Transcript java.ociweb.com

VoIP, Asterisk, and Java
Michael P. Plezbert
Agilis Systems, Inc
St. Louis Java Users Group
April 13, 2006
Overview

VoIP Basics

Asterisk PBX
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Asterisk Gateway Interface

Manager Interface
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Asterisk-Java Library
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Example

Security

Resources
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About Us
VoIP, Asterisk, and
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VoIP



Two-way (pseudo-) real-time
audio communication over IP
network
Allows “free” computer-tocomputer calls (disregarding
broadband connection fees),
e.g. Skype
Calls to “regular” phone
network requires specialized
hardware or service provider,
e.g. Vonage
VoIP, Asterisk, and
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VoIP

Pros

Cons

Allows use of single
network for voice and
data

Reliability of data
network becomes
paramount

Cost savings over
traditional PBX


Can leverage IT support
staff
Latency and jitter are
problems, requiring
overallocation of
bandwidth and/or QoS

Easier interaction with
computer/data systems
VoIP, Asterisk, and
St. Louis JUG

Requires VoIP phones
or other specialized
hardware to emulate
traditional phone
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Asterisk PBX


Open source software PBX system
Runs on commodity computer hardware (x86) and software
(linux/BSD)
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Supports standard VoIP protocols
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Hardware available for connection to POTS network
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Many features built in, e.g. voicemail, call queues, conference
calls
VoIP, Asterisk, and
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Asterisk Interaction

Asterisk can communicate with external programs in several
ways

Call a local script
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Connect via socket to an “AGI server”
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Simple text messages back and forth
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Server can be written in any language that supports socket comm
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Cannot be used to originate calls
Accept socket (telnet) connections to a manager interface
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
More suitable for scripting languages than Java
Can be used to originate calls and receive other events
Read local “call files”
VoIP, Asterisk, and
Simple way to originate
calls
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Asterisk Gateway Interface
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
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VoIP, Asterisk, and
interface
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1
Asterisk
Server
2
3
AGI
Server
AGI Commands
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The AGI contains many commands for controlling a call,
including
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answer

hangup
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stream file
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Limited to streaming local sound files on the asterisk
server, NOT over the socket interface
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wait for digit

record file
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VoIP, Asterisk, and
Records to local file on the asterisk server
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Manager Interface
1: client connects via socket
to the asterisk manager
interface and initiates a call
2
2: asterisk server places the
call
Asterisk
Server
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
VoIP, Asterisk, and
manager interface St. Louis JUG
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4 3
AGI
Server
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4
The Asterisk-Java Library
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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
St. Louis JUG April 13,
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
St. Louis JUG April 13,
Security
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VPN or ssl-tunnel suggested
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Socket comm is plain text (including authentication to
manager interface)
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AGI connection is not authenticated
Asterisk configuration
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Limit accessibility of external calls
VoIP, Asterisk, and
St. Louis JUG April 13,
Resources
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Asterisk:
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Asterisk@Home:
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http://www.asterisk.org
http://asteriskathome.sourceforge.net
Asterisk-Java Library:
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http://www.asteriskjava.org
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http://sourceforge.net/projects/asterisk-java
VoIP, Asterisk, and
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