[ih] Comments on Packet Radio

[Vint Cerf]

I was not sure whether Don's note got to the internet-history list, so
apologies if this is a duplicate.

I went back and re-read the long paper on Packet Radio in Proceedings of
the IEEE Special Issue published November 1978.  Don is correct that there
was a reliable Station-PRU protocol (called SPP) but I believe this was
only used for Station/PRU communication. Not all traffic was carried that
way and this, in part, motivated the development of the end/end TCP/IP
protocol.

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1455409

vint

On Thu, Mar 27, 2025 at 2:46 AM Don Nielson <nielsonz at pacbell.net> wrote:

> Sorry, didn't pay attention to limited addressees below.
> Also a few typos corrected below.  Don
>
>
> -------- Forwarded Message --------
> Subject: Re: [ih] TCP RTT Estimator
> Date: Wed, 26 Mar 2025 23:36:21 -0700
> From: Don Nielson <nielsonz at pacbell.net> <nielsonz at pacbell.net>
> To: Barbara Denny <b_a_denny at yahoo.com> <b_a_denny at yahoo.com>,
> Internet-history <internet-history at elists.isoc.org>
> <internet-history at elists.isoc.org>
>
> Hi, All,
> The threads here are a bit random so I think I'll just try to give
> a few comments that hopefully will answer much at issue.
>
> 1. The Packet Radio Network (PRNET) was, from the outset, to be a self-
> forming network with a central controlling node called a station, but with
> the ongoing potential of stationless operation.  That station had
> an ARPANET interface for maintaining its software. The PRNET was
> dynamic in the sense of self-restructuring with the addition or loss of
> nodes. As early as 1974-5 it interconnection to the ARPANET was planned.
>
> 2. The packet radio units (PRUs) were at once a network repeater
> and an entrance node to the network.  Some were placed at
> promontories for area coverage and some were sited at user sites
> as nodes for network access.  They were half digital/half radio and
> sophisticated for their time.  For example, any PRU could be
> software-maintained (debugged) remotely.  This obviously required
> reliable PRNET protocols I think we called SPP and NCP they rode atop a
> channel access layer that resided only in the PRUs.  That PRU layer
> faced all the early issues of contention, routing, and efficiency and
> the PRU radio section was designed as best to deal with mulitpath, etc.
>
> 3. The PRUs required interfaces to the terminals/hosts to which
> they were connected.  (Exceptions to that were some traffic
> generators built for early testing and some IMP interfaces to the PDP-11
> station computer.). SRI built the terminal interface units and it was
> in those that TCP was eventually placed.
>
> 4.  SRI was testing PRNET configurations in 1974-5 and doing so had
> a number of PRUs (and one station computer) available.  By the end
> of 1975 we had at least a half dozen in use and probably more in
> backup.  By the end of 1976 about 14 were on site.
>
> 5.  Before mentioning TCP it needs to be said that PRNET intranet
> protocols were end-to-end reliable, handling all the problems of
> flow control, duplicate detection, sequencing, and retransmission.
>
> 6.  TCP implementation was anticipated in 1975 and preparations for
> a station gateway that arrived in early 1976.  TCP for the SRI
> TIUs was, according to one report, based on Stanford Tech Note 68
> by Vint dated Nov 1975.  As Vint said, Jim Mathis lead that implementation.
> In early 1975 the BBN-provided gateway from Ginny Strazisar was
> first tested without PRUs and early problems resolved.
>
> 7. So, with the gateway operating, it was time to take TCP to the field
> and after some brief testing it was decided to have a little celebration
> in that regard.  Ron Kunzelman of SRI suggested a nice accessible spot
> for the SRI van and was at least one PRNET hop from the station/gateway
> was Rossotti's. (I don't recall or if anyone with ever know whether other
> PRNET repeaters that day were passing this traffic.  Given the absence
> of other PRNET traffic, it would have been improbable.)
>
> Several SRI participants were there, one Army visitor, and I took
> the pictures.  Please recall that the PRNET protocol was reliable,
> so testing TCP exclusively on it wouldn't have made sense.
> While the PRNET could halt under environmental issues, that didn't mean
