Media Exchange Module
     __________________________________________________________

   Table of Contents

   1. Admin Guide

        1.1. Overview
        1.2. Dependencies

              1.2.1. OpenSIPS Modules
              1.2.2. External Libraries or Applications

        1.3. Exported Functions

              1.3.1. media_fork_to_uri(URI[, leg[, headers[,
                      medianum]]])

              1.3.2. media_fork_from_call(callid[, leg[,
                      medianum]])

              1.3.3. media_fork_pause([leg[, medianum]])
              1.3.4. media_fork_resume([leg[, medianum]])
              1.3.5. media_exchange_from_uri(URI[, leg[, body[,
                      headers[, nohold]]]])

              1.3.6. media_exchange_to_call(callid[, leg[,
                      nohold]])

              1.3.7. media_terminate([leg[, nohold]])
              1.3.8. media_handle_indialog()

        1.4. Exported MI Functions

              1.4.1. media_fork_from_call_to_uri
              1.4.2. media_exchange_from_call_to_uri
              1.4.3. media_exchange_from_call_to_uri_body
              1.4.4. media_terminate

   2. Contributors

        2.1. By Commit Statistics
        2.2. By Commit Activity

   3. Documentation

        3.1. Contributors

   List of Tables

   2.1. Top contributors by DevScore^(1), authored commits^(2) and
          lines added/removed^(3)

   2.2. Most recently active contributors^(1) to this module

   List of Examples

   1.1. Use media_fork_to_uri() function to fork media to a Media
          Server

   1.2. Use media_fork_from_call() function to fork all media
          streams of a call

   1.3. Use media_fork_from_call() function to fork only the first
          caller's stream

   1.4. Use media_fork_pause() function to temporarily stop the
          entire media stream of the call

   1.5. Use media_fork_resume() function to resume a forking
          previously stopped

   1.6. Use media_exchange_from_uri() function to fetch media from
          a Media Server's call

   1.7. Use media_exchange_to_call() function to make an
          announcement

   1.8. Use media_terminate() function to terminate an
          announcement

   1.9. Use media_terminate() function to terminate an
          announcement

Chapter 1. Admin Guide

1.1. Overview

   This module provides the means to exchange media SDP between
   different SIP proxied calls, and calls started or received from
   a Media Server. The module itself does not have any media
   capabilities, it simply exposes primitives to exchange the SDP
   body between two or more different calls.

   The module can both originate calls, pushing an existing SDP to
   a media server, to playback, or simply record an existing RTP,
   as well as take the SDP of a new call and inject the SDP into
   an existing, proxied sip call. In order to manipulate the new
   calls, either generated, or terminated, the module behaves as a
   back-to-back user agent with the aim of the OpenSIPS B2B
   entities module.

   In terms of the SDP media exchanged, the module can have two
   different modes:
     * Two way Media - in this mode, the media of a new call will
       be pushed towards one of the legs of an existing call. This
       will result in a party of the call talking with the Media
       Server. By default, the other participant of the call will
       be put on hold, but this behavior can be tuned when the new
       leg is originated.
     * Fork Media - the new B2B call, either originated or
       terminated, will just have a copy of the RTP forked by
       RTPProxy. In this mode, the proxied call should have had
       RTPProxy already engaged in the media path before the
       forked call starts. One can fork only one media leg, or
       both legs. NOTE: RTPProxy currently does not support
       stopping media streaming, therefore if the streaming call
       terminates, RTPProxy will continue streaming, even if there
       is no one listening on the other end.

   This module can provide different functionalities and can be
   used in various use cases, such as:
     * Call Recording - similar to the OpenSIPS SIPREC module, it
       can be used to fork the RTP media to a new SIP destination,
       but without the SIPREC payload.
     * Call Listening - one might want to call into OpenSIPS and
       start listening an existing call.
     * Call Announcements - inject an announcement from a Media
       Server to the participants of an ongoing call.

1.2. Dependencies

1.2.1. OpenSIPS Modules

   The following modules must be loaded before this module:
     * TM - Transaction module.
     * Dialog - Dialog module for keeping track of the proxied
       calls.
     * RTPProxy - optional, the RTPProxy module is only used when
       running in media forking mode.
     * B2B_ENTITIES - Back-2-Back module used form manipulating
       calls with the Media Server.

1.2.2. External Libraries or Applications

   The following libraries or applications must be installed
   before running OpenSIPS with this module loaded:
     * None.

