91 lines
3.1 KiB
Plaintext
91 lines
3.1 KiB
Plaintext
== Location Services: Lb interface to SMLC
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OsmoBSC and OsmoSMLC support positioning by Timing-Advance (TA), since October
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2020.
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A Perform Location Request is initiated by the MSC via BSSMAP on the
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A-interface, for a specific subscriber. The request is typically passed on via
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BSSMAP-LE on the Lb-interface to the SMLC. If required, the SMLC may request the
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subscriber's Timing Advance (a.k.a. Access Delay) from the BSC via BSSLAP
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(encapsulated BSSLAP APDU in a BSSMAP-LE Connection Oriented Information
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message). The SMLC may combine several location and velocity estimate methods to
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form a GAD PDU containing the resulting geographic location information. In
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TA-based positioning, the Timing-Advance information from the BSC is combined
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with the preconfigured latitude and longitude of the serving cell to form a
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location estimate. This is returned to the BSC via the Lb-interface, and in turn
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to the MSC via the A-interface.
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[mscgen]
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----
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include::{srcdir}/message-sequences/location_services_ta.msc[]
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----
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Location Services (LCS) are described in 3GPP TS 43.059 <<3gpp-ts-43-059>>.
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Messages for LCS on the A-interface (BSSMAP, between BSC and MSC) are described
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in 3GPP TS 48.008 <<3gpp-ts-48-008>>, on the Lb-interface (BSSMAP-LE between BSC
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and SMLC) in 3GPP TS 49.031 <<3gpp-ts-49-031>>. The resulting geographic
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location and possibly velocity information is encoded in GAD, described in 3GPP
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TS 23.032 <<3gpp-ts-23-032>>.
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[[smlc-config]]
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=== Configure Lb-interface
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All Lb-interface related configuration is found in the `smlc` section of
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OsmoBSC's configuration.
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By default, the Lb-interface is disabled in OsmoBSC. It is started by `enable`.
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----
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smlc
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enable
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----
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On the Lb-interface, OsmoBSC always uses SSN "BSC (BSSMAP-LE)" (SSN code 250)
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and contacts the remote SMLC on SSN "SMLC (BSSMAP-LE)" (SSN code 252).
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The point-codes are configurable, and default to OsmoBSC's local point-code
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0.23.3 (187), and remote SMLC point-code 0.23.6 (190).
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Typically, multiple BSCs connect to the same SMLC, so that each BSC needs to
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have a distinct point-code, while the SMLC has a single, fixed point-code.
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To configure a different remote SMLC point-code, first configure an arbitrarily
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named SCCP address in the `cs7` address book, and then apply that to the
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`smlc-addr` configuration:
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----
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cs7 instance 0
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sccp-address my-smlc
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point-code 0.42.6
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smlc
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enable
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smlc-addr my-smlc
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----
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For the BSC side, it suffices to configure a point-code in the `cs7` section,
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so that the BSC typically uses the same point-code on A and Lb interfaces. In
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this example, the BSC has point-code `1.2.3` on the Lb interface:
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----
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cs7 instance 0
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point-code 1.2.3
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smlc
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enable
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----
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It is also possible to configure a distinct BSC's point-code on Lb, using the
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`bsc-addr` configuration. In the following example, the BSC uses point-code
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`0.42.3` only on the Lb interface, while the A interface remains unchanged:
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----
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cs7 instance 0
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sccp-address my-bsc-on-lb
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point-code 0.42.3
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smlc
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enable
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bsc-addr my-bsc-on-lb
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----
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The geographic locations of individual cells are configured at the SMLC. See
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for example OsmoSMLC's user manual <<userman-osmosmlc>>.
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