> it was lossy.  While the demo at Rossotti's was not mobile, we had
> countless mobile demos of numeric patterns in which transmission
> often would be interrupted, but we never saw errors.  We even would
> disable the PRU radio unit to halt transmission to show no errors.
>
> 8. TCP reliability was, now that I think about it, at that point mainly a
> test of the
> new gateway and possibly if the ARPANET routing was somehow lossy.
> If you saw the very lengthy weekly report entered manually from Rossotti's
> you would see how well it all worked end-to-end.
>
> If I haven't bent your ears enough, I could try and answer anything the
> above doesn't mention or errors in my memory.  I did look back at some
> of the packet radio notes for the dates and numbers.   Don
>
>
>
>
>
> On 3/26/25 5:30 PM, Barbara Denny wrote:
>
> Having trouble sending to the email list again so I shortened the original
> thread. Hope no duplicates.
>
> ****
> I might be repeating but I will add a few comments. Hope my memory is
> pretty good.
>
> Packet Radio nodes could act as sink, source, or repeater/relay for data.
> They could also have an attached device (like a station, end user host,
> tiu, etc).  I think the packet radio addressing space was broken up so you
> could determine the type of entity by the ID (need to double check this).
> The station provided routes to packet radios when the packet radio didn't
> know how to reach a destination. Any packet radio could be mobile.  I don't
> remember if there was a limit initially on how many neighbors a packet
> radio could have.  Packet radio nodes did not use IP related protocols but
> could handle IP traffic generated by other entities.
>
> Packet Radio nodes also had multiple hardware generations (EPR, UBR, IPR,
> VPR, and also  the LPR which was actually done under a follow-on  program
> called SURAN) .  There were also multiple versions of the radio software
> known as CAPX where X was a number.   I think the earliest version I
> encountered was CAP5 so I have no knowledge of the protocol implementation
> used in the simulation Greg Skinner presented in his email message.
>
> In the early 1980s packet radio was implementing multi-station so you
> could have more than one station in a packet radio network. I think this
> was known as CAP 6.2 (6.4???).  There was also a stationless design being
> discussed at the close of the packet radio program (CAP7).
>
> barbara
> On Wednesday, March 26, 2025 at 04:07:34 PM PDT, Vint Cerf
> <vint at google.com> <vint at google.com> wrote:
>
>
> Jim Mathis wrote TCP/IP for the LSI-11/23. Nice piece of work.
>
> v
>
>
> On Wed, Mar 26, 2025 at 5:26 PM John Day <jeanjour at comcast.net> wrote:
>
>
>
> On Mar 26, 2025, at 17:17, Vint Cerf <vint at google.com> wrote:
>
> yes, the gateway was colocated with the Station (on the same computer).h
>
>
> I missed something. What is the Station?
>
> The Station managed the Packet Radio network, maintained information about
> connectivity among the radio relays. PRNET was not a star network.
>
>
> That is what I was assuming.
>
> Topology changes were tracked by the mobile nodes periodically reporting
> to the station which other Packet Radios they could reach.
>
>
> So a sort of centralized routing on the Station. An early ad hoc network.
>
> Hosts on the PRNET nodes could communicate with each other and, through
> the gateway, with Arpanet and SATNET hosts. The PRNET nodes did NOT run
> TCP,
>
>
> So there were distinct machines acting as 'PRNET routers’ and PRNET hosts.
>
> that was running on the hosts like the LSI-11/23's or the Station or....
>
>
> ;-) an LSI-11/23 wasn’t a lot of machine. ;-)  We had a strip down Unix
> running on one the year before but as a terminal connected to our Unix on
> an 11/45 but it was running NCP.
>
> Thanks,
> John
>
>
> v
>
>
> On Wed, Mar 26, 2025 at 5:08 PM John Day <jeanjour at comcast.net> wrote:
>
> And those nodes relayed among themselves as well as with the gateway?
>
> IOW, PRNET wasn’t a star network with the gateway as the center, like a
> WIFI access point.
>
> So there would have been TCP connections between PRNET nodes as well as
> TCP connections potentially relayed by other PRNET nodes through the
> gateway to ARPANET hosts.  Right?
>
> Take care,
> John
>
>
>

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