The A&C reference number specified in 3GPP TS 24.008 § 10.5.5.19
identifies particular request sent by network with the related response
sent by MS. The value transparently copied from request to response by
MS: the spec do not specify what exactly should be in there so we use
rand() to decrease chance for collisions.
Note: variable named 'rand' clashes with standard function rand() so it
was renamed.
Change-Id: I3638821a9b4a0532b28dbbb50faa30c4082579f6
Related: OS#1582