This document provides an introduction to FreeSWITCH, an open source communications platform. It discusses IP telephony systems and what FreeSWITCH is. The document outlines FreeSWITCH's functions and architecture, including important modules like endpoints, dialplans and applications. It describes FreeSWITCH fundamentals like its threaded model and dynamic modules. Finally, it gives examples of PBX applications and provides a brief history of FreeSWITCH development.

1. Introduction to FreeSWITCH
Stanley Wu (吳建澄)
skyeyester@gmail.com
Mar. 04, 2016

2. Outline
• IP Telephony System Overview
• What is FreeSWITCH?
• FreeSWITCH Functions
• FreeSWITCH Architecture
• FreeSWITCH Fundamentals
• PBX Applications
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3. IP Telephony System Overview
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Internet
Enterprise
Communication
Service Vender
User
Network
Operator
Private Branch
Exchange
System

4. IP Telephony System Overview
• Deep in Private Branch Exchange (PBX) System
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Internet
Gateway
PSTN/ISDN
Analog
Gateway
IP Phone
Analog
Phone
Fax
Internal Network
PBX System
SIP Trunk
Gateway
Analog
Gateway
Database
IVR
PBX
Conference
Voice Mail

5. What is FreeSWITCH?
• FreeSWITCH™ is an open source
communications platform, licensed under the
MPL(Mozilla Public License)
• FreeSWITCH was created in 2006 to fill the
void left by proprietary commercial solutions
• Designed to be modular, scalable and stable
• FreeSWITCH current released version is 1.6
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6. FreeSWITCH Functions
• PBX Server (Transcoding B2BUA)
• IVR & Announcement Server
• Conference Server
• Voicemail Server
• Fax Server
• Session Border Controller
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7. FreeSWITCH Architecture
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8. FreeSWITCH Architecture
• Important modules: Endpoint, Dialplan and
Application
• Endpoint
– The primary role of endpoint is to take certain
common communication technologies and
normalize them into a common abstract entity
which we refer to as a session.
– A session represents a connection between
FreeSWITCH and a particular protocol
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9. FreeSWITCH Architecture
• Important modules: Endpoint, Dialplan and
Application
• Dialplan
– Dialplan is designed to lookup list of instructions
from the central XML registry within FreeSWITCH.
– The XML registry will parse a series of XML
extension objects using regular expression pattern
matching
– The extension object is selected based on the
configuration data for the calling Endpoint.
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10. FreeSWITCH Architecture
• Important modules: Endpoint, Dialplan and Application
• Application
– Each instruction defined in the dialplan for an extension
object is added to the session in the form of an application
name and data argument that will be passed to that
application.
– Example of application:
• Set: configure extension parameter
• Bridge: bridge a new channel to the existing one
• Answer: answer the call for a channel
• Hangup: hangup a current channel
• Ivr: run an IVR menu
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11. FreeSWITCH Architecture
• Example extension in a dialplan
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• In this scenario the Endpoint module turned SIP into a FreeSWITCH session and
the dialplan module turned XML into an extension.
• The bridge application will connect the call to the endpoint/channel defined as argument of
data in the application.
• Simply an incoming call for 1001 will be send to the sipendpoint/1001 to reach the actual
phone

12. FreeSWITCH Fundamentals (1/2)
• Threaded Model (Parallel Operations)
– Every connection has its own thread.
– Sub-systems run in background threads.
– Event handlers push events into threads.
• Stable Protected Core
– Critical data structures are opaque.
– Complicated code is all in one place.
– Complicated routines get maximum reuse.
– Higher level code cannot be misused.
– With each new level of API the power increases as the
complexity decreases.
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13. FreeSWITCH Fundamentals (2/2)
• Dynamic Modules to Extend Functionality
– FreeSWITCH API interface allows the addition of commands that can be accessed remotely.
– Application interface allows creation of custom IVRs and call routing apps.
– XML interface allows real-time dynamic access for user directory and configuration.
– Endpoint interface connects IM and phones.
– Formats, Automated Speech Recognition (ASR) & Text-to-Speech (TTS)
• Detailed Event and Logger System
– Events are fired whenever something significant happens.
– Detailed logging makes debugging easier.
– External applications can bind to events and track the status of the entire system.
• Hooks into Everything
– Embedded languages simplify the API even more.
– Same principle as the CGI / Web server.
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14. PBX Application (1/2)
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15. PBX Application (2/2)
• Intercom (Doorphone)
• Public Address System
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16. Reference
• FreeSWITCH Offical Website
– https://freeswitch.org/
• Open Source Software Lab
– http://www.osslab.org.tw/VoIP/IP_PBX
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17. Q&A
Thanks for your Listening
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18. FreeSWITCH Development History
• History
– 2006, the FreeSWITCH project was first announced at
O'Reilly Media's ETEL Conference
– 2008, FreeSWITCH's first official 1.0.0 release (Phoenix)
– 2012, FreeSWITCH development team had adopted
separate stable (version 1.2) and development (version 1.3)
branches
– 2014, released FreeSWITCH 1.4, the first version support
SIP over Websocket and WebRTC
– 2015, released FreeSWITCH 1.6, the first version that
supports video transcoding and video conferencing
• Developer
– Lead designer, Anthony Minessale
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