| SIP Express Media Server - README |
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)
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 and iLBC).
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
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.
See doc/COPYING for details.
The following applications are shipped with SEMS :
Announcements (Prompts, Ringbacktones, Pre-call-prompts):
* 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
* 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
* annrecorder users can record their personal greeting
* 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
* 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
* pin_collect collect a PIN, optionally verify it, and transfer
the call into a conference
Back-to-back User Agent
* sbc flexible SBC application, supports
- identity change
- header manipulation (filter etc)
- (multihomed) RTP relay
- SIP authentication
- Session timer, call timer, prepaid
* dsm DSM state machine scripting (use this)
* ivr embedded Python interpreter for simple apps
* py_sems another embedded Python interpreter
* echo test module to echo the caller's voice
* callback reject the call, call back caller later and have
her enter a number to call in b2bua with media relay
* reg_agent SIP REGISTER to register SEMS' contact to an aor
Developing and customizing Applications and services:
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.
o Python version >= 2.3 for the ivr (embedded python interpreter)
o flite speech synthesizer for TTS in the ivr
o lame >= 3.95 for mp3 file output, mpg123 for mp3 playback
o spandsp library for DTMF detection and PLC
(SEMS has its own implementations for both)
o libZRTP SDK (http://zfoneproject.com) for ZRTP
o libev for jsonrpc
How to get started with SEMS:
To try out SEMS, the easiest is to get a release from
http://ftp.iptel.org/pub/sems/, unpack and install it
using the usual make && make install. After installation, the
configuration file /usr/local/etc/sems/sems.conf needs to be
adapted, especially the parameters "sip_ip", "media_ip",
On Debian and Ubuntu, add the SEMS repository from OBS to
deb http://download.opensuse.org/repositories/home:/team-sems/Debian_5.0 ./
and install SEMS packages with:
wget http://download.opensuse.org/repositories/home:/team-sems/Debian_5.0/Release.key \
-O - |apt-key add -
apt-get update && apt-get install sems
If you want to build SEMS from source on debian/derivatives, see below.
On Fedora/CentOS, simply do
$ sudo yum install sems
and sems package will be installed.
You can also follow one of the tutorials linked from the SEMS homepage
The Application Modules Documentation page then gives an
overview of the application modules that come with SEMS
If you are interested in writing your own applications, the
application development tutorial is a good start
together with the design overview
(http://www.iptel.org/files/semsng-designoverview.pdf) and the example
SEMS needs to be told from the many possible applications that are
loaded which one to run. You can simply set the application
in sems.conf, e.g. application=conference. You can also define an
application mapping, i.e. numbers (R-URIs) that will be mapped to
applications, see the explanation of 'application' parameter in
Creating packages on debian (ubuntu, ...):
install debian package build tools:
$ apt-get install debhelper devscripts
$ apt-get install g++ make libspandsp-dev flite-dev libspeex-dev \
libssl-dev python-dev python-sip4-dev openssl
get the source:
$ wget ftp.iptel.org/pub/sems/sems-x.y.z.tar.gz ; tar xzvf sems-x.y.z.tar.gz
$ cd sems-x.y.z ; ln -s pkg/debian .
set version in changelog if not correct
$ dch -v x.y.z "SEMS x.y.z release"
$ dpkg-buildpackage -rfakeroot -us -uc
install package in .. using dpkg.
Installed files using 'make install':
/usr/local/sbin/sems : SEMS executable
/usr/local/lib/sems/plug-in/* : plug-ins
/usr/local/lib/sems/audio/* : default path for audio files
/usr/local/lib/sems/ivr/* : precompiled IVR scripts
/usr/local/etc/sems/sems.conf : configuration file
/usr/local/etc/sems/etc/* : modules configuration files
/usr/local/share/doc/sems/README : this README.
source_path/scripts/sems[.redhat] : example start-up scripts.
source_path/sems.conf.example : example configuration file.
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.
All this and more documentation is available online linked from
the SEMS homepage:
Support, mailing lists, bugs and contact:
Please have a look at the documentation and other information on
the SEMS homepage (www.iptel.org/sems).
Best-effort support is given through the mailing lists for SEMS,
email@example.com and firstname.lastname@example.org, which are the first address
to ask for help, report bugs and improvements. You need to be
subscribed to be able to post to the lists: http://lists.iptel.org.
The mailing list archives at http://lists.iptel.org/pipermail/sems/
and http://lists.iptel.org/pipermail/semsdev/ can be a great help as
well (especially with google site search on lists.iptel.org, e.g.
The bug tracker for SEMS is at http://tracker.iptel.org/browse/SEMS
Please submit all bugs, crashes and feature requests you encounter.
Raphael Coeffic (email@example.com), the father of SEMS,
Stefan Sayer (firstname.lastname@example.org), current lead developer,
and all contributors:
Alfred E Heggestad
Andriy I Pylypenko
Greger Viken Teigre
Rui Jin Zheng
Tom van der Geer
(if you feel you should be on this list, please mail to email@example.com)
Special thanks to 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 email one of the lists or the authors.
Please also have a look at the contributions license policy
SEMS - the media-S in the SLAMP.