Realtime multimedia and communication in packet networks

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Real-time multimedia and communication in packet
networks

• Asterisk AGI and Manager Interface

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Last Practical

• Create a calculator application using the
  Asterisk dialplan
• E.g. phone an extension
• answers and provide an IVR menu saying press 1
  to go to the calculator, 2 to go somewhere else,
  and 3 to go somewhere further
• If I press 1 must be routed to calculator where
  I am prompted to choose to go to multiplication
  menu, division menu, add menu or subtraction menu
• 1,2,3,4
• Within each menu prompt user for expression
  separated by star ()?
• So in addition menu, pressing 10020 should
  return 120
• While in multiplication menu pressing 10020 will
  return 2000
• Results can be played using Festival
• After each result should have option of another
  operation or going to one of the other menus
  (-/)?
• Remember to check out http//www.voip-info.org/ -
  Check out the Cut function!

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Controlling Asterisk

• Number of ways Asterisk can be controlled
• Dialplan
• Asterisk scheduling (call me)?
• Asterisk Gateway Interface (AGI)?
• Manager Interface

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AGI

• AGI allows us to add functionality to Asterisk
  with many different programming languages
• Java, Perl, PHP, C, Pascal Anything!
• Provides a standard interface through which
  programs may control asterisk
• Used for advanced logic or to communicate with
  resources such as relational databases and
  external devices
• Allows asterisk to perform tasks that would be
  otherwise difficult or impossible

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AGI How it works

• The AGI script is called from the dialplan?
• Asterisk and your program communicate via the
  STDIN, STDOUT and STDERR communications channels
  (file handles in programming)?
• Your AGI scripts reads input via its STDIN file
  handle
• Your AGI script writes back to asterisk via its
  STDOUT file handle
• Your AGI program writes error message back to
  asterisk via its STDERR file handle

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Starting your AGI program

• Syntax
• exten gt extennumber,priority,application,argument
  s
• The application is AGI
• The argument is the filename of your program
• The script must be
• executable (chmod x filename)?
• located in /var/lib/asterisk/agi-bin in source
  versions of asterisk
• Located in /usr/share/asterisk/agi-bin in binary
  vesions of asterisk
• Example Run a perl script agi-test.agi
• exten gt 1,2,AGI, agi-test.agi

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Passing args

• exten 1,2,AGI,agi-test.agiARG1ARG2
• AGI programs always receive two args
• 1 path to the AGI script
• 2 Arguments passed from the dialplan
• Notes about arguments
• If no arg is given the arg is empty.
• Consists of everything on the line following the
  verticle bar after the file name, up until the
  final vertical bar?
• Quotes are taken as being part of the argument

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Communicating with

• Use 'show agi' at the CLI will give you a list of
  commands
• At script startup time, sends a group of
  variables to your script which you have to read
  in
• Each item is sent on a line terminated with a
  newline. The last item is followed by an empty
  line
• agi_request agi-test.agi
• agi_channel SIP/1000-bcgd162
• agi_language en
• agi_context mtsietsi
• agi_extention 105
• agi_priority 2
• Commands sent to must be terminated with newline

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AGI examples?

• Perl - /usr/share/asterisk/agi-bin/agi-test.agi
• Java - /usr/share/asterisk/agi-bin/mosJava.java
• /usr/share/asterisk/agi-bin/mosJava.agi

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Manager API

• A client/server module that allows us to interact
  with via TCP/IP
• Similar to SMTP and HTTP
• Communicates using tags
• headervalue terminated with a newline
• First tag must be one of the following
• Action an action requested by the client.
• Response A response to an action from Asterisk
• Event An event reported by Asterisk to the client

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Manager interface (login)?

• telnet into 146.231.121.88 on port 5038
• Login
• Action Login
• Username voipuser
• Secret voipuser
• Events off
• /r/n

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Manager interface (Originate)?

• Action Originate
• Channel SIP/1000
• Exten s
• Context mtsietsi
• Priority 1
• Timeout 10000

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Manager interface (Monitor)?

• Action Monitor
• Channel SIP/ab5s51182s
• File monitor
• Mix 1

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Today's Practical

• 1) Extend your calculator to incorporate an AGI
  program
• Do the calculation
• Parse the numbers
• Take a number to a power
• Solve complex problems i.e. y ax4 ax3 ax2
  ax a