How to Build a Telephone

The old way.

The old way

The new way.

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Building Voice Applications with Tropo and Node.js

I’ve been smitten of late with Node.js.

Node.js is a framework for building server-based applications in JavaScript. Node.js is event driven, so if you got a fairly good understanding of state-driven development frameworks you’ll probably get it quickly. If not, start here.
Node.js
I wanted to learn more about Node.js, so I decided to build a module. There are lots of modules out there, but I wanted to do something very specific with mine. I wanted to use Node.js to build voice applications. (Not a shocker, it’s what I do.)

Turns out Node.js is a very nice match for the Tropo WebAPI, a cloud-based API for building sophisticated speech and communication applications. The Tropo WebAPI speaks JSON, and I can’t think of any more natural way of creating and consuming JSON than with good ‘ol JavaScript. Really, you can see why this gets me excited.

The Node.js module that I’ve been working on for interacting with the Tropo WebAPI is now available on GitHub. It comes with some very nice examples, and even a set of unit tests (yes, Virginia, you can write unit tests with Node.js). It has everything you need to get started using Node.js to write voice apps in JavaScript.

If you decide to give it a try (which I hope you do), there are some additional ingredients I would recommend adding to the mix:

  • The Express.js framework – a Node.js module very much like Sinatra in Ruby or Limonade in PHP.
  • CouchDB – The wonderfully powerful document-oriented storage engine that uses both JavaScript (for map/reduce and views) and JSON (for storing documents). There are also many fine Node.js modules available for interacting with CouchDB.

With these ingredients you’ve got a pretty powerful foundation on which to build robust, sophisticated multi-channel communication apps.

But why would you want to build a voice application with JavaScript?
Tropo
Pretty much all of the voice application development tools and technologies that have been developed over the last decade or so have one essential unifying characteristic – each of them seeks to leverage easy to understand, low cost web technologies to build phone applications.

This principle can be seen very clearly in the approach embodied by the new Node.js library for the Tropo WebAPI. If you can write JavaScript, you can build sophisticated, cloud-based communication applications that not long ago required specialized skills, training, software and hardware (Big bucks, people. Big bucks).

Cloud-based telephony services based around simple to use APIs that employ widely supported standards like HTTP and JSON are democratizing phone and voice application development.

It’s really exciting to be a part of this trend and to contribute tools that others can use to build powerful applications.

Make the Cloud Listen (and Understand)

Yesterday I wrote a post about the changing cloud telephony landscape, and highlighted some key factors that will dictate which cloud telephony providers are around for the long haul and deliver the next innovations.

One of those factors – support for speech recognition – is a good differentiator for developers to use when choosing a cloud telephony platform.

Speech recognition is becoming increasingly important in our everyday lives. Smartphones and powerful handheld devices enable multimodality, and there are more and more restrictions placed on our use of phones while doing other tings (like driving).

Plus, I can’t think of a more deflating concept than a cloud telephony provider that allows developers to build sophisticated apps and mashups in the language of their choice but that chains users of those apps to a telephone keypad. No fun.

To give an example of how powerful speech recognition can be, and how easy it is to use with a cloud telephony provider that supports it, I worked up a small demo to illustrate the point. The sample code for this demo is on Github, and we’ll dive into it in more detail below.

This demo uses two PHP libraries that are designed to work with the Tropo platform (one of the only cloud telephony providers to support speech recognition):

If you’ve read any of my previous posts on build applications for the Tropo platform, you’ll see lots of similarities between this and previous sample apps. Here I continue my use of the insanely awesome Limonade Framework for PHP.

Let’s take the example of a company directory that allows callers to dial a single number, select a person or department at the company and then be transferred to the person they select.

With cloud telephony, there is no need to have such a system live on a machine in the server room – it can be hosted externally in the cloud, making it easier to manage and to scale. In addition, with the Tropo Platform, it doesn’t have to be the same tired old DTMF-based menu telling callers to press an extension number or to “dial by name…”.

Using the PHP WebAPI Library and Limonade, we can construct a simple, yet power script that looks like this:

This script is pretty self-explanatory, but there are some key points I want to emphasize. First, note the $options array that holds the reference to an external grammar file (more on that in a bit). Tropo seems to need for this reference to be an absolute one and not a relative reference to the file (not hard to do with PHP – you just need to be aware of it).

