[ih] Fwd: Early internetworking ca. 1976 / First ARPANET Link Put Into Service

[Vint Cerf]

thanks Don!! we were trying to figure out early efforts at bridging
networks - PRNET was a key project for exploring that concept.

v


On Mon, Feb 9, 2026 at 3:46 AM Don Nielson <nielsonz at pacbell.net> wrote:

> Vint, Barbara, and all,
> I'm not sure I understand the impetus for all this but thought I'd try to
> help pin down some dates in the early use of the TIU and TCP.
>
> The first I could find was in a Packet Radio Quarterly Report covering
> 1 May 1976 to 31 July 1976.  During that time a gateway was in the
> station computer and was first just doing header swaps between the
> ARPANET and the PRNET.  But in the same period the LSI-11 TIU was
> there running a single-connection user version TCP.  Rather that try
> to describe what was written, I've attached three images of the report
> and the text.  Reference to the description of the TIU architecture
> also included Dave Retz as the lead author so his hand was in it
> as well, probably more to do with the MOS operating system and
> the ELF processes working there.  I've also attached a process
> diagram of the TIU circa Feb 1977.
>
> Hope this helps.
> Don
>
>
>
>
> On 2/5/26 4:10 AM, Vint Cerf wrote:
>
> Jim Mathis did the TIU system - must have been circa 1975/1976
> vint
>
>
> On Thu, Feb 5, 2026 at 1:01 AM Greg Skinner via Internet-history <
> internet-history at elists.isoc.org> wrote:
>
>> Forwarded for Barbara
>>
>> > ----- Forwarded Message -----
>> > From: Barbara Denny <b_a_denny at yahoo.com>
>> > To: internet-history <internet-history at elists.isoc.org>
>> > Sent: Wednesday, February 4, 2026 at 09:34:45 PM PST
>> > Subject: Re: [ih] Early internetworking ca. 1976 / First ARPANET Link
>> Put Into Service
>> >
>> > Having trouble with the mailing list again so not all the text for this
>> thread is included.
>> >
>> > This discussion covers a time period before I worked on packet radio.
>> John Shoch's recollection made me curious about when TCP was first used
>> over packet radio and when the first generation radios (EPRs?) were
>> available. The place I have started to look for this information is the TIU
>> (Terminal Interface Unit).  The TIU had TCP and TELNET. It also had SPP
>> (station-packet-radio protocol) to improve reliability and support for
>> other functions. FYI,  I think the early packet radios had an 1822
>> interface.
>> >
>> > I haven't found definitive answers to my questions but I did find a a
>> webpage that has some links to documentation in case you are interested in
>> the TIU.
>> >
>> > https://gunkies.org/wiki/Terminal_Interface_Unit
>> >
>> > BTW,  the use of DSP on this web page does not mean Digital Signal
>> Processing. It refers to the Dispatch/SPP modules.
>> >
>> >
>> > barbara
>> >
>> >
>> > On Tuesday, February 3, 2026 at 12:23:55 PM PST, John Shoch via
>> Internet-history <internet-history at elists.isoc.org> wrote:
>> >
>> >
>> > Towards the end of last year there was a thread here on the first
>> Arpanet
>> > link at SRI, and Barbara Denny was kind enough to share a note (11/3/25)
>> > from Don Nielsen also reminding us of the earliest multi-network tests
>> of
>> > the TCP Internet at SRI:
>> > // 3. First 2-net demo of TCP was on 27 Aug 1976.? PRNET and ARPANET.
>> > // 4. First 3-net demo of TCP was on 22 Nov 1977.? PRNET, SATNET, and
>> > ARPANET.
>> >
>> > As I recall, prior to that time all of the TCP design, implementation
>> and
>> > testing had been done just on the Arpanet.  Building on the early work
>> at
>> > Stanford, the effort grew to include people at SRI, BBN, and elsewhere.
