Section: 6.5.3 Data integrity protection method
Content: Figure 16 illustrates the use of the integrity algorithm f9 to authenticate the data integrity of a signalling message. Figure 16: Derivation of MAC-I (or XMAC-I) on a signalling message The input parameters to the algorithm are the Integrity Key (IK), the integrity sequence number (COUNT-I), a random value generated by the network side (FRESH), the direction bit DIRECTION and the signalling data MESSAGE. Based on these input parameters the user computes message authentication code for data integrity MAC-I using the integrity algorithm f9. The MAC-I is then appended to the message when sent over the radio access link. The receiver computes XMAC-I on the message received in the same way as the sender computed MAC-I on the message sent and verifies the data integrity of the message by comparing it to the received MAC-I.