[e2e] Reacting to corruption based loss

Cannara cannara at attglobal.net
Thu Jun 30 11:33:57 PDT 2005

Ethan, for someone who quotes Beccaria (a paesano of my family), you clearly
know how to read.  So, how could you gather from anything I've said that TCP
should have the knowledge you claim of the physical layer?  

The problem is that TCP is designed to assume the physical layer is not
involved in loss.  Thus, it slows down when it shouldn't, because it wrongly
ascribes all loss to network congestion.  Note that the words "network
congestion" refer to the network layer.  The kludge done in the '80s, to make
one transport at the transport layer protect the network layer from meltdowns
that were often nearly happening, is the issue.


Ethan Blanton wrote:
> Alex,
> Cannara spake unto us the following "wisdom":
> > Good one Clark!  Indeed FDDI and other fiber rings have dual interfaces &
> > fibers and anything can happen in any part of the hardware.  The assumptions
> > about the physical layer that have been made in most TCP discussions simply
> > evidence lack of understanding of the reality and complexity of underlying
> > layers.  This lack extends to the length of time the defects last and go
> > undiscovered, while folks struggle with peformance issues.
> Let me get this straight, for my benefit and for the benefit of those
> who may not understand you.  You're suggesting that TCP should have a
> mechanism by which the hardware layer can communicate that there is a
> particular sequence of bits which, due to physical imperfections in
> the transmission medium, cannot be reliably transmitted, and that
> given this information the TCP stack could choose a different method
> of communicating those particular bits?
> I can't believe no one has thought of implementing this richness of
> signalling before now.  This is certainly an inherent flaw in the TCP
> design.
> Ethan
> (On a side note:  I keep hearing that the Internet is completely
> broken and could never possibly work.  Why is it that certain emails
> to the e2e mailing list *unfailingly* reach my mailbox under these
> circumstances?)
> --
> The laws that forbid the carrying of arms are laws [that have no remedy
> for evils].  They disarm only those who are neither inclined nor
> determined to commit crimes.
>                 -- Cesare Beccaria, "On Crimes and Punishments", 1764

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