Defne's Mobile Positioning Platform: Technical Insights and Overview

Defne Mobile Positioning Platform (MPP) performs the location finding task, using the network, GSM network cells, and the positions of 2G-3G-4G-5G base stations. Positioning Method is CGI-TA (Cell Global Identifier - Timing Advance) and E-CGI (Enhanced Cell Global Identifier) for 2G Networks, CID (Cell Identity) and ECID (Enhanced Cell ID) for 4G networks. MPP contains Defne Mobile Positioning Gateway and  Defne Mobile Positioning Server nodes.

Defne Mobile Positioning Server (DMPS) is the module that calculates the location, which contains SMLC (Serving Mobile Location Center) in 2G, SAS (Stand Alone SMLC) in 3G, E-SMLC (Evolved SMLC) in 4G and LMF (Location Management Function) in 5G. The SAS module in 3G is practically not used because 3G already has inherent location calculation capability.

Defne Mobile Positioning Gateway (DMPG) directs incoming requests to the relevant components in the core network. GMLC (Gateway Mobile Location Center), SLP (Secure User Plane Location Platform), LRF (Location Request Function), RDF (Routing Determining Function) functions are contained within DMPG.

DMPG directly communicates with the LCS (Location Services) Clients, HLR, HSS, MSC, MME and NMS/OSS (Network Management System / Operations Support System). Requests from LCS clients and responses with location estimates are carried with the MLP (Mobile Location Protocol) which uses XML over HTTP.  DMPG communicates with HLR and MSC, to provide service for 3G networks with MAP over SIGTRAN protocol. HLR connection is used for retrieving serving nodes in the core network and MSC connection is to transmit the location requests and responses to serving nodes. For 4G networks, communication with HSS and MME is handled over Diameter protocol. HSS connection is used for retrieving serving nodes in the core network (MME and IMSI) and MME connection is to transmit the location requests and responses to serving nodes. To collect the cell data and to report OSS information; connection with NMS/OSS is run over SNMP (Simple Network Management Protocol),  FTP (File Transfer Protocol) or SFTP (Secure File Transfer Protocol) interfaces depending on the NMS type. 

DMPS directly communicates with the BSC (Base Station Controller), RNC (Radio Network Controller), MME, and NMS/OSS. By connection with the BSC, BSSAP-LE (Base Station System Application Part LCS Extension) and BSSLAP (Base Station Subsystem LCS Application Part) messages are carried with the SIGTRAN protocol. DMPG communicates with RNC with SIGTRAN protocol, to carry out the PCAP messages. Communication with MME to carry LCS-AP (Location Services Application Protocol) is handled over SCTP/IP (Stream Control Transmission Protocol / IP). LPP (LTE Positioning Protocol) and LPPa are carried as payloads to handle different positioning messages between SMPC (Serving Mobile Positioning Centre) and UE (User Equipment) and eNodeB (Evolved Node B). To receive the cell data and to report OSS information; connection with NMS/OSS  is run over the one of SNMP,  FTP or SFTP interfaces depending on the NMS type.  DMPS does not directly integrate with E-nodeB, instead it communicates with E-nodeB through MME.

Traffic Flow:

The sequence begins with the LCS Client initiating an MLP Positioning Request through the LB (Load Balancer) to DMPG, conveying essential MSISDN information. This sets off a series of orchestrated interactions: DMPG sends a Routing Info request (SRI_LCSReq) to the Home Location Register (HLR) and receives an acknowledgment (SRI_LCSConf) containing MSC and IMSI details. Subsequently, the DMPG requests the Subscriber Location from the MSC, involving comprehensive information like MSISDN, MSC, IMSI, and LCS Quality of Service/Privacy parameters.

The process continues with various nodes collaboratively exchanging data to perform location requests, transmit TA (Timing Advance) information for 2G networks, and eventually provide a Location Response. In 3G networks; Request Location Estimate is transmitted from the MSC to the RNC, with information including SAI (Service Area Identifier), IMSI, and LCS QoS. The RNC responds with a Location Estimate ACK, supplying crucial details such as the Location Estimate and Age. The subsequent step involves the MSC forwarding a Provide Subscriber Location Acknowledgement (PSL ACK) to the DMPG, containing the Location Estimate and Age. 

The entire process culminates with the DMPG delivering an MLP Positioning Response to the LCS Client, furnishing precise Location Coordinates. Throughout this intricate procedure, specific nodes play distinct roles: DMPG serves as the source for MSISDN and LCS QoS/Privacy, HLR contributes MSC and IMSI details in 2G and 3G networks, and HSS provides the MME and IMSI details in 4G networks, MSC delivers CGI ((Cell Global Identifier) in 2G networks and SAI in 3G networks, whereas MME provides E-CGI in 4G networks. BSC supplies TA for 2G networks, and DMPS furnishes the crucial Location Estimate in 2G and 4G networks and RNC supplies the Location Estimate in 3G networks.