Re: Fw: TCP adoption in 1984

from gemini:

The first internet gateway (router), developed by Ginny Strazisar at BBN in
1976/1977, was a *PDP-11/40* that used the *BBN 1822* interface on both
sides.
The Packet Radio Side

Just like the ARPANET connection, the Packet Radio Network (PRNET) side
used a *bit-serial (Distant Host) BBN 1822 interface*.

The Packet Radio Units (PRUs), manufactured by *Collins Radio* (Rockwell),
were specifically designed to emulate an ARPANET IMP's host interface. This
allowed existing hardware and drivers to be repurposed with minimal
physical modification.
Key Technical Details

   -

   *Physical Hardware:* In the PDP-11/40 gateway, the connection was
   typically handled by *ACC (Advanced Computer Communications)* interface
   cards, specifically the *ACC LH-DH/11* (Local Host-Distant Host) UNIBUS
   controller.
   -

   *The Interface Logic:* Even though the physical layer was the same 1822
   bit-serial interface used for the ARPANET, the *logical protocol* was
   different. Instead of the standard Host-to-IMP protocol (used to talk to
   ARPANET IMPs), the gateway used the *Channel Access Protocol (CAP)* to
   communicate with the PRU.
   -

   *Speed:* The 1822 interface on the PRNET side supported the radio
   network's data rates, which were either *100 kbps* or *400 kbps*
   depending on the specific PRU model and configuration.

Why use 1822 for both?

The use of the 1822 interface for the PRNET was a strategic choice by
DARPA. Since the ARPANET already had a well-defined, reliable
host-to-network interface, the developers of the PRU simply adopted the
same physical and electrical standards. This ensured that the BBN-developed
gateway software could use similar low-level drivers to talk to both a
fixed landline network (ARPANET) and a mobile radio-based network (PRNET).

Was there a particular reason you were looking into the hardware layer of
the PRNET gateway—are you researching the early development of TCP/IP or
the hardware of the PDP-11?

On Sun, May 3, 2026 at 12:47 PM Barbara Denny via Internet-history <
[email protected]> wrote:

>  Forgot to reply to the list.
>    ----- Forwarded Message ----- From: Barbara Denny <[email protected]>To:
> Vint Cerf <[email protected]>Sent: Sunday, May 3, 2026 at 09:45:36 AM
> PDTSubject: Re: [ih] TCP adoption in 1984
>   I think for the 1976 demo the gateway was still  in the packet radio
> station and only supported ARPAnet and PRnet. I think PRUs (Packet Radio
> Units) originally had an 1822 interface. By the time of the LPR I think the
> interface was HDLC but that change might have happened earlier.
> I think the 1977 demo used a separate box for the gateway and may have
> been ported to MOS by then. The packet radio station used ELF for the
> operating system.
> I am waiting to hear if the MIT gateway had an ethernet interface.  Quite
> some time ago on this mailing list, Noel mentioned he found my request for
> a gateway. I am begining to wonder if that is why i asked for one.   I
> think i had to specify exactly what interfaces i wanted.
> barbara
>     On Sunday, May 3, 2026 at 07:40:52 AM PDT, Vint Cerf via
> Internet-history <[email protected]> wrote:
>
>  I don't think it needed ethernet - it was connecting PRNET to Arpanet and
> SATNET and likely used BBN 1822 interfaces on the IMP sides. Less clear to
> me what the interface looked like on the packet radio side - maybe a bit
> serial link?
>
> v
>
>
> On Sun, May 3, 2026 at 9:25 AM Carsten Bormann via Internet-history <
> [email protected]> wrote:
>
> > On 2026-05-03, at 14:35, Craig Partridge via Internet-history <
> > [email protected]> wrote:
> > >
> > > I don't recall if it supported Ethernet or simply connected two
> > > ARPANET-technology networks (of which there were a few at the time).
> >
> > https://www.internethalloffame.org/inductee/virginia-travers/
> >
> > …talks about “radio and satellite”.
> > 1976/1977!
> >
> > Grüße, Carsten
> >
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