VoIP, Asterisk, and Java

Michael P. Plezbert

Agilis Systems, Inc

St. Louis Java Users Group

April 13, 2006

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Overview VoIP Basics

Asterisk PBX

Asterisk Gateway Interface

Manager Interface

Asterisk-Java Library

Example

Security

Resources

About Us

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

VoIP Two-way (pseudo-) real-time

audio communication over IP

network

Allows “free” computer-to-

computer calls (disregarding

broadband connection fees), e.g.

Skype

Calls to “regular” phone

network requires specialized

hardware or service provider,

e.g. Vonage

POTS

Internet

Bridge

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

VoIP

Pros Allows use of single

network for voice and data

Cost savings over

traditional PBX

Can leverage IT support

staff

Easier interaction with

computer/data systems

Cons Reliability of data network

becomes paramount

Latency and jitter are

problems, requiring

overallocation of

bandwidth and/or QoS

Requires VoIP phones or

other specialized hardware

to emulate traditional

phone experience

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Asterisk PBX Open source software PBX system

Runs on commodity computer hardware (x86) and software

(linux/BSD)

Supports standard VoIP protocols

Hardware available for connection to POTS network

Many features built in, e.g. voicemail, call queues, conference calls

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Asterisk Interaction Asterisk can communicate with external programs in several ways

Call a local script

More suitable for scripting languages than Java

Connect via socket to an “AGI server”

Simple text messages back and forth

Server can be written in any language that supports socket comm

Cannot be used to originate calls

Accept socket (telnet) connections to a manager interface

Can be used to originate calls and receive other events

Read local “call files”

Simple way to originate calls

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Asterisk Gateway Interface

AsteriskServer

AGIServer

1

2 3

1: a call comes into the asterisk server

2: the asterisk server makes a socket

connection to an AGI server

3: the AGI server sends commands

and receives results over the socket,

controlling the flow of the call

Note that the AGI server cannot

originate a call using this interface

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

AGI Commands The AGI contains many commands for controlling a call, including

answer

hangup

stream file

Limited to streaming local sound files on the asterisk server,

NOT over the socket interface

wait for digit

record file

Records to local file on the asterisk server

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Manager Interface1: client connects via socket to

the asterisk manager interface

and initiates a call

2: asterisk server places the call

3: when call connects, asterisk

server connects via socket to

the AGI server

4: the AGI server can send

commands and receive results

and events over both the AGI

socket connection and the

manager interface connection

AsteriskServer

AGIServer

1

2

34 4

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

The Asterisk-Java Library

Implements both the AGI server interface and the

manager client interface

Contains classes and methods for sending

commands and receiving events

Eliminates the need to manually build or parse

command strings

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

An Example

Simple example will

Originate a call

Play a sound file

Wait up to 5 seconds for a response

If 1, 2, or 3 is pressed then

Play sound files indicating digit pressed

Else

Play sound file indicating invalid choice

Hangup

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Security VPN or ssl-tunnel suggested

Socket comm is plain text (including authentication to

manager interface)

AGI connection is not authenticated

Asterisk configuration

Limit accessibility of external calls

VoIP, Asterisk, and Java St. Louis JUG April 13,

2006

Resources Asterisk:

http://www.asterisk.org

Asterisk@Home:

http://asteriskathome.sourceforge.net

Asterisk-Java Library:

http://www.asteriskjava.org

http://sourceforge.net/projects/asterisk-java