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       rtpproxy - RTP (Real-time Transport Protocol) Proxy Server


       rtpproxy [-?] [-2] [-f] [-v] [-R] [-l addr1[/addr2]] [-6 addr1[/addr2]]
                [-s ctrl_socket] [-t tos] [-p pidfile] [-T max_ttl]
                [-r rdir [-S sdir]]


       rtpproxy is a symmetric RTP proxy designed to be used in conjunction
       with the SIP Express Router (SER) or any other SIP proxy capable of
       rewriting SDP bodies in SIP messages that it processes.

       The main purpose of rtpproxy is to make the communication between SIP
       user agents behind NAT(s) (Network Address Translator) possible.
       Several cases exists when direct end-to-end communication is not
       possible and RTP streams have to be relayed through another host.
       Rtpproxy can be used to setup such a relaying host.

       When two listen interfaces have been specified using the command line
       parameters described below then rtpproxy will enter so called bridging
       mode. In briding mode rtpproxy forwards RTP packets received on one
       interface to the other interface and vice versa. This mode can be used
       to forward RTP packets between networks without direct network level
       connectivy (provided that the host running rtpproxy has one interface
       in both of them). One particular application of bridging mode is
       IPv4/IPv6 traversal of RTP packets.

       When instructured by SER rtpproxy can also record the entire RTP
       session in a file on a local harddisk or play a pre-recorded file to
       the user agent (so called Music-on-Hold).


           Show summary of options.

           Send every RTP packet twice in sessions that use low-bitrate
           codecs. Only packets that are smaller than 128 bytes will be sent
           twice. This option can improve audio quality on lossy links.

           Rtpproxy will stay in foreground mode if this option is set.

           Show version of program.

       -l addr1[/addr2]
           IPv4 listen IP address(es). You can specify either one or two
           addresses. If two addresses have been specified then rtpproxy will
           work in bridging mode.

       -6 addr1[/addr2]
           IPv6 listen IP address(es). You can specify either one or two
           addresses. If two addresses have been specified then rtpproxy will
           work in bridging mode.

       -s ctrl_socket
           This parameter configures rtpproxy control socket. The control
           socket is used by nathelper module of SER to create/modify/delete
           RTP sessions to be relayed. Format of ctrl_socket is
           <type>:<socket>. Following types are supported:

           ·    udp: Create UDP control socket. In this mode RTPProxy will
               listen on UDP for control messages from SER/nathelper.

               Example: -s udp:

               IP address can be ´*´ in which case rtpproxy will listen on all
               local interfaces. If omitted port 22222 is used.

                   RTPProxy control protocol has no built-in security
                   mechanisms. Make sure that you protect the listening IP and
                   port properly when using RTPProxy with UDP control socket.

           ·    udp6: Create IPv6 UDP control socket. In this mode RTPProxy
               will listen on UDP/IPv6 for control messages from

               Example: -s udp6:::1:9000

           ·    unix: Create UNIX domain socket for control interface. In this
               mode SER/nathelper and RTPProxy must be running on the same
               host. This is the default setting for both SER/nathelper and

               Example: -s unix:/var/run/rtpproxy.sock

               Default value is /var/run/rtpproxy.sock.

           -t tos
               Set this ToS (Type of Service) in outgoing packets. Default
               value is 0xB8.

           -r rec_dir
               Directory where recorded RTP sessions will be stored.

           -S spool_dir
               Spool directory for RTP sessions being recorded. The file will
               be moved to directory configured in -r option after the session

               Do not record RTCP when recording an RTP session. This option
               is disabled (rtpproxy will record RTCP) by default.

           -p pid_file
               This parameter configures the name of the file where PID of
               running rtpproxy will be stored. Default is

           -T max_ttl
               Limit the maximum TTL (Time To Live) of outgoing IP packets to
               the value of max_ttl.


       When SER receives an INVITE request, it extracts Call-ID from it and
       communicates it to rtpproxy via Unix domain socket or UDP. Rtproxy
       looks for an existing session with such Call-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 request as usually.

       When SER receives a 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 usually.

       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).




       This program is licensed under the BSD license. See COPYING file in the
       rtpproxy sources for details.


       The latest version of this program can be found at




       Maxim Sobolev


       Copyright © 2006 janakj

[FIXME: source]                  Feb 20, 2006