[ih] Arpanet raw messages, voice, and TCP

[Craig Partridge]

> Why exactly fragmentation didn't work so well I don't recollect very well
> (if we ever knew for sure exactly why).  I suspect that the network back
> then was 'lossier' (partly due to poor congestion control causing
> congestion drops, partly due to flakier transmission systems). Since
> end-end retransmission schemes don't work so well when loss rates go up
> (typically there's a 'knee' where performance goes over a cliff), with
> that many more packets involved for a given amount of data, we may have
> gone over the 'knee'.

The Mogul and Kent paper at SIGCOMM '87 and then the Floyd and Romanow paper
at the London SIGCOMM (don't recall year) pretty much nailed this.

The problem is that you lose a fragment and all the other fragments are now
worthless.  Mogul and Kent showed that certain packets would reliably fragment
in ways such that a fragment was always lost.   Floyd and Romanow showed that
what I call the "dead fragments walking" would then cause downstream loss
of fragments of other packets, causing more mayhem.

Thanks!

Craig