Section: G.3 Causes related to PLMN specific network failures and congestion/Authentication Failures
Content: Cause value = 20 MAC failure This cause is sent to the network if the USIM detects that the MAC in the AUTHENTICATION REQUEST or AUTHENTICATION_AND_CIPHERING REQUEST message is not fresh (see 3GPP TS 33.102[ 3G security; Security architecture ]  [5a]). Cause value = 21 Synch failure This cause is sent to the network if the USIM detects that the SQN in the AUTHENTICATION REQUEST or AUTHENTICATION_AND_CIPHERING REQUEST message is out of range (see 3GPP TS 33.102[ 3G security; Security architecture ]  [5a]). Cause value = 17 Network failure This cause is sent to the MS if the MSC cannot service an MS generated request because of PLMN failures, e.g. problems in MAP. Cause value = 22 Congestion This cause is sent to the MS if the network cannot serve a request from the MS because of congestion (e.g. congestion of the MSC or SGSN or GGSN or PDN Gateway; no channel; facility busy/congested etc.). Cause value = 23 GSM authentication unacceptable This cause is sent to the network in Iu mode if a USIM is inserted in the MS and there is no Authentication Parameter AUTN IE present in the AUTHENTICATION REQUEST or AUTHENTICATION_AND_CIPHERING REQUEST message.