Also, the file reference needs to include a trailing parameter indicating that this is an XML grammar (;type=application/grammar-xml). This seems to be true even if the grammar file is served with the correct MIME type by whatever is serving it.

Now lets have a look at this grammar file.

This simplistic example demonstrates how to use the PHPGrammar library. Note the simple array structure that is being used to hold the details of employees for our fictitious company. This could very easily be replaced with a dip into a data source of pretty much any kind, like an LDAP directory or database holding employee details.

Also note in this example that we want to do something referred to as Semantic Interpretation. Our grammar file is a set of rules that will be applied to what the caller says – Semantic Interpretation (SI) dictates the value that is given to our application from the grammar when a successful match occurs.

In this example, we want the caller to be able to say the name of the person they want to be transfered to. We make the first name optional so they may either say the last name of the person or (optionally) the full name. Obviously this may need to be changed based on the size of the directory to render in a grammar file (e.g., multiple employees with the same last name).

Do note that the Tropo platform seems to require the “Script” sytax for returning SI values on a successful match as opposed to the “String Literal” syntax. (More on these alternatives here.)

Works on Tropo (Script syntax):
<item>foo<tag>out="bar";</tag></item>

Does not work on Tropo (String Literal syntax):
<item>foo<tag>bar</tag></item>

So, when a caller says the name of a person in our company directory we want to return the number for that person to our Tropo script so we can transfer the call to them. This can clearly be seen when we examine the Result object that is delivered by the Tropo platform.

Tropo’s Result object includes the full grammar engine output, and lots of very detailed information about the recognition. As you can see, the utterance that the speech recognition engine heard was the name of one of our faux employees. The value that was returned is the number of that person.

We use this value in the transfer_call() method of our Tropo script.


// Create a new instance of the Result object.
$result = new Result();

// Get the value of the selection the caller made.
$phone = $result->getValue();

// Create a new instance of the Tropo object and transfer the call.
$tropo = new Tropo();
$tropo->transfer('+1'.$phone);

// Write out the JSON for Tropo to consume.
$tropo->RenderJson();

Using the PHP WebAPI library, it takes just 5 lines of code (excluding comments) to get the value of the grammar result and transfer the call. How cool is that?!

Obviously there are lots of things that can be done to enhance this script, to make it more robust, but it illustrates the essential concepts of speech recognition in the cloud.

What’s more, because of all of the great functionality provided by the Tropo cloud platform we can really push the envelope on the tired old company directory:

  • We could take an inbound call from a Skype user and transfer to a cell phone (or a SIP endpoint).
  • We could let our caller select a department in our company and then ring several different numbers at once, transferring the call to the first one answered (sort of a “hunt group in the cloud”).
  • We could use Tropo’s built in IM capabilities to send a screen pop to the person receiving the call.

The sky is the limit. Which I guess is the point of cloud telephony…

Building Cloud Communication Apps with Tropo: Part 4

This post is the final installment in the series on building cloud communication applications with Tropo, the PHP WebAPI Library and the Limonade framework for PHP.

If you’re just starting, you can take a look back at part 1, part 2 and part 3 to get caught up.

In the last installment, we finished our first complete script using the PHP WebAPI Library and Limonade. We tested this script by calling it using one of the numbers automatically provisioned for applications on the Tropo platform. In this case, we used the auto provisioned Skype number to make test calls.

In this post we’ll refine our script by optimizing it so that the exact same code can efficiently service users on an array of different communication channels. This is the definition of “multi-modality,” and the Tropo platform does it better than pretty much any other platform currently available to developers.

So Many Channels, So Little Code

Tropo’s strong suit is empowering developers to build applications that work across multiple channels from the same code base. Enabling different channels for existing application is easy – log into your Tropo account and go to “Your Applications.” Select the application we’ve been using for this series, and make note of the sections entitled “Phone Numbers” and “Instant Messaging Networks.”

