AsteriskNOW comes standard with Ruby but not RubyGems (for support reasons). Thankfully, RubyGems can be easily installed from the Ruby rPath trove with the following command:

conary update rubygems=ruby.rpath.org@rpl:devel
source /etc/profile

Most Linux distributions’ package managers host a Ruby package, though some do not yet have RubyGems. With your respective distro’s preferred software management application, install Ruby 1.8.5 or later and RubyGems if available. If RubyGems is not available in CentOS, you can install Ruby by typing:

yum install ruby

Next, we need RubyGems. You can get that by navigating to /usr/src/, and entering:

wget http://rubyforge.org/frs/download.php/20585/rubygems-0.9.3.tgz
tar zxvf rubygems-0.9.3.tgz
cd rubygems-0.9.3
ruby setup.rb

Ruby actually ships standard with OS X, but you will need to upgrade it and install RubyGems from MacPorts, an OS X package manager. With MacPorts installed, (available from http://www.macports.org if you do not already have it) you can install Ruby and RubyGems with the following command:

sudo port install ruby rb-rubygems

You may also need to add /opt/local/bin to your PATH variable in /etc/profile.

A fantastic “one-click installer” exists for Windows. This installer will automatically install Ruby, RubyGems, and a few commonly used gems all in a matter of minutes. You can download the installer from http://rubyforge.org/projects/rubyinstaller.

Once you’ve followed one of the previous set of instructions for your system to fetch Ruby and RubyGems, install Adhearsion with the following command:

gem install adhearsion

If any dependencies are found, you will probably need to allow them to install for Adhearsion to work correctly.

The ability to write dialplans in Adhearsion is typically the first feature newcomers use. Since Ruby permits such fine-grained modification of the language itself at runtime, one of the things Adhearsion does is make aesthetic changes, which are intended to streamline the process of developing dialplans.

Below is an Adhearsion Hello World application:

my_first_context {
  play "hello-world"
}

Though this is completely valid Ruby syntax, not all Ruby applications look like this. Adhearsion makes the declaration of context names comfortable by interpreting the dialplan script specially. Your scripts will be located in the root folder of your newly created Adhearsion application.

As calls come into Asterisk and subsequently Adhearsion, Adhearsion invokes its own version of the context name from which the AGI request originated. Given this, we should ensure that a context in extensions.conf has this same name and forwards calls properly to Adhearsion.

The syntax for directing calls to Adhearsion is as follows:

[my_first_context]
exten => _.,1,AGI(agi://127.0.0.1)

This catches any pattern dialed and goes off to Adhearsion via AGI to handle the call-processing instructions for us. The IP provided here should of course be replaced with the necessary IP to reach your Adhearsion machine.

Now that you have a basic understanding of how Adhearsion and Asterisk interact, here is a more real-world dialplan example in Adhearsion:

internal {
  case extension
when 10..99
  dial SIP/extension
when 6000..6020, 7000..7030
  # Join a MeetMe conference with "join"
  join extension
when _'21XX'
  if Time.now.hour.between? 2, 10
    dial SIP/"berlin-office"/extension[2..4]
  else speak "The German office is closed"
  end
when US_NUMBER
  dial SIP/'us-trunk-out'/extension
when /^\d{11,}$/ # Perl-like regular expression
  # Pass any other long numbers straight to our trunk.
  dial IAX/'intl-trunk-out'/extension
else
  play %w'sorry invalid extension please-try-again'
  end
}

With just this small amount of code we accomplish quite a lot. Even with limited or no knowledge of Ruby, you can probably infer the following things:

This is of course just a simple example and covers only the absolute basics of Adhearsion’s dialplan authoring capabilities.

Though immensely successful in the web development space for serving dynamic content, database integration has always been an underutilized possibility for driving dynamic voice applications with Asterisk. Most Asterisk applications that do accomplish database integration outsource the complexity to a PHP or Perl AGI script because the extensions.conf or AEL grammars are simply impractical for the level of sophistication required.

Adhearsion uses a database integration library, called ActiveRecord, developed by the makers of the Ruby on Rails framework. With ActiveRecord, the end user seldom, if ever, writes SQL statements. Instead, the developer accesses the database just like any Ruby object. Because Ruby allows such flexible dynamism, access to the database looks and feels quite natural. Additionally, ActiveRecord abstracts the differences between database management systems, making your database access implementation agnostic.

Without going too much into the internals of ActiveRecord and more sophisticated uses of it, let us consider the following simple MySQL schema:

CREATE TABLE groups (
 `id` int(11) DEFAULT NULL auto_increment PRIMARY KEY,
 `description` varchar(255) DEFAULT NULL,
 `hourly_rate` decimal DEFAULT NULL
);

CREATE TABLE customers (
 `id` int(11) DEFAULT NULL auto_increment PRIMARY KEY,
 `name` varchar(255) DEFAULT NULL,
 `phone_number` varchar(10) DEFAULT NULL,
 `usage_this_month` int(11) DEFAULT 0,
 `group_id` int(11) DEFAULT NULL
);

In practice we would obviously store much more information about the customer and keep the service usage information in a database-driven call detail record, but this degree of simplicity helps demonstrate ActiveRecord fundamentals more effectively.

To connect Adhearsion to this database, one simply specifies the database access information in a YAML configuration file like so:

adapter: mysql
host: localhost
database: adhearsion
username: root
password: pass

This tells Adhearsion how to connect to the database, but how we access information in the tables depends on how we model our ActiveRecord objects. Since an object is an instance of a class, we write a class definition to wrap around each table. We define simple properties and relationships in the class with the superclass’s methods.

