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diff --git a/doc/manuals/chapters/overview.adoc b/doc/manuals/chapters/overview.adoc new file mode 100644 index 000000000..9b619fb24 --- /dev/null +++ b/doc/manuals/chapters/overview.adoc @@ -0,0 +1,174 @@ +[[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 the Osmocom implementation of a Base Station Controller. It +implements: + +- an 'A-bis' interface towards BTSs and +- an 'A' interface towards an MSC. It is important to be aware that there are + two variants of the 'A' interface, see <<a-interface>>. + +=== Software Components + +OsmoBSC contains a variety of different software components, which +we'll briefly 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, Octasic and sysmocom, as well as +various USRP based BTS implementations, using OsmoBTS and OsmoTRX (like the +Ettus B200 series, the Fairwaves XTRX or the LimeSDR, to name a few). + +For more information, see <<bts>> and <<bts-examples>>. + +[[a-interface]] +==== A Implementation + +OsmoBSC implements a sub-set of the GSM A interface as specified in TS 08.08 +(BSSAP) and TS 04.08 (DTAP). + +Osmocom offers two variants of the 'A' interface's protocol stacking: + +- 'A/SCCPlite' +- 'A/SCCP/M3UA' + +Traditionally, OsmoBSC only implemented the A/SCCPlite protocol, but since a +proper M3UA implementation is available from 'libosmo-sigtran' +('libosmo-sccp.git'), the stock OsmoBSC now supports only A/SCCP/M3UA. (The +idea is that SCCPlite support may be added to libosmo-sigtran at some point +in the future, after which the new `osmo-bsc` would support both variants of +the A interface.) + +The difference between an A/SCCPlite and A/SCCP/M3UA is illustrated in +<<fig-sccplite>> and <<fig-sccp-m3ua>>. + +===== A/SCCPlite + +Unlike classic A interface implementations for E1 interfacs, +`osmo-bsc-sccplite` 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". + +At the time of writing, if you would like to use the old A/SCCPlite protocol, +look for binary packages named `osmo-bsc-sccplite`, or compile `osmo-bsc` from +the 'openbsc.git' repository. + +[[fig-sccplite]] +.`osmo-bsc-sccplite` operation using 'A/SCCPlite' +[graphviz] +---- +digraph G { + rankdir=LR; + MS0 [label="MS"]; + MS1 [label="MS"]; + MS2 [label="MS"]; + MS3 [label="MS"]; + BTS0 [label="BTS"]; + BTS1 [label="BTS"]; + BSC [label="OsmoBSC-SCCPlite"]; + MSC [label="3rd party MSC"]; + {MS0,MS1}->BTS0 [label="Um"]; + {MS2,MS3}->BTS1 [label="Um"]; + {BTS0,BTS1}->BSC [label="Abis\nTCP\nIP"]; + BSC->MSC [label="A\nSCCP\nTCP\nIP"]; +} +---- + +===== A/SCCP/M3UA + +The default OsmoBSC's A interface uses the M3UA variant of SIGTRAN protocol +stacking: + +|===== +|A +|SCCP +|M3UA +|SCTP +|IP +|===== + +To use the now-default A/SCCP/M3UA protocol, look for binary packages named +`osmo-bsc`, or compile `osmo-bsc` from the 'osmo-bsc.git' repository. It is +recommended to use the M3UA variant, which is required to operate with OsmoMSC. + +To route SCCP/M3UA messages between OsmoBSC and and MSC, an STP instance like +OsmoSTP is required. + +[[fig-sccp-m3ua]] +.`osmo-bsc` operation using 'A/SCCP/M3UA' +[graphviz] +---- +digraph G { + rankdir=LR; + MS0 [label="MS"]; + MS1 [label="MS"]; + MS2 [label="MS"]; + MS3 [label="MS"]; + BTS0 [label="BTS"]; + BTS1 [label="BTS"]; + BSC [label="OsmoBSC"]; + STP [label="OsmoSTP"]; + MSC [label="OsmoMSC\n(or 3rd-party MSC)"]; + {MS0,MS1}->BTS0 [label="Um"]; + {MS2,MS3}->BTS1 [label="Um"]; + {BTS0,BTS1}->BSC [label="Abis\nTCP\nIP"]; + BSC->STP->MSC [label="A\nSCCP\nM3UA\nSCTP\nIP"]; +} +---- + +==== 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? + |