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NSF and the Birth of the Internet
From: David Farber <dave () farber net>
Date: Wed, 20 Aug 2008 13:21:17 -0400



Begin forwarded message:

From: Steve Crocker <steve () shinkuro com>
Date: August 20, 2008 12:44:32 PM EDT
To: dave () farber net
Cc: Steve Crocker <steve () shinkuro com>, "ip" <ip () v2 listbox com>
Subject: Re: [IP] NSF and the Birth of the Internet

Western Electric series 303 modem. 12 voice grade lines multiplexed to achieve 50,000 bits per second. (Not 56Kbps. 56Kbps came later when digital lines came along.)

The IMPs were original designed with eight bit addresses, but before the design of the first IMP was finished, they realized they would have to allow more than one host to be connected to it. They partitioned the eight bit field into a six bit IMP address and a two bit host address, so the maximum number of sites was 63. (I don't think 0 was a permitted address, but I don't recall why.) The host addresses were the high order bits, so, for example, at UCLA which had IMP #1, the address of the first machine on the network, a Sigma 7, was 1, and the next machine connected to that IMP had a network address of 65. The max number of hosts from an addressing point of view was 252, but that could only be achieved by connecting four hosts at each of 63 sites. There were other limits that made it relatively rare for four hosts to be connected. In a few key locations, there were actually multiple IMPs just to create enough interfaces and addresses for more than four hosts.

Steve

On Aug 20, 2008, at 9:04 PM, David Farber wrote:



Begin forwarded message:

From: "David Lesher" <wb8foz () panix com>
Date: August 20, 2008 11:31:21 AM EDT
To: dave () farber net (David Farber)
Subject: NSF and the Birth of the Internet


A few facts I've picked up that seem to get little mention.

The IMP's were fed with an inverse mux & that with modems from Ma. (I've never read how many modems fed each mux.) It was quite a while before She
was able to provide better data connectivity than that to customers.

There were several isolated networks, for operational reasons but also
because the IMP's had a hard limit of ?255/256? addresses.






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