Subject: mail rispedita-il ccds

From: [email-masked]
Date: Thu, 26 Jun 1997 13:32:37 +0200

Date: Tue, 24 Jun 1997 10:32:53 +0200
From: [email-masked]
To: [email-masked], [email-masked]
Subject: mail rispedita - il ccds
Sender: [email-masked]

To: Dimitrios Stiliadis <[email-masked]>
Cc: [email-masked] (Roch Guerin), [email-masked]
Subject: Re: Traffic Policing and domino effect 
Date: Fri, 20 Jun 97 19:17:37 -0400
From: Roch Guerin <[email-masked]>
Sender: [email-masked]

>Reshaping is of course a solution, although an expensive one if it
>is required for every flow at every node. 
>
>However, if a router is unaware of the buffer sizes of up-stream nodes, 
>and no re-shaping has been done upstream, I can not see how the 
>*amount* of tolerance can be specified and engineered. Interference
>in up-stream nodes can be arbitrarly large when large aggregations
>have been made, or proprietary scheduling mechanisms have been
>used.
>
>Don't we need some estimate of the effective bandwidth of the flow 
>as seen by donwstream nodes and after several hops ?

Dimitrios,

You certainly cannot give hard guarantees such as those of GS, but
you still can do a lot to ensure adequate performance.  For example,
with a WFQ like scheduler I can give the flow a rate guarantee and
also allocate some (dedicated) buffering plus access to a shared
buffer pool with some limitations on how much each flow can grab 
from the shared pool.  This wont avoid real bad cases, where you
have schedulers that do a lot of lumping, but you can still go a
long way.

In any case, the main point I was trying to make is that you should
not do hard policing within the network.  Instead, you need to have
mechanisms to ensure that excess traffic from one flow does not 
degrade overall performance, but without assuming that anything
that does not conform to the TSpec is excess.

Roch