From mboxrd@z Thu Jan 1 00:00:00 1970 From: pnr@planet.nl (Paul Ruizendaal) Date: Wed, 18 Jan 2017 15:29:26 +0100 Subject: [TUHS] TUHS Digest, Vol 14, Issue 63 In-Reply-To: <20170117153207.B39A518C094@mercury.lcs.mit.edu> References: <20170117153207.B39A518C094@mercury.lcs.mit.edu> Message-ID: I asked over at the internet history list (http://mailman.postel.org/pipermail/internet-history/2017-January/thread.html) Short of it is that it used Bell 303C modems which operated at 50kb/s operating over an analog "broadband" channel predating the T1. It used the space of 12 voice channels and some fairly fancy modulation techniques. Connection to the trunk exchange was over a leased line. On 17 Jan 2017, at 16:32 , Noel Chiappa wrote: > >> From: Joerg Schilling > >> Was T1 a "digital" line interface, or was this rather a 24x3.1 kHz >> channel? > > Google is your friend: > > https://en.wikipedia.org/wiki/T-carrier > https://en.wikipedia.org/wiki/Digital_Signal_1 > > >> How was the 64 ??? Kbit/s interface to the first IMPs implemented? >> Wasn't it AT&T that provided the lines for the first IMPs? > > Yes and no. Some details are given in "The interface message processor for the > ARPA computer network" (Heart, Kahn, Ornstein, Crowther and Walden), but not > much. More detail of the business arrangement is contained in "A History of > the ARPANET: The First Decade" (BBN Report No. 4799). > > Details of the interface, and the IMP side, are given in the BBN proposal, > "Interface Message Processor for the ARPA Computer Network" (BBN Proposal No. > IMP P69-IST-5): in each direction there is a digital data line, and a clock > line. It's synchronous (i.e. a constant stream of SYN characters is sent > across the interface when no 'frame' is being sent). > > The 50KB modems were, IIRC, provided by the Bell system; the diagram in the > paper above seems to indicate that they were not considered part of the IMP > system. The modems at MIT were contained in a large rack, the same size as > the IMP, which stood next to it. > > I wasn't able to find anything about anything past the IMP/modem interface. > Perhaps some AT+T publications of that period might detail how the modem, > etc, worked. > > Noel