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-== OsmoBTS Interfaces
-
-OsmoBTS offers a set of interfaces to interact with external entities:
-
-* A-bis/IP interface to talk to the BSC
-* bts_model specific PHY interface
-* VTY interface
-* Osmocom control interface
-* GSMTAP interface
-* PCU interface
-
-
-=== OsmoBTS Abis/IP Interface
-
-OsmoBTS implements the GSM A-bis interface as described in the relevant
-3GPP specifications:
-
-* A-bis RSL according to 3GPP TS 08.58
-* A-bis OML according to 3GPP TS 12.21
-
-As the 3GPP specifies A-bis only over E1 interfaces and not over IP,
-significant enhancements and modifications to the 3GPP specifications are
-employed. Nevertheless, the implementation tries to stay as close as
-possible to the 3GPP specifications.
-
-Please see the _OsmoBTS Abis Protocol Specification_
-<<osmobts-abis-spec>> for more information on this subject.
-
-
-=== bts_model specific PHY interface
-
-This interface is specific to the bts_model that OsmoBTS was compiled
-for. It can take any form as required by the respective hardware.
-
-Please see the PHY documentation of your respective BTS hardware for more
-details.
-
-
-=== OsmoBTS VTY Interface
-
-See <<vty>> for further information.
-
-
-=== OsmoBTS Control Interface
-
-The general structure of the Omsocom control interface is described in
-<<common-control-if>>.
-
-The number of control interface commands/attributes is currently quite
-limited and largely depends on the bts_model used.
-
-==== trx.N.thermal-attenuation
-
-The idea of this parameter is to attenuate the system output power as part of
-thermal management. In some cases the PA might be passing a critical level,
-so an external control process can use this attribute to reduce the system
-output power.
-
-Please note that all values in the context of transmit power calculation
-are integers in milli-dB (1/10000 bel), so the below example is setting
-the attenuation at 3 dB:
-
-----
-bsc_control.py -d localhost -p 4238 -s trx.0.thermal-attenuation 3000
-Got message: SET_REPLY 1 trx.0.thermal-attenuation 3000
-----
-
-----
-bsc_control.py -d localhost -p 4238 -g trx.0.thermal-attenuation
-Got message: GET_REPLY 1 trx.0.thermal-attenuation 3000
-----
-
-
-
-=== OsmoBTS GSMTAP Interface
-
-GSMTAP is a standard created by Osmocom to UDP-encapsulate GSM protocol
-messages normally communicated over non-IP interfaces for the primary
-purpose of protocol analysis in the wireshark dissector.
-
-The initial purpose was to encapsulate GSM Um frames including some
-meta-data like ARFCN and GSM frame number into something that can be
-parsed and dispatched within the wireshark dissector.
-
-This interface has since been extended to many other
-GSM/GPRS/UMTS interfaces and protocols, and even to TETRA and GMR.
-
-In OsmoBTS, it is possible to export both uplink and downlink Um
-messages via GSMTAP. There is a set of VTY configuration options to
-specify for which logical channels of the Um interface GSMTAP messages
-shall be emitted, and to which destination IP address they shall be
-sent.
-
-Using GSMTAP it is possible to place a virtual tap at the air interface
-between BTS and MS, without going through the trouble of setting up an
-actual radio receiver at the same frequencies. Also, GSMTAP export is
-performed before the Um air-interface encryption (A5) is performed, so
-all frames are always in plain text.
-
-Please refer to <<gsmtap>> for more information on how to configure and
-use this interface.
-
-
-=== OsmoBTS PCU Socket Interface
-
-In order to assist the provisioning of GPRS services over the same radio
-interface as circuit-switched GSM, OsmoBTS exposes a Unix domain socket
-based interface towards OsmoPCU.
-
-OsmoPCU is the Osmocom implementation of the GPRS Packet Control Unit
-(PCU), which is co-located with the BTS in the Osmocom implementation.
-Contrary to that, many classic E1-based implementations of the GSM RAN
-co-locate the PCU with the BSC. However, the GSM specifications keep
-the location up to the implementor.
-
-The GPRS network architecture is shown in <<fig-gprs-pcubts>>.
-
-[[fig-gprs-pcubts]]
-.GPRS network architecture
-[graphviz]
-----
-digraph G {
- rankdir=LR;
- MS0 [label="MS"];
- MS1 [label="MS"];
- BTS;
- BSC;
- MSC;
- PCU;
- SGSN;
- GGSN;
- MS0->BTS [label="Um"];
- MS1->BTS [label="Um"];
- BTS->BSC [label="Abis"];
- BSC->MSC [label="A"];
- BTS->PCU [label="pcu_sock"];
- PCU->SGSN [label="Gb"];
- SGSN->GGSN [label="GTP"];
-}
-----
-
-The PCU socket interface serves the following purposes:
-
-* to pass PCU relevant configuration from BTS to PCU
-* to forward paging requests from BTS to PCU
-* to forward RACH Requests from BTS to PCU
-
-Depending on your bts_model, the PCU may also be passing actual
-PH-DATA.request / PH-DATA.indication / PH-RTS.indication primitives for
-the PDCH. This is considered sub-optimal, and some BTS models offer a
-direct interface by which the PCU can exchange those primitives directly
-with the PHY.
-
-The default PCU socket interface name is `/tmp/pcu_sock`, but this can
-be overridden by the `pcu-socket` VTY command in the BTS configuration
-VTY node.