[ih] The origin of variable length packets

[John Day]

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