Subject: AW: [Fwd: L2TP Diffserv Draft]

From: Klausberger Walter <[email-masked]>
Date: Wed, 27 Sep 2000 15:22:42 +0200

Hi,

well I like this draft and the comments, but I think there is still
something missing.

When a better service is granted to someone (from a LAC point of view), I
know the maximum bandwidth this user is capable to send, but when he
downloads a file the prioritized traffic can exceed this maximum (may be a
problem with UDP traffic).

Maybe the LNS should take the link speed in the L2TP session setup message
as a hint, or the granted bandwidth should be added to the DSCP AVP.
Shouldn't there be a hint in this draft? Or am I missing something?

Awaiting comments
with best regards
Walter

-----Ursprüngliche Nachricht-----
Von: Danny McPherson [mailto:[email-masked]]
Gesendet am: Samstag, 16. September 2000 00:49
An: Evan Caves
Cc: [email-masked]
Betreff: Re: [Fwd: L2TP Diffserv Draft] 

> I sent this out several weeks ago but got no response. This time can
> anyone respond (not just the authors :-).

I just picked it up from Ken & Pat so I'll give it a shot.

> > 1. Is the DSCP AVP a six or eight bit value?

The format as currently specified is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1|1|0|0|        Length         |              43               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                1              |        DSCP  Value            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This means that the total length is 8 octets, with 2 octets representing the

DSCP value.  The value will remain at least one octet, as two octets seem to

enable little more than tidy packets encoding pictures.

> > 2. What DSCP value is used for tunnel control messages? If the
> >    session DSCP has a 'higher priority' than the tunnels then
> >    payload packets may arrive before session setup completion.

The next version of the draft, which is hopefully no more than a couple
weeks 
out, will specify the behavior in this scenario.

> > 3. Why is this AVP restricted to just sessions? One could conceive
> >    bringing up a tunnel for each PHB and forwarding all tunnel
> >    traffic (control and payload) with one of the PHB class DSCPs.

Agreed.  And this is something that we were just discussing.  I'll ensure
that 
the upcoming draft provides provisions for this as well (comments welcome!).

> > 4. This draft makes a big assumption that the tunnel traverses a
> >    single DS domain. If the tunnel traverses multiple DS domains
> >    the DSCP to PHB mappings could be different (this may mean
> >    that each tunnel endpoint uses different DSCP marks that get
> >    translated at some DS boundary). How is this resolved?

Multiple DS domains is of course is a very well-know and interesting
problem, 
and again, the next version of the draft will take a stab at addressing this

as well.  We plan to do our best to be in alignment with similar work being 
done in the diffserv WG.  (Again, comments welcome!).

> > 5. Related to 4 it would seem that it may be more appropriate that
> >    the tunnel initiator ask for a PHB rather than a DSCP and then
> >    let each endpoint decide how that PHB maps to a DSCP.

Though you still have lots of problems with this model as well when
traverses 
multiple DS domains.  Again, we'll take a stab at it and work with the DS 
folks to ensure that we're aligned.  Comments here are welcome!

Thanks for the input, hope to have something useful within a couple of weeks

at most.

-danny