Asterisk: The Definitive Guide: Open Source Telephony for the Enterprise

Description

Design a complete Voice over IP (VoIP) or traditional PBX system with Asterisk, even if you have only basic telecommunications knowledge. This bestselling guide makes it easy with a detailed roadmap that shows you how to install and configure this open source software, whether you’re upgrading your existing phone system or starting from scratch. Ideal for Linux administrators, developers, and power users, this updated fifth edition shows you how to set up VoIP-based private telephone switching systems within the enterprise. You’ll get up to speed on the features in Asterisk 16, the latest long-term support release from Digium. This book also includes new chapters on WebRTC and the Asterisk Real-time Interface (ARI). • Discover how WebRTC provides a new direction for Asterisk • Gain the knowledge to build a simple but complete phone system • Build an interactive dialplan, using best practices for Asterisk’s advanced features • Learn how ARI has emerged as the API of choice for interfacing web development languages with Asterisk Copyright Table of Contents Foreword Joshua Colp (Senior Software Developer, Sangoma/Digium) Dan Jenkins (Founder, Nimble Ape Ltd) Joyce Wilmot (Senior Web Developer) Matt Florell (Founder, VICIdial) Matt Fredrickson (Director of Asterisk Engineering, Sangoma/Digium) Preface Audience Software Conventions Used in This Book O’Reilly Online Learning How to Contact Us Acknowledgments from Jim Van Meggelen Chapter 1. A Telephony Revolution Asterisk and VoIP: Bridging the Gap Between Traditional and Network Telephony The Zapata Telephony Project Massive Change Requires Flexible Technology Asterisk: The Hacker’s PBX Asterisk: The Professional’s PBX The Asterisk Community Asterisk’s Discourse-Based Community Site The Asterisk Mailing Lists Asterisk Wiki Sites The IRC Channels Conclusion Chapter 2. Asterisk Architecture Modules Applications Bridging Modules Call Detail Recording Modules Channel Event Logging Modules Channel Drivers Codec Translators Format Interpreters Dialplan Functions PBX Modules Resource Modules Add-on Modules Test Modules File Structure Configuration Files Modules The Resource Library The Spool Logging The Dialplan Hardware Asterisk Versioning Conclusion Chapter 3. Installing Asterisk Linux Installation Choosing Your Platform VirtualBox Steps Linux (OpenStack) Host Dependencies Asterisk Installation Download and Prerequisites Compiling and Installing Initial Configuration SELinux Tweaks Firewall Tweaks Final Tweaks Validating Your New Asterisk System Common Installation Errors Some Final Configuration Notes Sample Configuration Files for Future Reference The Asterisk Shell Command safe_asterisk Conclusion Chapter 4. Certificates for Endpoint Security The Inconvenience of Security Securing SIP Subscriber Names Secure SIP Signaling Securing Media Encrypted RTP Conclusion Chapter 5. User Device Configuration Telephone Naming Concepts Hardphones, Softphones, and ATAs Configuring Asterisk How Channel Configuration Works with the Dialplan chan_pjsip Testing to Ensure Your Devices Have Registered A Basic Dialplan to Test Your Devices Under the Hood: Your First Call Conclusion Chapter 6. Dialplan Basics Dialplan Syntax Contexts Extensions Priorities Applications The Answer(), Playback(), and Hangup() Applications A Basic Dialplan Prototype A Simple Dialplan Hello World Building an Interactive Dialplan The Goto(), Background(), and WaitExten() Applications Handling Invalid Entries and Timeouts Using the Dial() Application Using Variables Pattern Matching Includes Conclusion Chapter 7. Outside Connectivity The Basics of Trunking Fundamental Dialplan for Outside Connectivity The PSTN Traditional PSTN Trunks VoIP Network Address Translation PSTN Termination and Origination Configuring SIP Trunks Emergency Dialing Conclusion Chapter 8. Voicemail The voicemail.conf File An Initial voicemail.conf File The [general] Section The [zonemessages] Section Mailboxes Voicemail Dialplan Integration The VoiceMail() Dialplan Application The VoiceMailMain() Dialplan Application Standard Voicemail Keymap Creating a Dial-by-Name Directory Voicemail to Email Voicemail Storage Backends Linux Filesystem IMAP Message Storage in a Database Conclusion Chapter 9. Internationalization Devices External to the Asterisk Server PSTN Connectivity, DAHDI, Digium Cards, and Analog Phones DAHDI Drivers Internationalization Within Asterisk Caller ID Language and/or Accent of Prompts Time/Date Stamps and Pronunciation