Osmocom Base Transceiver Station (BTS) https://osmocom.org/projects/osmobts
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Andreas Eversberg 1013ca3b8b Handle empty (idle) PDCH blocks gracefully
An empty PDCH block contains no payload, sysmo-bts and similar BTS
models crash, because they expect the msg->l2h to be set. The function
l1sap_pdch_req() will not set msg->l2h for empty PDCH blocks, so these
models crash.

The current osmo-pcu does not send empty PDCH blocks to these BTS
models. But there shouldn't be a crash, if we receive empty PDCH blocks
over the PCU socket interface.

Change-Id: Icb52c896766425fcf453c65530c4c0b8d06b8821
2023-12-11 10:06:19 +01:00
contrib Increase RR scheduler priority to 20, to avoid dropped bursts 2023-10-09 08:04:56 +00:00
debian Bump version: → 1.7.0 2023-09-12 16:05:31 +02:00
doc Use uniform log format for default config files 2023-12-01 11:50:12 +01:00
include LAPDm: Reject (release) establishment on DCCH, SAPI 0 without L3 payload 2023-12-11 10:06:16 +01:00
src Handle empty (idle) PDCH blocks gracefully 2023-12-11 10:06:19 +01:00
tests meas: lchan_meas_check_compute(): fix -SUB frame substitution 2023-10-04 09:18:11 +00:00
.gitignore l1sap: proper rate adaptation for CSD (RFC4040 'clearmode') 2023-07-30 16:08:01 +07:00
.gitreview Add .gitreview 2016-06-17 15:33:01 +00:00
.mailmap Add .mailmap for mapping mail addresses in shortlog 2016-08-08 11:31:00 +00:00
COPYING re-work original osmo-bts with support for sysmocom femtobts 2011-06-27 11:25:35 +02:00
Makefile.am Makefile.am: EXTRA_DIST: debian, contrib/*.spec.in 2020-05-22 13:37:41 +02:00
README.md update git URLs (git -> https; gitea) 2022-06-18 11:39:25 +02:00
TODO-RELEASE ASCI: Add library requirements for uplink access to TODO-RELEASE 2023-10-27 10:35:21 +00:00
configure.ac Bump version: → 1.7.0 2023-09-12 16:05:31 +02:00
git-version-gen auto-generate a version 2011-09-07 21:28:27 +02:00


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)


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 https://gitea.osmocom.org/cellular-infrastructure/osmo-bts

There is a web interface at https://gitea.osmocom.org/cellular-infrastructure/osmo-bts


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

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.


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 support of TS 08.58 MultiRate Control
  • No support of TS 08.58 Supported Codec Types
  • No support of Bter frame / ENHANCED MEASUREMENT REPORT


  • 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.


  • 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()