[Tmrg] Traffic Generators (Harpoon and Tmix)

[Sally Floyd]

 From Michele:
> Regarding the pauses that are part of the Tmix model, these pauses are
> used to represent the time between complete application data units
> (ADUs), which are essentially files.  If you were modeling HTTP
> connections, for example, the 'a's would be requests and 'b's would be
> responses.  You are right that Tmix can model persistent HTTP
> connections, where there are pauses in a single connection.  If you
> wanted to have a set of long-lived greedy TCP flows, you could
> construct connection vectors to give you such behavior.

But if one wanted to use a realistic traffic model in one's scenarios,
that would have to include non-greedy TCP traffic (e.g., HTTP 1.1
traffic, telnet traffic or other user-generated data, etc.)   Non-greedy
TCP traffic is not unusual in the real world, and can be a significant
stressor on congestion control mechanisms that it would be a pity
to ignore - e.g., TCP flows that *might* ramp up to a high sending rate,
have a data-limited or idle period, and then continue with a lot of
data to send again.

When we are measuring file completion times, we can use
greedy TCP connections to measure them, in a mix with other traffic.

The heavy-tailed distribution of user wait times within TCP connections
has been under discussion since 1994.  E.g., "Wide-Area Traffic: The
Failure of Poisson Modeling", Paxson, V. and Floyd, S., SIGCOMM 1994
(or the 1995 IEEE/ACM Transactions on Networking version).  And has
been included in traffic models in ns-2 for many years (e.g., in Polly
Huang's traffic generator listed in
"http://www.icir.org/models/trafficgenerators.html".

- Sally
http://www.icir.org/floyd/