Excerpts from Randy Buck's message of Tue Apr 27 12:23:04 -0500 2010: > I think I should make something a bit more clear regarding this post. In > that I am working with a mesh network, I am running these tests over > multiple hops. For the previous email I sent, I was transferring over 2 > hops: > > A->B->C > > I doubt that I am at the capacity of the network card, because when I cut > the number of hops down to 1: > > A->B > > I am able to achieve a much high send rate. Here is the same 10Mbps report, > only this time for one hop (and yes I am running this many times to make > sure this isn't an anomaly) : > ------------------------------------------------------------ > Client connecting to 5.0.0.9, UDP port 4000 > Sending 1470 byte datagrams > UDP buffer size: 112 KByte (default) > ------------------------------------------------------------ > [ 3] local 5.0.0.1 port 59795 connected with 5.0.0.9 port 4000 > [ ID] Interval Transfer Bandwidth > [ 3] 0.0-10.0 sec 12209 KBytes 10000 Kbits/sec > [ 3] Sent 8505 datagrams > [ 3] Server Report: > [ 3] 0.0-10.0 sec 12198 KBytes 9991 Kbits/sec 0.327 ms 7/ 8504 > (0.082%) > [ 3] 0.0-10.0 sec 1 datagrams received out-of-order > > > It seems as though the longer my chain of nodes are, the lower my max send > rate can be. The issue is that I am running UDP, which, unlike TCP, doesn't > care about reliability (and therefore doesn't send any ACKs). So, why is > iperf (or something else) causing my maximum send rate to suffer? I will be > posting the plateau of one hop as soon as the tests are done.
In UDP mode Iperf sends as much as it can until it's reached the desired bitrate or the send() call blocks. So I don't think your problem here is with Iperf. My intuition about the problem is that it is the turnaround time on the radio. IIRC 802.11b is half duplex. When you send a burst from A->B->C, B receives the data from A and then pauses receiving from A whilst it sends the data on to C. I could be incorrect here, but based on my understanding of your topology and my recollection of how 802.11b works, I think this is probably your problem. This sort of behaviour would also explain why longer chains get even poorer performance as well. Hope that helps, Jon -- Jon M. Dugan <[email protected]> ESnet Network Engineering Group Lawrence Berkeley National Laboratory ------------------------------------------------------------------------------ _______________________________________________ Iperf-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/iperf-users
