MNCC<->SIP bridge; attaches to OsmoMSC to interface with external SIP VoIP telephony
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Neels Hofmeyr d50637eec6 forward SDP between SIP and MNCC
We have added support for sending SDP via MNCC a long time ago, but so
far the SDP section remained empty. Now, implement actually forwarding
SDP codec information between SIP and MNCC.

The aim is to let the MSC know about all codec choices the remote SIP
call leg has to offer, so that finding a codec match between local and
remote call leg becomes possible.

Store any SDP info contained in incoming SIP and MNCC messages, and send
the stored SDP to the other call leg in all outgoing SIP and MNCC

In sdp_create_file(), we used to compose fixed SDP -- instead, take the
other call leg's SDP as-is, only make sure to modify the mode (e.g.
"a=sendrecv") to reflect the current call hold state.

The RTP address and codec info in the MNCC structures is now essentially
a redundant / possibly less accurate copy of the SDP info, but leave all
of that as-is, for backwards compat.

There is codec checking that may reject unexpected codecs. The
overall/future aim is to leave all codec checking up to the MSC, but so
far just leave current behaviour unchanged, until we notice problems.

Related: SYS#5066
Related: osmo-ttcn3-hacks Ib2ae8449e673f5027f01d428d3718c006f76d93e
Change-Id: I3df5d06f38ee2d122706a9ebffde7db4f2bd6bae
2023-09-15 04:21:06 +02:00
contrib Bump version: → 1.6.3 2023-09-12 17:24:27 +02:00
debian Bump version: → 1.6.3 2023-09-12 17:24:27 +02:00
doc doc: Expand the virtually empty user manual with some basics 2023-03-21 20:00:04 +01:00
src forward SDP between SIP and MNCC 2023-09-15 04:21:06 +02:00
tests tests: $(BUILT_SOURCES) is not defined, depend on osmo-sip-connector 2023-03-30 02:13:00 +07:00
.gitignore .gitignore: Get rid of new autofoo tmp files 2021-02-02 16:42:12 +01:00
.gitreview Add git review config 2017-08-25 18:38:05 +02:00
COPYING Initial commit for a MNCC to SIP gateway (and maybe auth GW too) 2016-03-21 09:54:37 +01:00 EXTRA_DIST: debian, contrib/* 2020-05-22 13:46:54 +02:00 Convert + Expand README file 2022-06-18 13:41:01 +02:00
TODO-RELEASE Add TODO-RELEASE 2022-01-03 12:26:58 +01:00 Bump version: → 1.6.3 2023-09-12 17:24:27 +02:00
git-version-gen Fix git-version-gen 2017-10-28 18:20:00 +02:00 switch to python 3 2019-12-11 09:43:11 +01:00

osmo-sip-connector - Osmocom SIP connector

This implements an interface between the MNCC (Mobile Network Call Control) interface of OsmoMSC (and also previously OsmoNITB) and SIP.

Call identities can be either the MSISDN or the IMSI of the subscriber.

Requirements of Equipment

  • DTMF need to be sent using SIP INFO messages. DTMF in RTP is not supported.
  • BTS+PBX and SIP connector+PBX must be in the same network (UDP must be able to flow directly between these elements)
  • No handover support.
  • IP based BTS (e.g. Sysmocom sysmoBTS but no Siemens BS11)
  • No emergency calls


  • PT of RTP needs to match the one used by the BTS. E.g. AMR needs to use the same PT as the BTS. This is because rtp_payload2 is not yet supported by the osmo-bts software.

  • AMR SDP file doesn't include the mode-set params and allowed codec modes. This needs to be configured in some way.


You can find the osmo-sip-connector issue tracker and wiki online at and

GIT Repository

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

    git clone

There is a web interface at


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 Manual

Mailing List

Discussions related to osmo-sip-connector are happening on the mailing list, please see for subscription options and the list archive.

Please observe the Osmocom Mailing List Rules when posting.


Our coding standards are described at

We us a gerrit based patch submission/review process for managing contributions. Please see for more details

The current patch queue for osmo-sip-connector can be seen at