[ih] ARPA initial IMP-IMP line speed

[Mike Brescia]

>There are lots of documents mentioning the initial line speed of ARPAnet in
>1969 was 50Kbps.

That was the speed of the modem.

>As far as I know, the line speed at that time over the voice band
>transmission was
>less than 9,600bps. Most probably 4,800bps or 2,400bps.

The best voice band modem available then coded 9600 bps on 1200 baud 
half-duplex; for full duplex you would need 4 wires (two "phone 
lines") which were "conditioned" (at least tested for quality, maybe 
more).

>Some document says 50Kbps over analog wideband. But this causes other
>question of what modem was used and who provided that.

The 50kb was called "wideband" because it did baseband signalling at 
a rate higher than the 3kHz voice bandwidth, in other words, the data 
signalling was actually 50kbaud, not like today's 50+kbps on top of 
1200 baud (remember Nyquist)

I'm really out of my depth here, but recollection is that the lines 
(4-wire again) were bare copper, no filters etc, and had to be 
specially patched through each level of the telco office wiring.  The 
wiring had to maintain DC polarity correctly, otherwise the data came 
out inverted.  For "long" distances, there must have been some sort 
of repeater.

You really need to find someone familiar with the circuitry and signalling.

Regards,
  -- Mike