[ih] The origin of variable length packets

[Guy Almes]

John et al.,
   Hmm.  This note invites anyone with experience on the Cambridge ring 
to chime in.
	-- Guy

On 3/1/11 6:25 AM, John Day wrote:
> Undoubtedly, this is correct.
>
> But it also occurred to me that this was not such a big deal and was
> probably discovered by everyone who went to build one.
>
> Sending fixed length packets would be more work (or as much work) as
> sending variable length ones! In both cases, you need a length to
> indicate how much data is there. But in the fixed length case you have
> to send more bits than you need and fill out the packet with zeros.
>
> Wastes bandwidth and is more work. Not a lot more, but in those days one
> saved everyplace you could!
>
> The historians should remember that for engineers, Laziness is a virtue!
> ;-) Not everything that looks like a major insight to the historians
> was. Much of it was just common sense.
>
> Anyone who went to build it would have done the same thing.
>
> Baran's emphasis was that data was not voice. Voice networks send
> streams of fixed length frames, e.g. T-1, because they are continuously
> sampling sound. Data is going to be very different.
>
> At 22:50 -0500 2011/02/28, Noel Chiappa wrote:
>> > From: Stephen Suryaputra <ssurya at ieee.org>
>>
>> > Any pointer or reasons why the packet becomes variable length later on?
>>
>> I would assume/guess that the first well-known and wide-scale use was
>> in the
>> ARPANet. (Which was pretty much the first general packet network I
>> know of -
>> were they any proprietary things before that, does anyone know?)
>>
>> The first variable length data items transmitted between compturers
>> (although
>> I would tend to doubt they thought of them as packets) might be hard
>> to track
>> down.
>>
>> It might have been some of the early computer-computer experiments,
>> e.g. the
>> kind of thing Larry Roberts did at Lincoln Labs (which definitely had
>> variable
>> length messages); another early system that might have had variable
>> length
>> data items was SAGE (since that also had computer-computer links between
>> centers, although I don't know offhand of a source that talks about
>> that level
>> of detail on the communication aspects of SAGE).
>>
>>
>> > A reference would be really appreciated.
>>
>> For Larry Roberts' work:
>>
>> Thomas Marill, Lawrence G. Roberts, "Toward A Cooperative Network Of
>> Time-Shared Computers", Fall AFIPS Conference, October 1966
>>
>> For the ARPANET:
>>
>> Frank Heart, Robert Kahn, Severo Ornstein, William Crowther, David
>> Walden,
>> The Interface Message Processor for the ARPA Computer Network (1970
>> Spring
>> Joint Computer Conference, AFIPS Proc. Vol. 36, pp. 551.567, 1970)
>>
>> For SAGE, although there are a number of things about it, for instance
>> the one
>> listed here:
>>
>>
>> http://en.wikipedia.org/wiki/Semi_Automatic_Ground_Environment#Further_reading
>>
>>
>> Like I said, I don't know of anything there that goes into a lot of
>> technical
>> detail on the communication stuff, though. (I looked through a couple,
>> including the 'Annals of the History of Computing' issue.) In particular,
>> there's a rumor that SAGE had the first email, but the communication
>> part of
>> the system especially is so poorly documented in the open literature I've
>> never been able to track that down. There is a fair amount on the
>> AN/FSQ-7
>> computer, and some on the programming, but the whole communication aspect
>> (other than the early radar data transmission) is seemingly not covered
>> anywhere.
>>
>> Noel
>
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