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

[Joe Touch]

Tristan Henderson wrote:
> 
> In message <3AA08A3E.541D233 at ehsco.com>, "Eric A. Hall" said:
> >
> >People don't play action-oriented multi-player games over long-haul
> >networks. Shoot-em-up games are very sensitive to latency and packet loss.
> >Playing a shoot-em-up with >200ms RTT will get you killed fast by players
> >with <20ms (client-side events have to wait for server-side messages to
> >arrive so the "closer" player gets a distinct advantage in terms of
> >shorter inter-command gap). After a while, you learn to play on servers
> >that are close.

As Sean indicated, these are application dependent.
More precisely, they depend on the level of 
predicatability in the feedback system, and how
high in the human the processing occurs.

The most basic human feedback loops (single flashing light,
hit a switch) are in the 100 ms range. That means the
network portion must be in the 20ms range to be 'noise'
on the overall system delay. However, it gets longer
for things like "multiple lights, hit the switch only if
one of the lights is red". The response delay gets
larger the more complicated the task.

E.g., ask someone for a review of War and Peace,
and you're liable to be willing to wait a few days. :-)
It's all about expectations.

Figures in the 100-200ms range are for maximum auditory
delay for telephone echos, and date back to the early
Bell Labs days.

> OTOH, there are plenty of usenet postings from people playing with RTTs of
> 300-1000ms, e.g.

Many old video games had artificial delays incorporated 
(e.g., sluggishness in the controls of space invaders, etc).
Part of the 'game' is getting acclimated to those delays.

> It would be useful to know the absolute highest delays that gamers can
> tolerate.

People play chess by mail. It's more about expectations than
about the inherent delay of the system. 

----------------------

Regarding latency papers, there is Stuart Cheshire's from 1996, 
as well as more recent notes from David Reed. My dissertation
was on this stuff, and examined the fundamental limits of 
latency in communication (pub'd 1992, links on my home page).

Joe
http://www.isi.edu/touch