Asterisk 1.4 : The Professional’s Guide

Table of Contents

Asterisk 1.4

Credits

Foreword

About the Authors

About the Reviewers

Preface

Reviewing the basics

No compromise

What this book covers

Onwards

Conventions

Reader feedback

Customer support

Downloading the example code for the book

Errata

Piracy

Questions

1. The Dialplan

Dialplan location

Extensions and contexts

Pattern matching

Why use contexts?

Call barring made simple

Time and day call routing

Variables

Inheritance of channel variables through the dialplan

Using the AstDB

Dialplan features and additions

func_devstate

What can we use the DEVSTATE() function for?

Outgoing trunk selection

Calling extensions

Setting lights

Boosting outgoing call capacity

Using multiple broadband lines

Configuration overview

Setting up the routing in Linux

Configuring Asterisk

Explanation of the macro

Downsides

System() application

Summary

2. Network Considerations when Implementing Asterisk

Centralized and distributed installations

Centralized installations

Distributed solutions

Latency and jitter

Jitterbuffer

Echo

Do your homework

SLAs are for everyone

Achieving the goal

Backups

To share or not to share

Ensuring quality

When things go wrong

Red

Amber

Green

Increasing resilience

Summary

3. Call Routing with Asterisk

Routing methods

Where to start

Internal calls

Local calls

National calls

International calls

Alternative options

ENUM

DUNDi

Types of routing

Routing techniques

Summary

4. Call Centers—Queues and Recording

Asterisk queues

Queue gotchas

A practical queue

Using queues to cascade calls

Call recording—the issues

Show-stoppers

VoIP recording approaches

Impact of VoIP on recording systems

Hardware convergence

Distributed call centers

Home working

VoIP recording challenges

Routing

Bandwidth

Encryption

Solutions

Asterisk call center solutions

How VICIDIAL works

Handling inbound calls

Installation

Timing sources

Scalability

Summary

5. Asterisk and Speech Technology

Why speech-enable?

Types of speech technologies

Automatic Speech Recognition (ASR)

Isolated Word Recognition

Connected Word Recognition

Natural Language Recognition

Text-to-Speech (TTS)

Speaker Verification and Identification (SVI)

MRCP

Implementation considerations

ASR and Asterisk

Installing LumenVox speech recognition with Asterisk

Checking that things are working

SpeechCreate()

SpeechLoadGrammar (yesno,/etc/lumenvox/Lang/BuiltinGrammars/ABNFBoolean.gram)

SpeechActivateGrammar(yesno)

SpeechBackground(beep)

Verbose(1,Result was ${SPEECH_TEXT(0)})

Verbose(1,Confidence was ${SPEECH_SCORE(0)})

SpeechStart()

SpeechDeactivateGrammar(label)

SpeechUnloadGrammar(label)

SpeechDestroy()

${SPEECH(results)}

Grammar files

Implementation advice for ASR

TTS with Asterisk

Implementation advice for TTS

Summary

6. Call Accounting and Billing

Call Data Records (CDRs)

CDR frontends

Call accounting

Providing termination billing

Every little helps

Selecting a billing platform

Introducing A2Billing

Reasons to consider A2Billing

A2Billing requirements

Monitoring usage

Coding for A2Billing

Billing gotcha!

High call volumes

Other high-call-volume solutions

SER/OpenSER

FreeSWITCH

Summary

7. Resilience and Stability

Increasing availability

Stability

Network

Cables

Switches and routers

Endpoints

Telephony switches and gateways

Server

Environment

Dealing with failure

Network resilience

Server

High availability

Ultra Monkey

Telephony switches/gateways

Redfone foneBRIDGE2

Junghanns ISDNguard

Endpoints

Round robin DNS

Say hello to Rsync

Limiting the number of calls per server

Summary

8. Localization and Practical Security

Tones

Time and date and localization

Changing the language of system prompts

Local telephony interfaces

Analog

Digital

Localizing caller ID signaling on Digium analog interfaces

Checklist

Practical security

Out of hours

Summary

9. Interfacing with Traditional Analog and Digital Telephony

Analog

Digital

ISDN BRI (Basic Rate Interface)

ISDN PRI (Primary Rate Interface)

Choices, choices

Using external adaptors

Using cards

Installing a Digium card

Card installation—physical

Installing the DAHDI software

Configuring the DAHDI files to enable the card

What about the other cards?

framing

coding

Troubleshooting with Digium cards

Summary

10. Integrating Asterisk with Wireless Technologies

Why integrate Asterisk with wireless technologies?

