[e2e] UDP checksum field?

Ethan Blanton eblanton at cs.ohiou.edu
Tue Apr 5 16:48:36 PDT 2005

Cannara spake unto us the following wisdom:
> Of course, David, but the opposite is: no checksum = no chance of
> correctness.  And, the way NAT and other boxes have been intended and
> deployed, many people consider them as "ends", making the mythical End-End
> Principle even more of a fantasy.

I'm not sure exactly what you're trying to say here (I seldom am), but I
think it misses a very important point.  There  are  in  fact  a  _very_
large  number  of applictions which obey the end-to-end principle exten-
sively.  Take as an example class of such applications all  SSL  or  TLS
streams over TCP.

If  [heh]  you  have a particular axe to grind, you can probably come up
with some little semantic corner where this is not end-to-end  in  every
respect, but it will be just that -- a semantic little corner.  SSL over
TCP performs end-to-end flow  control,  end-to-end  congestion  control,
weak end-to-end integrity checking at the transport layer, and extremely
robust end-to-end integrity checking (possibly as  well  as  authentica-
tion)  at the application layer.  Note that, in this example, each layer
of the stack provides the largest reasonable set of  guarantees  it  can
provide,  and  the  ultimate  "end-to-end"  integrity and authentication
checks are performed at the _true_ ends of the connection -- the  appli-

I  realize  this  message is probably futile, but I hope it will end the
bickering over semantics in this particular  thread,  and  provide  some
food  for thought for future such threads.  No, the end-to-end principle
isn't practiced everywhere, but it is far from a "fantasy". And yes, I'm
sure  Ma  Bell  provided perfect end-to-end service via POTS in 1908 and
the Internet is so far behind we might as well not even  bother  talking
about  it,  no need to tell me that.  Since I use the Internet every day
(and, miraculously, it works), I'll leave  mailing-list  theories  about
how it can't possibly work on the shelf for now.


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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