LTE: CS Service Notification

·         The CS SERVICE NOTIFICATION message is sent by the network to notify a UE in EMM-CONNECTED mode (i.e. NAS signalling connection is already established for the UE) about an incoming CS service (excluding SMS) over SGs

Note:  SGs interface (between MME and MSC server) is used for the mobility management and paging procedures between EPS and CS domain

·        This is basically paging procedure for CS services (excluding SMS) for the UEs in EMM-CONNECTED mode

·        This message may also include CS service related parameters e.g. Calling Line Identification, SS or LCS related parameters

·        After receiving the CS SERVICE NOTIFICATION message, the UE may request upper layers input i.e. to accept or reject CS fallback before responding with an EXTENDED SERVICE REQUEST. The response is indicated in the CSFB response IE in the EXTENDED SERVICE REQUEST message

·         The purpose of the Paging identity IE is to indicate the identity used for paging for non-EPS services. This identity could be either IMSI or TMSI

·         If the network receives Calling Line Identification (CLI) via SGs, then it shall include it in the IE CLI

·         The network shall send the IE SS Code if it was received via SGs. It contains information on the supplementary service transaction in the CS domain, which triggered the paging via SGs

·         The network shall send the IE LCS Indicator if it was received via SGs. It indicates that the paging was triggered by a terminating LCS request in the CS domain

Reference: 3GPP TS 24.301

Example: CS SERVICE NOTIFICATION message