Asterisk: The Definitive Guide

Leif Madsen first got involved with the Asterisk community when he was looking for a voice conferencing solution. Once he learned that there was no official Asterisk documentation, he co-founded the Asterisk Documentation Project. Leif is currently working as a consultant, specializing in Asterisk clustering and call-center integration. You can get more information at http://www.leifmadsen.com.

Jim Van Meggelen is President and CTO of Core Telecom Innovations, a Canadian-based provider of open-source telephony solutions. He has over fifteen years of enterprise telecom experience for such companies as Nortel, Williams and Telus, and has extensive knowledge of both legacy and VoIP equipment from manufacturers such as Nortel, Cisco, and Avaya. Jim is one of the principal contributors to the Asterisk Documentation Project, and is co-author of the bestselling O'Reilly book, Asterisk: The Future of Telephony.

Russell Bryant is the Engineering Manager for the Open Source Software team at Digium, Inc. He has been a core member of the Asterisk development team since the Fall of 2004. At the first AstriCon in 2004, he was named the release maintainer for Asterisk's first major release series, Asterisk 1.0. He has since contributed to almost all areas of Asterisk development, from project management to core architectural design and development.

Chapter 1 A Telephony Revolution
Asterisk and VoIP: Bridging the Gap Between Traditional and Network Telephony
Massive Change Requires Flexible Technology
Asterisk: The Hacker’s PBX
Asterisk: The Professional’s PBX
The Asterisk Community
The Business Case
Conclusion
Chapter 2 Asterisk Architecture
Modules
File Structure
The Dialplan
Hardware
Asterisk Versioning
Conclusion
Chapter 3 Installing Asterisk
Installation Cheat Sheet
Distribution Installation
Software Dependencies
Downloading What You Need
How to Install It
Base Configuration
Updating Asterisk
Common Issues
Upgrading Asterisk
Conclusion
Chapter 4 Initial Configuration Tasks
asterisk.conf
modules.conf
indications.conf
musiconhold.conf
Additional Configuration Files
Conclusion
Chapter 5 User Device Configuration
Telephone Naming Concepts
Hardphones, Softphones, and ATAs
Configuring Asterisk
Digium Phones with Asterisk
Loading Your New Channel Configurations
Testing to Ensure Your Devices Have Registered
Analog Phones
A Basic Dialplan to Test Your Devices
Under the Hood: Your First Call
Conclusion
Chapter 6 Dialplan Basics
Dialplan Syntax
A Simple Dialplan
Building an Interactive Dialplan
Conclusion
Chapter 7 Outside Connectivity
The Basics of Trunking
Fundamental Dialplan for Outside Connectivity
PSTN Circuits
VoIP
Emergency Dialing
Conclusion
Chapter 8 Voicemail
Comedian Mail
Dialplan Integration
Storage Backends
Using Asterisk as a Standalone Voicemail Server
Database Integration
Conclusion
Chapter 9 Internationalization
Devices External to the Asterisk Server
PSTN Connectivity, DAHDI, Digium Cards, and Analog Phones
Asterisk
Conclusion—Easy Reference Cheat Sheet
Chapter 10 Deeper into the Dialplan
Expressions and Variable Manipulation
Dialplan Functions
Conditional Branching
Macros
GoSub
Local Channels
Using the Asterisk Database (AstDB)
Handy Asterisk Features
Conclusion
Chapter 11 Parking, Paging, and Conferencing
features.conf
Overhead and “Underchin” Paging (a.k.a. Public Address)
Advanced Conferencing
Conclusion
Chapter 12 Internet Call Routing
DNS and SIP URIs
ENUM and E.164
ISN, ITAD, and freenum.org
Security and Identity
Conclusion
Chapter 13 Automatic Call Distribution (ACD) Queues
Creating a Simple ACD Queue
Queue Members
The queues.conf File
The agents.conf File
Advanced Queues
Queue Statistics: The queue_log File
Conclusion
Chapter 14 Device States
Device States
Extension States
SIP Presence
Using Custom Device States
Distributed Device States
Shared Line Appearances
Creating a Callback Service
Conclusion
Chapter 15 The Automated Attendant
An Auto Attendant Is Not an IVR
Designing Your Auto Attendant
Building Your Auto Attendant
Conclusion
Chapter 16 Relational Database Integration
Installing and Configuring PostgreSQL and MySQL
Installing and Configuring ODBC
Managing Databases
Powering Your Dialplan with func_odbc
A Gentle Introduction to func_odbc
Getting Funky with func_odbc: Hot-Desking
Using Realtime
Storing Call Detail Records (CDR)
ODBC Voicemail Message Storage
Database Integration of ACD Queues
Conclusion
Chapter 17 Interactive Voice Response
What Is IVR?
Components of an IVR
IVR Design Considerations
Asterisk Modules for Building IVRs
A Simple IVR Using CURL
A Prompt-Recording Application
Speech Recognition and Text-to-Speech
Conclusion
Chapter 18 External Services
Calendar Integration
Voicemail IMAP Integration
Using XMPP (Jabber) with Asterisk
Out-of-Band Messaging (Messaging Infrastructure)
LDAP Integration
Text-to-Speech Utilities
Conclusion
Chapter 19 Fax
What Is a Fax?
Ways to Handle Faxes in Asterisk
spandsp
Digium Fax For Asterisk
Incoming Fax Handling
Outgoing Fax Handling
Fax Pass-Through
Conclusion
Chapter 20 Asterisk Manager Interface (AMI)
Quick Start
Configuration
Protocol Overview
Call Files
Example Usage
Development Frameworks
Interesting Applications
Conclusion
Chapter 21 Asterisk Gateway Interface (AGI)
Quick Start
AGI Variants
AGI Communication Overview
Example: Account Database Access
Development Frameworks
Conclusion
Chapter 22 Clustering
Traditional PBXs
Hybrid Systems
Pure Asterisk, Nondistributed
Asterisk and Database Integration
Asterisk and Distributed Device States
Multiple Queues, Multiple Sites
Conclusion
Chapter 23 Distributed Universal Number Discovery (DUNDi)
How Does DUNDi Work?
The dundi.conf File
Configuring Asterisk for Use with DUNDi
Conclusion
Chapter 24 System Monitoring and Logging
logger.conf
Call Detail Records
CEL (Channel Event Logging)
SNMP
Conclusion
Chapter 25 Web Interfaces
Flash Operator Panel
Queue Status and Reporting
Call Detail Records
A2Billing
Conclusion
Chapter 26 Security
Scanning for Valid Accounts
Authentication Weaknesses
Fail2ban
Encrypted Media
Dialplan Vulnerabilities
Securing Asterisk Network APIs
IAX2 Denial of Service
Other Risk Mitigation
CLI Permissions
Resources
Conclusion—A Better Idiot
Chapter 27 Asterisk: A Future for Telephony
The Problems with Traditional Telephony
Paradigm Shift
The Promise of Open Source Telephony
The Future of Asterisk

Appendix Understanding Telephony
Analog Telephony
Digital Telephony
The Digital Circuit-Switched Telephone Network
Packet-Switched Networks
Conclusion
Appendix Protocols for VoIP
The Need for VoIP Protocols
VoIP Protocols
Codecs
Quality of Service
Echo
Asterisk and VoIP
VoIP Security
Conclusion
Appendix Preparing a System for Asterisk
Server Hardware Selection
Environment
Telephony Hardware
Types of Phones
Linux Considerations
Conclusion
Colophon