To SMS-enable your application (so that users can simply send a text message to get weather information) select Add a New Phone Number. The phone number you add can be used for both voice phone calls and for SMS messages. Under “Instant Messaging Networks” you can add any one of the many networks supported by Tropo – for this example, we’ll add a Jabber account so we can test a channel other than voice.

If you set up a Jabber account for your app, you can interact with it by sending it a message – try starting things off by sending a simple message like “Hello.” Once you do, you’ll see the same series of prompts that you can hear when you call into your application via Skype.

IM Bot Before Changes

Now that we can see how our application behaves when we interact with it using an IM client, it becomes obvious that there are some things we’d like to change to optimize it for this channel. User interface elements like a welcome message, reprompts (playing a prompt over again when a user has not entered any input), etc. don’t really make much sense in the context of an IM session. More importantly, it would be nice if we could simply send a zip code to our application to begin the session, as opposed to sending a message like “Hello.”

Fortunately, Tropo was built with multi-modality baked into it so changes like these are rather trivial. To illustrate how to optimize our application so that it can be used on multiple channels, consider the Session object we examined in detail in one of the previous posts in this series.

That Session object was created when we placed a phone call to our application – note that the property name initialText is null.

When we access our application using an IM client, the Session object looks like this:

This Session objects looks considerably different than the one created when we made a phone call to our application. In particular, you can see that the initialText property is now populated with the text we first sent – the string “Hello.”

We can access this property using the PHP WebAPI Library like so:

$session = new Session();
$initial_text = $session->getInitialText();

After accessing the value of this property, we need to do something with it:

if(strlen($initial_text) == 5 && is_numeric($initial_text)) {
	// Since the user submitted a zip code, look up weather info.
}

Now that we can access the initialText sent to our application, and we can examine it to determine if the user has sent us a valid zip code. This allows us to tailor the behavior of our app more efficiently to an IM channel without changing how it behaves when a caller makes a telephone call to it.

IM Bot Before Changes

The modified script with changes to optimize it for IM can be found here.

Conclusion

Clearly there are lots of other things we could do to tweak our application, to tailor it more efficiently to different channels supported by Tropo. For example, breaking out the weather information into discreet segments for temperature, wind, etc. (by using a separate Say object for each) might work well with a voice or IM channel, but it would probably not work well for SMS or Twitter.

Additional changes to optimize this script for these other channels is pretty straightforward. I won’t get into it in this post, but now that you’ve got the hang of how easy it is to create multi-modal communication apps with Tropo, Limonade and the PHP WebAPI Library you should give it a try.

Rock on!

Building Cloud Communication Apps with Tropo: Part 3

This post is a continuation of the series on building cloud communication applications with Tropo, the PHP WebAPI Library and the Limonade framework for PHP .

If you’re just starting, you can take a look back at part 1 and part 2 to get caught up.

In this post, we’ll continue our work from the last post and complete a simple, yet powerful multi-channel application that can be accessed via telephone, SMS or IM client.

In the previous post, we looked closely at the Session and Result objects – these are JSON objects that are sent to your application by the Tropo platform that contain information about how a user is accessing your app (i.e., through which channel) and any input they have provided in response to prompts. If you worked through the last post, you have a partially complete script that looks like this:

You should save this script to a server that can be accessed by the Tropo platform – any web hosting platform that supports PHP >= 5.2.0 will do. Let’s call our script get_zip_code.php.

When you set up the start URL for this script in the Tropo Application Manager, you’ll want to structure it like so:

http://name_of_my_host.com/path/to/get_zip_code.php?uri=start

As you can see, we’ve added a querystring parameter called uri. This will ensure that the initial HTTP POST to this script by the Tropo platform matches our /start pattern and executes our zip_start() method, which is where we want users to begin. Make sure you review the Limonade documentation on setting up routes, as there are multiple options for configuring route pattern matching.

Next, we’ll want to start modifying our partially constructed script. First go to step 6 in the zip_start() method, where we had set up a PostBin URL for Tropo to send a user’s input to so we could examine the Result object. Now that we know what the Result object looks like, we want to start using it to look up information and present it to the caller.

