[ih] Ethernet, was Why TCP?

Jack Haverty jack at 3kitty.org
Wed Aug 31 21:29:50 PDT 2016

There was a paper, also in that early 80s timeframe, where someone 
analyzed the wire-level protocols with queuing theory and other magic, 
and came to an elegant mathematical conclusion.  Unfortunately I can't 
remember whether it applied to Ethernet or Alohanet, or what the elegant 
conclusion was, or the title/author.  It proved mathematically something 
like "the system remains stable as long as you keep this key timer below 
a value of 1/e".  Hence there would be no performance collapse on 
Ethernets if you followed the rules.

Curiously, in the neighboring world of TCP and Internets at the time, 
there was a similar conclusion reached about stability albeit not very 
well quantified or elegant.  Something like "everything will be fine as 
long as there is a lot more capacity in the network than the amount of 
traffic being carried".

Another one was that packet loss rates of 1% on a TCP connection were OK 
and could be handled with no problems.  As I recall, there was no 
blackboard full of equations involved.  We just went around the room and 
1% seemed reasonable to most people.

Rough consensus and running code.....


On 08/31/2016 07:09 PM, John Levine wrote:
>> So if one wanted a cheaper mechanism, tossing out the extreme discipline
>> made sense to me.  We always hear about computing/storage tradeoffs.
>> This was a cost/channel-efficiency tradeoff.
> It is my recollection that at the time a lot of people thought that
> Ethernet sounded too good to be true.  If it were heavily loaded, all
> those collisions would surely cause a storm of interference and
> performance collapse, unlike a token ring that shared the capacity in
> a predictable way.
> As we all know, Ethernets worked just fine.  A lot of people didn't
> believe it until they saw it, and sometimes not even then.
> R's,
> John
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