Conclusion—Easy Reference Cheat Sheet Chapter 10. Deeper into the Dialplan Expressions and Variable Manipulation Basic Expressions Operators Dialplan Functions Syntax Examples of Dialplan Functions Conditional Branching The GotoIf() Application Time-Based Conditional Branching with GotoIfTime() GoSub Defining Subroutines Returning from a Subroutine Local Channels Using the Asterisk Database Storing Data in the AstDB Retrieving Data from the AstDB Deleting Data from the AstDB Using the AstDB in the Dialplan Handy Asterisk Features Conferencing with ConfBridge() Handy Dialplan Functions CALLERID() CHANNEL() CURL() CUT() IF() and STRFTIME() LEN() REGEX() STRFTIME() Conclusion Chapter 11. PBX Features, Including Parking, Paging, and Conferencing features.conf The [general] Section The [featuremap] Section The [applicationmap] Section Application Map Grouping Parking and Paging Call Parking Paging (aka Public Address) Places to Send Your Pages Zone Paging Advanced Conferencing Video Conferencing Conclusion Chapter 12. Automatic Call Distribution Queues Creating a Simple ACD Queue Queue Members Controlling Queue Members via the CLI Defining Queue Members in the queue_members Table Controlling Queue Members with Dialplan Logic Automatically Logging Into and Out of Multiple Queues Advanced Queues Priority Queue (Queue Weighting) Queue Member Priority Changing Penalties Dynamically (queuerules) Announcement Control Overflow Using Local Channels Queue Statistics: The queue_log File Conclusion Chapter 13. Device States Device States Checking Device States Extension States Using the hint Directive Hints Checking Extension States SIP Presence Using Custom Device States Conclusion Chapter 14. The Automated Attendant An AA Is Not an IVR Designing Your AA The Greeting The Main Menu Timeout Invalid Dial by Extension Building Your AA Recording Prompts The Dialplan Delivering Incoming Calls to the AA IVR Conclusion Chapter 15. Relational Database Integration Your Choice of Database Managing Databases Troubleshooting Database Issues SQL Injection Powering Your Dialplan with func_odbc A Gentle Introduction to func_odbc Getting Funky with func_odbc: Hot-Desking Using Realtime Static Realtime Dynamic Realtime Storing Call Detail Records Database Integration of ACD Queues Storing Dialplan Parameters for a Queue in a Database Writing queue_log to Database Conclusion Chapter 16. Introduction to Interactive Voice Response Components of an IVR IVR Design Considerations Asterisk Modules for Building IVRs CURL() func_odbc AGI AMI ARI A Simple IVR Using CURL() The Dialplan A Prompt-Recording IVR Function Speech Recognition and Text-to-Speech Text-to-Speech Speech Recognition Conclusion Chapter 17. Asterisk Manager Interface and Call Files Call Files Your First Call File Notes About Call Files AMI Quick Start AMI over TCP AMI over HTTP Configuration manager.conf http.conf Protocol Overview Message Encoding AMI over HTTP Example Usage Originating a Call Redirecting a Call Development Frameworks Conclusion Chapter 18. Asterisk Gateway Interface Quick Start AGI Variants Process-Based AGI FastAGI—AGI over TCP Async AGI—AMI-Controlled AGI AGI Communication Overview Setting Up an AGI Session Commands and Responses Ending an AGI Session Example: Account Database Access Development Frameworks Conclusion Chapter 19. Asterisk REST Interface ARI Quick Start Basic Asterisk Configuration Testing Your Basic ARI Environment Working with Your ARI Environment Using Swagger The Building Blocks of ARI REST WebSocket Stasis Frameworks ari-py (and aioari) for Python node-ari-client AsterNET.ARI ari4java phpari aricpp asterisk-ari-client Conclusion Chapter 20. WebRTC The Browser as a Telephone Preliminary Knowledge Configuring Asterisk for WebRTC Cyber Mega Phone More About WebRTC Conclusion Chapter 21. System Monitoring and Logging logger.conf Reviewing Asterisk Logs Logging to the Linux syslog Daemon Verifying Logging Log Rotation Call Detail Records CDR Contents Dialplan Applications cdr.conf Backends Example Call Detail Records Caveats Channel Event Logging Conclusion Chapter 22. Security Scanning for Valid Accounts Authentication Weaknesses Fail2ban Installation Configuration Encrypted Media Dialplan Vulnerabilities Securing Asterisk Network APIs Other Risk Mitigation Resources Conclusion—A Better Idiot Chapter 23. Asterisk: A Future for Telephony The Telephone Is Dead (Except When It’s Not) Communications Overload The Problems with Open Source Development The Future of Asterisk WebRTC The Future of Telephony Index About the Authors Colophon