You’ll want to set up a URL to the get_zip_code.php script that will match the route for the zip_end() method. This is where we will access the Tropo Result object and process it. Change the URL in the “next” array element to look like this:

$tropo->on(array(“event” => “continue”, “next” => “get_zip_code.php?uri=end“, “say” => “Please hold.”));

This change tells Tropo that when the “continue” event is raised (after the caller has completed entering input) POST the Result object back to the get_zip_code.php script using a relative URL and a querystring parameter that will ensure matching of our /end pattern.

Next, we need to build out the zip_end() method to process the results:

dispatch_post('/end', 'zip_end');
function zip_end() {

        // Step 1. Create a new instance of the result object
	$result = new Result();
	$zip = $result->getValue(); // get the value of the user input.

        // Step 2. Get weather information for the zip code the caller entered.
	$weather_info = getWeather($zip);
	$city = array_pop($weather_info);

        // Step 3. Create a new instance of the Tropo object.
	$tropo = new Tropo();

        // Step 4. Begin telling the user the weather for the city their zip code is in.
	$tropo->say("The current weather for $city is...");

        // Step 5. Iterate over an array of weather information.
	foreach ($weather_info as $info) {
	    $tropo->say("$info.");
	}

        // Step 6. Say thank you (never hurts to be polite) and end the session.
	$tropo->say("Thank you for using Tropo!");
        $tropo->hangup();

        // Step 7. Render the JSON for the Tropo WebAPI to consume.
       return $tropo->RenderJson();

}

As you can see, our zip_end() method looks similar to our zip_start() method – both use a Tropo object to format information that will be presented to the user, and both call the RenderJson() method of the Tropo object at the end.

You may be wondering about the getWeather() method that is called in step 2. Let’s build that out now and examine how it works – to keep things simple, we’ll make use of the Google Weather API, which provides weather information by zip code and returns the information in XML format.

// The URL to the Google weather service. Renders as XML doc.
define("GOOGLE_WEATHER_URL", "http://www.google.com/ig/api?weather=%zip%&hl=en");

// A helper method to get weather details by zip code.
function getWeather($zip) {

	$url = str_replace("%zip", $zip, GOOGLE_WEATHER_URL);
	$weatherXML = simplexml_load_file($url);
	$city = $weatherXML->weather->forecast_information->city["data"];
	$current_conditions = $weatherXML->weather->current_conditions;
	$current_weather = array(
		"condition" => $current_conditions->condition["data"],
		"temperature" => $current_conditions->temp_f["data"]." degrees",
		"wind" => formatDirection($current_conditions->wind_condition["data"]),
		"city" => $city
	);
	return $current_weather;

}

// A helper method to format directional abbreviations.
function formatDirection($wind) {
	$abbreviated = array(" N ", " S ", " E ", " W ", " NE ", " SE ", " SW ", " NW ");
	$full_name = array(" North ", " South ", " East ", " West ", " North East ", " South East ", " South West ", " North West ");
	return str_replace($abbreviated, $full_name, str_replace("mph", "miles per hour", $wind));
}

The mechanics of these functions are pretty straighforward, so I won’t go in to too much detail – you can now see the connection between the call to the getWeather() method mentioned above and the array of weather data that it returns.

The last thing we need to do in order to complete our zip code weather demo script is to finish the zip_error() method. This is a method we’ll use to tell a user an error occurred (never hurts to be prepared for the unexpected):

dispatch_post('/error', 'zip_error');
function zip_error() {

	// Step 1. Create a new instance of the Tropo object.
	$tropo = new Tropo();

	// Step 2. This is the last thing the user will be told before the session ends.
	$tropo->say("Please try your request again later.");

	// Step 3. End the session.
	$tropo->hangup();

	// Step 4. Render the JSON for the Tropo WebAPI to consume.
	return $tropo->renderJSON();
}

In order for this method to be invoked, we need to make sure that we set up the proper handler in our zip_start() method for it. The Tropo WebAPI makes it possible to set up callback methods that handle things when certain events are raised. This is done by using the On object.

