US Patent 7570764 Sequence number calculation and authentication in a communications system

In a mobile communications system, a batch of sequence numbers is generated via an algorithm wherein each sequence number comprises a suffix and a prefix. The method comprises; calculating a new sequence number suffix from an existing sequence number suffix, calculating a prefix of a first new sequence number of the batch by addition to the prefix of the existing sequence number if the new suffix is not equal to a predetermined value or by a randomizing process if the new suffix is equal to said predetermined value, and calculating prefixes for the other sequence numbers of the batch by modular addition of integers to the prefix of said first new sequence number. The sequence numbers are used in the authentication procedure.