CS Fallback in the Evolved Packet System (EPS) enables the provisioning of CS-domain services (e.g. voice call,
Location Services (LCS) or supplementary services) by reuse of CS infrastructure when the UE is served by E-UTRAN.
Additionally, SMS delivery via the CS core network is realized without CS fallback.
This TS specifies the procedures and the SGs Application Part (SGsAP) messages used on the SGs
interface between the Mobility Management Entity (MME) in the EPS and the Visitor Location Register (VLR), to
allow location management coordination and to relay certain messages related to GSM circuit switched services over
the EPS system.
This TS also specifies the use of Stream Control Transmission Protocol (SCTP) for the transport of
This TS is applicable to the MME in the EPS and to the VLR. The functional split between the MME and
the VLR is defined in TS 23.272