Re: Why was hop by hop flow control eventually abandonded?

On 7/17/2013 1:36 AM, Jon Crowcroft wrote:
> so most systems in the world do hop by hop as well as end to end
> e.g.
> transportation systems  (traffic lights, stacks of planes, semaphores to
> control trains entry/exit from track sections etc etc)
> power systems (elec ant gas)
> water systems (valves etc)
> eco-systems (food chains/feast/famine etc)
> political systems (you switch from feudal to democract, btut you still
> have periodic elections - you switch from city states to countries,
> but still have border and immigration/emigration controls...:)
>
> so why do we think comms should be different?

Router-router links can also have flow control, e.g., on ethernet using 
pause frames.

However, not all links have that sort of back-pressure capability; many 
are treated as fixed-capacity simplex channels. A lot of the examples 
above have that sort of backpressure built-in, or we have engineered it 
because we don't want (or can't afford) to lose the 'message' (as was 
noted, dropping a car or a plane would be bad). IP networks don't 
require that sort of engineering - which makes them simpler to 
implement, but also means they have in-network drops in response to 
congestion.

Joe