Section: C.2.3 Notes
Content: 1. Using the above array mechanism, it is not required that a previously visited VLR/SGSN deletes the unused authentication vectors when a user de-registers from the serving network (super-charger concept). Retaining the authentication vectors for use when the user returns later may be more efficient as regards signalling when a user abroad switches a lot between two serving networks. 2. The array mechanism may also be used to avoid unjustified rejection of user authentication requests when authentication vectors in two VLR/SGSNs from different mobility management domains (circuit and packet) are used in an interleaving fashion. 3. When a VLR/SGSN uses fresh authentication vectors obtained during a previous visit of the user, the USIM can reject them although they have not been used before (because the array size a and the age limit L are finite). Rejection of a sequence number can therefore occur in normal operation, i.e., it is not necessarily caused by (malicious) replay or a database failure. 4. The mechanism presented in this section may allow the USIM to exploit knowledge about which authentication vectors were sent to the same VLR/SGSN. It may be assumed that authentication vectors sent to the same VLR/SGSN are always used in the correct order. Consequently, only one sequence number among those sent to the same VLR/SGSN has to be stored. 5. With the exception of SQNMS , the entries of the array need not be stored in full length if a limit L (age limit) on the difference between SEQMS and a received sequence number component SEQ is applied. 6. Condition (2) of Annex C.2.1 on means that SQNMS can reach its maximum value only after a minimum of SEQmax / successful authentications have taken place. 7. There is a dependency of the choice of and the size n of global counter GLC in Annex C.1.1.1: shall be chosen larger than 2n.