[ih] ARPA initial IMP-IMP line speed

[David L. Mills]

Kent,

Depends who you talk to. AT&T had several special-order circuits,
including 48, 50 and 56-kbps circuits, each individually engineered. The
48 and 50 kbps circuits were defintely ananlog, but the 56-kbps circuits
were digital derived from 64-kbps voice circuits with a supervisory bit
every 192 bits. It might not make much difference from the viewpoint of
today and especially because of the ubiquitous nature of AT&T
penetration of the 1970s.

Dave

kent at icann.org wrote:
> 
> On Tue, Feb 24, 2004 at 09:39:40PM +0000, David L. Mills wrote:
> > Chris,
> >
> > The IMP interface is described in BBN Report 1822, which I have. There
> > were companion documents for the Digital Equipment IMP-11A interface for
> > the PDP-11 Unibus which I don't have. My first ARPAnet connection at
> > COMSAT Labs was a 4800-bps analog link to BBN; later I connected with
> > 56-kbps DDS and IMP 29 at Mitre. Toward the end of ARPAlife I connected
> > from UDel via 56-kbps DDS to IMP 112 somewhere in WashDC. Scary to think
> > now I have 100-Mbps desktop-desktop just about anywhere in Internet2.
> > How the heck did we get along with only a 50-kbps network?
> 
> I wasn't closely connected at the time, and my memory is dim, but I
> always thought that the early long line arpanet connections were all 56
> kbs.  Where does 50 kbs come from?
> 
> Kent
> 
> --
> Kent Crispin
> kent at icann.org    p: +1 310 823 9358  f: +1 310 823 8649
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