Call control is being reinvented in several exciting new ways. In this talk, we explore existing models for building voice applications using the Asterisk Dialplan, Asterisk AGI/AMI, and how new in-cloud voice APIs are reinventing the way that build, host, and scale voice applications. such as in-cloud dialplan API with Twilio. Taking a programmer's perspective, we highlight desirable dialplan properties such as simplicity, automatic scalability, integration with existing databases and servers, and separation of business logic from telephony logic. We also explore the tradeoffs that Twilio has made to simplify the experience of building voice applications, including the concept of encapsulating the state of a voice call in a URL. We conclude with thoughts about how Asterisk could be streamlined for in-cloud dialplan APIs and the services that support them.

1. Reinventing the
Dialplan
Astricon Oct 14, 2009
Copyright 2009 Twilio

2. -Call
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Voice Applications
Asterisk

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Voice Applications
The Cloud
Asterisk

4. Voice Applications
Voice Guru

5. Maintained by your Voice Guru
Asterisk
Native scripting language
Dialplan written by your Voice Guru
Application
Asterisk Dialplan
Language: Native Scripting Where: Local on call router

6. IP
Asterisk AGI/AMI
Java/C/Ruby...
Application
Asterisk AGI/AMI
Language: AGI/AMI API + Where: Remote via IP
Java/C/Ruby/Python/Etc

7. Maintained by your Voice Guru
IP
Asterisk AGI/AMI
Java/C/Ruby...
Application
Asterisk AGI/AMI
Language: AGI/AMI API + Where: Remote via IP
Java/C/Ruby/Python/Etc

8. Maintained by your Programmer
IP
Asterisk AGI/AMI
Java/C/Ruby...
Application
Asterisk AGI/AMI
Language: AGI/AMI API + Where: Remote via IP
Java/C/Ruby/Python/Etc

9. Enter the Programmer
• Commodity skillset
• Easy to hire
• Cheap
Programmer

10. Better but...
IP
Asterisk
Large API with "lite" documentation. AGI/AMI
The distinction between AGI/AMI can
be confusing.
Tight integration between call router
and voice app: direct socket Java/C/Ruby...
connections Application
SCALING=HARD
Asterisk AGI/AMI
Language: AGI/AMI API + Where: Remote via IP
Java/C/Ruby/Python/Etc

11. IP
Asterisk AGI/AMI
Lets mull this over...

12. IP
Asterisk AGI/AMI
Why do I need a
Voice Guru?

13. IP
Asterisk AGI/AMI
Expert
What if I outsourced
my voice guru?

14. IP
AGI/AMI
Asterisk in
the Cloud

15. IP
?????
Asterisk in
the Cloud
What is the ideal voice app API?

16. Web developers are (one of)
the largest engineering workforces
on the planet
• HTTP
• Request/Response
• XML/JSON
• WAV/MP3

17. Magic
Ruby
Java
Asterisk in
PHP
the Cloud
Python
.
.
.
Create new messaging protocol
and new API for each language?

18. HTTP/XML
Ruby
REST
Java
Asterisk in
PHP
the Cloud
Python
.
.
.
Normal Web Server
HTTP/XML/REST

19. HTTP/XML
Ruby
REST
Java
PHP
Python
Twilio .
.
.
Normal Web Server
HTTP/XML/REST

20. HTTP/XML
REST Google App Engine
Microsoft Azure
Twilio Heroku
Leverage existing cloud hosting
Scale: 1-10,000’s of simultaneous calls

21. Request/Response
1 Procedural programming
digits = GetKeypadPresses();
switch(digits) {
case 1:
blah();
break;
}

22. Request/Response
1 Procedural programming
digits = GetKeypadPresses();
switch(digits) {
case 1:
blah();
break;
}
Not how HTML works!

23. Request/Response
2 Web programming
<form action=”digits.php”>
<input type=”text” name=”digits” />
<input type="submit" value="Go"/>
</form>

24. Request/Response
2 Web programming
<form action=”digits.php”>
<input type=”text” name=”digits” />
<input type="submit" value="Go"/>
</form>
Submit back to digits.php
on input

25. Request/Response
3 Web-like voice programming
<Gather numDigits=”5”
action=”digits.php”/>
Apply the same model for
voice applications

26. Request/Response
3 Web-like voice programming
<Gather numDigits=”5”
action=”digits.php”/>
Submit back to digits.php
on input

27. Request/Response
4 Language-specific libraries
$r = new Response();
$r->append(new Say("Hello World"); PHP
$r->Respond();
r = twilio.Response()
r.append(twilio.Say("Hello World")) Python
print r
@r = Twilio::Response.new
@r.append(Twilio::Say.new "Hello World") Ruby
puts @r.respond
TwiMLResponse response = new TwiMLResponse();
Say say = new Say("Hello World"); Java
System.out.println(response.toXML());

28. ⤸
⤸
⤸
HTTP 307 HTTP 307
u.com b.com c.com
PBX Application Authorization CRM
Service Integration
Response Chaining

29. Stateless ‘Twimlet’ URLs + REST

30. curl -fSs -u "$ACCOUNTSID:
$AUTHTOKEN" -d "Caller=$CALLERID" -d
"Called=$PHONE" -d "Url=http://
twimlets.com/message?Message=$MSG"
"https://api.twilio.com/2008-08-01/
Accounts/$ACCOUNTSID/Calls
Stateless ‘Twimlet’ URLs + REST

31. Put the Voice Guru in the Cloud
1 Asterisk in the cloud
Adopt a standards-based web API
2 HTTP/XML/REST
Leverage existing web infrastructure
3 Apache/Tomcat/AWS/AppEngine/Azure/Heroku
Let the cloud handling scaling
4 1-10,000’s simultaneous calls
Don’t break request/response model
5 Build libraries for PHP/Python/Java/C#/Ruby etc.

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Voice Applications
The Cloud
Asterisk

33. Simplifying Telecom
Simple • Powerful • Pay-As-You-Go
Evan Cooke
Co-Founder & CTO
twitter: @twilio
phy@twilio.com
http://www.twilio.com