> The usage that is actually envisaged is more limited: an identifier that > provides disambiguation in a limited environment, normally a single > site, possibly a small number of sites directly linked by VPN-like > relations. In that scenario, the collisions that matter are those that > occur within this "working set" of connected sites. The probability of > such a collision is determined by the probability of collision "x" > between two identifiers (x = 2^-40 in our example) and by the size "W" > of the working set. The probability that single site does not collide > with any member of a working set is: > > P(collision in a set of size W) = 1 - (1-x)^(W-1)
Seems incorrect. Assuming that the pool size is "n", where n = 2^40. As per your formula the probability of choosing two unique numbers is (n-1)/n, and of three unique numbers is ((n-1)/n)*((n-1)/n). As per Geoff, the probability of choosing two unique numbers is (n-1)/n, and of three unique numbers is ((n-1)/n)*((n-2)/n). Since the space from which you can choose a unique number diminishes by one with each draw. I think Geoff's formula is correct in this regards. CP -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
