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Re: [8023-CMSG] Proposed Upper Layer Compatibility Objective

Title: 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>>