>> > Those demonstrations in 1976 and 1977 -- with a gateway and multiple
>> > networks -- were  tremendously important milestones along the path to
>> what
>> > became the Internet as we know it today.
>> >
>> > In response to that post, though, I was asked about the actual state of
>> the
>> > Xerox PUP internetworking effort at that time, in mid-1976.  It took me
>> a
>> > while to do an archeological dig -- I wanted to find the original
>> documents
>> > to ensure that we got the history right.  I found a couple of
>> interesting
>> > things and wrote up a summary.  My friends at the Computer History
>> Museum
>> > have long encouraged us to document some of the work, and it was
>> suggested
>> > "you should share it before we lose this history."
>> >
>> > So, some of the notes, documents, and insights on internetworking in
>> 1976
>> > (as seen from a slightly different perspective):
>> >
>> > --In 1972, about 4 years earlier, the first INWG meeting had taken
>> place at
>> > the ICCC meeting in Washington DC.
>> > --In the summer of 1973, about 3 years earlier, there were ongoing
>> meetings
>> > at Stanford, and Cerf and Kahn were drafting the TCP paper at the Cabana
>> > hotel in Palo Alto.  That same summer there were early discussions at
>> PARC
>> > about the proposed Ethernet (as well as an alternative design simply
>> called
>> > LOCAL network), and the need to interconnect them.  A memo from Aug.
>> 1973
>> > reported a discussion on "...the problems of interfacing the LOCAL and
>> > ETHER networks.  This memo describes a rather general proposal for
>> > introduction of a message format standard which emerged from the
>> > discussion.  The adoption of the standard would enable us to
>> interconnect
>> > different networks—essentially forming a network of networks…..”  A
>> drawing
>> > includes ARPA, ETHER, and LOCAL networks.
>> > --In the Spring of 1974 the Ethernet was maturing (while the alternative
>> > LOCAL net never emerged), and there were some basic Ethernet-specific
>> > protocols implemented (EEFTP).  Yet it was clear that there would be a
>> need
>> > to interconnect Ethernet networks, both locally and across geographies.
>> > Metcalfe had been participating in some of the INWG meetings, but it was
>> > also evident that we could not wait for that effort -- we needed
>> something
>> > immediately.
>> > --That led to Bob's initial draft memo, "A Proposed PUP -- PARC
>> Universal
>> > Packet" dated March 19, 1974, which began:
>> > "This memo is written and should be read with caution; its purpose is to
>> > promote a standard.  Because there isn’t an ice cube's chance in hell
>> that
>> > our (or anyone else's) standard will be adopted without interminable
>> debate
>> > and revision, the memo itself is quick and dirty. This way we get the
>> ball
>> > rolling early. ...  A list of the packet networks at Parc would
>> include, in
>> > arbitrary order of pedigree, (1) Ethernets, (2) Localnets, (3) Arpanets,
>> > (4) MCAnets, and (5) EIAnets.”
>> > [MCANets connected Data General Novas.  "EIAnets" evolved into a
>> backbone
>> > packet switching network among Gateways, made up of leased serial
>> lines.]
>> > .
>> > --Over the next two years the further design, implementation, and
>> > refinement of PUP were done primarily by David Boggs and Ed Taft.
>> Progress
>> > was reported in a series of memos, initially by Metcalfe and later by
>> Boggs
>> > and Taft:
>> >   PUP Revisited
>> >   PUP Converging
>> >   Naming and Addressing Conventions for PUP
>> >   A Nova Gateway
>> >   Implementation of PUP in Tenex
>> >   PUP Again
>> >   PUP Connection State Diagram
>> >   PUP Servers on Maxc
>> >   etc., etc., etc.
>> >
>> > --So where did things stand, after two years of work, in mid-1976?  The
>> > best document I have found describing things ca. 1976 is from 6 months
>> > earlier, a "draft" of "PUP Overview" by Taft dated Dec. 21, 1975.  He
>> > reports:
>> > "Local communication is carried on by means of several independent
>> Ethernets
>> > (passive broadcast networks operating at 3 mb/s) and two MCAs
>> > (Multiprocessor
>> > Communications Adaptors for interconnecting Nova computers, operating at
>> > 1.6 mb/s).
>> > Long-haul communication is carried on over the Arpanet (a
>> store-and-forward
>> > packet
>> > switched network·operating at 50 kb/s). We are considering making use of
>> > other
>> > transport mechanisms, such as optical fibers for very high bandwidth
>> local
>> > communication, leased phone lines for regional communication at modest
>> > bandwidths,
>> > and commercial·packet switching services such as Telenet."
>> > The memo goes on at length to describe Basic Principles, Levels of
>> > Protocol, Standard Packet Format, Inter-Network Addressing,
>> Fragmentation,
>> > etc.
>> > I only have a draft of this memo;  I have not yet found a copy of the
>> > complete final version.
>> >
>> >
>> https://drive.google.com/file/d/106a4W2mXsi4Ii-YzRgzsTAwe9_34IqJg/view?usp=sharing
>> >
>> > --To further describe the operational state of the PUP Internet in the
>> > Spring of 1976, though, I have also found a copy of the then-current
>> text
>> > file used to define assigned network numbers, host numbers, well-known
>> > sockets, and name-to-internet-address mapping.  This file was used to
>> > initially configure the gateways, and to load the name server.  The
>> Tenex
>> > header shows this as the 50th copy of the file that was created --
>> > PUP-NETWORK.TXT;50, dated March 19, 1976.
>> > It shows that the PUP Internet at that time included 2 Ethernets, 2
>> MCAs,
>> > and the Arpanet.
>> > Well-known Sockets were defined for Telnet, Gateway-Info (routing
>> updates),
>> > FTP, Misc. Services (name, time, etc.), and Echo.
>> > The name server database allowed a machine to have multiple names (e.g.,
>> > MAXC = Maxc1 = Parc-Maxc), and multiple internet addresses (if
>> connected to
>> > more than one network).
>> > I count 27 Novas on the PUP Internet at the time.  This includes 3
>> machines
>> > acting as Gateways:
>> >   --The Portola Gateway, on both Ethernets, one MCA, and the Arpanet,
>> >   --The front end to the MAXC time sharing system, on one Ethernet, both
>> > MCAs, and the Arpanet.
>> >   --A Nova on one Ethernet and one MCA.
>> > There were 7 Novas only on one Ethernet (including a machine for font
>> > design and two for laser printer units).
>> > The remaining 17 Novas had both Ethernet and MCA interfaces (but were
>> not
>> > necessarily running as Gateways).  These included Novas configured as
>> > servers controlling the older XGP printer,  the newer EARS laser
>> printer,
>> > the Woodstock File System (WFS), and others.
>> > There were also 67 individual Altos on the Ethernets.  Most of these
>> were
>> > for personal use, but the list also included one Alto as a dedicated
>> Data
>> > Line Scanner system (i.e., a TIP, for in-bound and out-bound terminal
>> > traffic).
>> > [My hand-written notes suggest that there were at least 9 other Altos in
>> > our group which were not in the database (including mine).  Even if no
>> one
>> > could find them via the name server, they could operate as client
>> machines
>> > on the PUP Internet.]
>> > This system was in regular use, day and night, with over 100 machines
>> on 5
>> > networks of 3 types.
>> >
>> >
>> https://drive.google.com/file/d/1SZ6yRLp6UqpbFKxbKK4D2stB6BcBX5qq/view?usp=sharing
>> >
>> >
>> > That was the state of the first and largest operational Internet in
>> March
>> > 1976, 5 months before the important 2-net SRI demo of the TCP Internet.
>> >
>> > John
>> >
>> > PS:  A few additional notes and quick lessons from that period.
