Tim Berners-Lee and the Toilet Paper Protocol

From: Tim Berners-Lee timb@w3.org

To: gsb-announce@csail.mit.edu

Subject: [csail-related] Toilet Paper Protocol

At 15:41, Andrew Jamoozy Correa wrote:

Have you ever noticed how there are 2 rolls of toilet paper in each stall in the mass-toilets around CSAIL? I’ve been thinking about it, and I think it has to do with two major things:
1) that if we use up one first, then the other, no stall will ever run out of paper (there’s a backup!)

This depends on the people who use the stall using the Toilet Paper Protocol.

The TPP is:

a) Always use the smallest roll (users)

b) Replace empty rolls with new (maintenance crew)

The TPP is a great example of a protocol, as it has simple rules by which each participant has to abide, and rewards them by maintaining a common good, the invariant that no user is left without paper. It is relatively resilient to a small proportion k of users not following it. A critical parameter is the ratio of the frequency µ of visits by maintenance compared to users.

For further study questions:

1) Find the probability of catastrophic failure of the protocol as a function of k and µ, stating your assumptions.

2) Find examples in the field where the TPP has been egregiously violated. What sort of people use those stalls? What do they study? Build a sociological model of the violations.

3) Compare and contrast the TPP with (a) the Golden Rule, (b) HTTP Caching, © The Highway Code (d) PGP (e) The Strategic Arms Limitation Treaty (SALT).


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