Here are two classes we may use with the aforementioned tables:

class Customer < ActiveRecord::Base
  belongs_to :group

  validates_presence_of   :name, :phone_number
  validates_uniqueness_of :phone_number
  validates_associated    :group

  def total_bill
self.group.hourly_rate * self.usage_this_month / 1.hour
  end
end

class Group < ActiveRecord::Base
  has_many :customers
  validates_presence_of :description, :hourly_rate  
end

From just this small amount of information, ActiveRecord can make a lot of logical inferences. When these classes interpret, ActiveRecord assumes the table names to be customers and groups respectively by lowercasing the classes’ names and making them plural. If this convention is not desired, the author can easily override it. Additionally, at interpretation time, ActiveRecord actually peeks into the database’s columns and makes available many new dynamically created methods.

The belongs_to and has_many methods in this example define relationships between Customers and Groups. Notice again how ActiveRecord uses pluralization to make the code more expressive in the has_many :customers line. From this example, we also see several validations—policies that ActiveRecord will enforce. When creating a new Customer we must provide a name and phone_number at the bare minimum. No two phone numbers can conflict. Every Customer must have a Group. Every Group must have a description and hourly_rate. These help both the developer and the database stay on track.

Also, notice the total_bill method in the Customer class. On any Customer object we extract from the database, we can call this method, which multiplies the hourly_rate value of the group to which the Customer belongs by the Customer’s own phone usage this month (in seconds).

Here are a few examples that may clarify the usefulness of having Ruby objects abstract database logic:

everyone = Customer.find :all

jay = Customer.find_by_name "Jay Phillips"
jay.phone_number # Performs a SELECT statement
jay.total_bill   # Performs arithmetic on several SELECT statements
jay.group.customers.average :usage_this_month

jay.group.destroy
jay.group = Group.create :description => "New cool group!",
                         :hourly_rate => 1.23
jay.save

Because the database integration here becomes much more natural, Asterisk dialplans becomes much more expressive as well. Below is a sample dialplan of a service provider that imposes a time limit on outgoing calls using information from the database. To remain simple:

# Let's assume we're offering VoIP service to customers
# whom we can identify with their callerid.

service {
  # The line of code below performs an SQL SELECT
  # statement on our database. The find_by_phone_number()
  # method was created automatically because ActiveRecord
  # found a phone_number column in the database. Adhearsion
  # creates the "callerid" variable for us.
  caller = Customer.find_by_phone_number callerid

  usage = caller.usage_this_month
  if usage >= 100.hours
    play "sorry-cant-let-you-do-that"
  else
    play %w'to-hear-your-account-balance press-1 
            otherwise wait-moment'
    choice = wait_for_digit 3.seconds

    p choice
    if choice == 1
      charge = usage / 60.0 * caller.group.hourly_rate
      play %W"your-account will-reflect-charge-of $#{charge}
              this month for #{usage / 60} minutes and
              #{usage % 60} seconds"
    end

    # We can also write back to the "usage_this_month"
    # property of "caller". When the time method finishes,
    # the database will be updated for this caller.
    caller.usage_this_month += time do
      # Code in this block is timed.
      dial IAX/'main-trunk'/extension
    end
    caller.save
  end
}

Robust database integration like this through Adhearsion brings new ease to developing for and managing a PBX. Centrally persistent information allows Asterisk to integrate with other services cleanly while empowering more valuable services whose needs are beyond that of traditional Asterisk development technologies.

Because an Adhearsion application resides within a single folder, completely copying the VoIP application is as simple as zipping the files. For one of the first times in the Asterisk community, users can easily exchange and build upon one another’s successful application. In fact, open sourcing individual Adhearsion applications is greatly encouraged.

Additionally, on a more localized level, users can reuse Adhearsion framework extensions, called helpers, or roll their own. Helpers range from entire sub-frameworks like the Micromenus framework for integrating with on-phone micro-browsers to adding a trivial new dialplan method that returns a random quote by Oscar Wilde.

Below is a simple Adhearsion helper written in Ruby. It creates a new method that will exist across the entire framework, including the dialplan. For simplicity’s sake, the method downloads an XML document at a specified HTTP URL and converts it to a Ruby Hash object (Ruby’s associative array type):

def remote_parse url
  Hash.from_xml open(url).read
end

Note that these three lines can work as the entire contents of a helper file. When Adhearsion boots, it executes the script in a way that makes any methods or classes defined available anywhere in the system.

For some issues, particularly ones of scaling Adhearsion, it may be necessary to profile out bottlenecks to the king of efficiency: C. Below is a sample Adhearsion helper that returns the factorial of a number given:

int fast_factorial(int input) {
  int fact = 1, count = 1;
  while(count <= input) {
    fact *= count++;
  }
  return fact;
}

Again, the code here can exist as the entire contents of a helper file. In this case, because it is written in C, it should have the name factorial.alien.c. This tells Adhearsion to invoke its algorithm to read the file, add in the standard C and Ruby language development headers, compile it, cache the shared object, load it into the interpreter, and then wrap the C method in a Ruby equivalent. Below is a sample dialplan that simply speaks back the factorial of six using this C helper:

fast_test {
  num = fast_factorial 6
  play num
}

Note that the C method becomes a first-class Ruby method. Ruby number objects passed to the method are converted to C’s “int” primitive, and the return value is converted back to a Ruby number object.

Helpers promise robust albeit simple extensibility to a VoIP engineer’s toolbox, but, best of all, useful helpers can be traded and benefit the entire community.