Deployment Considerations of Implementing Differentiated Services BOF (decides)

Tuesday, November 9 at 1415-1515
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CHAIR: Jon Crowcroft <J.Crowcroft@cs.ucl.ac.uk>

DESCRIPTION:

The IETF WG on Differentiated Services (diff-serv) has been meeting now for 
over a year now and has made excellent progress. The framework, architecture, 
DS Field definition, and format for traffic conditoners document, and most
importantly, two PHB definitions have been specified.

So what is the problem?

The Integrated Services WG (int-serv) (with its related groups such as ISSLL 
and RSVP and others), has also defined a set of protocols and mechanisms for 
enhanced services in the Internet. The difference between the int-serv and 
diff-serv approaches is that int-serv (at least the Guaranteed and Controlled 
Load services) is amenable to analysis. Effective bandwidth calcualations, and 
the thesis by Parekh shows how the admission tests for leaky bucket characterised 
traffic and delay bound for the path can be calculated. The difficulty with IS 
has been in designing implementations that scale (hence a great deal of work in 
state aggregation in RSVP, and in fast generalized port specification classifiers,
as well as the work on efficient queue data structures and insert/retrieve 
algorithms, such as WF2Q and approximations such as SFQ). Indeed, there are 
network QoS calculi (by Rene Cruz and also by Jean-Yves le Boudec).

Meanwhile, with diff-serv, the difference is that there can be no obvious 
analytic theory of diff-serv. A path can be constructed out of a sequence of 
hops each with a PHB and some associated SLA. However, the service (and 
provisioning of service) necessarily depend on the actual network topology 
and traffic conditions that prevail.

This is a positive aspect of diff-serv, since it gives providers (and 
router vendors) a lot of design freedom in how they deploy actual services 
(and associated tarrif structures).

However, to evaluate a diff-serv PHB is now a complex task, and requires 
simulation or measurement. To date, only modest simulations and measurements 
have been carried out.

[Aside: of course the exact same argument applies to figuring out call 
blocking probabilities in int-serv type networks]

OBJECTIVES

To prepare a document that outlines evaluation framework for PHBs by 
suggesting realistic topologies and traffic patterns for measurement 
or simulation work. Note that there is a health warning associated 
with simualtion - see reference [2] below.

READING

1/ http://www.cs.columbia.edu/~hgs/internet/traffic.html

2/ Paxson, V., and Floyd, S., Why We Don't Know How To Simulate The
   Internet, Proceedings of the 1997 Winter Simulation Conference,
   December 1997. at
      http://www.aciri.org/floyd/papers/wsc97.ps

AGENDA:

Problem Re-Statement and News (see the Document) - Jon Crowcroft 15 mins

PHB router implementations news - some Nortel folks

Practical Results - Cisco folks

SLAs, PHBs and Theory - EPFL

More about Simulation