osmo-bts - Osmocom BTS Implementation

This repository contains a C-language implementation of a GSM Base Transceiver Station (BTS). It is part of the Osmocom Open Source Mobile Communications project.

This code implements Layer 2 and higher of a more or less conventional GSM BTS (Base Transceiver Station) - however, using an Abis/IP interface, rather than the old-fashioned E1/T1.

Specifically, this includes

• BTS-side implementation of TS 08.58 (RSL) and TS 12.21 (OML)
• BTS-side implementation of LAPDm (using libosmocore/libosmogsm)
• A somewhat separated interface between those higher layer parts and the Layer1 interface.

Several kinds of BTS hardware are supported:

• sysmocom sysmoBTS
• Octasic octphy
• Nutaq litecell 1.5
• OpenCellular 2G (OC-2G)
• software-defined radio based osmo-bts-trx (e.g. USRP B210, UmTRX, LimeSDR)

Homepage

The official homepage of the project is https://osmocom.org/projects/osmobts/wiki

GIT Repository

You can clone from the official osmo-bts.git repository using

git clone git://git.osmocom.org/osmo-bts.git

There is a cgit interface at https://git.osmocom.org/osmo-bts/

Documentation

User Manuals and VTY reference manuals are [optionally] built in PDF form as part of the build process.

Pre-rendered PDF version of the current "master" can be found at User Manual as well as the VTY reference manuals

• VTY Reference Manual for osmo-bts-sysmo
• VTY Reference Manual for osmo-bts-trx
• VTY Reference Manual for osmo-bts-lc15
• VTY Reference Manual for osmo-bts-oc2g
• VTY Reference Manual for osmo-bts-octphy

There also is an Abis reference Manual describing the OsmoBTS specific A-bis dialect.

Mailing List

Discussions related to osmo-bts are happening on the openbsc@lists.osmocom.org mailing list, please see https://lists.osmocom.org/mailman/listinfo/openbsc for subscription options and the list archive.

Please observe the Osmocom Mailing List Rules when posting.

Contributing

Our coding standards are described at https://osmocom.org/projects/cellular-infrastructure/wiki/Coding_standards

We us a gerrit based patch submission/review process for managing contributions. Please see https://osmocom.org/projects/cellular-infrastructure/wiki/Gerrit for more details

The current patch queue for osmo-bts can be seen at https://gerrit.osmocom.org/#/q/project:osmo-bts+status:open

Known Limitations

As of January 2021, the following known limitations exist in this implementation:

Common Core

• No Extended BCCH support
• System Information limited to 1,2,2bis,2ter,2quater,3,4,5,6,9,13
• No RATSCCH in AMR
• Will reject TS 12.21 STARTING TIME in SET BTS ATTR / SET CHAN ATTR
• No support of TS 08.58 MultiRate Control
• No support of TS 08.58 Supported Codec Types
• No support of Bter frame / ENHANCED MEASUREMENT REPORT

osmo-bts-sysmo

• No CSD / ECSD support (not planned)
• GSM-R frequency band supported, but no NCH/ASCI/SoLSA
• All timeslots on one TRX have to use same training sequence (TSC)
• No multi-TRX support yet, though hardware+L1 support stacking
• Makes no use of 12.21 Intave Parameters and Interference Level Boundaries
• MphConfig.CNF can be returned to the wrong callback. E.g. with Tx Power and ciphering. The dispatch should take a look at the hLayer3.

osmo-bts-octphy

• No support of EFR, HR voice codec (lack of PHY support?)
• No re-transmission of PHY primitives in case of time-out
• Link Quality / Measurement processing incomplete
• impossible to modify encryption parameters using RSL MODE MODIFY
• no clear indication of nominal transmit power, various power related computations are likely off
• no OML attribute validation during bts_model_check_oml()