Wireless technology overview

Wi-Fi (only) phones

SIP desk phones with a wireless link

Dual-mode (GSM and SIP) phones and PDA/smart phones

SIP/DECT phones

Connecting Asterisk to mobile networks

Why connect to mobile networks?

The GSM gateway (box)

The GSM card

Configuring wireless devices

Configuring Asterisk to work with wireless technologies

Deployment choices

Neat money saving tricks

Calling a mobile phone

Avoiding those nasty roaming charges that arise from receiving calls

Summary

11. Graphical User Interfaces

Reasons for going GUI

Good to GUI

Ease of administration

Access to enhanced features

Easier upgrade process

Standardized code

GUI, phooey!

Performance

Stability

Restricted functions

FreePBX

How it works

Installation

Configuration

Extensions

Inbound routes

Outbound routes

Trunks

Other records

Summary

A. Selling Your Solution

In the beginning ...

Drivers for changing phone systems

A word on cost

Generating interest

Alliances

Advertising

Search engines

Become an expert

Relationship marketing

Email as a marketing tool

Tracking prospects

Converting the prospect into a sale

Determining your customer's hardware requirements

Choosing the right phones

Tales of woe

Aastra

Linksys

Siemens Gigaset IP DECT phones

Snom M3

Remote support

Make it secure

Do's and don'ts

The do's

First impressions

Get brochures printed

Take notes

Send the quote in a timely manner

Follow up the quote

Target the decision makers, but don't ignore IT

The don'ts

You don't need a fancy office

Don't cut corners on the solution

Don't under price

Don't have a huge margin on handsets

Don't supply a PC as the phone server

Summary

B. Sample Email Content

What is VoIP?

Why should I consider VoIP?

Cost savings

Call costs

Line rental costs

Wiring costs

Reduced infrastructure costs

Centralized management

System integration

Unified messaging

Reliability

Closed and open systems

Superior sound

Fallback solutions

Broadcasting calls

A number for life

Number porting

Local numbers

About XYZ

Our philosophy

Our passion

C. Sample Appointment Sheet

Index

Asterisk 1.4

The Professional's Guide

Colman Carpenter

Ian Plain

David Duffett

Nik Middleton

Asterisk 1.4

The Professional's Guide

Copyright © 2009 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the authors, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: August 2009

Production Reference: 1030809

Published by Packt Publishing Ltd.

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ISBN 978-1-847194-38-1

www.packtpub.com

Cover Image by Vinayak Chittar (<[email protected]>)

Credits

Authors

Colman Carpenter

David Duffett

Nik Middleton

Ian Plain

Reviewers

Ian Plain

Jared Smith

Philippe Lindheimer

Acquisition Editor

James Lumsden

Technical Editors

Gagandeep Singh

Charumathi Sankaran

Indexer

Rekha Nair

Editorial Team Leader

Gagandeep Singh

Project Team Leader

Lata Basantani

Project Coordinator

Neelkanth Mehta

Proofreader

Laura Booth

Production Coordinator

Aparna Bhagat

Cover Work

Aparna Bhagat

Foreword

Watching Asterisk move from being a personal coding project to a community of tens of thousands of programmers and millions of users has been quite the ride so far! Asterisk is only now hitting its prime, and there are so many more things that creative people are going to do with the code. The growth of the project over the years has stunned and pleased me, and it's amazing that well-written and comprehensive books like this now exist to help more advanced users navigate the waters of larger and more complex Asterisk installations. Asterisk installations are now huge, both in numbers of locations and the unimaginably large size of many of those locations—thousands or tens of thousands of users! Asterisk implementations are rarely limited by the capability of the software but more often by not knowing how to utilize it. Books like this play an important role in getting the experience of those who have already done in the hands of those who want to do.

Hopefully the knowledge here allows you to continue your adventure with Asterisk, moving from the basics of PBX construction to having the ability to quickly implement advanced call logic processes and work with the more exotic telephony and VoIP interfaces. The motto of There's more than one way to do it! is almost always true with Asterisk—this book seems to contain an excellent cross-section of at least one of those ways to do it (whatever it happens to be for your application) and you'll quickly think of many other ways once you've mastered the methods shown.

