[rescue] uucp

[Mouse]

>> [C]ommon internet lore seems to say modems can't work over VoIP, due
>> to the codec / compression.

"Common [I]nternet lore" is wrong.

The real problem is that codecs are designed to deal with particular
kinds of errors.  Most modem codecs are designed to be robust against
the errors POTS copper lines introduce.  But VoI telephony introduces
very different error characteristics.  In contrast to copper, with VoI,
if data gets through, it generally gets through uncorrupted; the errors
introduced by VoI are (broadly speaking) dropouts and timing jitter,
not corrupted (but properly-timed) data.

I am not aware of any codecs designed for VoI use, though it would not
surprise me if someone had designed one.  But, in particular, if your
VoI connection is loss-free, modems can work just fine over it.

It will always help to negotiate as null a codec as you can.  For
example, prefer ulaw or alaw over GSM.  The lossier the codec, the more
it will interfere.

But, in most cases, you're better off taking the data stream you want
to send and shoving it over a TCP connection instead of encoding it in
(conceptual) sound, encoding _that_ with a codec, shoving it over UDP
(with potential loss and reordering), then reversing the process at the
other end.  In the case of UUCP, this amounts to UUCP-over-TCP instead
of UUCP-over-VoI.

I say "VoI" not "VoIP" because voice-over-IP is actually used heavily
by traditional telcos; they just send the IP over private links that
are circuit-switched, not packet-switched, with no bandwidth
overcommit.  This leads to essentially zero loss.  Modems over a POTS
last-mile thus often _do_ use VoIP under the hood.  VoI, "voice over
Internet", meaning voice over the general-purpose packet-switched
Internet, is what is "VoIP" is typically used to refer to.  This is
actually part of the reason modems-over-"VoIP" work at all: ulaw/alaw
encoding is lossy in that it quantizes the analog level fairly
coarsely, and is typically used when sending voice over, for example,
one channel of a T1.  Thus, modem codecs are designed to deal with that
quantization, with other errors coming mostly from the analog side of
the circuit.

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