Recon Overview

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Overview[edit]

What is recon?[edit]

recon (Conversation Manager) is a SIP User Agent API that allows conversations and participants to be created. Participants can then be placed into conversations. Recon could be used to create the following types of applications:

  • Multi-line Phone
  • Conference Server
  • Media Server

In general all participants belonging to the same conversation can be heard and can hear each other. A participants contribution level to a particular conversation can be modified such that they appear quiter or louder to other participants.

There are three types of participants:

  1. Local participant - this participant type consists of the default local speaker and microphone of the computer that is running recon. Local participants are always only explicitly destroyed. Each application should only have one local participant created at startup time. This paricipant can be moved between/added to conversations as desired.
  2. Media participant - this participant type consists of an audio file, audio stream, or a tone being played out. Media participants are destroyed when the file is complete or when explicitly destroyed.
  3. Remote Participant - this participant type uses audio from an external source. The current implementation uses SIP to create/connect to remote participants. Remote participants are destroyed by the API user, or a "hangup" signal from the remote party.

A typical phone conversation consists of 3 components:

  • 1 conversation
  • 1 local participant
  • 1 remote participant.

recon currently uses the sipXtapi project as the RTP/codec/mixing library. It is responsible for processing incoming RTP packets to and from the reflow layer. The reflow project is then used to send RTP packets to the network. See the What is reflow? and What is sipXtapi? sections for information on these two projects.


What is reflow?[edit]

The flow manager is a layer that faciltates the flow of media to/from a media based application. It is responsible for any NAT traversal logic, and will eventually implement ICE as a NAT traversal solution. reflow uses the reTurn project for NAT traversal. The flow manager also implements SRTP encryption of RTP packets, and is capable of sending media via:

  • UDP
  • TURN UDP Allocation
  • TURN TCP Allocation with UDP relay
  • TURN TLS Allocation with UDP relay
  • SRTP encrypted over any of the above transports
  • DTLS-SRTP encrypted

For more details check out:


What is sipXtapi?[edit]

recon uses only the media framework portion of the LGPL licensed sipXtapi open source project. sipXtapi is full SIP User Agent SDK. It consists of a number of underlying libraries, that include a media framework, called sipXmediaLib that is capable, amongst other tasks, of the following:

  • RTP encoding and decoding
  • Codec encoding and decoding - including support for G.711A/u, AMR NB/WB, G.722, G.726, G.729, GSM FR, iLBC, Speex NB/WB/UWB, RFC4733 DTMFs
  • Media mixing capabilities (Bridge Mixer)
  • Packet Loss Concealment
  • Echo cancellation
  • Tone generation
  • Media file playback
  • PC/device Speaker and Microphone mixing

recon uses the sipXmediaAdapterLib, sipXmediaLib, sipXportLib, and sipXsdpLib projects to add the above capabilites.

For more details check out:

To view source code:

Initial Project Team[edit]

  • Rohan Mahy
  • Scott Godin ( s g o d i n AT s i p s p e c t r u m DOT c o m )


Key Features[edit]

  • Correct and comprehensive implementation of the relevant standards from the SIP working groups
  • Support for SIP signalling over UDP/TCP/TLS protocols over both IPv4 and IPv6
  • Asynchrounous client APIs
  • Sending media over TURN UDP/TCP/TLS allocations using a UDP relay
  • STUN binding discovery for SDP body
  • SRTP via SDES key negotiaion
  • SRTP via DTLS-SRTP key negotiation
  • Supported Codecs (via sipXtapi): G711u/a, GSM, iLBC, speex
  • Audio file memory cache
  • Target-Dialog support (draft-ietf-sip-target-dialog)
  • Auto-answer support
  • SIP Subcription support
  • Multi-Registration support with Digest Authentication
  • Bridge Mixing
  • Variable Participant Contribution Levels
  • Both In-dialog and Out-of-dialog REFER handling
  • Test console program (testUA)
  • SDP Media Capability Negotiation (draft-ietf-mmusic-sdp-capability-negotiation)
  • Single step transfers
  • Supervised transfers


Upcoming Features[edit]

  • Media layer abstraction interface - so that plugging in other media libraries is easier
  • TODO - more details here


How to Participate[edit]

Project Details[edit]

Working with recon[edit]


Current External Library Usage[edit]

  • recon uses the reflow project which has the following dependencies
    • OpenSSL - minimum version is 1.0.1 that is the first version to include DTLS-SRTP support
    • ASIO 1.2.0 or above (http://asio.sourceforge.net/) - recently tested with ASIO 1.4.8
    • BOOST 1.34.1 or above - recently tested with BOOST 1.53.0
    • libSrtp
  • sipXtapi
Note:  Using boost 1.53.0 that includes ASIO 1.4.8 was considered, but this adds 
       an extra requirement to build the boost system library.  Use of boost 1.35.0 
       (or above) and a standalone ASIO release allows us to use boost without needing
       to link with any boost libraries, thus making builds easier (especially on 
       Windows based platforms).

Licensing[edit]

recon is distributed under a standard 3-clause BSD license:

/* ====================================================================

Copyright (c) 2007-2008, Plantronics, Inc.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are 
met:

1. Redistributions of source code must retain the above copyright 
   notice, this list of conditions and the following disclaimer. 

2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution. 

3. Neither the name of Plantronics nor the names of its contributors 
   may be used to endorse or promote products derived from this 
   software without specific prior written permission. 

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

==================================================================== */

Also see the following applicable licenses for surrounding code: