Subject: Re: differential services tos octet

From: Steven L Blake <[email-masked]>
Date: Mon, 20 Oct 1997 10:42:13 EDT

Fred Baker wrote:

> What I have been saying all along is that
> 
> >   However, I'll argue again that the sender in each case has no idea what
> >   algorithms are being implemented on the interfaces en route. Some routers
> >   or switches will manage congestion by drops, and some will manage it by
> >   delay.
> 
> and that trying solve all problems with one set of semantics (dp) is akin
> to saying "I have a hammer, everything looks like a nail." 

The most important semantic of the "precedence" bits which needs to be
defined if used in conjunction with a Clark/Wroclawski- or Kalevi-style
profile scheme is the implicit packet ordering behavior.  If the "precedence"
of a flow is being modulated as a function of its rate relative to some
service profile, then it is important to know whether or not the packets
may be reordered by the routers, either due to scheduling in multiple
queues, or due to transmission over alternative (TOS) paths.

Regards,
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From: Juha Heinanen <[email-masked]>
Date: Mon, 20 Oct 1997 20:03:51 +0300

The most important semantic of the "precedence" bits which needs to
   be defined if used in conjunction with a Clark/Wroclawski- or
   Kalevi-style profile scheme is the implicit packet ordering behavior.
   If the "precedence" of a flow is being modulated as a function of its
   rate relative to some service profile, then it is important to know
   whether or not the packets may be reordered by the routers, either
   due to scheduling in multiple queues, or due to transmission over
   alternative (TOS) paths.

yes. i have said in many earlier emails that a router should not reorder
packets that use the same path and have the same tos.  in order to
reduce confusion, i need to add this explicitly also to the i-d, since
it is currently said only implicitly:

   In a typical router implementation, each TOS has its own queue, which
   it serves with such a policy that meets the characteristics of the
   TOS.  The DPs, on the other hand, map to queue thresholds so that an
   incoming packet with a DP value i may be discarded if the length of
   the corresponding queue has exceeded a threshold value th(i) of that
   queue.

-- juha