SEMS is a free, high performance, extensible media server for SIP (RFC3261) based VoIP services.

It is intended to complement proxy/registrar servers in VoIP networks for all applications where server-side processing of audio is required, for example away or pre-call announcements, voicemail, or network side conferencing. Another use case is for interconnecting SIP networks, where a back-to-back user agent (B2BUA) is required.

SEMS can be used to implement simple high performance components like announcement servers as building blocks of more complex applications, or, using its powerful framework for application development including back-to-back user agent (B2BUA) and state machine scripting functionality, complex VoIP services can be realized completely in SEMS.

SEMS supports all important patent free codecs out of the box (g711u, g711a, GSM06.10, speex, G.726, L16, OPUS, iLBC etc). There is a wrapper for the IPP G.729 codec implementation available. Integrating other codecs in SEMS is very simple (patented or not).

SEMS shows very good performance on current standard PC architecture based server systems. It has sucessfully been run with 1200 G.711 conference channels on a quad-core Intel(R) Xeon at 2GHz (700 GSM, 280 iLBC channels), and up to 5000 channels on a dual quad Xeon at 2.9GHz. Its back-to-back user agent has been run with up to 19000 TPS on the latter machine. On the other hand it also runs on very small devices - for example small embedded systems like routers running OpenWRT, for which of course the achievable channel count is not that high.

SEMS is free (speech+beer) software. It is licensed under dual license terms, the GPL (v2+) and proprietary license. This program is released under the GPL with the additional exemption that compiling, linking, and/or using OpenSSL is allowed.

For a license to use SEMS under non-GPL terms, please contact FRAFOS GmbH at info@frafos.com .

See doc/COPYING for details.

The following applications are shipped with SEMS :

• sbc - flexible SBC application, supports
  • identity change
  • header manipulation (filter etc)
  • (multihomed) RTP relay, NAT handling, transcoding
  • SIP authentication
  • Session timer, call timer, prepaid
  • etc

• announcement - plays an announcement

• ann_b2b - pre-call-announcement, plays announcement before connecting the callee in B2BUA mode

• announce_transfer - pre-call-announcement, plays announcement and then transfers the caller to the callee using REFER

• early_announce - (pre-call) announcement using early media (183), optionally continues the call in B2BUA mode

• precoded_announce - plays preencoded announcements

• voicebox - users can dial in to the voicebox to check their messages

• annrecorder - users can record their personal greeting message

• mailbox - auto-attendant that saves voicemails into an IMAP server. Users can dial in to check their messages (simpler version)

• voicemail - records voice messages and sends them as email, saves them to a voicebox, or both

• conference - enables many people to talk together at the same time

• webconference - conference application that can be controlled from an external program, e.g. a website

• conf_auth - collect a PIN number, verify it against an XMLRPC authentication server and connects in B2BUA mode

• pin_collect - collect a PIN, optionally verify it, and transfer the call into a conference

• dsm - DSM state machine scripting (use this)

• ivr - embedded Python interpreter for simple apps

• py_sems - another embedded Python interpreter

• click2dial - XMLRPC-enabled way to initiate authenticated calls

• callback - reject the call, call back caller later and have caller enter a number to call in b2bua with media relay mode

• mobile_push - mobile push notification support for call routing

• reg_agent - SIP REGISTER to register SEMS' contact to an aor

• registrar_client - SIP registrar client functionality

• db_reg_agent - database-based registration agent using MySQL++

• diameter_client - simple DIAMETER client implementation for AAA integration

• jsonrpc - JSON-RPC protocol version 2.0 over TCP/Netstrings

• xmlrpc2di - makes DI interfaces accessible via XMLRPC, also XMLRPC client

• monitoring - in-memory AVP DB for call monitoring and generic data storage

• msg_storage - message storage functionality

• mwi - Message Waiting Indication (MWI) support

• mp3 - MP3 codec support and media processing

• rtmp - RTMP (Real-Time Messaging Protocol) support

• echo - test module to echo the caller's voice

• early_dbprompt - early media database prompts example

• gateway - ISDN gateway functionality (requires mISDN)

• twit - example Twitter integration application

SEMS comes with a set of example applications intended to help development of custom services, including a calling card application, a traffic generator, a component to control the media server via XMLRPC, and announcements played from DB.

DSM state machine scripting is a powerful yet simple method to rapidly implement custom applications. With this method, the service logic is written as an easy to understand textual definition of a state machine, which is interpreted and executed for every call. The (domain specific) language for defining state machines can be extended by implementing modules. A set of useful modules are shipped with SEMS, including MySQL database access module, Python module, conference support, Amazon AWS and more.

