| Harald Welte | b53e2bf | 2020-08-21 16:33:42 +0200 | [diff] [blame] | 1 | [[overview]] |
| 2 | == Overview |
| 3 | |
| 4 | This manual should help you getting started with OsmoSMLC. It will cover |
| 5 | aspects of configuring and running the OsmoSMLC. |
| 6 | |
| 7 | [[intro_overview]] |
| 8 | === About OsmoSMLC |
| 9 | |
| 10 | OsmoSMLC is the Osmocom implementation of a Serving Mobile Location Center. |
| Neels Hofmeyr | eec6a6d | 2020-10-29 23:52:47 +0100 | [diff] [blame] | 11 | |
| 12 | A Perform Location Request is initiated by the MSC via BSSMAP on the |
| 13 | A-interface, for a specific subscriber. The request is typically passed on via |
| 14 | BSSMAP-LE on the Lb-interface to the SMLC. If required, the SMLC may request the |
| 15 | subscriber's Timing Advance (a.k.a. Access Delay) from the BSC via BSSLAP |
| 16 | (encapsulated BSSLAP APDU in a BSSMAP-LE Connection Oriented Information |
| 17 | message). The SMLC may combine several location and velocity estimate methods to |
| 18 | form a GAD PDU containing the resulting geographic location information. |
| 19 | |
| 20 | So far, OsmoSMLC implements only Timing Advance based positioning. In TA-based |
| 21 | positioning, the Timing-Advance information received from the BSC is combined |
| 22 | with the preconfigured latitude and longitude of the serving cell to form a |
| 23 | location estimate. This is returned to the BSC via the Lb-interface, and in |
| 24 | turn to the MSC via the A-interface. |
| 25 | |
| 26 | Location Services (LCS) are described in 3GPP TS 43.059 <<3gpp-ts-43-059>>. |
| 27 | Messages for LCS on the A-interface (BSSMAP, between BSC and MSC) are described |
| 28 | in 3GPP TS 48.008 <<3gpp-ts-48-008>>, on the Lb-interface (BSSMAP-LE between BSC |
| 29 | and SMLC) in 3GPP TS 49.031 <<3gpp-ts-49-031>>. The resulting geographic |
| 30 | location and possibly velocity information is encoded in GAD, described in 3GPP |
| 31 | TS 23.032 <<3gpp-ts-23-032>>. |
| 32 | |
| 33 | == Lb Interface |
| 34 | |
| 35 | The Lb interface connects BSC to SMLC and consists of BSSMAP-LE/SCCP/M3UA. It |
| 36 | is routed via an STP instance, as is typical for SCCP. The BSSMAP-LE messages |
| 37 | may encapsulate BSSLAP and GAD PDUs. |
| 38 | |
| 39 | OsmoSMLC by default connects to an STP at 127.0.0.1:2905, and registers with |
| 40 | its own point-code, default is 0.23.6, on SSN "SMLC (BSSMAP-LE)" (SSN code |
| 41 | 252). |
| 42 | |
| 43 | A BSC on an Lb link typically uses SSN "BSC (BSSMAP-LE)" (SSN code 250). Each |
| 44 | BSC connecting to the SMLC must have a distinct own point-code. OsmoBSC's own |
| 45 | default point-code is 0.23.3, but when more than one BSC is in use, BSC point |
| 46 | codes should be configured explicitly. |
| 47 | |
| 48 | OsmoSMLC waits for BSC instances to establish Lb interface connections. It does |
| 49 | not require knowledge of individual BSCs' point-codes (OsmoSMLC does require |
| 50 | preconfigured cell location information, see <<cell-locations>>). |
| 51 | |
| 52 | On establishing the Lb link, a BSC should send a BSSMAP-LE RESET; the Lb link |
| 53 | is usable for per-subscriber connections as soon as OsmoSMLC responds with a |
| 54 | BSSMAP-LE RESET ACKNOWLEDGE. |