[ih] ARPAnet Type 3 packets (datagrams)

[Matthias Bärwolff]

John Day wrote:
> As with most early attempts they don't quite fit the categories that
> coalesce later.  The ARPANET was not as pure connection as X.25, but
> not pure datagram either.  Although, I remember one evening around
> 74-75 Danthine sitting in my living room insisting that the ARPANET
> was not a datagram network!  ;-)  But then that was Danthine.

>From the 1977 McQuillan/Walden paper, which surely must be one of the
most comprehensive and informed account on the Arpanet design, it
becomes fairly clear that it really was both -- at the IMP-IMP level it
was datagram (though with an error control, ack, and retransmit scheme
applied to every packet exchanged between any two IMPs), and at the
source-IMP-to-destination-IMP it was VC, featuring flow control,
reassembly of messages from a sequence of packets that may well have
arrived unordered and with duplicates in it (because individual packets
could take different paths, IMP-IMP retransmissions could delay
packets), etc.

>
> If I remember right, weren't there also hop-by-hop RFNMs in the
> IMP-IMP protocol?

That would be the error check, ack, and retransmit in case of missing
ack scheme, not a RFNM.



-- 
Matthias Bärwolff
www.bärwolff.de