1.3. Exported Functions

1.3.1.  media_fork_to_uri(URI[, leg[, headers[, medianum]]])

   Behaves as a B2B user agent client to initiate a call to a SIP
   URI and then stream the media to the SDP received in the 200 OK
   response.

   Parameters:
     * URI (string) - destination where to push the current call's
       media
     * leg (string, optional) - the leg that will be streamed.
       Possible values are caller, callee and both. If missing,
       the direction of the indialog request is used.
     * headers (string, optional) - optional headers added to the
       generated request.
     * medianum (integer, optional) - the media stream that will
       be forked within the call. First index is 0. If missing,
       all media streams of that leg(s) are streamed.

   This function can be used from any route.

   Example 1.1. Use media_fork_to_uri() function to fork media to
   a Media Server
...
if (!has_totag() && is_method("INVITE"))
        media_fork_to_uri("sip:record@127.0.0.1:5080");
...

1.3.2.  media_fork_from_call(callid[, leg[, medianum]])

   Starts streaming the media of an existing proxied call,
   identified by the callid parameter to the SDP in the request's
   body.

   Parameters:
     * callid (string) - the identifier of the callid to
       stream/fork media from
     * leg (string, optional) - the leg that will be streamed.
       Possible values are caller, callee and both. If missing,
       both legs will be streamed.
     * medianum (integer, optional) - the media stream that will
       be forked within the call. First index is 0. If missing,
       all media streams of that leg(s) are streamed, as long as
       the body has enough streams.
       Note: RTPProxy does not do any media mixing, therefore you
       need to make sure that the INVITE has enough SDP streams to
       handle all the media streams selected to fork.

   This function can be used from REQUEST_ROUTE, BRANCH_ROUTE,
   FAILURE_ROUTE and ONREPLY_ROUTE.

   NOTE: the request of this call is completely handled by the B2B
   engine. Therefore, after running this function, please make
   sure you do not relay the message further, otherwise you will
   run into an unexpected behavior. Best thing to do is to exit
   the processing after running the function.

   Example 1.2. Use media_fork_from_call() function to fork all
   media streams of a call
...
if (!has_totag() && is_method("INVITE") && $hdr(X-CallID) != NULL)
        media_fork_from_call($hdr(X-CallID));
...

   Example 1.3. Use media_fork_from_call() function to fork only
   the first caller's stream
...
if (!has_totag() && is_method("INVITE") && $hdr(X-CallID) != NULL)
        media_fork_from_call($hdr(X-CallID), "caller", 0);
...

1.3.3.  media_fork_pause([leg[, medianum]])

   Pauses an existing RTP media streaming session. This function
   does not terminate the forking call, but only stops sending the
   RTP. It also re-invites the Media Server to inform about the
   change.

   Parameters:
     * leg (string, optional) - the leg that will be paused.
       Possible values are caller, callee and both. If missing,
       all ongoing media sessions will be paused.
     * medianum (integer, optional) - the media stream to be
       paused. First index is 0. If missing, all ongoing media
       streams associated to the selected leg will be paused.

   This function can be used from any route.

   Example 1.4. Use media_fork_pause() function to temporarily
   stop the entire media stream of the call
...
if (has_totag() && is_method("INVITE"))
        media_fork_pause();
...

1.3.4.  media_fork_resume([leg[, medianum]])

   Resumes the RTP media stream of an existing session/call. This
   function relies on the fact that a media fork session has been
   previously started.

   Parameters:
     * leg (string, optional) - the leg that will be resumed.
       Possible values are caller, callee and both. If missing,
       all existing media legs that are stopped will be started.
     * medianum (integer, optional) - the media stream to be
       paused. First index is 0. If missing, all ongoing media
       streams associated to the selected leg will be paused.

   This function can be used from any route.

   Example 1.5. Use media_fork_resume() function to resume a
   forking previously stopped
...
if (has_totag() && is_method("INVITE"))
        media_fork_resume();
...

1.3.5.  media_exchange_from_uri(URI[, leg[, body[, headers[,
nohold]]]])

   Originates a call to the specified URI. The SDP in the response
   is fetched and pushed towards one of the call's legs, resulting
   in two way audio between the participant of the ongoing call,
   and the new call. By default, the other participant leg is put
   on hold.

   Can be called for an in-dialog request, such as a re-INVITE
   (for example when putting an entity on hold), or for an INFO
   request (triggered for example by a DTMF).

