[ih] The classful <net>.<host> IPv4 address format

[Jack Haverty]

In the late 1970s, SRI built a device called a TIU (Terminal Interface 
Unit), which was used in the Packet Radio projects.   I recall at one 
point struggling to use a TIU because its user interface required IP 
addresses in the form of decimal numbers.  An IP address such as 
10.0.0.5 (a BBN PDP-10 on the ARPANET at the time) had to be specified 
to the TIU as a rather large, and very hard to remember, decimal number 
derived from the 32-bit IP address.

This user interface was described in documents from SRI.   There was a 
collection of published documents called PRTNs (Packet Radio Technical 
Notes) that may have been where you saw the TIU address format you 
described.  Sorry, I don't know where to find PRTNs today.   A search on 
discover.dtic.mil for "sri tiu internet" will give you a place to 
start.  There's an index of PRTNs at: 
https://apps.dtic.mil/sti/tr/pdf/ADA141528.pdf

Personally I never saw most of the PRTNs, since their distribution was 
typically limited to people working on the various Packet Radio 
contracts.  The Index notes that PRTNs were available only after ARPA 
approval as well as approval by the authoring company of each specific 
PRTN.   Unlike RFCs and IENs, PRTNs were more difficult to access, even 
in the 1970s/80s, but I don't know why.   I don't recall that they were 
available from the NIC like RFCs and IENs.

Jack Haverty


On 9/14/25 05:21, Michael Kjörling via Internet-history wrote:
> Every once in a while I see people being surprised that IPv4 addresses
> can be expressed in formats other than dotted-decimal-quad; more
> specifically, in classful-style <net>.<host> (where net and host can
> add up to less than four octets) or even single-large-integer format.
>
> I am _almost_ certain that I have seen an early IP or TCP RFC which
> actually describes this representation, but have been unable to locate
> that.
>
> Can anyone point me at an authoritative source where the
> dotted-not-quad textual IPv4 address representation format is defined
> or at least described? Thanks!
>

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