Setting up an event handler using the On object with the PHP WebAPI Library is easy. In fact, we’ve already done it once – look at the zip_start() method and you’ll see a hander for the “continue” event (which is raised when a user has finished entering the proper input). We want to set up something similar for when an error event is raised. Let’s add a handler in our zip_start() method for an error event:

	// Step 6. Tell Tropo what to do when the user has entered input, or if there is an error.
	$tropo->on(array("event" => "continue", "next" => "get_zip_code.php?uri=end", "say" => "Please hold."));
	$tropo->on(array("event" => "error", "next" => "get_zip_code.php?uri=error", "say" => "An error has occured."));

Our script is now complete and ready to test.

Make sure you log into your Tropo account and set up the start URL to your script as discussed above. You can test this script with the phone numbers that are automatically provisioned by Tropo when you set up your account.

Tropo will automatically provision a Skype number, a SIP number and an iNum. You can additionally add a PSTN number in a range of different area codes at no charge. This PSTN number can also be used to send an SMS to, so you can interact with this script via text message. Additionally, you can add an IM account, so you can test this script using your favorite IM client/network.

You may notice, if you test this script using SMS or IM that there are things that don’t yet work perfectly. In the next post, we will make some very simple changes to this script to optimize it for use with SMS and IM (and even Twitter!).

This will transform our simple PHP script into a powerful unified communications application.

Stay tuned…

Building Cloud Communication Apps with Tropo: Part 2

This post is a continuation of the series on building cloud communication applications with Tropo and the PHP WebAPI Library.

In this post, we’ll be looking at Tropo’s support for multi-channel applications and using the incredibly flexible and powerful Limonade library for PHP (think Sinatra for PHP).

Working with the Session Object

As I explained very briefly in the previous post on this subject, the Tropo WebAPI is an HTTP/JSON API for building multi-channel communication apps.

What this means essentially is that the Tropo platform does all of the hard stuff involved with executing a communication app – DTMF/speech recognition, rendering Text-To-Speech (TTS), maintaining and managing all of the connections to the different communication networks (PSTN, SMS, IM networks, Twitter). You tell Tropo how to govern the interaction between a caller and your application on a specific channel by sending it a set of instructions in JSON format.

In this series of posts, we’re using the PHP WebAPI Library for Tropo to generate the JSON that gets sent to, and consumed by Tropo. But this exchange of JSON isn’t one-way – Tropo also sends JSON packages to your application with important information about (among other things) the network a user selects to interact with your application on and any input they have provided in response to prompts.

At the beginning of a user session (when a user first connects to your application), Tropo will deliver a JSON Session object to your application. This object contains all sorts of useful information that your app can use when rendering out JSON instructions to send back to Tropo. Let’s examine what a real life Session object looks like.

The easiest way to do this is to simply go over to PostBin.org and make a new PostBin. PostBin is a service that lets you see HTTP posts that get sent to the special URL that is generated when you create a new PostBin.

After you have created a new PostBin, log into your Tropo account and create a new WebAPI application. Use the PostBin URL as the URL that powers your new Tropo WebAPI app. After your app is created, you will have a newly provisioned Skype number that you can use to call it.

When you call your application using the Skype number provisioned by Tropo, you won’t hear anything – remember, we haven’t yet generated any JSON to tell the Tropo platform what to say or do when a user connects. After you make your call (it will be over quickly), go back to your PostBin URL (you may need to refresh) and you will see an object in JSON format, like this:

This is the Session object for the call you just made. It’s what is sent to your application (via HTTP POST) each time a new session is started on Tropo. Working with this object using the PHP WebAPI Library is easy. You just create a new instance of the Session object in PHP and you can start accessing the properties of this object:


$session = new Session();
$from_info = $session->getFrom();
echo $from_info['channel'];

// Using the example Session object JSON from above would render VOICE.

Being able to access the channel and network a user is accessing your application from can be useful when you want to tailor prompts or actions to a specific channel – e.g., a phone call vs. an IM session.

Also make note of the initialText property – this will be important when building SMS and IM applications, where a user will begin an interaction with your application by sending information to it. This property will allow you to process the initial input for those channels without having to ask the user for it again (something users generally dislike).

Next, let’s take a look a the Result object that is sent from Tropo to your application when a user provides input in response to a prompt or direction. In order to do this, we need to take a sip of Limonade.