   Parameters:
     * URI (string) - destination used to originate the new call.
     * leg (string, optional) - the leg where the new media SDP
       will be pushed. Possible values are caller and callee. If
       missing, the module considers it is an hold re-INVITE, and
       exchanges the media SDP of the other leg.
     * body (string, optional) - custom body used for the
       generated INVITE. If missing, the body stored in the dialog
       associated with the involved leg will be used.
     * headers (string, optional) - optional headers added to the
       generated request.
     * nohold (integer, optional) - if set to true, the other
       participant will not be put on hold. This is useful when a
       new call will be generated for the other leg as well.

   This function can be used from any route.

   Example 1.6. Use media_exchange_from_uri() function to fetch
   media from a Media Server's call
...
if (has_totag() && is_method("INVITE") && is_audio_on_hold())
        media_exchange_from_uri("sip:moh@127.0.0.1:5080");
...

1.3.6.  media_exchange_to_call(callid[, leg[, nohold]])

   Pushes the SDP of a new call received in an existing proxied
   call, resulting in two-way audio between a Media Server that
   originated the call, and the existing participant of the
   ongoing proxied call.

   Parameters:
     * callid (string) - the identifier of the callid to exchange
       media.
     * leg (string) - the leg that will be streamed. Possible
       values are caller and callee.
     * nohold (integer, optional) - if set to true, the other
       participant will not be put on hold. This is useful when a
       new call will be generated for the other leg as well.

   This function can be used from REQUEST_ROUTE, BRANCH_ROUTE,
   FAILURE_ROUTE and ONREPLY_ROUTE.

   NOTE: the request of this call is completely handled by the B2B
   engine. Therefore, after running this function, please make
   sure you do not relay the message further, otherwise you will
   run into an unexpected behavior. Best thing to do is to exit
   the processing after running the function.

   Example 1.7. Use media_exchange_to_call() function to make an
   announcement
...
if (!has_totag() && is_method("INVITE") && $hdr(X-CallID) != NULL)
        media_exchange_to_call($hdr(X-CallID), "caller");
...

1.3.7.  media_terminate([leg[, nohold]])

   Terminates an ongoing media session exchange, whether the media
   is only streamed, or two way audio is flowing. If the
   participant leg is involved in a different media exchange, the
   current leg is put on hold.

   Parameters:
     * leg (string, optional) - the leg to terminate the media
       exchange. Possible values are caller and callee. If
       missing, the direction of the indialog request is used.
     * nohold (integer, optional) - if set to true, and the other
       participant is involved in a different media exchange, the
       current leg is no longer put on hold. Note: if the request
       that terminates the media exchange is a re-INVITE within
       the dialog, this function will not un-hold the other leg,
       as the re-INVITE itself should be relayed further to do
       that. This behavior can be changed by explicitly setting
       the nohold parameter

   This function can be used from any route.

   Example 1.8. Use media_terminate() function to terminate an
   announcement
...
if (has_totag() && is_method("INVITE") && !is_audio_on_hold())
        media_terminate();
...

1.3.8.  media_handle_indialog()

   Searches for an existing media session started for any leg, and
   if there is ongoing session found, it performs additional logic
   for handling that request. For example, if media has been
   started in forking mode, and the INVITE is for activating
   on-hold, then the function will also pause the forked stream.

   Depending on the return code of this function, one has to
   perform additional logic in the script. Possible return codes
   are:
     * 1 - indicates that the message has been handled, but
       there's no additional tasks to be performed in the script.
     * -1 - indicates that there is no ongoing media exchange or
       fork happening for that call, or that there was no
       additional logic to do for that request.
     * -2 - indicates that all additional handling of the request
       was performed, and that the request should not be forwarded
       to the user agent, but instead it should be dropped.
     * -3 - signals an internal error.

   This function can be used from REQUEST_ROUTE, BRANCH_ROUTE and
   ONREPLY_ROUTE.

   Example 1.9. Use media_terminate() function to terminate an
   announcement
...
if (has_totag() && loose_route()) {
        # handling sequential
        media_handle_indialog();
        switch ($rc) {
        case -2:
                drop;
        case -1:
                xlog("no ongoing media session for $ci!\n");
        case 1:
                break;
}
...

1.4. Exported MI Functions

1.4.1.  media_fork_from_call_to_uri

   MI command that has the same behavior as media_fork_to_uri(),
   only that the triggering is not script driven, but exterior
   driven. Useful for starting listening a call.

   Name: media_fork_from_call_to_uri

   Parameters
     * callid (string) - the callid of the dialog that will have
       its RTP streamed to the new call towards the Media Server
     * uri (string) - the destination URI of the new call
     * leg (string, optional) - indicates the participant leg that
       will have its RTP streamed in the new call. Possible values
       are “caller”, “callee” or “both”. If missing, both media
       streams are forked
     * headers (string, optional) - extra headers to add to the
       outgoing request
     * medianum (integer, optional) - the media stream that will
       be forked within the call. First index is 0. If missing,
       all media streams of that leg(s) are streamed.

   MI FIFO Command Format:
# start streaming a callid to record media server
opensips-cli -x mi media_fork_from_call_to_uri \
        callid=c6fdb0f9-47dc-495d-8d38-0f37e836a531 \
        uri=sip:record@127.0.0.1:5080

1.4.2.  media_exchange_from_call_to_uri

   MI command that has the same behavior as
   media_exchange_from_uri(), only that the triggering is not
   script driven, but exterior driven. Useful for injecting media
   announcements during a call.

   Name: media_exchange_from_call_to_uri

   Parameters
     * callid (string) - the callid of the dialog that will have
       it's leg mixed with the new call to the Media Server
     * uri (string) - the destination URI of the new call
     * leg (string) - indicates the participant that will have its
       media pined into the new call. Possible values are “caller”
       and “callee”.
     * headers (string, optional) - extra headers to add to the
       outgoing request
     * nohold (integer, optional) - if set to a non-zero value,
       the module avoids putting the other participant on hold
       when the media exchanging starts

   MI FIFO Command Format:
# start playing back an annoucement to caller
opensips-cli -x mi media_exchange_from_call_to_uri \
        callid=c6fdb0f9-47dc-495d-8d38-0f37e836a531 \
        uri=sip:announcement@127.0.0.1:5080 \
        leg=caller

1.4.3.  media_exchange_from_call_to_uri_body

   MI command that does the same thing as the
   media_exchange_from_call_to_uri MI function, but also allows
   you to specify a custom body in the outgoing request. The body
   has to be specified in the mandatory body parameter, all the
   other parameters being the same as the ones of
   media_exchange_from_call_to_uri.

1.4.4.  media_terminate

   MI command to terminate an ongoing media exchange.

   Name: media_terminate

   Parameters
     * callid (string) - the callid of the dialog that will have
       the media exchange terminated.
     * leg (string, optional) - the leg for whom to terminate the
       media exchange. Accepted values are caller, callee and
       both. If missing, all media sessions are terminated.
     * nohold (integer, optional) - if specified and has a
       non-zero value, the leg that is being terminated is not put
       on hold if the other participant still has an ongoing media
       session.

   MI FIFO Command Format:
# terminate a caller announcement
opensips-cli -x mi media_terminate \
        callid=c6fdb0f9-47dc-495d-8d38-0f37e836a531 \
        leg=caller

Chapter 2. Contributors

2.1. By Commit Statistics

   Table 2.1. Top contributors by DevScore^(1), authored
   commits^(2) and lines added/removed^(3)
                   Name               DevScore Commits Lines ++ Lines --
   1. Razvan Crainea (@razvancrainea)   113      47      5606     1178
   2. Vlad Patrascu (@rvlad-patrascu)    5        3       15       9
   3. Zero King                          3        1       1        1

   (1) DevScore = author_commits + author_lines_added /
   (project_lines_added / project_commits) + author_lines_deleted
   / (project_lines_deleted / project_commits)

   (2) including any documentation-related commits, excluding
   merge commits. Regarding imported patches/code, we do our best
   to count the work on behalf of the proper owner, as per the
   "fix_authors" and "mod_renames" arrays in
   opensips/doc/build-contrib.sh. If you identify any
   patches/commits which do not get properly attributed to you,
   please submit a pull request which extends "fix_authors" and/or
   "mod_renames".

   (3) ignoring whitespace edits, renamed files and auto-generated
   files

2.2. By Commit Activity

   Table 2.2. Most recently active contributors^(1) to this module
                   Name                 Commit Activity
   1. Razvan Crainea (@razvancrainea) Feb 2020 - Jun 2020
   2. Vlad Patrascu (@rvlad-patrascu) Mar 2020 - Apr 2020
   3. Zero King                       Mar 2020 - Mar 2020

   (1) including any documentation-related commits, excluding
   merge commits

Chapter 3. Documentation

3.1. Contributors

   Last edited by: Razvan Crainea (@razvancrainea).

   Documentation Copyrights:

   Copyright © 2020 www.opensips-solutions.com
