LTE: Service Request

Ø     The SERVICE REQUEST message is sent by the UE to the network to request the establishment of a NAS signalling connection and of the radio and S1 bearers

Ø     The UE shall send the SERVICE REQUEST message when:

a)    The UE in EMM-IDLE mode receives a paging request with CN domain indicator set to "PS" from the network

b)    The UE, in EMM-IDLE mode, has pending user data to be sent

c)    The UE, in EMM-IDLE mode, has uplink signalling pending

d)    The UE, in EMM-IDLE mode, has uplink cdma2000^® signalling pending to be transmitted over E-UTRAN

e)     The UE performs an inter-system change from S101 mode to S1 mode and has user data pending

Ø     For the above cases, if the UE is not configured for NAS signalling low priority, the UE initiates the service request procedure by sending a SERVICE REQUEST message to the MME

Ø     For the above cases, if the UE is configured for NAS signalling low priority, but the network doesn’t support EXTENEDED SERVICE REQUEST for packet services, the UE shall send SERVICE REQUEST message to the MME

Ø     Upon receipt of the SERVICE REQUEST message, the MME may initiate the EMM common procedures e.g. the authentication procedure and security mode control procedure

Ø     The UE shall treat that the service request procedure as successful, when the lower layers indicate that the user plane radio bearer is successfully set up

Ø     The structure of SERVICE REQUEST message doesn’t follow the structure of standard L3 message (see the example below)

Ø     The IE KSI and sequence number’s purpose is to provide the network with the key set identifier (KSI) value of the current EPS security context and the short sequence number (5 LSBs of the NAS COUNT value) applicable for the message that includes this IE

Ø     The purpose of the Short MAC IE is to protect the integrity of a SERVICE REQUEST message. This field contains the 2 least significant octets of the MAC calculated for the SERVICE REQUEST message

Reference: 3GPP TS 24.301

Example: SERVICE REQUEST message