Telephony Service Development on Asterisk Platform

Hamid FadisheiAssistant Professor, University of [email protected] http://www.fadishei.irSpring 2015

Telephony Service Development on Asterisk Platform

Workshop

Hamid Fadishei University of Bojnord Telephony Service Development on Asterisk Platform

What's Asterisk?

Hard to tell in one sentence A very powerful, flexible, and extensible piece of integrated

telecommunications software An Open Source Telephony Swiss Army Knife A Linux Based PBX w/ Minimal Hardware Reqs A Community Driven Development Project

Asterisk turns an ordinary computer into a communications server. Asterisk powers IP PBX systems, VoIP gateways, conference servers and is used by small businesses, large businesses, call centers, carriers and governments worldwide.


Its birth

Asterisk was created in 1999 by Mark Spencer

This guy!


Telecom technology, once upon a time...

No switch


Human switch!


Mechanical switch


Soft switch Digital switch


Soft switch


Its capabilities

Asterisk can do many cool things... It can be used as a... Legacy PBX Replacement Voicemail Server Conferencing Server Call Center ACD Queue VoIP Endpoint for IP Phones Calling Card Application Predictive Dialer Home Answering Machine …

In this workshop, we'll use it to implement a software-based IVR machine. At the end of this workshop, we will hopefully implement a simple telephony weather service


It's architecture

Asterisk's power comes from its modular architecture Its core's functionality can be extended by loading additional

modules

Core

Module Module Module...

Techn. a Techn. b Techn. c...


Feature a Feature b Feature c


Core


SIP Phone Analog Phone

chan_sip chan_dahdi

IP PSTN

Google Talk

chan_gtalk

IP


How to install Asterisk

Different approaches Compile from source codes

Obtain the source code from asterisk.org Compile and install it (make install)

Install precompiled binaries Some Linux distributions offer Asterisk in their official repos

Debian, Ubuntu, and Fedora Some offer it by third-party repos

Centos (via EPEL), Arch (via AUR) Install an Asterisk-bundled operating system

Such as AsteriskNow or Elastix The Choice is yours... but I would recommnd...

The second approach less installation hassles, good understanding of the system internals takes advantage from regular OS updates

I prefer packages from either Centos+EPEL or Debian


Experimental environment

We will try asterisk in this environment Hardware

A VM inside Virtualbox RAM: 1024MB, CPU:1, HDD: 8GB

Operating Systems: Latest Debian stable release as of today which would be Debian

8.0.0 Jessie


Step 1 - Creating a VM

Make sure hardware virtualization support is enabled in your BIOS settings

Install Virtualbox if you haven't already Also install the extension pack

Create a new VM 32-bit Debian Linux Name it astN where N is the number of your seat (mine is ast1) Select 1024MB of RAM and 8GB of HDD Configure its network in Bridge mode (because we need it to

be visible from the Lab LAN)


Step 2 - Install Debian

We will install a minimal debian with no graphical Desktop Insert CD#1 ISO image of Debian 8 inside the CD drive of your

new VM and start it Select the first boot menu option, "Install"

Use guided partitioning Do not opt to use a network mirror Deselect Desktop Environment when it asks which features to

install Finally, you will get a login prompt

Log in!Debian GNU/Linux 8 ast1 tty1ast1 login: _


Step 2 - Setup remote access to OS

Working inside VM console is not easy enough We will setup an SSH server on our Debian system Then you can an SSH client such as Putty to access your

Debian command line remotely

Now you should be able to SSH to your Debian using Putty

root@ast1:~# apt-get install openssh-server...root@ast1:~# nano /etc/ssh/sshd_configPermitRootLogin yesroot@ast1:~# systemctl restart sshd


Step 3 - Install asterisk

First, make sure that apt is configured to use debian repos

Then, install asterisk

root@ast1:~# nano /etc/apt/sources.list

deb http://ftp.de.debian.org/debian jessie main contrib non-freedeb http://ftp.de.debian.org/debian/ jessie-updates main contrib non-freedeb http://security.debian.org/ jessie/updates main contrib non-free

root@ast1:~# apt-get update

root@ast1:~# apt-get install asterisk...:)


