Subject: [manet] AODV v11: Ratelimit of control messages

From: Erik Nordström <[email-masked]>
Date: 02 Sep 2002 11:06:03 +0200

Hi

I am in the process of updating my AODV implementation (AODV-UU) to
conformance with the AODV draft v11. Having gone through most of the
changes in the new draft, there are still a couple of things that I find
strange, and would like the help of the list to understand.

AODV draft 11 introduces rate limiting of control messages. Specifically
for RREQs, a node should not generate more than RREQ_RATELIMIT RREQs per
second. I cannot make any sense of this, since RREQs should already be
rate limited by, for example, the expanding ring search algorithm.

In a similar way RERRs are rate limited. A node should not generate more
than RERR_RATELIMIT messages per second. However, since each RERR
message is unique by its combination of destination (i.e. the node(s)
that are supposed to receive the message) and the list of unreachable
destinations in the RERR message, I can not see how this is supposed to
be implemented. It is very difficult to rate limit messages on a per
unique message basis (lots of state must be kept). And to blindly limit
all types of RERRs by RERR_RATELIMIT  per second seems just wrong since
that would possibly hinder some important RERRs to ever being sent...

Comments?

Erik Nordström, 

Uppsala University, Sweden.

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From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 4 Sep 2002 08:36:40 -0600

Hi Erik,

I suspect that the rate limiting is there to prevent a node from
monopolizing the channel.  I also assume that such limiting will force the
imposition of some sort of message management at the higher levels.

The bottom line is that there is generally not enough bandwidth to go around
and some mechanism needs to be introduced to see to it that a few nodes
doesn't take it all.  Otherwise, the channel will be used on a
first-come-first-transmit basis without consideration of the importance of
the individual communications.

That is, if one doesn't apply limiting at the source, you will get limiting
at the channel.  Generally, the second option is less desirable because it
is more variable and less controllable.

John Mullen

-----Original Message-----
From: Erik Nordström [mailto:[email-masked]]
Sent: Monday, September 02, 2002 3:06 AM
To: MANET LIST
Subject: AODV v11: Ratelimit of control messages

Hi

Comments?

Erik Nordström,

---

From: "Mullen, John P. (Contractor)" <[email-masked]>
Date: Wed, 4 Sep 2002 08:36:40 -0600

Hi Erik,

John Mullen

-----Original Message-----
From: Erik Nordström [mailto:[email-masked]]
Sent: Monday, September 02, 2002 3:06 AM
To: MANET LIST
Subject: AODV v11: Ratelimit of control messages

Hi

Comments?

Erik Nordström,