[Tmrg] Traffic generators

[Jay Aikat]

Sangtae,
	Just fyi, I think this example in the paper is actually quite low in terms of 
active connections etc. that we've seen and been able to handle in the lab. 
I've run experiments with 30,000 active connections per second, but of course 
with a larger number of much slower machines.

Now to specifically answer your question, from my experience, I would guess you 
would need 2 pairs of machines of the class you specify, for the 2500 active 
connections.  This assumes of course highly well-tuned machines in terms of 
kernel limits.  I doubt you'll get away with one pair - the CPU utilization in 
handling so many connections may get you down, although I checked my experiments 
and see a (1GHz, 1GB) did handle upto 2500 active connections with under 50% CPU 
util just fine.

As you know, a LOT depends on your trace characteristics.  e.g. I am looking at 
a recently captured UNC trace with less than 2% concurrent connections (rest 
being sequential connections); but these concurrent connections are carrying 26% 
of the bytes.

This is a separate question I am curious about -- I could not join the round 
table discussion remotely.  So, is there a document that may be released from 
those discussions?  I'd be eager to look at that.  Thanks.
--Jay.


SANGTAE HA wrote:
> Jay,
> 
> Thank you for the answer. One more question about this.
> 
> Suppose that we extract N connection vectors (Ai, Bi, Ti), which are
> identified by their (sip, dip) or (sip, sport, dip, dport), Tmix will
> delegate each connection vector to one of machines in the testbed.
> Yes, we can distribute these vectors evenly to each machine in the
> testbed, or can dedicate all connection vectors to only one machine. I
> just want to know how many connection vectors (or aggregate
> throughput) can be handled by one commodity hardware (as you listed,
> 1or 2GHz CPU 1GB RAM server). I can see the number of connections
> extracted from the UNC trace is around 2500, and my simple calculation
> from CDFs given in the paper gives < 250Mbps for burst traffic
> (100Kbps per connection and 2500 connections at this time instance).
> From your experience, this traffic can be handled by one or two pairs
> of machines? :-) I know it highly depends on the socket buffer size
> for each connection as well as other system specs.
> 
> Sangtae
> 
> 
>> It really depends on the capability of the machines.  I have used medium grade
>> machines, ~1GHz CPU 1GB RAM as well as 500MHz CPU with 256 MB RAM, within a lab
>> network (I have not used tmix in ns2).  The idea with tmix is that, given the
>> original trace, you create a set of connection vectors for each pair of machines
>> in the network, knowing the target throughput you wish to generate, and the
>> capability and number of machines in your network.