[e2e] Historical question: Link layer flow control / silent discard

Jon Crowcroft jon.crowcroft at cl.cam.ac.uk
Sat May 25 01:45:39 PDT 2013

if by catenet you mean the specific deployed technologies of the arpanet,
milnet, arpa packet radio, satnet, and IPSS, then the answer is
a) no, it didn't specifiy lin layer flow control
b) yes, sone of the links had flow control
i) its sometimes a bad idea - due to poor interactions between nested
control loops
ii) occasionally, it helps, but you have to get quite lucky...

for example, IP over X.25 (treating x.25' layer 3 packet protocol as a link
layer in true cavalier fdashion, as one does), causes weird things to
happen to TCP's end2end behaviour due to the sudden step functions in
measured RTT up and down as the link layer does odd stuff - thi hurt badly
in the UK academic early IP deployments which had to run this way..

on the other hand, there was nice work at bell labs (debasis mitra et al)
that showed you could get optimal traffic distribution in a homogenous
enough network by using link layer flow control to sprad out traffic
load....but it does NOT work in a catenet (or internet) when all the links
are very heterogeneous....youre better off doing multipath and e2e flow
(and congrestion control) -  of course, we don't have much catenet/internet
layer multipath yet, which is a shame as it was in the origianl thinking
and has re-emerged recently with lots of nice results that show it would
benefit in may places (edge, core, and data center nets) - for references
on multipath, see

but maybe I am just treading on the toes of giants again....
bald and grey


On Fri, May 24, 2013 at 4:34 PM, Detlef Bosau <detlef.bosau at web.de> wrote:

> O.k., perhaps this is for all readers with grey hair (if there is still
> hair at all....) and grey beards ;-)
> When I read the original catenet work by Cerf, the Catenet employed link
> layer flow control.
> To my understanding, this was abandoned when the ARPAnet turned into the
> Internet (in 1981?). After this change, the link layer flow control was
> replaced by a "silent discard" of packets which cannot be accepted for
> delivery.
> Is this correct?
> What was the reason for this decision and have there been any alternative
> approaches?
> --
> ------------------------------**------------------------------**------
> Detlef Bosau
> Galileistraße 30
> 70565 Stuttgart                            Tel.:   +49 711 5208031
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>                                            skype:     detlef.bosau
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