Section: 5.5.1.2.7 Abnormal cases on the network side
Content: The following abnormal cases can be identified: a) Lower layer failure If a lower layer failure occurs before the message ATTACH COMPLETE has been received from the UE, the network shall locally abort the attach procedure, enter state EMM-DEREGISTERED and shall not resend the message ATTACH ACCEPT. If a new GUTI was assigned to the UE in the attach procedure, the MME shall consider both the old and the new GUTI as valid until the old GUTI can be considered as invalid by the network or the EMM context which has been marked as detached in the network is released. If the old GUTI was allocated by an MME other than the current MME, the current MME does not need to retain the old GUTI. If the old GUTI is used by the UE in a subsequent attach message, the network may use the identification procedure to request the UE's IMSI. b) Protocol error If the ATTACH REQUEST message is received with a protocol error, the network shall return an ATTACH REJECT message with one of the following EMM cause values: #96: invalid mandatory information; #99: information element non-existent or not implemented; #100: conditional IE error; or #111: protocol error, unspecified. c) T3450 time-out On the first expiry of the timer, the network shall retransmit the ATTACH ACCEPT message and shall reset and restart timer T3450. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3450, the attach procedure shall be aborted and the MME enters state EMM-DEREGISTERED. If a new GUTI was allocated in the ATTACH ACCEPT message, the network shall consider both the old and the new GUTI as valid until the old GUTI can be considered as invalid by the network or the EMM context which has been marked as detached in the network is released. If the old GUTI was allocated by an MME other than the current MME, the current MME does not need to retain the old GUTI. If the old GUTI is used by the UE in a subsequent attach message, the network acts as specified for case a above. d) ATTACH REQUEST received after the ATTACH ACCEPT message has been sent and before the ATTACH COMPLETE message is received - If one or more of the information elements in the ATTACH REQUEST message differ from the ones received within the previous ATTACH REQUEST message, the previously initiated attach procedure shall be aborted if the ATTACH COMPLETE message has not been received and the new attach procedure shall be progressed; or - if the information elements do not differ, then the ATTACH ACCEPT message shall be resent and the timer T3450 shall be restarted if an ATTACH COMPLETE message is expected. In that case, the retransmission counter related to T3450 is not incremented. e) More than one ATTACH REQUEST received and no ATTACH ACCEPT or ATTACH REJECT message has been sent - If one or more of the information elements in the ATTACH REQUEST message differs from the ones received within the previous ATTACH REQUEST message, the previously initiated attach procedure shall be aborted and the new attach procedure shall be executed; - if the information elements do not differ, then the network shall continue with the previous attach procedure and shall ignore the second ATTACH REQUEST message. f) ATTACH REQUEST received in state EMM-REGISTERED If an ATTACH REQUEST message is received in state EMM-REGISTERED the network may initiate the EMM common procedures; if it turned out that the ATTACH REQUEST message was sent by a genuine UE that has already been attached, the EMM context, EPS bearer contexts, if any, are deleted and the new ATTACH REQUEST is progressed, otherwise if network considers ATTACH REQUEST message was not sent by a genuine UE based on authentication procedure the network shall maintain the EMM-context, if any, unchanged. NOTE 1: The network can determine that the UE is genuine by executing the authentication procedure as described in clause 5.4.2. g) TRACKING AREA UPDATE REQUEST message received before ATTACH COMPLETE message. Timer T3450 shall be stopped. The allocated GUTI in the attach procedure shall be considered as valid and the tracking area updating procedure shall be rejected with the EMM cause #10 "implicitly detached" as described in clause 5.5.3.2.5. h) DETACH REQUEST message received before ATTACH COMPLETE message. The network shall abort the attach procedure and shall progress the detach procedure as described in clause 5.5.2.2. i) If EMM-REGISTERED without PDN connection is supported by the UE and the MME, the MME receives an ATTACH REQUEST message with an ESM message included in the ESM message container information element, and the ESM sublayer in the MME detects a message error according to clause 7, the MME may decide to proceed with the attach procedure or to reject it. When sending the ATTACH ACCEPT or ATTACH REJECT message to the UE, the MME shall include the ESM message provide by the ESM layer in the ESM message container information element. j) UE security capabilities invalid or unacceptable If the ATTACH REQUEST message is received with invalid or unacceptable UE security capabilities (e.g. no EPS encryption algorithms (all bits zero), no EPS integrity algorithms (all bits zero), mandatory EPS encryption algorithms not supported or mandatory EPS integrity algorithms not supported, etc.), the MME shall return an ATTACH REJECT message. NOTE 2: EMM cause value to be used in ATTACH REJECT message is up to the network implementation.