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

Jon Crowcroft Jon.Crowcroft at cl.cam.ac.uk
Wed Jul 17 01:36:08 PDT 2013

so most systems in the world do hop by hop as well as end to end
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.
 >>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



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