Tropo’s conference function makes it easy for you to join multiple callers onto a single call together. One line of code and you have a conference call…

<?php conference('someid'); ?>

That’s it. A basic conference line. Use that as your application and everyone calling into your number will be joined into a single conference call. How many users? By default, Tropo allows up to 100 users into a single conference. We can do more if you need it, but you might want to think through your use case a bit first. 100 people all talking on one line gets crazy fast.

Now let’s take this basic concept and turn it into a full-fledged application. Our requirements for the conference call start with allowing the entry of a conference ID so that this number can be used for more than one call.

<?php
$response = ask('Enter your conference ID', array(
    'choices' => '[4 DIGITS]'
));
conference($response->value);
?>

We’d also like to allow conference IDs of multiple lengths (instead of just 4 digits), and to let the caller tell us when they’re done with entry by pressing #. How about conference IDs of 3-10 digits?

<?php
$response = ask('Enter your conference ID. Press the pound key when finished.', array(
    'choices' => '[3-10 DIGITS]',
    'terminator' => '#'
));
conference($response->value);
?>

In noisy rooms offices, background noise sometimes get misinterpreted as input. Since we’re only accepting numeric conference IDs, let’s turn off speech recognition and restrict input to the keypad

<?php
$response = ask('Enter your conference ID. Press the pound key when finished.', array(
    'choices' => '[3-10 DIGITS]',
    'terminator' => '#',
    'mode' => 'keypad'
));
conference($response->value);
?>

Let’s tell them if their conference ID was accepted and notify them they’re entering the room.

<?php
$response = ask('Enter your conference ID. Press the pound key when finished.', array(
    'choices' => '[3-10 DIGITS]',
    'terminator' => '#',
    'mode' => 'keypad'
));
say('Conference ID ' . $response->value . ' accepted. You will now be placed into the conference. Please announce yourself.');
conference($response->value);
?>

Hmm. That conference id is being read as a number (one thousand two hundred thirty four) instead of as digits (one two three four). A little ssml magic will fix that.

<?php
$response = ask('Enter your conference ID. Press the pound key when finished.', array(
    'choices' => '[3-10 DIGITS]',
    'terminator' => '#',
    'mode' => 'keypad'
));
say('<speak>Conference ID <say-as interpret-as="vxml:digits">' . $response->value . '</say-as> accepted. You will now be placed into the conference. Please announce yourself.</speak>');
conference($response->value);
?>

Often I hit the wrong conference id and need to hang up and try again. For our conference line, how about we let someone exit the room and pick another one.

We’ll add a loop that loops as long as the call is active. Once someone exits, the loop starts over and they’ll be prompted for their conference id again. We’ll also add a terminator to the conference so someone can exit and let them know that option is available.

<?php
answer();
while ($currentCall->isActive()) {
	$response = ask('Enter your conference ID. Press the pound key when finished.', array(
	    'choices' => '[3-10 DIGITS]',
	    'terminator' => '#',
	    'mode' => 'keypad'
	));
	say('<speak>Conference ID <say-as interpret-as="vxml:digits">' . $response->value . '</say-as> accepted. You will now be placed into the conference. Press pound to exit without disconnecting. Please announce yourself.</speak>');
	conference($response->value, array('terminator' => '#'));
}
?>

What if someone doesn’t enter a conference id? Or enters too few or too many numbers? Let’s check the return of the ask function to see if the ask succeeded, failed, or timed out. If it’s a timeout or failure, play a message and the loop starts again, asking for the conference id again.

<?php
answer();
while ($currentCall->isActive()) {
	$response = ask('Enter your conference ID. Press the pound key when finished.', array(
	    'choices' => '[3-10 DIGITS]',
	    'terminator' => '#',
	    'mode' => 'keypad'
	));
	switch($response->name) {
    case 'choice':
      say('<speak>Conference ID <say-as interpret-as="vxml:digits">' . $response->value . '</say-as> accepted. You will now be placed into the conference. Press pound to exit without disconnecting. Please announce yourself.</speak>');
      conference($response->value, array('terminator' => '#'));
      // Pause a moment before asking for another conference.
      sleep(1);
      break;
    case 'badChoice':
      say('Sorry, that is not a valid conference ID.', array('voice' => $voice));
      break;
    case 'silenceTimeout':
    case 'timeout':
      say('Sorry, I didn\'t hear anything.', array('voice' => $voice));
      break;
  }
}
?>

Now that we are handling a timeout, the default timeout seems way too long for this type of application. If the user doesn’t enter a conference ID in 8 seconds, prompt again.

