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[ih] ARPAnet Type 3 packets (datagrams)

Not priority at all.  The lines were flaky enough that the 
reliability required by the connections (for both the ARPANET and 
X.25) created with hop-by-hop retransmissions at the data link layer 
created sufficient delay and jitter that you couldn't do voice. 
There was no way to get a connection-oriented unreliable service.

After all, the argument for packet switching (made by Baran) was that 
data was not like voice.  Data required reliability, short 
connections, and was bursty.  So a network was built do that.

At 16:16 -0800 2009/11/25, 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 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 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