Subject: [Diffserv] Bidirectional flows

From: "Steve Silverman" <[email-masked]>
Date: Mon, 28 Jan 2002 14:18:21 -0500

Has anything been done in this WG on setting up bidirectional flows with
Diffserv? RFC2475 says:

     “This architecture only provides service differentiation in one
      direction of traffic flow and is therefore asymmetric.”

I have a prospective service that requires setting up such a bidirectional
flow.

Steve Silverman
Houston Associates
[email-masked]

_______________________________________________
diffserv mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/diffserv
Archive: http://www.ietf.org/mail-archive/working-groups/diffserv/current/maillist.html

---

From: Brian E Carpenter <[email-masked]>
Date: Tue, 29 Jan 2002 13:59:38 +0100

No. Diffserv is unidirectional. If you need the same behavior in both directions,
you simply have to configure it the same way in both directions.

If you think your traffic flows are in fact roughly symmetric, it's easy
enough. If they are in fact asymmetric, it may be better to set up an
asymmetric configuration to optimize resource usage. This is an operational
choice.

In general this sort of discussion fits better on the diffserv-interest
list, but since it goes to the heart of the architecture it seems
appropriate here.

    Brian

P.S. I've just deleted about 6 copies of the infamous MyParty worm from
the diffserv list filter - somebody on this list is spraying us with
multiple copies of it.

---

From: Fred Baker <[email-masked]>
Date: Tue, 29 Jan 2002 05:24:57 -0800

At 11:18 AM 1/28/2002, Steve Silverman wrote:
>Diffserv?

>list, but since it goes to the heart of the architecture it seems

this is very much an architectural question, and not the first time is has 
come up. See draft-atarashi-dscp-policy-00.txt

Here's the deal, according to various customers (note the plural) who have 
asked me about it. Suppose that they offer several grades of service at 
various prices to various folks. When a customer approaches a server at a 
given class of service, the server should reply with the same class of service.

Atarashi-san's application (digital libraries and related applications) 
goes on to suggest that the metadata for an object may specify a class of 
service for the reply to over-ride the user class of service; there are 
clearly also other approaches. So her proposal is to have the host mirror 
the user's class of service by default, and provide an override capability 
through the host's API.

An alternative that I have been asked for is that (since the hosts don't 
mirror the class of service) my router should do it for them. As in, 
isolate each incoming session in the router, record the DSCP used incoming, 
and force the outbound DSCP to the same value. Personally, I think that's 
architecturally broken (did anyone mention 'state'?), so we have not done 
that. But something like Atarashi-san's approach is necessary for that 
service to be offered.