<?php
answer();
while ($currentCall->isActive()) {
	$response = ask('Enter your conference ID. Press the pound key when finished.', array(
	    'choices' => '[3-10 DIGITS]',
	    'terminator' => '#',
	    'mode' => 'keypad',
	    'timeout' => 8
	));
	switch($response->name) {
    case 'choice':
      say('<speak>Conference ID <say-as interpret-as="vxml:digits">' . $response->value . '</say-as> accepted. You will now be placed into the conference. Press pound to exit without disconnecting. Please announce yourself.</speak>');
      conference($response->value, array('terminator' => '#'));
      // Pause a moment before asking for another conference.
      sleep(1);
      break;
    case 'badChoice':
      say('Sorry, that is not a valid conference ID.', array('voice' => $voice));
      break;
    case 'silenceTimeout':
    case 'timeout':
      say('Sorry, I didn\'t hear anything.', array('voice' => $voice));
      break;
  }
}
?>

What if we want to restrict the conference IDs that someone can use? Maybe create a conference application that uses reservations and creates rooms for people. We could fetch a list of currently-valid conference IDs from a database. In this sample, I’m just going to hard-code those in an array.

<?php
$pins = array();
$pins['1337'] = '';
$pins['1234'] = '';
$pins['2600'] = '';
answer();
while ($currentCall->isActive()) {
	$response = ask('Enter your conference ID. Press the pound key when finished.', array(
	    'choices' => '[3-10 DIGITS]',
	    'terminator' => '#',
	    'mode' => 'keypad',
	    'timeout' => 8
	));
	switch($response->name) {
    case 'choice':
	    if (!array_key_exists($response->value, $pins)) {
	      say('Sorry, that is not a valid conference ID.');
	      break;
	    }
      say('<speak>Conference ID <say-as interpret-as="vxml:digits">' . $response->value . '</say-as> accepted. You will now be placed into the conference. Press pound to exit without disconnecting. Please announce yourself.</speak>');
      conference($response->value, array('terminator' => '#'));
      // Pause a moment before asking for another conference.
      sleep(1);
      break;
    case 'badChoice':
      say('Sorry, that is not a valid conference ID.', array('voice' => $voice));
      break;
    case 'silenceTimeout':
    case 'timeout':
      say('Sorry, I didn\'t hear anything.', array('voice' => $voice));
      break;
  }
}
?>

Now for a fun feature. Let’s let conference ID owners — the room administrator — get a text message any time someone joins their conference room. Never miss a conference call again. And for kicks, send a text message when they leave, too.

<?php
// An array of conference IDs and phone numbers to alert.
// If a conference ID is used that has a phone number attached,
// when someone joins or leaves that conference, the attached phone
// number will get an SMS alerting them.
$pins = array();
$pins['1337'] = '14075551212';
$pins['1234'] = '19255556789';
$pins['2600'] = '';
answer();

while ($currentCall->isActive()) {
  $response = ask('Enter your conference ID. Press the pound key when finished.', array(
      'choices' => '[3-10 DIGITS]',
      'terminator' => '#',
      'mode' => 'keypad',
      'timeout' => 8
  ));
  switch($response->name) {
    case 'choice':
      if (!array_key_exists($response->value, $pins)) {
        say('Sorry, that is not a valid conference ID.');
        break;
      }
      if (array_key_exists($response->value, $pins) && !empty($pins[$response->value])) {
        // Send an alert that someone has entered the conference
        message($currentCall->callerID . ' has entered conference ' . $response->value, array('to' => $pins[$response->value], 'network' => 'SMS'));
      }
      say('<speak>Conference ID <say-as interpret-as="vxml:digits">' . $response->value . '</say-as> accepted. You will now be placed into the conference. Press pound to exit without disconnecting. Please announce yourself.</speak>');
      conference($response->value, array('terminator' => '#'));
      if (array_key_exists($response->value, $pins) && !empty($pins[$response->value])) {
        // Send an alert that someone has left the conference
        message($currentCall->callerID . ' has left conference ' . $response->value, array('to' => $pins[$response->value], 'network' => 'SMS'));
      }
      // Pause a moment before asking for another conference.
      sleep(1);
      break;
    case 'badChoice':
      say('Sorry, that is not a valid conference ID.', array('voice' => $voice));
      break;
    case 'silenceTimeout':
    case 'timeout':
      say('Sorry, I didn\'t hear anything.', array('voice' => $voice));
      break;
  }
}
?>

And there’s a full-featured conference calling application in about 50 lines of code. We started with a basic one-liner and slowly added features to build a conference calling service that rivals the professional conference applications. The full code is available from the Tropo Samples repository on Github. The download on Github has some additional configuration, like allowing you to set a voice for all the prompts and turn on and off the feature that restricts this to known conference IDs.

How robust is the code? This exact application is what we use every day as our conference calling line. Calls with customers, sales prospects, and each other all happen over a conference line backed by the code in this tutorial.