>> > 1.  For some software-intensive projects a smaller team can be very
>> > productive.  There may have been ~6 of us helping and kibitizing, but
>> the
>> > vast majority of the programming and documentation was done by Taft and
>> > Boggs.
>> > 2.  As best we could, we did try to share some of our general progress
>> with
>> > others.
>> > --I had been full-time at PARC since 1971, but had also been encouraged
>> to
>> > "try to get a quick PhD" at Stanford.  I took part in Vint's networking
>> > seminar.
>> > --In the Spring of 1976 (before the 2-network demo at SRI), three of us
>> > from Parc were enrolled in a Systems Programming class being taught by
>> > Vint.  We had to do a group programming project, so the 3 of us
>> undertook
>> > implementation of the 2nd generation simple file transfer:  evolving
>> from
>> > the Ethernet-based EEFTP (written in Nova assembler) to a new
>> > internet-capable Pup-based EFTP (written in BCPL).  We turned in the
>> > listings, complete with some packet traces (from an Ethernet watcher) to
>> > show how it worked.  We all got an A+ -- thank you, Vint!
>> > --Later, Vint graciously arranged for us to attend some of the TCP
>> working
>> > group meetings.  In July 1977 (before the 3-network demo) Yogen Dalal
>> (who
>> > had been a graduate student under Vint) and I attended a TCP Working
>> Group
>> > meeting held at MIT.  Jon Postel's TCP Meeting Notes (later registered
>> as
>> > IEN 65) reflected some of our overview:  "PARC has 5 different networks
>> > with peices [sic] in Palo Alto, Los Angeles and various places on the
>> East
>> > Coast.  Approximately 14 different networks, approximately 300 hosts
>> > connected."
>> > --In the following month, Aug. 1977, we attended an Internet meeting at
>> ISI
>> > -- where we mentioned our gateway routing, gateway services,
>> > naming/addressing/routing, etc. [IEN 3] [IEN 19] [IEN 20]
>> > --Later, with the help of Don Nielsen and the crew at SRI, we became
>> users
>> > of the PRNet -- adding it as a network in our internet, carrying
>> > encapsulated Pups wirelessly between two Pup gateways.  This was
>> reported
>> > in IEN 78, https://www.rfc-editor.org/ien/ien78.pdf
>> > 3.  At this time the TCP Internet was designed to expose a reliable byte
>> > stream interface.
>> > The PUP Internet architecture provided interfaces at multiple levels:
>> > --Reliable byte stream (BSP), used for Telnet, FTP, etc.
>> > --Reliable packet stream (EFTP), used for simple file transfer, esp. to
>> a
>> > print server.
>> > --Raw packet access, for very simple tasks (name server, time server,
>> echo,
>> > etc.)
>> > Two years later, in 1978, the split of TCP into TCP and IP eventually
>> > allowed that kind of flexibility.
>> > 4.  Network-relative addresses were used in both the TCP Internet and
>> the
>> > PUP Internet, with a network ID and a host ID.  This worked OK in the
>> early
>> > days of both TCP and PUP, but we quickly realized that a) this did not
>> work
>> > well if you wanted to move a machine from one network to another, and b)
>> > this would not scale adequately.  We tried to learn from both the
>> > Experimental Ethernet and the PUP Internet.  Thus, Yogen Dalal developed
>> > the 48-bit flat address space -- used in what became the 2nd generation
>> DIX
>> > Ethernet standard, and used in the 2nd-generation Xerox Network Systems
>> > (XNS) protocols.  The 48-bit Ethernet address design has scaled and
>> endured
>> > for ~50 years -- great work by Yogen.
>> >   https://dl.acm.org/doi/epdf/10.1145/800081.802680
>> >
>>
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>
>
> --
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> Vint Cerf
> Google, LLC
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>
>
>
>
>

-- 
Please send any postal/overnight deliveries to:
Vint Cerf
Google, LLC
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until further notice