The authors here have really shown some excellent detailed explanations of how to use Asterisk, and I hope this provides the incentive for you, the reader, to experiment in more wide-ranging ways with Asterisk once you've understood the basics. Most of the Asterisk community has learned with hands-on experimentation, and it's great to see more encouragement of this type of learning as is contained in these pages. Kudos to the authors, especially David Duffett, who has been involved with Asterisk for so long and has taught so many people their first dialplan routines (and hopefully has left them uninjured from his famous habit of throwing candy at people who give correct answers in class or in his talks).

Soon you'll be doing least-cost-routing, integrating your instant messenger system with your mobile phone calls, controlling robots with voice commands via your phone, or dreaming up a new company based on some voice-based service that nobody has tapped into yet. And the best thing about Asterisk is that it remains open source—if you come up with a feature or enhancement that you think must be in Asterisk, then the good news is that it can be! Become a member of the Asterisk community, and your contributed code could be included. We all anxiously await your book, your product, or just your involvement with the Asterisk community.

Mark Spencer

Chairman and CTO of Digium

About the Authors

Colman Carpenter is the MD of Voicespan, a Kent-based company that offers Asterisk-based systems to the SME market across the UK. He is an IT professional of over 20 years standing, with experience in diverse areas such as IBM mid-range software development, Lotus Notes and Domino consultancy, Data Management, E-marketing consultancy, IT Management, Project Management, Wordpress Website Design, and lately, Asterisk consultancy. He is a qualified PRINCE2 practitioner.

Voicespan (http://www.voicespan.co.uk) offers Asterisk-based systems as the cornerstone of a holistic VoIP-telephony service for SMEs. They offer companies a one-stop shop for implementing a VoIP-capable system, encompassing Asterisk-based systems, endpoints, trunks, telephony interfaces and network equipment, and the consultancy necessary to bring it all together into a coherent whole. This is his first book.

I would like to thank my wife, Hazel, and daughters, Caiti and Fay, for their support during the writing of this book. At times it seemed like you believed more than I in my ability to do so!

David Duffett delivers Asterisk training and consultancy around the world through his own company (TeleSpeak Limited, www.telespeak.co.uk), in addition to designing and delivering training for a number of companies, including Digium, Inc.

A keen Asterisk enthusiast, David also enjoys podcasting, radio presenting, and teaching public-speaking skills. He is a Chartered Engineer with experience in fields including Air Traffic Control communications, Wireless Local Loop, Mobile Networks, VoIP, and Asterisk. David has been in the telecoms sector for nearly 20 years and has had a number of computer telephony, VoIP, and Asterisk articles published through various industry publications and web sites.

Nik Middleton has been in wide-area communications since the mid-eighties. He spent most of the nineties working in the US, where he developed a shareware Microsoft mail to SMTP/POP3 connector that sold some 287,000 copies. He spent six years working for DuPont in VA, developing remote monitoring systems for their global Lycra business. In late 2000, he returned to the UK where he held various senior positions in British Telecom, LogicaCMG, and Computer Science Corp.

In 2005, tired of working in London, he set up his own company (Noble Solutions) providing VoIP solutions in rural Devon, where he now lives with his wife Georgina and three children, Mathew, Vicky, and Isabel. A keen amateur pilot, his favorite place when not in the office is flying over the beautiful Devon countryside.

Ian Plain has worked in the telecoms industry since 1981 and has designed some of the largest PBX networks in the UK. Since the late 1990s, he has been involved with VoIP initially for links between systems, and with IP PBX systems since 1999. Since 2003, he has been running a telecoms consultancy based near Bath in the UK, working primarily on high-availability Asterisk-based solutions for corporate customers.

About the Reviewers

Ian Plain: Please see the entry in About the Authors.

Jared Smith is the Training Manager for Digium, Inc. As a long time Asterisk user, contributor, and evangelist, he has spent the last several years helping the Asterisk community. Jared is a dynamic and knowledgeable instructor with several years of experience in leading various Asterisk training classes.

He is also co-author of Asterisk: The Future of Telephony, O'Reilly Media and regularly writes other Asterisk documentation as well.

Jared holds a Bachelors of Science degree in Computer Engineering from the Utah State University and currently lives in Virginia with his wife and two children.