Asterisk CLI

Asterisk comes with a command line interface (CLI) You can use it to manage and monitor your asterisk software

Asterisk is configured via editin some conf files in /etc/asterisk Next, we will setup some VoIP accounts

root@ast1:~# asterisk -rCreated by Mark Spencer <[email protected]>Asterisk comes with ABSOLUTELY NO WARRANTY; type 'core show warranty' for details.This is free software, with components licensed under the GNU General PublicLicense version 2 and other licenses; you are welcome to redistribute it undercertain conditions. Type 'core show license' for details.=========================================================================Connected to Asterisk 11.13.1~dfsg-2+b1 currently running on ast1 (pid = 3153)ast1*CLI> _


Step 4 - A

dd

a coup

le of SIP acco

unts

root@ast1:~# nano /etc/asterisk/sip.conf[general]allowguest=nodisallow=allallow=gsmjbenable=nodeny=0.0.0.0/0.0.0.0permit=0.0.0.0/0.0.0.0

[101]secret=asdf1234context=phoneshost=dynamictype=friendmailbox=101@defaultcallerid=Test 1 <101>

[102]secret=asdf1234context=phoneshost=dynamictype=friendmailbox=102@defaultcallerid=Test 2 <102>


Step 4 - Adding SIP accounts...

Now, tell asterisk to reload SIP configuration

Install Zoiper on your host OS if you haven't already Configure it to user the 101 account on your Asterisk box

Zoiper tells that the account is registerd, but... Calling any number will fail. why? Because no dial plan is configured on Asterisk

root@ast1:~# asterisk -rast1*CLI> sip reload...ast1*CLI> sip show peers101...201...... 2 offline


Step 5 - Configuring a dial plan

Add a simple dial plan

And,...

Then, dial 876

root@ast1:~# nano /etc/asterisk/extensions.conf

[general]static=yeswriteprotect=noautofallthrough=yes

[phones]exten => 876,1,Answer()exten => 876,2,Playback(hello-world)exten => 876,3,Hangup()

ast1*CLI> dialplan reload


Dialplan structure

Add a simple dial planroot@ast1:~# nano /etc/asterisk/extensions.conf

[general]static=yeswriteprotect=noautofallthrough=yes

[phones]exten => 876,1,Answer()exten => 876,2,Playback(hello-world)exten => 876,3,Hangup()

Context

Extension

PriorityApplication


Some hints

You don't have to explicitly mentions priorities:

You can use Goto application to write neater dialplans

[phones]exten => 876,1,Answer()exten => 876,n,Playback(hello-world)exten => 876,n,Hangup()

[phones]exten => 876,1,Goto(hello,s,1)

[hello]exten => s,1,Answer()exten => s,n,Playback(hello-world)exten => s,n,Hangup()


Calling phones

In order to make a call to another phone registerd at the same Asterisk server, You'll need to use the "Dial" application inside dialplan

...

[phones]exten => 876,1,Goto(hello,s,1)exten => 101,1,Dial(SIP/101)exten => 102,1,Dial(SIP/102)

...


Power of Asterisk dialplan

Asterisk allows you to write very complex dialplans But the focus of this workshop is not mastering dialplan

development We will focus on developing services using

programming languages such as Java or PHP


Asterisk Gateway Interface

Asterisk can perform so many tasks by itself But sometimes we need to perform tasks

programmatically AGI is the solution!

AGI and Asterisk servers can be on the same machine We'll use PHP language to develop our AGI applications

But other languages (Java, C#, etc) could be used

Asterisk Server AGI Server

AGI Protocol


Step 6 - Install PHP Interpreter

Simply install it from debian repo

Test it really works

root@ast1:~# apt-get install php5-cli php5-curl

root@ast1:~# nano hello.php

<?php echo "hello\n"; ?>

root@ast1:~# php ./hello.phphello


Step 7 - AGI hello world

Extract and copy PHPAGI library files:

Create a simple AGI script:

