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Re: [ns] TCP traffic generation rate



Thanks Brian,
    Sorry for not having provided enough information. Here are the
details
I am trying to study TCP performance over an optical link. So the
bandwidth typically is about 2.5 -10Gbps/channel and we have 32-128
channels.
Taking the least case i will need 2.5Gbps*32 = 40Gbps.
The link delay is 100ms.
So at what rate will i have to generate traffic to saturate the link and
what should be the window size?

Thanks again
Sunil


Brian Lee Bowers wrote:

> On Tuesday 31 July 2001 14:24, Sunil Gowda wrote:
> > Hello everyone,
> >     My simulations require TCP traffic in terms of GBps. I was able
> > to achieve just 200KBps of traffic per agent when i attached a FTP
> > application to the agent. The window size was 1000.
>
> What are the characteristics of your network (bandwidth and delay of
> each link)?  Which version of TCP are you using (Tahoe, Reno, New
> Reno, Vegas)?  Is a window size of 1000 large enough (I routinely run
> sims where a window size of 5183 would only just keep the pipe full).
>
> I just ran a 150 second sim that managed to deliver ~7.6M packets of
> 1500 bytes (or 12000 bits) each.  That is an average of over 600Mbps
> on a 622Mbps bottleneck link.  I needed 62.2Mb to keep the pipe full
> (622Mbps bottleneck link with a 100ms RTT) so a window size of 1000
> packets would not have been enough for my sim (your actual mileage
> may vary based on bottleneck bandwidth and RTT for your sim).
>
> > How can i generate such large scale traffic?
>
> I'm not sure the problem is with the traffic generator.  Without
> knowing more about your network, I can't say if your network setup is
> to blame.  I'm getting more than a few hundred Kbps from my traffic
> generators (using FTP).
>
> > What is the maximum rate that can be achieved?
>
> Well, I've seen a 622Mbps bottleneck link reach saturation from a
> single sender.  Never tried to go much higher.
>
> > What is the largest window size that we can have?
>
> Well, the variable maxcwnd_ is an int, so I would have to guess about
> 2,000,000,000 (give or take several hundred million).  That number is
> in packets, so it really is quite large.  There is also a variable,
> wnd_, that is a double.  I've forgotten the maximum value an IEEE
> compliant double can hold but it is pretty doggone big - I should
> probably wander off to google and find the value, but I'm being lazy
> AND snobbish today :)
>
> > Also is the window scaling option implemented in ns?
>
> It really isn't.  ns uses sequence numbers to count packets, not
> bytes.  I've yet to run a sim that got close to 2,000,000,000.
>
> > Connecting thousands of agents is not a viable option as the
> > simulation will be very slow.
>
> I normally run with 100 senders on one side of the bottleneck and 100
> receivers on the other side of the bottleneck, or I run with 200
> nodes, half on one side and half on the other side of the bottleneck,
> with every node being both sender and receiver.  It really isn't that
> much slower than running with one sender and one receiver.
>
> > Any help is highly appreciated.
>
> More information please.  You haven't given enough for anyone to make
> more than a wild guess about the problem.
>
> > Thanks in advance
>
> You're welcome (for what, I have no idea).
>
> > Sunil
>
> --
> Brian Lee Bowers        |       RADIANT Team (Summer Intern)
> bowersb@lanl.gov        |       Los Alamos National Laboratory

--
Sunil Gowda
School of EECS
Washington State University
Ph: 509-335-5934 Fax:413-723-0160