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Neels Hofmeyr 2020-10-29 23:52:47 +01:00
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doc/manuals/chapters/cells.adoc
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[[cell-locations]]
== Configure Cell Locations
To determine geographic location estimates based on the serving cell, OsmoSMLC

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doc/manuals/chapters/overview.adoc
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=== About OsmoSMLC
OsmoSMLC is the Osmocom implementation of a Serving Mobile Location Center.
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.
So far, OsmoSMLC implements only Timing Advance based positioning. In TA-based
positioning, the Timing-Advance information received 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.
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>>.
== Lb Interface
The Lb interface connects BSC to SMLC and consists of BSSMAP-LE/SCCP/M3UA. It
is routed via an STP instance, as is typical for SCCP. The BSSMAP-LE messages
may encapsulate BSSLAP and GAD PDUs.
OsmoSMLC by default connects to an STP at 127.0.0.1:2905, and registers with
its own point-code, default is 0.23.6, on SSN "SMLC (BSSMAP-LE)" (SSN code
252).
A BSC on an Lb link typically uses SSN "BSC (BSSMAP-LE)" (SSN code 250). Each
BSC connecting to the SMLC must have a distinct own point-code. OsmoBSC's own
default point-code is 0.23.3, but when more than one BSC is in use, BSC point
codes should be configured explicitly.
OsmoSMLC waits for BSC instances to establish Lb interface connections. It does
not require knowledge of individual BSCs' point-codes (OsmoSMLC does require
preconfigured cell location information, see <<cell-locations>>).
On establishing the Lb link, a BSC should send a BSSMAP-LE RESET; the Lb link
is usable for per-subscriber connections as soon as OsmoSMLC responds with a
BSSMAP-LE RESET ACKNOWLEDGE.