The present document contains the definition of the SMLCPP protocol to be used between two Serving Mobile Location Centres (SMLC).

The LCS architecture is described in 3GPP TS 43.059. The following aspects of it are relevant to the issue:

• each SMLC controls a number of LMUs, and a given LMU is under the direct control of a single SMLC;
• there is a direct communication path, independent of SMLCPP, between a LMU and the SMLC that controls it;
• deciphering keys are controlled by one SMLC in the location area and sent to other SMLCs in the same location area.

SMLCPP runs between two SMLC functions in the same PLMN. Transport is outside the scope of the present document. It assumes a transport service between these functions, as provided by BSSAP-LE. The present document assumes that the underlying transport (e.g., as described by BSSAP-LE specifications) provides for transport and routing for any two pairs of SMLCs which need to run SMLCPP exchanges.

The main functions of SMLCPP are described in [5]. The key aspects are:

• allowing an SMLC to ask for and obtain information about Radio Interface Timing (RIT), as known from measurements done by LMUs not under its direct control;
• allowing an SMLC, that controls deciphering keys in the location area, to sent them to other SMLCs in the same location area.