d Mobile Network) node that external LCS clients can access, allowing the terminals to access applications not residing on the operator's own ISP domain. The GMLC may request routing information from the HLR via the Lh interface. After performing registration authorization, it sends positioning requests to and receives final location estimates of terminals from the visiting MSC. In one PLMN, there may be more than one GMLC. GMLC interacts with the external LCS client via Le interface and with MSC via Lg interface. SMLC: Serving Mobile Location Center manages the overall coordination and scheduling of resources required to perform positioning of a mobile user. It also calculates the final location estimate and accuracy. It is responsible for obtaining measurements results from the target terminal in E-OTD. The SMLC is administered with the capabilities and types of measurement produced by each of its LMUs. Two types of SMLC are possible, namely NSS (network and switching subsystem) based SMLC and BSS (base station subsystem) based SMLC. An NSS based SMLC supports positioning of a target MS via signaling on the Ls interface to the visited MSC. A BSS based SMLC supports positioning via LCS Client Client handling component LCF. 1 LCF n Type A Location Service Request Location Service Response System Client Subscriber handling handling handling component component component External MSC/VLR Gateway LCS client LSAF - - LSPF Type B) LSOF-LSBF LCCTF LCAF Positioning Type B gsm SCF component Gateway Resources: Other PLMN GSM protocols LCS Server Figure 9.26 LCS architecture. Reproduced with permission from C 2006 3GPP [38] IMS, Services and Applications signaling on the Lb interface to the BSC serving the target MS. Both types of SMLC may support the Lp interface to enable access to information and resources owned by another SMLC. LMU: LMU makes radio measurements to support one or more positioning methods. LMU is addi- tional measurement hardware in the GSM network and it is needed to make accurate Observed Time Differen