Subject: Policing and merging - a correction

From: [email-masked] (Bruce Davie)
Date: Fri, 12 May 1995 12:17:20 -0400

I think I'll take a shot at correcting my response to John's
message. A good situation to consider (and which I had not thought
about very hard previously) is one where I've made a wildcard-filter
reservation for, say, enough bandwidth to support 2 simultaneous
speakers on an audio conference. If 3 people speak at once, then there
could be a point on the tree where the 3 flows merge but I've only
installed enough reservation for 2. So even though all 3 flows are
within their Tspec, they exceed my reservation, so some sort of action
is needed, e.g. dropping/marking one third of the packets. 
(Interestingly, in this case, it would be potentially more 
useful to drop all packets from one sender than 1/3 from each. I think
this is application-dependent.)

So, I now concede that policing at source merge points is not
uniformly a bad idea. I am now off to refine my previously one-eyed
viewpoint. 

Bruce

(Thanks to Scott Shenker for patiently explaining the error of my
ways.)

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From: [email-masked] (John Krawczyk)
Date: Fri, 12 May 95 14:21:19 EDT

I wanted to cut this down to one list, but I really couldn't decide
which one.  Anyone?

   On Fri, 12 May, Bruce Davie ([email-masked]) wrote:

What about at the points where the receivers split and have different
Rspecs?  For example, suppose a multicast flow received on interface A
is forwarded out B and C.  The receivers downstream of B and C have
done wildcard filters, but the B receivers have asked for 3 speakers
worth of bandwidth while the C receivers asked for 2.  Is policing to
be done on the traffic sent out B, or is it up to the next downstream
router to do this?  Neither is an edge nor a source merge point.

-jj

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From: [email-masked]
Date: Fri, 12 May 1995 12:44:36 -0700

Following up only to int-serv...

>>>>> [email-masked] (John Krawczyk) writes:

> router to do this?  Neither is an edge nor a source merge point.

It seems like edge point policing only works for unicast flows.  With
multicast, a flow can fan-out to multiple receivers, so you need to
police at receiver merge points.  With wildcard reservations, a
reservation can fan-out to multiple senders, so you need to police at
sender merge points.  If you combine multicast with wildcard
reservations, it seems that you need to police at both sender and
receiver merge points.

Daniel Zappala
[email-masked]