[Udpcast] UDPcast performance on high speed networks?

Felix Rauch rauch at inf.ethz.ch
Wed Dec 18 17:03:02 CET 2002

On Tue, 17 Dec 2002, Alain Knaff wrote:
> > I did so but it didn't help. What surprises me somewhat, is the fact
> > the the performance is also very low for only 1 sender and 1
> > receiver. Here's what I tried:
> Interesting...
> From your previous mail, I see that there are retransmissions starting
> at 1.41.  It might be interesting to experiment with smaller slice
> sizes (i.e. less than 40 packets), and half-duplex. With these
> settings performance would still be bad (40 packets are far too few
> packets for half-duplex operation), but probably not as bad as it is
> now: Performance around 10 Mbps should be possible (due to small slice
> size, latency probably wouldn't allow to go faster than this).
> It might also be worthwhile experimenting with FEC. Performance around
> 40 Mbps (here, processing power of the CPU might be the limiting
> factor).
> Another thing to try is to use the --max-bitrate flag to limit how
> fast the sender sends. Try limiting to 500 Mbps, and check whether
> this makes it faster.... It is possible that for some strange reason,
> attempting to transmit at full speed might overflow some internal
> buffers on the switch, causing it to drop loads of packets, which
> makes the transmission slow due to retransmissions (but should it make
> the transmission _that_ slow?).

Thanks for your help, I was able to improve the Bitrate to
around 375 Mbps with the following commands:

time ./udp-sender --file /dev/zero --half-duplex --interface eth1 --max-bitrate 500m

time ./udp-receiver --file /dev/null --interface eth1

I was able to maintain the performance up to 8 clients.

> And, knowing that the problem can be reproduced with just two
> computers, you might try to link the computers with a cross cable,
> rather than the switch. At least, that will allow us to tell whether
> it is a problem with the switch, or with udpcast.

Since the initial problem seems to be solved I did not try this.

- Felix
Felix Rauch                      | Email: rauch at inf.ethz.ch
Institute for Computer Systems   | Homepage: http://www.cs.inf.ethz.ch/~rauch/
ETH Zentrum / RZ H18             | Phone: +41 1 632 7489
CH - 8092 Zuerich / Switzerland  | Fax:   +41 1 632 1307

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