UDP vs. TCP distribution [was: Re: [e2e] Can feedback be generated...]

[Craig Partridge]

In message <11047.983830631 at cs.ucl.ac.uk>, Jon Crowcroft writes:

>go look at the original bell labs papers on interative audio RTTs :
>that was just opinion too

Hi Jon:

In defense of the Bell Labs folks.  There were some badly done studies in
the 1950s and 1960s [not all at Bell Labs if I recall] -- many of which had
the property that the people doing the studies didn't understand echo
cancellers, with the result that, *surprise surprise*, they all reported
that interactive voice couldn't be sustained with a delay of more than
something like 100ms (exact number no longer remembered) which was the
point at which the lack of echo cancellation started to be a problem.

But there were three very good studies, all out of Bell Labs, which did
the tests properly.  They're still worth reading:  Riesz and Klemmer in
Bell System Technical Journal of Nov 1963, Klemmer in Bell System Technical
Journal of July-August 1967, and P.T. Brady's article in the Bell System
Technical Journal of January 1971.

Incidentally, Klemmer sent me a note in the early 1990s says that, in
retrospect, his studies didn't account for learned delay sensitivity --
that is, a delay which previously was acceptable will become annoying if
you've become used to a much shorter delay.

Side note: the BSTJ studies often used the following test procedure:

    * every time you picked up your phone handset, a delay was randomly
      chosen from a pool of possible delay times
    * on the phone was a button that you could press if you were unhappy
      with the audio quality, and I think you were rewarded by having
      the delay eliminated

Something like this might work for gaming (though we'd have to get the
incentives right -- if pressing the button eliminates the delay, everyone
will do it all the time)

Craig