Philippe Lindheimer is the project leader and primary developer of FreePBX and serves as the Open Source Community Director at Bandwidth.com, the corporate sponsor of the FreePBX project (the most widely deployed Asterisk-based PBX/GUI open-source application in the world). He cofounded and runs the Open Telephony Training Seminar providing FreePBX/Asterisk technical and marketing training to resellers and end users. Originally with Hewlett Packard, he has been in the engineering industry for over two decades, working on a range of technical consulting roles with many Fortune 500 Companies.

He has a BS (Hons) in EE/CS from the University of Colorado, Boulder. He now lives in the Seattle, WA area.

Preface

This book is a sequel to Building Telephony Systems with Asterisk, which started you on a journey to the summit of Asterisk knowledge, taking you from base camp to camp two, from being a complete Asterisk newbie to a competent telephony system builder and manager. Now it's time to push to the top, to take your telephony knowledge to a point where you can build high-performance, resilient, and professional PBXs using the most popular open source telephony software in the world—Asterisk.

In that book, the focus was very much on installing and configuring Asterisk for a number of common scenarios, including both home and office use. This it achieved admirably, so you may now wonder why another book is needed. Well, there are three main reasons for writing this book. Firstly, Asterisk is such a highly-capable and configurable telephony engine that the 150-odd pages in the book necessarily had to exclude discussion of some of the more advanced features, which we now have the opportunity to explore. Secondly, Asterisk is invariably implemented as part of an IP network, and further examination of network considerations is warranted. Finally, like all popular open source software, Asterisk is constantly being updated, and while this book still assumes the version 1.4 of Asterisk is in use, we do point out any differences in version 1.6 where relevant, such as the change from Zaptel to DAHDI.

Therefore, the goal of this book is to give you enough knowledge to build and install a telephony system with Asterisk at its core, which will stand comparison with the market-leading commercial IP-enabled systems. Whether you are building such a system as a result of an internal company requirement, or you plan to offer it as an element of a commercial package to customers, this book will take you through all the areas that require consideration. On reading this book you will also be in a position to understand the real-life issues you are likely to experience when deploying such a system, both technical and otherwise.

By its very nature, Asterisk demands that much of the focus of this book be on the technical aspects of building your professional system. However, as with most IT implementations, success will also rely on soft issues such as managing expectations, understanding and meeting the customer's particular needs, and ensuring delivery is on time and up to the budget. Hence, where appropriate, we make mention of the non-technical aspects that may make a difference to your deployment.

To achieve our goal, this book will build on knowledge already gained by reinforcing that learning and adding extra skills covering:

Security

Networks

Large-scale considerations

Resilience

Scalability

Integration with complementary products

Commercial aspects

Reviewing the basics

If you have not already done so, it is recommended that you read Building Telephony Systems with Asterisk, or achieve a good degree of competence in building basic Asterisk PBXs through other means. These could include commercial training courses (see www.digium.com/en/training for further details) or openly available internet resources such as the excellent VoIP wiki at http://www.voip-info.org.

While most people with a day-to-day exposure to Asterisk systems should stand to gain much from this book, it has been written in the expectation that you will possess the following Asterisk skills and experience, ideally gained through text file configuration:

Connecting Asterisk to analogue and digital PSTN lines, and VoIP services

Configuring different types of terminal equipment (phones, communication devices, other PBXs)

Installing Asterisk, Zaptel and LibPRI

Configuring features (Voicemail, Music On Hold, Queues, Conference Rooms, and so on)

Creating a dialplan, including call distribution

CDRs, call monitoring and recording

Backups and restores

Basic security and load balancing

Once equipped with this knowledge you stand to gain the maximum from the topics covered in this book, enabling you to build professional Asterisk systems to be deployed internally, or to form the cornerstone of a commercial offering.

No compromise

In this book you will, hopefully, learn many new things. At its conclusion you will have the knowledge to build and successfully implement systems that combine great performance, resilience and stability. In order to do so, we will mainly consider pure Asterisk systems that require a deep understanding of the dialplan and configuration files without the safety-net of a GUI in between. Think of it as learning to become a great car mechanic. You can certainly be a good mechanic earning a good living by learning how to use a laptop plugged into an engine management system. But if you want to take that extra step to being a true master of the trade then you need to understand at a very deep level just how the internal combustion engine works. So it is with Asterisk. It is perfectly feasible to put very good solutions together using GUI-based systems such as the Digium-owned Switchvox, Trixbox (formerly Asterisk@Home) or PBX in a Flash, but to construct the best systems you will need to understand what is happening under the hood so that you can tweak them appropriately to achieve or exceed the customers' expectations.

