Re: TCP Representative Stream Problems
On Tue, 5 Nov 2002, Victor Pate wrote:
> When I attempt to use a TCP "representative stream" (either as a file or
> STDIN) with Iperf 1.6.3, the client will cease sending data after 1-2
> seconds and will not recover. There are no problems doing the same thing
> using UDP, nor any problems with a TCP stream originating from memory. This
> also happens with or without parallel streams.
Yeah the problem is due to the MSS detection code. It assumes that
the incoming stream is the pattern that we generate in memory, namely that
there exists no byte containing the value 0xA. This is not the case when
using representative streams, the time to failure is simply the probablity
that a packet will have the first byte as 0xA, once one of these packets
arrives then the server starts sending information back to the client to
detect window size and since the client never reads this information
buffer space is used untill one or the other gives a window size of 0 and
then everything halts. I will fix this for next version.
> I have 3 machines available for testing: 2 Windows 2000 & 1 FreeBSD v4.7.
> This situation occurs regardless of which machine is used as the client or
> server and is indifferent to buffer settings (-l). Any ideas?
This is based on the contents of the file and not the operating system, or
buffer settings.
> My apologies if this question has been asked/answered before; I haven't
> encountered an Iperf discussion archive. Thanks.
Haven't encoutered one myself, and I work here. =-)
Kevin
PS If you want to apply a hack to have representative streams work you
will need to effectively disable the MSS detection code. To do
this simply add a "return;" as the first command in the
"PerfSocket::Server_Send_TCP" around line 360 of src/PerfSocketTCP.cpp
This will make MSS detection not work and will most likely halt any
clients attempting to do MSS detection with that server. But it will get
the representative streams working properly.
--
Mitch Kutzko | mitch --at-- dast.nlanr.net | mitch --at-- ncsa.uiuc.edu | 217-333-1199
http://hobbes.ncsa.uiuc.edu/