[e2e] UDP checksum field?

Lynne Jolitz lynne at telemuse.net
Mon Apr 4 11:58:12 PDT 2005

Absolutely right Craig - this was exactly the case with the Sunbox project I described earlier, as well as the datacenter mirror example. Too much damage too late.

As implicit dependence on reliability increases, the value of checksums becomes very clear - in the early deep space probes they learned the hard way the importance of always providing enough redundancy and error correction, because a single bit error might be the one that leads to the destruction of the communications ability of the spacecraft. One spacecraft had a corruption error like this that destroyed it for precisely this reason. They optimized out reliability to get a slightly greater data rate, and lost the spacecraft (this has happened more than once).

We're reaching a point where you have to seriously think about whether an "optimization" is really valuable - since as Craig notes, you may not notice a problem until too late. In this age of ubiquitous   computing, with plentiful processor, memory, and network bandwidth, we should be focussed on increased reliability and integrity, but old habits of a more parsimonious age die hard.

Another very recent example of ignoring the value of checksums is reflected in the recent 'fasttrack' problems of incorrect billing of tolls.
> -----Original Message-----
> From: end2end-interest-bounces at postel.org
> [mailto:end2end-interest-bounces at postel.org]On Behalf Of Craig Partridge
> Sent: Monday, April 04, 2005 11:32 AM
> I vaguely recall that some part of BBN had experience with the NSF
> checksum problem and that it took a while for the corruption of the
> filesystem to become visible.  That is, errors are infrequent enough
> that NIC (or switch, or whatever, ...) testing doesn't typically catch
> them.  So bit rot is slow and subtle -- and when you find it, much has
> been trashed (especially if one ignores early warning signs, such as
> large compilations occasionally failing with unrepeatable 
> loading/compilation
> errors).
> Craig

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