Subject: RE: [ippm] Comments on OWDP IETF draft

From: "Geib, Ruediger" <[email-masked]>
Date: Fri, 16 Feb 2001 08:50:08 +0100

Stan,

>> 2- [...] I think the DSCP must be taken into account in the request
>> session messages.
 
> We heard the request before and want to include something to that
> effect.  As you know, DSCP values per se have only local significance,
> and we're still unsure how we should approach this (one could use a
> 16-bit PHB descriptor, but then you have the problem of mapping those
> to DSCP values, and the only reasonable way for an implementor to
> solve that problem for now is via a config file; ouch).
> 
> Unfortunately, for now there's not a lot of understanding how DSCP
> values will actually be used.
> 
> We may simply include DSCP, or go for PHB descriptor.

The above mentioned usage of the 16 bit PHB descriptor is the better one.
The mapping which may occur could very well be one of the issues why a
remote domain wants to initiate a measurement. As a remote domain doesn't
know which DSCPs are used in your local network, there's no point in
requesting a DSCP only.

Another attempt may be to signal for a test stream making use of a "globally
well known service", which would be mapped to a PHB and from there to a
DSCP. Today that's obviously science fiction, but it may be good to leave
space for extension in the protocol which would allow to signal for a
globally well defined service. Maybe having some two bits in front of the 16
bit PHB descriptor saying: 00-DSCP, 01-PHB Descriptor and 10-Globally Well
Known Service. You'll always need just one of these. default would be "all
zero"-Best Effort. (If we can agree about the idea, we'll replace "globally
well known service" by a suitable term then.)

Regards, Rüdiger
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---

From: stanislav shalunov <[email-masked]>
Date: 16 Feb 2001 11:45:33 -0500

> The above mentioned usage of the 16 bit PHB descriptor is the better

Vote recorded.

> The mapping which may occur could very well be one of the issues why
> a remote domain wants to initiate a measurement.

How so?  If I initiate measurements (using PHB descriptor or
well-known service) wouldn't I see the DSCP I'd expect to see in my
network because of mappings?

> As a remote domain doesn't know which DSCPs are used in your local
> network, there's no point in requesting a DSCP only.

The idea was I think that this way you can get a shot at what you
think it could be ("umm, will 46 work"?).  If it comes out right on
your end, you know you got it right if your network polices/remaps
uniformly.

> Maybe having some two bits in front of the 16 bit PHB descriptor
> saying: 00-DSCP, 01-PHB Descriptor and 10-Globally Well Known
> Service. You'll always need just one of these.

This seems like an excellent resolution of the problem to me
personally (with possible reservation about well-known services).
Thanks a lot for the suggestion.

Would you like to go into detail in re space needed for expressing a
globally well-known service, and where should we refer for a list?
(Wishful thinking.)  What do you think should we do?

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

"Computer Science is no more about computers than astronomy is about
telescopes."					-- E. W. Dijkstra
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