Subject: interpretation of bucket size in intserv flowspecs, by hosts

From: Yoram Bernet <[email-masked]>
Date: Fri, 27 Mar 1998 11:09:28 -0800

Folks:

We've had an interesting issue come up and I'm wondering what your opinions
are:

In our traffic control module on our hosts, we shape traffic to the token
bucket parameters advertised in the flowpsec. We have a shape mode and a
discard mode. In discard mode, we discard everything that is non-conforming.
In our shape mode, we delay packets (that are submitted by apps), in a
shaper, and send them to the wire when they become conforming. In this
manner we provide conformance shaping for the app, so that it can be assured
that its data is sent to the net in compliance with the token bucket
parameters advertised in the RSVP/intserv flowspec.

The problem arises when we consider the token bucket size parameter. If the
token bucket size is smaller than the MTU size. Then, if an app submits a
packet which is greater than the bucket size, there is nothing that we can
do in the shaper to make it compliant (since the smallest thing we can send
on the wire, is a packet, which is greater than the bucket size).

So - we are faced with the option of sending it (not taking the bucket size
literally) or discarding it (taking the bucket size literally but somewhat
compromising the application).

If we do not take the bucket size literally, we could at least delay the
burst so that it conforms with the token rate... It may well be that the
first hop router will discard it becuase the bucket size is violated. Then
again - it may not. I need to understand router implementations better. If
routers always discard, then the right thing to do is probably for us to
discard.

We're providing flowspec parameters to our apps from codec parameters. I
wonder if the bucket sizes are intended to represent maximum burst sizes or
typical burst sizes. I'm wondering what apps generally expect if they submit
a packet that exceeds the burst size...

How would you all expect hosts to behave?

Yoram

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From: Craig Partridge <[email-masked]>
Date: Tue, 31 Mar 1998 09:58:00 -0800

In message <[email-masked]

>on the wire, is a packet, which is greater than the bucket size).

The app is not supposed to submit a packet larger than the MTU of
the flow, and the bucket size should be larger than the MTU of the flow.
So this shouldn't occur.

Craig