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[ih] ARPAnet Type 3 packets (datagrams)

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 1972.

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 


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