Location Services » History » Revision 5
Revision 4 (laforge, 08/21/2020 04:07 PM) → Revision 5/7 (neels, 10/01/2020 12:44 PM)
h1. Location Services *NOTE: This page describes our current understanding of the 3GPP specification; +none of this is implemented so far in Osmocom!+* LCS includes a variety of different methods, such as * Timing Advance * E-OTD * GNSS * U-TDOA * Multilateration TA * Multilateration OTD The most simple and hence most wide-spread approach is _Timing Advance_ h2. Relevant specs * 3GPP TS 43.059 "Functional stage 2 description of Location Services (LCS) in GERAN" * 3GPP TS 48.031 "SMLC-SMLC Protocol" (SMLCPP) ** Based on ASN.1 PER; transferred via BSSAP-LE * 3GPP TS 49.031 BSSAP LCS extension (BSSAP-LE) ** spoken on Lb (BSC-SMLC) and Lp (SMLC-SMLC) interface *** Lp uses connectionless SCCP only *** Lb uses connection-oriented SCCP and is very much like BSSAP/BSSMAP/DTAP on A interface * 3GPP TS 48.071 "SMLC-BSS interface Layer 3" (BSSLAP) ** On Lb interface, encapsulated as _BSSLAP APDU IE_ h2. Procedures See 8.5.3 of TS 43.059 h3. TA based positioning in CS domain for A interface See Section 9.3 of 3GPP TS 43.059 !location_services_ta.png! h4. MS in idle state * MSC sends @BSSAP Perform Location Request@ * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ to SMLC * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ * BSC sends PAGING REQUEST via BTS to MS * MS sends PAGING RESPONSE via BTS to BSC; BTS adds timing offset information * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ * SMLC returns @BSSAP-LE Perform Location Response@ to BSC * BSC returns result to MSC in @BSSAP Perform Location Response@ h4. MS in dedicated state * MSC sends @BSSAP Perforl Location Request@ * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ * BSC checks current TA (as per measurement processing) for lchan of MS * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ * SMLC returns @BSSAP-LE Perform Location Response@ to BSC * BSC returns result to MSC in @BSSAP Perform Location Response@ h2. Functionality in BSC * BSC receives requests for LCS information from CN via A interface * BSC passes those requests to the SMLC via Lb interface ** BSSAP-LE protocol stack (on top of SCCP) implementatioon h2. Functionality in SMLC Protocol stack looks like this: * BSSLAP (TS 48.071) * BSSAP-LE h3. Communication with MS Protocol stack looks like this: * RRLP (TS 48.031) * BSSLAP (TS 48.071) * BSSAP-LE (TS 49.031) h3. Communication with peer SMLC * SMLCPP (TS 48.031) * BSSAP-LE (TS 49.031) h3. Message Segmentation LCS messages can be segmented either * at the SMLCPP layer * At RR layer (TS 44.018) and BSAP-LE Layer (TS 4.031) for segmentation of RRLP (TS 44.031) for legacy MS (<= Release 4) h2. Functionality in SMLC *
