[e2e] Why was hop by hop flow control eventually abandonded?

Michael Welzl michawe at ifi.uio.no
Wed Jul 17 02:13:26 PDT 2013

i agree like i haven't agreed to anything in a long time! in fact i agree with every single word jon wrote here

Sent from my iPhone

On 17. juli 2013, at 10:36, Jon Crowcroft <Jon.Crowcroft at cl.cam.ac.uk> 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?
> in fact, I suggest we do some flow control inside nets - its called
> traffic engineering and operates on aggregates - when we do 
> multipath routing, we also select a modest number of routes (obviously
> more than 1 but a lot less than actually would give connectivity or
> even some additional capacity)....
> so i think the design decision to throw out all hop by hop flow
> control was probably an error (not a disastrous one: as many people
> have pointed out, it simplified early router design a lot to be
> completely stateless - but you don't need to keep per-5-tuple based
> e2e state to do hop by hop flow control if its on aggregates, right?)
> In missive <1374014873.23736.140661256474709.49B0CF90 at webmail.messagingengine.c
> om>, Mark Handley typed:
>>> It's before my time, but I'd always assumed it was also influenced by
>>> the NVP work, which would not have wanted hop-by-hop flow control.
>>> Mark
>>> On Tue, Jul 16, 2013, at 02:24 PM, Bob Braden wrote:
>>>> I believe that hop-by-hop flow control only works with per-flow state in 
>>>> the routers (see X.25 for example). Once the decision was made that the 
>>>> routers should be stateless, end-to-end flow control was the only 
>>>> option. That is what the end-to-end principle is all about.
>>>> Bob Braden
> cheers
>   jon

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