Automated Speech Recognition (ASR) as-a-Service can be powered via Tropo and SIP using this simple open source code provided below.  This service is perfect for adding speech recognition to your existing Asterisk, FreeSwitch, YATE, or enterprise app from the stone ages.

Here’s how it works!

You can transfer a phone call via SIP from a platform that doesn’t support ASR to Tropo along with the following SIP headers: prompt, choices, and returnaddress (SIP address). Tropo automatically answers the call and prompts the user the the text-to-speech (TTS) prompt passed. It automatically loads the ASR grammar with the choices passed. Upon successfully processing the speech recognition, Tropo transfers the call and the recognized result back to the return SIP adrress along with an x-voxeo-result SIP header containing your keyword spoken by the user.

Here’s the Tropo code using our hosted Scripting API:

This code is written in Ruby using our Tropo Scripting API.  You can use $currentCall.getHeader to get the SIP headers passed to your Tropo application and you can send headers to other SIP applications using the Tropo transfer method.  The speech recognition magic happens in the Ask method.

recoresult = ask $currentCall.getHeader("x-sbc-prompt"), {
   :choices => $currentCall.getHeader("x-sbc-choices")}

transfer $currentCall.getHeader("x-sbc-returnaddress"), {
    :headers => {'x-voxeo-result' => recoresult.value}
    }

Here’s how we tested it.

We used Phono, our browser-based webphone, to call Tropo and pass the prompt, choices, and returnaddress parameters.

phono.phone.dial("sip:9996106030@sip.tropo.com", {
  	headers: [
	{
		name:"returnaddress",
		value: "sip:9996106032@sip.tropo.com" // you could use returnaddress var to send the results back to Phono's SIP address
	},
	{
		name:"prompt",
		value: "What is your favorite color?"
	},
	{
		name:"choices",
		value: "blue,green,red,yellow"
	}
	],

Just to prove that yet another SIP application could receive the speech recognition results, we created another Tropo application in Ruby using the Scripting API to simple say the results.

say "You said " + $currentCall.getHeader("x-voxeo-result")

This second test application would typically be omitted for a real application since the returnaddress would most likely be the originating SIP address of your switch to return to your original callflow.  It’s cool that you could transfer to yet another application for additional processing!

What’s Next?

You can clone or fork this open source project on Github and use it today for as little as $.03 per minute for the Tropo call.  Let us know if you would prefer for us to build this service out for commercial use.

 

Related posts:

1. Meet Phono – Tropo’s Web Phone
2. How-To: Distinguish PSTN, Skype, iNum, and SIP in your Tropo applications
3. How to Build a Reminder Service Using Tropo and Ruby on Rails
4. Create a Group SMS Service Using Tropo in 5 Lines of Code!
5. Tropo-Powered Hamradio Callsign Lookup App

Tags: asr, phono, service, sip, speech, speechrecognition, text to speech

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