[e2e] TCP flow count estimation

[Jon Crowcroft]

In message <5.1.0.14.2.20011129094501.0391f488 at mail.reed.com>, "David P. Reed" typed:

 >>Jon - A cute estimator, but besides doubling the header overhead and 
 >>routing overhead network wide ...

well, most apps that do long transfers are using MSS and many MSSs are 1500 bytes, so
its not so bad:-)

 >>  Has the IP layer's function been redefined so that it guarantees that all 
 >>datagrams must be sent along the same physical path and through 
 >>order-preserving queues?

 >>We know that IP does not have order preserving queues in general - fast 
 >>path processing and service-types violate order.  We also know that in some 
 >>cases, path stability is violated even in the short term.

well its easy to try look at this with traceroute - time for some experiments

but the various pathchar programs rely on this hack, and the tiems when i have seen them
break are always when there's a level two hop with some type of bandwidth on demand
(e.g. ATM VC, or frame relay hop with committed access rate policing via a window/token
bucket scheme).....

so i dont think there's too many cases in the real net out there that would confuse this
besides, like MTU discovery, you only need to do it at the start of every route's
lifetime (icmp "route changed" message considered useful ? :-)




 >>At 06:24 AM 11/29/2001 +0000, Jon Crowcroft wrote:
 >>
 >>
 >>>here's a daft idea for xmas:
 >>>
 >>>if tcp is sending instead of MSS, alternate packets of size
 >>>MSS-1, and size 1
 >>>(well payload size)
 >>>and every packet elicits an ack,
 >>>it can use path char style estimation of the bottleneck line rate
 >>>
 >>>it can use equation basedestimation of the bottlenck avaialble
 >>>capacity
 >>>
 >>>between these two, it can deriv an estimate of the number of other
 >>>tcps (wel module notknowing their RTTs)
 >>>
 >>>this might be useful for somethig....
 >>>
 >>>j.
 >>>oh, if every other packet elicits an ack, then you need to intersperse
 >>>the small/large alternation over  3 packets - simple tho
 >>>
 >>>think of it like running 2 seperate tcp flows tho, one with MSS 1
 >>>bute, one with mtu-41 and estimators for both
 >>

 cheers

   jon