The RTPproxy is a high-performance software proxy for RTP streams that can
work together with SER or OpenSER. Originally created for handling NAT
scenarious it can also act as a generic media relay as well as gateway RTP
sessions between IPv4 and IPv6 networks. RTPproxy was developed by Maxim
Sobolev and now is being actively maintained by the Sippy Software, Inc.
The RTPproxy supports some advanced features, such as remote control mode,
allowing building scalable distributed SIP VoIP networks. The nathelper module
included into the SER or OpenSER SIP Proxy software allows using multiple
RTPproxy instances running on remote machines for fault-tolerance and
The software also supports video relaying and RTP session recording.
II. How it works
This proxy works as follows:
- When SER receives INVITE reqiest, it extracts call-id from it and
communicates it to the proxy via Unix domain socket. Proxy looks for an
existing sessions with such id, if the session exists it returns UDP port
for that session, if not, then it creates a new session, binds to a first
empty UDP port from the range specified at the compile time and returns
number of that port to a SER. After receiving reply from the proxy, SER
replaces media ip:port in the SDP to point to the proxy and forwards
reqiest as usually;
- when SER receives non-negative SIP reply with SDP it again extracts
call-id from it and communicates it to the proxy. In this case the proxy
does not allocate a new session if it doesn't exist, but simply performs a
lookup among existing sessions and returns either a port number if the
session is found, or error code indicating that there is no session with
such id. After receiving positive reply from the proxy, SER replaces media
ip:port in the SIP reply to point to the proxy and forwards reply as
- after the session has been created, the proxy listens on the port it has
allocated for that session and waits for receiving at least one UDP
packet from each of two parties participating in the call. Once such
packet is received, the proxy fills one of two ip:port structures
associated with each call with source ip:port of that packet. When both
structures are filled in, the proxy starts relaying UDP packets between
- the proxy tracks idle time for each of existing sessions (i.e. the time
within which there were no packets relayed), and automatically cleans
up a sessions whose idle times exceed the value specified at compile
time (60 seconds by default).
Currently, rtpproxy does not support command-line definition of RTP port
range. By default rtpproxy uses UDP ports 35000-65000 and these should be
opened any firewalls in front of rtpproxy. The ports used can be modified in
rtpp_defines.h file (PORT_MIN and PORT_MAX) and then recompile/reinstall.
IV. TODO (in no particular order)
- Port to another OSes;
- make more parameters (e.g. ports range, max idle time etc.) to be
adjustible via command line.
Community-based support could be obtained via SER mailing lists
Commercial support is available from the Sippy Software, Inc. - visit
http://www.sippysoft.com for details.
$Id: README,v 1.3 2007/07/28 01:55:12 sobomax Exp $