Mmmm… Limonade!

Limonade is a lightweight PHP framework that is very much like the Sinatra framework for Ruby. I won’t go into too much detail on it, as there is ample documentation available on the Limonade site , but here is quick introduction that will let us build enough of a structure to see the Tropo result object.

When you use Limonade, you set up routes for HTTP requests. A route is comprised of an HTTP method, a URL matching pattern and a PHP method. When an HTTP request is made to a URL that matches the pattern, and uses the method specified in the route, the designated PHP function gets invoked. For example:

dispatch_post('/', 'test');
  function test() {
    echo 'This is a test.';
}

The ‘dispatch_post()’ directive specifies that the HTTP method for this route with be POST (which is what is used by Tropo to send JSON to your application). The two parameters to this directive specify the URL pattern to match (in this case, the root directory on the domain were this script is located) and the PHP method to invoke, which is defined below this directive. In a nutshell, whenever an HTTP POST is made to the root domain where this script is located, the text This is a test will be rendered.

Let’s build out a simple shell that we’ll use to construct our Tropo application for the next few posts in this series:

// Include Tropo classes.
require('TropoClasses.php');

// Include Limonade framework (http://www.limonade-php.net/).
require('path/to/limonade/lib/limonade.php');

dispatch_post('/start', 'zip_start');
function zip_start() {
	// Tell the user to enter their zip code.
}

dispatch_post('/end', 'zip_end');
function zip_end() {
	// Do something with the entered zip code.
}

dispatch_post('/error', 'zip_error');
function zip_error() {
	// Tell the user an error has occurred.
}

// Run this sucker!
run();

Our Tropo application will collect a user’s zip code and then look up some information based on the input they provide. As you can see, we’ve included the PHP WebAPI Library and the Limonade Framework. We’ve also set up three Limonade routes start, end and error (all using the HTTP POST method) and stubbed out the PHP function that will render JSON for Tropo to consume.

To get a look at the Tropo Result object, lets add some logic to the zip_start() function:


dispatch_post('/start', 'zip_start');
function zip_start() {

	// Step 1. Create a new instance of the Session object, and get the channel information.
	$session = new Session();
	$from_info = $session->getFrom();
	$network = $from_info['channel'];

       // Step 2. Create a new instance of the Tropo object.
	$tropo = new Tropo();

	// Step 3. Welcome prompt.
	$tropo->say("Welcome to the Tropo PHP zip code example for $network");

	// Step 4. Set up options for zip code input.
	$options = array("attempts" => 3, "bargein" => true, "choices" => "[5 DIGITS]", "name" => "zip", "timeout" => 5);

	// Step 5. Ask the caller for input, pass in options.
	$tropo->ask("Please enter your 5 digit zip code.", $options);

	// Step 6. Tell Tropo what to do when the user has entered input. Enter your PostBin URL in the "next" array element.
	$tropo->on(array("event" => "continue", "next" => "http://www.PostBin.org/xxxxxxx", "say" => "Please hold."));

	// Step 7. Render the JSON for the Tropo WebAPI to consume.
	return $tropo->RenderJson();

}

As you can see, inside this function we create a new instance of the Session object and get the channel the user is accessing our application from. We also create a new instance of the Tropo object (this is what we’ll use to send JSON instructions back to the Tropo platform).

The next several steps are fairly self explanatory, but take special note of Step 6. Here we are telling the Tropo platform that when a ‘continue’ event is raised (when a user finishes entering input) tell them to ‘Please hold’ and then POST the results of their input to a PostBin URL. (Note – replace the value above with the PostBin URL you used at the beginning of this tutorial.)

Working with the Result Object

Save your script and change the URL for your WebAPI application in the Tropo Applications manager to point to it. You can now test your script using the the Skype number for your app as we did before . When you access your script, you’ll get the instructions to enter a zip code, after which Tropo will POST the results to the PostBin URL you inserted into the script in Step 6 above.

Now, when you look at your PostBin URL, you’ll see something like this:

As you can see, the Result object that gets sent from Tropo to your app has a wealth of information on what the user entered, how it was interpreted by Tropo and even the confidence level of the recognition (if speech recognition is used).

