[[overview]]
== Overview

This manual should help you getting started with OsmoBSC. It will cover
aspects of configuring and running the OsmoBSC.

[[intro_overview]]
=== About OsmoBSC

OsmoBSC is one particular version of the OpenBSC software suite.

Unlike the highly integrated OmsoNITB, OsmoBSC implements a more classic
GSM Base Station Controller with A-bis interface towards BTSs and A
interface towards a MSC.


=== Software Components

OsmoBSC contains a variety of different software components, which
we'll quickly describe in this section.

==== A-bis Implementation

OsmoBSC implements the ETSI/3GPP specified A-bis interface, including
TS 08.56 (LAPD), TS 08.58 (RSL) and TS 12.21 (OML). In addition, it
supports a variety of vendor-specific extensions and dialects in order
to communicate with BTSs from Siemens, Nokia, Ericsson, ip.access and
sysmocom.

For more information, see <<bts>> and <<bts-examples>>.

==== A Implementation

OsmoBSC implements a minimal sub-set of the GSM A interface as specified
in TS 08.08.

Unlike classic A interface implementations for E1 interfacs, OsmoBSC
implements a variant of encapsulating the A interface over IP.  To do
so, the SCCP messages are wrapped in an IPA multiplex and then
communicated over TCP.  The audio channels are mapped to RTP streams.

This protocol stacking is sometimes called "SCCPlite".

For more information, see <<alink>>.


==== BSC Implementation

The BSC implementation covers the classic functionality of a GSM Base
Station Controller, i.e.

* configuring and bringing up BTSs with their TRXs and TSs
* implementing the A-bis interface / protocols for signalling and actual
  voice data (TRAU frames).
* processing measurement results from the mobile stations in dedicated
  mode, performing hand-over decision and execution.
* Terminating the TS 04.08 RR (Radio Resource) sub-layer from the MS.

For more information, see <<net>>, <<bts>> and <<bts-examples>>.


==== TRAU mapper / E1 sub-channel muxer

Unlike classic GSM networks, OsmoBSC does not perform any transcoding.
Rather, a compatible codec is selected for both legs of a call, and
codec frames are passed through transparently.  In order to achieve this
with E1 based BTS, OsmoBSC contains a E1 sub-channel de- and
re-multiplexer as well as a TRAU mapper that can map uplink to downlink
frames and vice versa.

=== Control interface

The actual protocol is described in <<common-control-if>> section. Here we
describe variables specific to OsmoBSC.

.Variables available over control interface
[options="header",width="100%",cols="20%,5%,5%,50%,20%"]
|===
|Name|Access|Trap|Value|Comment
|msc_connection_status|RO|Yes|"connected", "disconnected"|Indicate the status of connection to MSC.
|bts_connection_status|RO|Yes|"connected", "disconnected"|Indicate the status of connection to BTS.
|location|RW|Yes|"<unixtime>,(invalid\|fix2d\|fix3d),<lat>,<lon>,<height>"|Set/Get location data.
|timezone|RW|No|"<hours>,<mins>,<dst>", "off"|-19 <= hours <= 19, mins in {0, 15, 30, 45}, and 0 <= dst <= 2
|notification|WO|Yes||
|inform-msc-v1|WO|Yes||
|ussd-notify-v1|WO|Yes||
|===

Some comments.
FIXME: commands defined in src/ctrl/control_if.c? Nodes? Traps?