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[ih] ARPAnet Type 3 packets (datagrams)

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.

Did the Xmas lock up occur because they were multi-packet control 
messages and not subject to the end-to-end RFNM in NCP?

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

Which brings up another question.  I had always thought that X.25 
originated mostly with the French PTT.  I have heard stories that the 
Telenet guys had a strong hand in its design.  What is the case?

At 0:32 -0500 2009/11/26, Vint Cerf wrote:
>Richard, ARPANET was not circuit switched in the traditional sense 
>of the word. Packets were dynamically routed. There was end/end RFNM 
>for flow control (that actually inhibited use of things like the 
>TCP/IP window in the NCP protocol). Buffer space was reserved at the 
>far end to deal with reassembly lockup. "get a block" "got a block" 
>handshake assured that no multi-packet message would be initiated 
>without adequate space in the destination IMP.  There was no 
>priority for type 3 packets. there was priority for ARPANET (IMP 
>level) control packets.
>On Nov 25, 2009, at 7:16 PM, Richard Bennett wrote:
>>That really is ironic. If the circuit-switched service in ARPA and 
>>X.25 was good for anything at all, it should have been good for 
>>voice, but I'm guessing you guys tried voice over datagram over 
>>circuits and found it didn't work worth crap, probably because of 
>>high loss rates and excessive queuing inside the ARPANET. I also 
>>wonder of the type 3 service didn't have the effect of boosting the 
>>priority of voice packets in some way.
>>Vint Cerf wrote:
>>>the type 3 packets were explicitly used for real-time packet voice 
>>>and later packet video experiments. This would have been in the 
>>>1975 time frame (but Danny Cohen and Steve Casner would know for 
>>>sure as they were at ISI; Lincoln Labs was also involved and we 
>>>used their packet digitizers/compressors. Duane Adams managed the 
>>>packet voice activity during the time I was at DARPA so I am 
>>>copying him too. I don't seem to have steve casner's email but I 
>>>think he is now at PARC.
>>>On Nov 25, 2009, at 6:05 PM, Richard Bennett wrote:
>>>>I've discussed this issue recently with a key member of the IMP 
>>>>team at BBN and he (unsurprisingly) has a very different 
>>>>recollection of the facts. A datagram mode was added to the IMP 
>>>>and to X.25 switches fairly early. Datagrams appeared on research 
>>>>networks well before TCP/IP was defined; CYCLADES had them in 
>>>>The BBN people have not been able to tell me whether the NWG ever 
>>>>took advantage of the datagram mode in the IMP; that was outside 
>>>>their department.
>>>>Bob Braden wrote:
>>>>>My memory was that BBN included type 3 (Uncontrolled or "raw") 
>>>>>messages in the IMP protocol as an experiment, which they then 
>>>>>considered too dangerous to use . BBN disabled them at (almost?) 
>>>>>all hosts (almost?) all the time, I believe.  TCP/IP used 
>>>>>standard reliably-delivered IMP traffic. But the facility must 
>>>>>have been enabled for the packet voice experiments shown in that 
>>>>>marvelous video.
>>>>>My memory on this point is hazy, but probably Vint can correct 
>>>>>me. When Barry Leiner became (D)ARPA Program Manager for the 
>>>>>Internet research program, he became determined that BBN should 
>>>>>try using Type 3 IMP-IMP packets for normal TCP/IP flows. He 
>>>>>complained to the ICCB/IAB that BBN was resisting.  He insisted 
>>>>>that the experiment be tried for 24 hours. Unfortunately I don't 
>>>>>recall that the experiment ever happened;
>>>>>it is more than possible that BBN stone-walled his demand.
>>>>>Bob Braden
>>>>Richard Bennett
>>>>Research Fellow
>>>>Information Technology and Innovation Foundation
>>>>Washington, DC
>>Richard Bennett
>>Research Fellow
>>Information Technology and Innovation Foundation
>>Washington, DC