Date: Fri, 9 Apr 1999 20:52:19 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: net@freebsd.org Subject: possible dummynet enhancement (random pkt reordering) Message-ID: <199904091852.UAA01251@labinfo.iet.unipi.it>
next in thread | raw e-mail | index | archive | help
Some time ago, a few people asked me on how to simulate pkt reordering
with dummynet. I did have a few ideas but not so clear. However,
the following seems a reasonably good method if someone feels like
implementing it. (this is an excerpt from a reply i sent to Rick Jones
at HP):
... reordering is slightly harder to do in a realistic way. I had an
email exchange with somebody who wanted to implement it, and turned
out that the simplest way would be to randomly decide to swap a
pair of packets while they are in the first queue (the bw limiter).
This way you preserve the throughput. Depending on which pkts you
swap and how frequently you might have different effects which i
have not studied in detail. But one reasonable way could be:
whenever you can move a pkt from the R-queue to the P-queue,
swap the first two pkts (i.e. the one that you would move, and the
next one) with a random probability. Then, move the pkt to the
P-queue.
i think translating the above sentence from english to C should not
take much more than a few lines of code... if you can do that, i would
be much more interested to know how it works than in the actual code :)
cheers
luigi
-----------------------------------+-------------------------------------
Luigi RIZZO .
EMAIL: luigi@iet.unipi.it . Dip. di Ing. dell'Informazione
HTTP://www.iet.unipi.it/~luigi/ . Universita` di Pisa
TEL/FAX: +39-050-568.533/522 . via Diotisalvi 2, 56126 PISA (Italy)
-----------------------------------+-------------------------------------
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-net" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199904091852.UAA01251>