Subject: Re: Slow UDP traffic
To: <>
From: David Laight <>
List: netbsd-users
Date: 06/05/2004 09:22:11
On Fri, Jun 04, 2004 at 08:43:14PM -0400, Perry E. Metzger wrote:
> Schamil Wackenhut <> writes:
> > I did some benchmarking in my private network today, and i saw that
> > the udp transferrate between my server(NetBSD 1.6.2/GENERIC/ipf
> > disabled) and my firewall(OpenBSD 3.5/GENERIC/pf disabled) (both
> > have 100mbit ethernet link) is down to only ~25MBit/s. TCP transferrate
> > is ok (90MBit/s). What can be a reason for such slow udp traffic?
> I'd read TCP/IP Illustrated, volume 1, to learn the answer, but
> in general UDP tends to be pretty slow unless you implement all the
> nice things TCP does, at which point you have TCP.

On a 10M HDX local LAN segment, UDP should be faster then TCP because
there are no acks being sent.
With a large TCP window, the receiving system can have many acks
queued to be sent by the time the cable becomes idle enough to
send any of them - they then go out as back-to-back packets.

Provided no packets are being lost UDP should be faster than TCP.
I suspect this is one reason why NFS used TCP.


David Laight: