Subject: [ippm] IP Network Performance Objective Function

From: Huan Pham <[email-masked]>
Date: Wed, 28 Aug 2002 23:06:28 -0700 (PDT)

Dear folks,

I am doing a project on optimizing IP network
performance, but I am having difficulty in defining a
commonly accepted network performance criterion. Since
I am optimizing the network in a offline mode, before
it is implemented, any measurement QoS are not
practical. 

Network operators most commonly turn to maximum link
utilization as the (resource oriented) performance
objective function. This does not always mean the
optimal QoS performance for end users, especially at
low load. For example a very long path may be chosen,
meaning a much higher end-to-end delay, just to reduce
the maximum link utilisation by a small fraction.
Other approaches use a piece-wise convex function of
the link utilisation. However, this does not directly
relate to end-user QoS and therefore does not
reasonably represent QoS from users' point of view.

I am keen to use theoretical average end-to-end packet
delay, given unlimited queue size at routers, as the
objective function. This is because, at low load
(Utilisation <30%), the packet delay is the most
significant QoS for end-users (compared to throughput,
and packet loss). At higher load (utilisation =
30-70%), unlike practical packet delay which may level
off, the theoretical packet delay increases very
sharply as the link utilisation increases. As a
result, minimizing the e2e theoretical delay gives
priority in reducing the maximum link utilisation,
which has most influence on end users' QoS.

More detailed discussion on this topic can be found at

http://www.cs.jcu.edu.au/~huan/draft/net_perofmance.pdf
  (35 KB) or
http://www.cs.jcu.edu.au/~huan/draft/net_perofmance.doc
(500 KB)

Your comments on this are very appreciated.

Huan

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