1. ASTERISK “Open Source Communications Platform”
Presentation by:
Rahul Dev Parashar
MTech(CSE)
IIT Bombay

2. References: 1. 2.

3. Outline: 1. Introduction 2. Critical Architectural Concepts
--> Channels
--> Channel Bridging
--> Frames
3. Asterisk Component Abstractions
--> Channel Drivers
--> Dialplan Applications
--> Dialplan Functions
--> Codec Translators
4. Threads
5. Call Scenarios
--> Checking Voic
--> Bridged Call

4. Introduction:
--> Open source telephony applicatios plateform
--> Server application for performing custom processing of calls
--> Started by Mark Spencer in 1999
--> Name comes from wildcard character(*) of linux
--> Customization of phone call features can be done like:
Voic , Playing back a sound file, Speech recognition
--> It supports:
VoIP(Voice over IP)
Analog and digital connectivity to traditional telephone n/w
Connects to PSTN(Public Switched Telephone N/W)

5. Critical Architectural Concepts:
1. Channels:
Ex: caller interacting with voic
Figure: A Single Call Leg, Represented by a Single Channel

6. Ex: Connection between two phones
2. Channel Bridging:
Ex: Connection between two phones
Figure: Two Call Legs Represented by Two Channels

7. Types of bridging: 1. Generic bridging 2. Native bridging
Figure: Example of a Native Bridge

8. 3. Frames:
--> Communication within the Asterisk code during a call is done by using frames
--> Signalling frames are used to send messages about call signalling events, such as a digit being pressed, a call being put on hold, or a call being hung up.
Some available frames:
* VOICE --- These frames carry a portion of an audio stream
* VIDEO --- These frames carry a portion of a video stream
* MODEM --- The encoding used for the data in this frame
* CONTROL --- These frames are used to indicate call signalling events. These events include a phone being answered, hung up, put on hold, etc.
* DTMF_BEGIN --- Frame is sent when a caller presses a DTMF key
* DTMF_END --- Frame is sent when caller stops pressing DTMF key
DTMF stands for Dual-Tone Multi-Frequency. This is the tone that is sent in the audio of a phone call when someone presses a key on their telephone.

9. Asterisk Component Abstractions:
1. Channel Drivers:
This component is responsible for translating between the Asterisk channel abstraction and the details of the telephony technology that it implements
Figure: Channel Technology and Abstract Channel Layers

10. --> send_digit_begin --> send_digit_end --> read --> write
The most important methods in ast_channel_tech are:
--> requester
--> type
--> call
--> answer
--> hangup
--> indicate
--> send_digit_begin
--> send_digit_end
--> read
--> write
--> bridge

11. 2. Dialplan Applications:
# It defines how asterisk handles inbound and outbound calls.
There are 4 main concepts in dialplan:
1. Contexts: Dialplans are divided into parts. Contexts keeps these different parts interect with each other.
2. Extensions: Unique sequence of steps that Asterisk follows.
3. Priorities: Extension has priorities.
4. Applications: Workhorses of dialplans.
Ex: answer(), hangup() etc.
* This code define the rules for what happens when someone dials 1234.
exten => 1234,1,Answer()
same => n,Playback(demo-congrats)
same => n,Hangup()
* This code define the rules for what happens when someone dials 5678.
exten => 5678,1,Answer()
same => n,Read(DIGITS,beep,4)
same => n,SayDigits(${DIGITS})