[ih] ARPA initial IMP-IMP line speed

[Toru Nohzawa ,]

Hello, all,
I have a following question about the subject.
If you know the fact, please let me know it

Question:
There are lots of documents mentioning the initial line speed of ARPAnet in
1969 was 50Kbps.
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.
In addition, no modems for 50Kbps become available.
Some document says 50Kbps over analog wideband. But this causes other
question of what modem was used and who provided that.

How many line speed is used with what modem at initial ARPA IMP-IMP?

Regards,

Toru Nohzawa
nohzawa at w-tri.com