Re: [Diffserv] problems with Virtual Wire and RFC2598

[Anna Charny <[e-mail]>]

Kathie,

At 05:13 PM 3/27/00 -0800, Kathleen Nichols wrote:


>Jean-Yves Le Boudec wrote:
> >
> > I have some problems understanding RFC2598 and
> > draft-ietf-diffserv-ba-vw-00
> >
> > a) RFC2598 requires that the service given to an aggregate flow
> > guarantees a rate down to a small time scale and further gives as
> > example
> > "A simple priority queue will give the appropriate behavior as long as
> > there is no higher priority queue that could preempt the EF for more
> > than a packet time at the configured rate. "
> >
> > I have the impression that this statement ignores the phenomenon of
> > jitter accumulation due to aggregate multiplexing. When several flows
> > share their fate in a multiplex, then there is accumulation of jitter
> > from network node to network node, well beyond the bounds given in
> > this internet draft. The fact that flows are shaped at the network
> > input does not guarantee a bound on jitter after several hops. Some
> > bounds do exist, but they are not straightforward, and it is not even
> > clear whether finite bounds exist in all cases where the maximum
> > network utilization factor is less than 1. In the particular case
> > where the network topology is a ring, the answer is yes, however, in
> > general, it is unknown (as far as I know). See for example the
> > references below.
> >
>
>So this is what a lot of the discussion in the vw draft is
>attempting to address. We've tried to spell out what
>the assumptions are and how they get used. I'm hoping
>that in today's meeting we can figure out what is
>missing in the explanation so the next roll can make
>this clearer. Anna Charney's work uses a different set
>of assumptions.

I am not sure how  assumptions of my work differ from the assumptions in 
the draft.  Can you please be more specific ?

Thanks,
Anna Charny


>There are some university folks who believe they can work
>out the analysis under the assumptions we work under.
>Hopefully, they'll get something worked out and made
>publically available.
>
> > It seems to me that the only way to guarantee the requirement
> > described in RFC2598 is to shape every aggregate at the output of
> > *every* network node, a solution that requires per aggregate
> > information which is not compatible with diffserv.
>This comes out under Charney's assumptions since they are
>no more restrictive than the rules we assume for individual
>domains. Thus this is like the rules for shaping at the
>edge of every domain.
>
>         Kathie
>
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