You can access the Result object using the PHP WebAPI Library just like you can the Session object:

$result = new Result();
$zip = $result->getValue();
echo $zip

// Using the example Result object JSON from above would render 12345

You would use the Result object in the zip_end() function we stubbed out above. You use the value of the zip code entered to look up information relevant for that zip code (like a weather forecast) and present it to the caller.

In the next post in this series, we’ll complete our simple zip code example by adding a weather forecast lookup and present it to the user. We’ll also tweak our script to optimize it for different channels that a user might employ to access it, to ensure the experience is optimized for phone, IM and SMS.

Stay tuned…

Building Cloud Communication Apps with Tropo: Part 1

A few months back, I wrote a series of posts on building NoSQL telephony applications with Tropo and CouchDB. Today I’m going to start a continuation of that series, focusing on how to build cutting edge cloud communications apps with the Tropo WebAPI.

What is the Tropo WebAPI?

The Tropo WebAPI is, in a nutshell, an HTTP/JSON API for building multi-channel communication applications – applications that you interact with via phone, IM, SMS or Twitter. While my earlier series on Tropo focused on building applications in Tropo’s scripting environment (another fine option for developers), this series will focus on building JSON-based applications (generated using PHP) that can be hosted anywhere and executed in the Tropo cloud environment.

Faithful readers will recognize some similarities here to a post I did a while back on the HTTP/JSON API provided by CloudVox, another cloud telephony provider. While the concept behind these two API’s is very similar, there are some key differences that make Tropo a highly attractive option for developers.

First, the Tropo service is truly multi-channel – using the Tropo WebAPI you can build applications that work on a range of different communication channels, not just phones (although you can build some pretty slamming phone apps as well).

Since I’m a phone app developer at heart, some of the features that Tropo provides for phone applications really get me excited. Tropo supports both DTMF entry and speech recognition. It also has broad multilingual support. In addition, Tropo gives phone application developers the ability to manipulate SIP headers, an important feature in building sophisticated cloud communication apps that I hope to demonstrate down the road a bit.

Getting Started

Head on over to Tropo.com and set up a new account (if you don’t have one already). Take a little time to review the documentation for the Tropo WebAPI. For the example applications in this series of blog posts I’ll be using a PHP class library I developed specifically to interact with the Tropo WebAPI.

The crew behind Tropo have provided a Ruby Gem for interacting with the Tropo WebAPI. However, since I like to do my cloud telephony work with PHP I decided to write my own set of classes for doing this. Whether you’re a Ruby-head or a PHP enthusiast, using one of these tools to generate JSON for consumption by the Tropo WebAPI can make build an application significantly easier, particularly as you get into more sophisticated application development.

You can get the PHP Library, as well as some of the sample apps we’ll be looking at, from GitHub:

$ git clone git://github.com/tropo/tropo-webapi-php.git

You’ll need to host these classes and the PHP scripts you write with them on a server that can be accessed from the Tropo environment. Any web server that supports PHP will do.

My First Tropo WebAPI Application

Let’s start with the standard Hello World app:


Say("Hello World!");

// Render the JSON for the Tropo WebAPI to consume.
$tropo->RenderJson();

?>

You can look at the rendered JSON in your browser, and you should see something like this:


{
    "tropo": [
        {
            "say": [
                {
                    "value": "Hello World!"
                }
            ]
        }
    ]
}

Go to the Applications section in your Tropo account and set up a new WebAPI application that points to the location of this script.

Create a new Tropo WebAPI application

Assign a URL to your new Tropo WebAPI application

When you create your application, Tropo will automatically provision a Skype number, a SIP number and an iNum. You can additionally add a PSTN number in a range of different area codes at no charge.

You may also notice the section below the provisioned phone numbers entitled “Instant Messaging Networks” – this section allows you to set up any number of different IM accounts (and Twitter!) that your application can use. We’ll dive deeper into this in future posts.

For now, we’ll keep it simple and use the auto provisioned Skype number – when you call this number, you will hear it say “Hello World.”

The next post in this series will focus on a more sophisticated application that uses the TropoPHP classes and the utterly awesome Limonade PHP framework.

Stay tuned…