[e2e] congestion collapse definition

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Sep 8 19:58:05 PDT 2009

    > From: "David P. Reed" <dpreed at reed.com>

    > If I look at Wikipedia, for example, at the definition of congestion
    > collapse there, it says that CC is characterized by large buffering
    > delays AND lost packets. 

I was responsible for the original version of that page, so any faults in it
can probably be laid at my door... :-)

When writing it, I was probably thinking of the examples of congestive
collapse I had seen (e.g. the ARPANet TCP email meltdown, TFTP Sorcerer's
Apprentice Syndrome, etc) in which high packet drop rates were seen. Of
course, that was 'back in the day', when routers had a _lot_ less buffering
than they do now, so the symptoms naturally differed somewhat.

    > should this phenomenon be included in "congestion collapse" (I believe
    > so), or should we invent a new more specific name (Buffer Madness?).

Both, I think.

In general terms, they are both examples of the same basic concept; people
give the network a lot more traffic than it can handle, and as a result things
turn to total alimentary byproduct. To me, the term 'congestive collapse' is a
perfect term for that general situation, because the network is, well,
congested; so congested it effectively ceases to function. (Ceases to function
effectively?) Congestion + failure -> congestive collapse. (Somehow
'congestive failure' doesn't have the same ring - probably the alliteration.)

At the same time, they are interestingly different (in terms of the
symptoms), so this subvariant (which we will probably be seeing more of,
until the lessons gets into the global conciousness) could probably use a
specific term. 'Buffer Madness' sounds good to me; another possibility is
some term related to blockage of the alimentary canal, where stuff just keeps
building up - but my brain won't cough up, right at this moment, the term I'm
thinking of.


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