[ih] Fwd: Comments on Packet Radio

[Greg Skinner]

Forwarded for Barbara

> Begin forwarded message:
> 
> From: Barbara Denny <b_a_denny at yahoo.com>
> Subject: Fw: [ih] Comments on Packet Radio
> Date: March 27, 2025 at 10:28:40 AM PDT
> 
> ******
> 
> More details than I was expecting. I would add a couple things that I think might be interesting to some people and reflect the multi hop broadcast nature of the network.
> 
> These features were available when I worked on packet radio.  I don't think pacing was available during the first demos. I don't know when alternate routing was included.
> 
>  Packet radios also did something called pacing to try to eliminate the hidden terminal problem: clobbering the receipt of a packet at the next node because you didn't hear a transmission of another radio two hops away from you.  Rather than relying on my memory to recreate the details, I found a paper by the Rockwell folks if you are interested.
> 
> N. Gower and J. Jubin, "Congestion Control using Pacing in a Packet Radio Network," MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications, Boston, MA, USA, 1982, pp. 23.1-1-23.1-6, doi: 10.1109/MILCOM.1982.4805945.
> 
> Packet radios also performed alt (alternate) routing. If a packet radio did not hear the follow on transmission of its packet to the next hop, or the explicit ack if the next hop was the destination,  after three attempts, the sending radio could request help from a neighboring packet radio to transmit the packet if it had a route whose tier level (think hop count) to the destination was equal or less than the tier level in the packet header. An alt route request bit? was used for this help request.  If the new next hop radio was equal to tier level in the packet header, this was known as lateral alternate routing and a flag was set so no other radio at the same tier level would try to forward the packet if help was needed using this new next hop.  Hope I got that description right.
> 
> BTW.  I never got written information about  the protocols in the radios. My knowledge is from meetings or asking Rockwell packet radio folks about a problem I was looking into. 
> 
> Packet radios did use omnidirectional antennas so it was a broadcast network.  Challenges presented to later DARPA packet radio projects included the use of unidirectional antennas. 
> 
> barbara