Configure dialplan to call the script

root@ast1:~# tar -xf phpagi-2.20.tgzroot@ast1:~# cp phpagi-2.20/phpagi*.php /usr/share/asterisk/agi-bin/

root@ast1:~# nano /usr/share/asterisk/agi-bin/hello.php#!/usr/bin/php<?php set_time_limit(0); require('phpagi.php'); $agi = new AGI(); $agi->answer(); $agi->stream_file('hello-world'); $agi->hangup();?>root@ast1:~# chmod a+x /usr/share/asterisk/agi-bin/hello.php

[phones]exten => 875,1,AGI(hello.php)


Step 7 - AGI hello world

Let's see PHP AGI class documentations answer() stream_file() hangup()


Step 8 - Developing the weather service

Internet


Step 8a - The welcome message

Create another PHP AGI script named weather.php Upload the provided weather sounds folder to your

Asterisk server path /usr/share/asterisk/sounds Start with a simple welcome message on extension

874...

#!/usr/bin/php<?php

set_time_limit(0); require("phpagi.php"); $agi = new AGI();

$agi->answer(); $agi->stream_file("weather/welcome");


Step 8b - Getting the area code

Let's see two more PHP AGI methods get_data() verbose()

... $agi->stream_file("weather/welcome");

$data = $agi->get_data("weather/enter-area-code", 20000, 5); $code = $data["result"]; $agi->verbose("got area code: $code");


Step 8c - Calculating the woeid

Yahoo! weather webservice requires a region code We need to convert city area code to Yahoo! region

code A table can do the job

... $agi->verbose("got area code: $code");

$woeids = array( 11 => 2255150, // Sari 13 => 2255086, // Rasht 17 => 2217763, // Gorgan 21 => 2251945, // Tehran ... 86 => 2254333, // Arak 87 => 2255130, // Sanandaj ); $woeid = $woeids[$code]; $agi->verbose("got woeid: $woeid");


Step 8d -Always validate user input!

Change this segment:

to:

... $data = $agi->get_data("weather/enter-area-code", 20000, 5); ... $woeid = $woeids[$code]; $agi->verbose("got woeid: $woeid");

... get_area_code; $data = $agi->get_data("weather/enter-area-code", 20000, 5); ... $woeid = $woeids[$code]; if (!$woeid) { $agi->stream_file("weather/invalid-number"); goto get_area_code; } $agi->verbose("got woeid: $woeid");


Step 8e - Calling the webservice

Now we can call Yahoo! weather web service Start a music-on-hold before calling

$agi->stream_file("weather/wait"); $agi->set_music(true); $base = "http://query.yahooapis.com/v1/public/yql"; $yql = "select item.condition from weather.forecast where woeid = ".$woeid." and u='c'"; $session = curl_init($base."?q=".urlencode($yql)."&format=json"); curl_setopt($session, CURLOPT_RETURNTRANSFER, true); $json = curl_exec($session); $weather = json_decode($json); $temp = $weather->query->results->channel->item->condition->temp; $agi->set_music(false);


Step 8f - Say temperature

Finally, playback the temperature returned by Yahoo! Play it in sweet Persian!

if (!$temp || $temp<0 || $temp>99) $agi->stream_file("weather/error"); else { $agi->verbose("got temperature: $temp"); $agi->stream_file("weather/temperature");

if ($temp >= 0 && $temp <= 19 || $temp % 10 == 0) $agi->stream_file("weather/".$temp); else { $d10 = (int)($temp/10)*10; $d1 = $temp%10; $agi->stream_file("weather/".$d10."-o"); $agi->stream_file("weather/".$d1); } $agi->stream_file("weather/degrees"); } $agi->stream_file("weather/thanks"); $agi->hangup();


A few words on selecting hardware

You don't have to use a PC for Asterisk SOHO applications A low-cost small ARM board will do the task


Next steps

Study other AGI operations Learn about FastAGI Learn about AMI (Asterisk Manager Interface) Master Asterisk configuration and dialplanning Develop FastAGI applications in Java Try FreeSwitch

(The Asterisk rival) Study Asterisk's

webservice interface added in new releases

Date post:	08-Aug-2015
Category:	Technology
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Telephony Service Development on Asterisk Platform

Technology