how this is likely to affect the operation of DiffServ. I
haven't dug deep enough into DiffServ to know if it is counting on L2 devices to
discard. My intuition is telling me it is likely to improve the operation of
DiffServ, as well as other upper layer protocols of
interest.
Gary
-----Original Message-----
From:
owner-stds-802-3-cm@LISTSERV.IEEE.ORG
[mailto:owner-stds-802-3-cm@LISTSERV.IEEE.ORG] On Behalf Of Jeff
Warren
Sent: Wednesday, May 12, 2004 7:58 PM
To:
STDS-802-3-CM@LISTSERV.IEEE.ORG
Subject: Re: [8023-CMSG] Proposed
Upper Layer Compatibility Objective
Gary,
You mentioned improved operation of DiffServ as a
goal for CM. DS is a collection of a number of RFC's, here's the basic
set of DS RFCs.
-
RFC2474 "Definition of the Differentiated Services Field (DS Field)
in the IPv4 and IPv6 Headers"
-
RFC2475 "An Architecture for Differentiated
Services"
-
RFC2597 "Assured Forwarding PHB"
-
RFC2598 "An Expedited Forwarding
PHB"
What
did you have in mind for supporting ULP's such as DS? For example this L3
protocol's purpose in life is to decide drop probabilities for individual
packets on a hop-by-hop basis. For example assured forwarding has three levels
of drop precedence (red, yellow, green). Then there's expedited forwarding in
the highest priority queue, plus best effort, etc......
I've
been wondering how an "Ethernet" standard is going to assist a L3 protocol
such as DS by classification MAC traffic? Would you propose
duplication of or cooperation with DS protocols? Maybe you let DS do its
thing and present a CM enabled Ethernet egress port with remarked packets
that are fortunate enough to have passed across the devices fabric w/o
being dropped. This CM enabled Ethernet port would then align the
offered MAC load to the queues it has available, it does this for example
by inspecting DSCP values and comparing these DSCP values to a predefined
buffer table. Bla bla bla......
The
lights haven't gone off for me yet, I don't see the value in CM supporting DS
because switch manufactures have already figured this one out and
implemented this concept of multiple egress queues working at line rate.
Plus these implementations require global knowledge of networking policies to
configure them properly, and more importantly to standardize them were
talking about linking behavior of ingress and egress ports, knowledge of
system wide (e.g. switch or router) buffer management capabilities, all very
much vendor specific capabilities that would be very difficult to get everyone
to agree to.
Regards,
- Jeff Warren
----- Original Message -----
Sent: Wednesday, May 12, 2004 5:44
PM
Subject: [8023-CMSG] Proposed Upper
Layer Compatibility Objective
My A.R. from last meeting (thank you Ben).
Here's a first shot at a Upper Layer
Compatibility objective:
The objective is:
"To
define 802.3 congestion control support that, at a minimum, will do nothing
to degrade the operation of existing upper layer protocols and
flow/congestion control mechanisms, but has the explicit goal
of
facilitating the improved operation of some existing and emerging
protocols, over 802.3 full-duplex link technology."
If we can narrow the scope and still make it meaningful,
I'm all for it.
I have attached RFC3168 (on ECN) as a reference.
It contains a very good overview of congestion control at the TCP and IP
layers. I would also consider this and DiffServ as examples of existing ULPs
we would want to do our part to improve the operation of. IMO, what we can
do at the 802.3 level to better support these will also provide the support
we need for improved operation of some emerging protocols such as iSCSI and
RDMA.
Gary
<<rfc3168.txt>>
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