[ih] More Topology, Packet Radio

[Barbara Denny]

 Eventually under the SURAN contract we/SRI got a version of the radio code.  What we received was probably BCPL because at this point I am thinking I got asked to do a modification because I was probably the only one around with BCPL experience from the Packet Radio station software.  There is a chance it was in C.  The big thing I remember was the code reminded me of more like something that might have been written by people used to a lower level language, like assembler. 
My memory might be wrong but I seem to remember Packet Radio had 256 byte packets.  
The different CAP version numbers indicated functionality in the Packet Radio network so if I remember correctly CAP6.2 included the Packet Radio Station while CAP7 was stationless.
barbara
    On Tuesday, August 31, 2021, 05:56:47 AM PDT, Lawrence Stewart via Internet-history <internet-history at elists.isoc.org> wrote:  
 
 I can contribute a few bits of information about the Packet Radio Network.

In 1978 I designed the 1822 interface for the Xerox Alto.  It was used to connect to the Bay Area Packet Radio Network and for connecting PARC-MAXC2 to the Arpanet.

The Radios used an entirely different low level protocol than the IMPs.  It was called CAP, for Channel Access Protocol.  CAP was notable for a very small MTU - it had an 11 (16-bit) word header and up to 116 words of data.

PARC used the PRNet for a while to encapsulate PUP traffic between the PARC building and the Xerox Advanced Systems Devision (Ben Wegbreit and Charles Simonyi) building.

I wrote the CAP driver in Mesa, for connection to Hal Murray’s Mesa Gateway code.  It may still be around, in the files Paul McJones put up on the CHM servers at http://xeroxalto.computerhistory.org/Indigo/Alto-1822/.index.html <http://xeroxalto.computerhistory.org/Indigo/Alto-1822/.index.html>
The BCPL test software for the 1822 is definitely there. 

I don’t know what language the radio code used. It was written by Collins Radio and they had (from SRI accounts) a truly stone age attitude about it.  The master version was kept in a box of cards in the manager’s office.

I found the writeup of the Xerox work in IEN-78 at http://www.watersprings.org/pub/rfc/ien/ien78.pdf <http://www.watersprings.org/pub/rfc/ien/ien78.pdf>

-Larry

I guess I am surprised by the comments here about the subleties of the 1822 distant host signaling.  I don’t think the Alto board had optoisolaters and it did work in both local and distant host modes, but was never tried with very long cables or ground problems.

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