After seeing some improved connections to (3:850/100), I spoke with Frank
Nitzsche and Ross Mudie from Telstra today, who went into great detail on
what was happening with connections to Nhulunbuy.

Although Nhulunbuy is 600 km from Darwin, the Nhulunbuy RSS sends *all*
calls, even local ones to the Casuarina AXE node in Darwin for switching
(unless the link to Casuarina fails, when local calls get switched
locally).

Because of the limited capacity of the microwave bearer between Nhulunbuy
and Casuarina, the majority of the circuits are 32 kbps ADPCM (which isn't
good for modems). 3:850/100 is on a 64 kbps PCM line with some special
equipment. Some of this equipment involved less than ideal 2W/4W hybrids
and was generating an intermediate echo in the signal path. Echo cancelling
modems (V.32/V.32bis and V.34) are designed to cope with local and remote
echoes (where echoes from a number of close sources are treated as a single
echo), but are apparently not designed to cope with another source of echo
distant from both the local and remote echo.

When this problem existed, I could force a 2400 bps / V.34 connection, but
had no success with automoding V.34.

Ross Mudie made several adjustments to reduce intermediate echo, and since
then 24000 bps V.34 connections have been possible.

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