One advantage of eschewing the GUI approach is a potential increase in performance and scalability through the use of a highly-optimized dialplan and a reduction in applications running on the server. However, there are many situations where a GUI is at least as appropriate, particularly if the customer wishes to carry out day-to-day management tasks. Therefore, in Chapter 12 we look at the implications of choosing a GUI-based solution over a vanilla system.

Note

To follow the trusted network of Asterisk developers please visit: www.asteriskpro.co.uk

What this book covers

As a result of reading this book, you can expect to build on existing knowledge and gain new skills. Each chapter covers a particular topic, but throughout there is a focus on building an Asterisk system that can form the cornerstone of a serious commercial product, capable of matching or even exceeding the performance of well-known licensed products.

Chapter 1 talks about dialplan techniques including modular implementations by using macros, contexts, and so on to both refine the dialplan and improve the security of the system. It also discusses the use of the devstate() function.

Chapter 2 discusses customer network requirements and offers some good advice about potential issues within the customer network and how to resolve them, including the use of VLANs and Quality of Service.

Chapter 3 looks at routing in general, including Least Cost Routing (local, national, and international GSM gateways), fall-back routing, alternate routing, and so on. ENUM and DUNDi are also explained within this context.

Chapter 4 considers call center requirements, including queues, agents, call distribution strategies, performance monitoring and call recording issues. An Asterisk-based call center solution, VICIDIAL, is also discussed in some detail.

Chapter 5 introduces speech technology in the form of ASR, TTS, and SVI; followed by implementation advice and examples. Both Lumenvox and Cepstral packages are explored in detail.

Chapter 6 looks at methods that can be used to implement call accounting and billing solutions for Asterisk. In particular, Asterisk-stat and A2Billing are explored.

Chapter 7 discusses resilience and stability, giving you a guide to implementing highly-available Asterisk solutions for mission-critical applications. Use of failover and load-balancing techniques are explored.

Chapter 8 explores the comprehensive localization options within Asterisk, and also suggests some easily deployed security measures.

Chapter 9 considers interfaces with traditional analogue and digital telephony, giving more in-depth explanations of Libpri and DAHDI (formerly Zaptel), and discussing implementation considerations.

Chapter 10 tackles the good and bad points of using wireless technologies with Asterisk, covering Wi-Fi, dual-mode and DECT handsets. Some suggestions on routing via cell/mobile networks are also offered.

Chapter 11 looks at the good and bad points of Asterisk Graphical User Interfaces (GUIs), focusing on one of the most popular incarnations, FreePBX.

In Appendix A we also explore some of the softer skills required when selling Asterisk-based solutions, suggesting some sales strategies that can help you in a commercial environment.

In Appendix B you will find information you might want to include in sample emails when pitching.

In Appendix C you will find a sample appointment sheet which can be used as a template.

Onwards

So now our campsite has been packed away and it is time for the next part of our journey to begin, for those first purposeful steps to be taken towards the summit. We will start in Chapter 1 by looking at the heart of any Asterisk system, the dialplan. You will already have significant knowledge in this area, but we are about to show you some of the techniques that are used in systems with thousands of extensions that handle many tens of thousands of calls per day. Without these techniques, a dialplan can become an unholy mess as system size increases. However, using these techniques will ensure that complexity is avoided and performance is maintained.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: We can include other contexts through the use of the include directive.

A block of code is set as follows:

exten => s,1,Dial(Zap/1,30)

exten => s,n,Goto(s-${DIALSTATUS},1)

exten => s,n,Hangup()

exten => s-NOANSWER,1,Voicemail(100,u)

exten => s-BUSY,1,Voicemail(100,b)

exten => i,1,Voicemail(0,s)

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

[default]

exten => s,1,Dial(Zap/1|30)

exten => s,2,Voicemail(u100)

exten => s,102,Voicemail(b100)

exten => i,1,Voicemail(s0)

Any command-line input or output is written as follows:

# cp /usr/src/asterisk-addons/configs/cdr_mysql.conf.sample

/etc/asterisk/cdr_mysql.conf

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: clicking the Next button moves you to the next screen.

Note

Warnings or important notes appear in a box like this.

Note

Tips and tricks appear like this.

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