Comments inline: On 02/11/05, Bruce Barnett <[EMAIL PROTECTED]> wrote: > Is anyone testing DCCP with limited bandwidth on a low latency network? > I want the system to drop packets instead of buffering them. > I'm having a hard time setting this up, and would appreciate advice from > anyone else.
I don't think we do queue at the moment - if you have a look at ttcp I think it retries if it hits a delay.... We are talking about queing but that should be user settable. Have you tried writing DCCP code directly rather than using ttcp or iperf? Both of these are slightly peculiar in their own ways.... > > I tried to use tc/netem as follows: > ---------------- > tc qdisc add dev eth0 root handle 1:0 netem > tc qdisc add dev eth0 parent 1:1 handle 10: tbf rate 70kbit burst 1000 > latency 20ms > ------------------- > > I have two machines on a Fast Ethernet lan, (no bridge - which may be > my problem) and I use this command on both systems. > > > 1) First of all, when I use ttcp or iperf, one side has twice the > throughput as the other. So netem doesn't seem symmetric. > I always use netem on a middle box as only works on outbound queuing but what you are doing may solve that - not quite sure what you are doing there! My setup is at http://wlug.org.nz/DCCPTesting - another thing to note is that with ttcp and iperf that you get inaccurate results if you don't set the size the same at both ends. I also got that when I used ttcp even when doing that and just switched to iperf as not sure why... > > 2) Second, I used ttcp to send a small number of packets: > > > ttcp -n200 -l100 -t receiver > > This stalls, even after waiting for an hour. I ran tcpdump during this, > and no packets were being sent, except for arp and the pings I > initiated. Wnen I removed the filter, ttcp completed. I'm not sure I > understand why. Will test at some time if you want but not in next few days > > > 3) When I try to use DCCP with the above filter, tfrc.tfrcrx_rtt grows > to some very large values (e.g. 44936) even when I setsockopt(fd, > SOL_SOCKET, SO_SNDTIMEO,..) to 400. I don't recall that we do anything with that option in DCCP... > > Thanks for any advice. Hopefully I am some use - don't think I have fully answered as I don't know it yet... > > > Bruce -- Ian McDonald http://wand.net.nz/~iam4 WAND Network Research Group University of Waikato New Zealand - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
