On Sun, 10 Dec 2000, List Server Account wrote:

> The biggest thing (imho) is the latency. A modem can either send or
> receive, but not both at the same time - at least not at 56k.

Not strictly true. Only the very low speed modem modulations are
half-duplex; V.34, V.90 et al are capable of transmitting and receiving
simultaneously.

V.92 supports PCM upstream - so you'll be able to get 48kbps transmit from
the client as well.

> This is a contributing factor to the latency. You would expect the
> ping time to drop quite a bit (nominally by half).

Well - yes - but the biggest contributor is the encoding/modulation
scheme. A very good V.90 modem connection might get you 110ms; it
takes time for the modem to decide on a constellation, transmit it, and
verify the transmission, let alone for the other modem to receive it.

The Sega DreamCast actually turns off V.42 error correction and 'bis
compression altogether, in the name of decreasing latency for gameplay.

I got a very consistant 20-30ms latency on Telstra's OnRamp basic rate
service (when I lived in Australia, I had ISDN in my apartment; couldn't
get DSL/cable internet at that time in central Melbourne). 2B1Q is a much
more simple encoding scheme that takes less time to execute.

--
Josh Bailey (josh@vandervecken.com - Berkeley, CA, USA)
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