| == Location Services: Lb interface to SMLC |
| |
| OsmoBSC and OsmoSMLC support positioning by Timing-Advance (TA), since October |
| 2020. |
| |
| A Perform Location Request is initiated by the MSC via BSSMAP on the |
| A-interface, for a specific subscriber. The request is typically passed on via |
| BSSMAP-LE on the Lb-interface to the SMLC. If required, the SMLC may request the |
| subscriber's Timing Advance (a.k.a. Access Delay) from the BSC via BSSLAP |
| (encapsulated BSSLAP APDU in a BSSMAP-LE Connection Oriented Information |
| message). The SMLC may combine several location and velocity estimate methods to |
| form a GAD PDU containing the resulting geographic location information. In |
| TA-based positioning, the Timing-Advance information from the BSC is combined |
| with the preconfigured latitude and longitude of the serving cell to form a |
| location estimate. This is returned to the BSC via the Lb-interface, and in turn |
| to the MSC via the A-interface. |
| |
| [mscgen] |
| ---- |
| include::{srcdir}/message-sequences/location_services_ta.msc[] |
| ---- |
| |
| Location Services (LCS) are described in 3GPP TS 43.059 <<3gpp-ts-43-059>>. |
| Messages for LCS on the A-interface (BSSMAP, between BSC and MSC) are described |
| in 3GPP TS 48.008 <<3gpp-ts-48-008>>, on the Lb-interface (BSSMAP-LE between BSC |
| and SMLC) in 3GPP TS 49.031 <<3gpp-ts-49-031>>. The resulting geographic |
| location and possibly velocity information is encoded in GAD, described in 3GPP |
| TS 23.032 <<3gpp-ts-23-032>>. |
| |
| [[smlc-config]] |
| === Configure Lb-interface |
| |
| All Lb-interface related configuration is found in the `smlc` section of |
| OsmoBSC's configuration. |
| |
| By default, the Lb-interface is disabled in OsmoBSC. It is started by `enable`. |
| |
| ---- |
| smlc |
| enable |
| ---- |
| |
| On the Lb-interface, OsmoBSC always uses SSN "BSC (BSSMAP-LE)" (SSN code 250) |
| and contacts the remote SMLC on SSN "SMLC (BSSMAP-LE)" (SSN code 252). |
| |
| The point-codes are configurable, and default to OsmoBSC's local point-code |
| 0.23.3 (187), and remote SMLC point-code 0.23.6 (190). |
| |
| To configure a different remote SMLC point-code, first configure an arbitrarily |
| named SCCP address in the `cs7` address book, and then apply that to the |
| `smlc-addr` configuration: |
| |
| ---- |
| cs7 instance 0 |
| sccp-address my-smlc |
| point-code 0.42.6 |
| smlc |
| smlc-addr my-smlc |
| ---- |
| |
| Similarly, OsmoBSC's local point-code on the Lb-interface is configured by the |
| `bsc-addr` configuration: |
| |
| ---- |
| cs7 instance 0 |
| sccp-address my-bsc-on-lb |
| point-code 0.42.3 |
| smlc |
| bsc-addr my-bsc-on-lb |
| ---- |
| |
| The geographic locations of individual cells are configured at the SMLC. See |
| for example OsmoSMLC's user manual <<userman-osmosmlc>>. |