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

LTE: Extended Service Request

Ø      The EXTENEDED SERVICE REQUEST message is sent by the UE to the network to initiate a "CS fallback or 1xCS fallback call" or respond to an "MT CS fallback or 1xCS fallback" request from the network

Ø     This message is also used if the UE wants to request the establishment of a NAS signalling connection (and of the radio and S1 bearers) for packet services and if the UE needs to provide additional information that cannot be provided via a SERVICE REQUEST message

Ø    The UE shall send  EXTENEDED 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 or EMM-CONNECTED mode is configured to use CS fallback and has a mobile originating CS fallback request from the upper layer

e)    The UE in EMM-IDLE mode is configured to use CS fallback and receives a paging request with CN domain indicator set to "CS", or the UE in EMM-CONNECTED mode is configured to use CS fallback and receives a CS SERVICE NOTIFICATION message

f)       The UE in EMM-IDLE or EMM-CONNECTED mode is configured to use 1xCS fallback and has a mobile originating 1xCS fallback request from the upper layer

g)    The UE in EMM-CONNECTED mode is configured to use 1xCS fallback and accepts cdma2000^® signalling messages containing a 1xCS paging request received over E-UTRAN

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

i)        The UE, in EMM-IDLE or EMM-CONNECTED mode, is configured to use 1xCS fallback, accepts cdma2000^® signalling messages containing a 1xCS paging request received over cdma2000^® 1xRTT, and the network supports dual Rx CSFB or provide CS fallback registration parameters

j)        The UE, in EMM-IDLE or EMM-CONNECTED mode, has uplink cdma2000^® signalling pending to be transmitted over cdma2000^® 1xRTT, and the network supports dual Rx CSFB or provide CS fallback registration parameters

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

NOTE:      For cases a, b, c, h and k above, the EXTENEDED SERVICE REQUEST message is used only if the UE is configured for NAS signalling low priority and the network supports EXTENEDED SERVICE REQUEST for packet services. Otherwise, SERVICEREQUEST is used

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

Ø      The Service type IE specifies the purpose of the service request procedure. This IE can indicate “mobile originating CS fallback or 1xCS fallback” or “mobile terminating CS fallback or 1xCS fallback” or “mobile originating CS fallback emergency call or 1xCS fallback emergency call”, or “packet services via S1”

Ø     The purpose of the CSFB response IE is to indicate whether the UE accepts or rejects a paging for CSFB. The IE’s values could be either “CS fallback rejected by the UE” or “CS fallback accepted by the UE” (see example2 below)

Ø     The IE EPS bearer context status shall be included if the UE wants to indicate the EPS bearer contexts that are active within the UE

Ø     The UE shall include the IE Device properties if the UE is configured for NAS signalling low priority. The network uses this IE for core-network congestion handling and for charging purposes

 Reference: 3GPP TS 24.301

Example1: EXTENDED SERVICE REQUEST message – MO CS fallback or 1xCS fallback

Example2: EXTENDED SERVICE REQUEST message – MT CS fallback or 1xCS fallback