initial checkin of manuals to public repo
The manuals existed in different form for several years in an internal
sysmocom repository. However, since they had just recently been
converted from docboox-xml to asciidoc and all files have been
re-shuffled for enabling the public release, there's not much point in
keeping the history with git-filter-branch.
diff --git a/doc/manuals/chapters/overview.adoc b/doc/manuals/chapters/overview.adoc
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+[[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 impleents 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 protcol 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.