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Re: Diffserv service classes

  • From: Marshall Eubanks
  • Date: Sun Nov 21 11:50:36 2004

On Sun, 21 Nov 2004 00:09:31 -0500 (EST)
 Sean Donelan <sean@donelan.com> wrote:
> 
> On Sat, 20 Nov 2004, Vicky wrote:
> > interesting read at:
> > http://qbone.internet2.edu/papers/non-architectural-problems.txt
> 
> There is a long history of problems.  But Internet2 also shows a success
> for Diffserv, namely there is demand for a "worse" effort.
> 
> Are a dozen differnt classes useful to a network operator?
> 

Dear Sean;

You raise an interesting point. There are some emerging wide bandwidth
applications (eVLBI is one, particle physics experiments are another) where
bandwidth demands are high but the value of each individual bit is low.
(In VLBI it is typical for each bit sent to only contain about 10^-3 to 10^-4 bits
of actual information.) As a result, these applications are (or can be made to be)
very tolerant of packet losses. eVLBI, for example, would take 1 Gbps with 25% loss
over 100 Mbps with no loss any day.

An "Internet standby" worse than best effort QOS would be easy to implement, according to
router vendors, and there
seems no reason why ISP's would not want to propagate such a COS flag. 

This is not really a new idea. When I was programming  on a mainframe as a student (back when
dinosaurs walked the Earth)  I routinely used a service class that only gave me CPU when there were
no other uses  for the system. This would extend the same idea to the Internet, and it fits with
with the QBone experience that it's hard to impossible to raise priorities interdomain, but easy to
lower them.

Would commercial operators support a reduced cost standby system with a "do not queue" or
"drop these bits first" policy flag attached ? I would be curious to receive re-world experiences
or suggestions off list, and would be glad to summarize later on list.

Regards
Marshall Eubanks

P.S. Note that such a system would easily interoperate with non-participating networks, who
could either drop such traffic entirely (it is worse than best effort, after all), or
forward it with normal priority, as they see fit.