[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[ih] ARPAnet Type 3 packets (datagrams)

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.
>> vint
>> 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.
>>> RB
>>> 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