SEMS' core implements basic call and audio processing, and loads plug-ins which extend the system. Audio plug-ins enable new codecs and file formats, application plug-ins implement the services' logic. Other modules called component modules provide functionality for other modules to use.

You can easily extend SEMS by creating your own plug-ins. Applications can be written using the SEMS framework API in C++, or in Python using an embedded python interpreter of the ivr or py_sems modules, or the DSM.

All requirements are optional.

• Python 3 for the ivr (embedded python interpreter) and py_sems
• flite speech synthesizer for TTS in the ivr
• lame >= 3.95 for mp3 file output, mpg123 for mp3 playback
• spandsp library for DTMF detection and PLC (SEMS has its own implementations for both)
• libZRTP SDK (http://zfoneproject.com) for ZRTP
• libev for jsonrpc

SEMS server hes been build-tested with the following:

• RHEL 7 with Python 3
• RHEL 8 with Python 3
• RHEL 9 with Python 3
• RHEL 10 with Python 3
• Debian 11 with Python 3
• Debian 12 with Python 3
• Debian 13 with Python 3

Please see appropriate Dockerfiles for reference.

git clone git@github.com:sems-server/sems.git
cd sems
mkdir -p build && cd build
cmake ..
make
ctest -V
./core/sems -v
sudo make install

Install debian package build tools:

sudo apt-get install debhelper devscripts

Install dependencies (those below or let dpkg-buildpackage below tell you which ones):

sudo apt-get install debhelper g++ make libspandsp-dev flite1-dev \
                     libspeex-dev libgsm1-dev libopus-dev libssl-dev python-dev \
                     python-sip-dev openssl libev-dev libmysqlcppconn-dev libevent-dev \
                     libxml2-dev libcurl4-openssl-dev libhiredis-dev

Get the source:

git clone https://github.com/sems-server/sems.git

cd sems; ln -s pkg/deb/buster ./debian

Set version in changelog if not correct:

dch -v x.y.z "SEMS x.y.z release"

or:

dch -b -v `git describe --always` "sems git master"

Build package:

dpkg-buildpackage -rfakeroot -us -uc

Install sems and sems-python-modules packages in .. using dpkg.

This example is for RHEL7, for other OSes please see the appropriate Dockerfile.

mkdir -p /tmp/sems-rpms
# build the image which also builds the packages
docker build -t sems-rhel7 -f Dockerfile-rhel7 .
# create temporary container instance
docker create --name temp-sems-rhel7 sems-rhel7
# extract RPMs into host system
docker cp temp-sems-rhel7:/root/rpmbuild/RPMS /tmp/sems-rpms
# remove temporary container
docker rm temp-sems-rhel7
# list available SEMS RPMs
ls -al /tmp/sems-rpms/RPMS/x86_64/

In the doc/ directory there is a set of files describing the applications shipped with SEMS, alongside some more documentation. Generate the doxygen documentation with 'make doc' in doc/doxygen_doc, that contains all these files as well.

Best-effort support is given for SEMS. Use https://github.com/sems-server/sems/issues which is the first address to ask for help, report bugs and improvements.

Bugs can be filed as issues on this site. Please submit all bugs, crashes and feature requests you encounter.

Raphael Coeffic (rco@iptel.org), the father of SEMS

Stefan Sayer (stefan.sayer@gmail.com), the lead developer

Contributors:

• Alex Gradinar
• Alfred E Heggestad
• Andreas Granig
• Andrey Samusenko
• Andriy I Pylypenko
• Anton Zagorskiy
• B. Oldenburg
• Balint Kovacs
• Bogdan Pintea
• Carsten Bock
• Greger Viken Teigre
• Grzegorz Stanislawski
• Helmut Kuper
• Jeremy A
• Jiri Kuthan
• Joe Stusick
• Jose-Luis Millan
• Juha Heinanen
• Marcel Hecko
• Matthew Williams
• Michael Furmur
• Ovidiu Sas
• Pavel Kasparek
• Peter Lemenkov
• Peter Loeppky
• Richard Newman
• Robert Szokovacs
• Rui Jin Zheng
• Tom van der Geer
• Ulrich Abend
• Vaclav Kubart
• Victor Seva

(if you feel you should be on this list, please submit PR)

Special thanks to FRAFOS GmbH, sipwise GmbH, IPTEGO GmbH, iptelorg GmbH and TelTech Systems Inc. for sponsoring development of SEMS.

All kinds of contributions and bug fixes are very welcome, for example new application or codec modules, documentation pages, howtos etc.

Please also have a look at the contributions license policy (see doc/COPYING).

SEMS - the media-S in the SLAMP.