The IE Authentication parameter AUTN (EPS challenge) will carry the AUTN of length 128-bits. It provides the MS with a means of authenticating the network. The AUTN consists of (SQN xor AK)||AMF||MAC = 48 + 16 + 64 = 128-bits. In the AUTHENTICATION REQUEST example below, AUTN value = 6e323b36c46c5555a3df0e6e323b6391 which means that,