Asterisk Jargon

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Asterisk Jargon

• Alex Vishnev
• Chief Technical Office, VoIP
• ACN

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What is Asterisk?

• Popular open source PBX (Private Branch Exchange)
• Private Telephone Network inside the Enterprise
• Provides a library of basic telephony functions
  which you then use as script building-blocks.
• Common PBX functionality such as voicemail, call
  queuing, conferencing, music on hold and others
  are all included.
• Asterisk is one of the few PBXs in existence that
  connects legacy telephony technologies (Analog,
  PRI) to VoIP interfaces (SIP,H.323)

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AGENDA

• What is Asterisk?
• PBX Definition and Functionality
• Architecture Overview
• Jargon
• Network Interfaces
• VoIP Connections
• Dial Plan
• Codec
• Channel
• Context
• Extension
• Application
• Variable
• Macro

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Asterisk Architecture
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Network Interfaces

• PSTN
• Analog (FXS/FXO)
• Digital (E1/T1,BRI)
• IP
• SIP
• H.323
• IAX

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FXS/FXO

• Analog Line Interface
• FXS Foreign Exchange Station
• Generates Dialtone
• Generates Ring
• Connect Analog Phones
• FXO Foreign Exchange Office
• Accepts Dialtone from CO
• Connect Line from Telco

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T1

• Primarily Used In US
• T1 PSTN Digital Interface
• CAS Channel Associated Signaling (Wink,
  Immediate, etc)
• 24 Voice Channels
• MF/DTMF In-band Signaling
• PRI Primary Rate Interface (D Channel)
• 23 Voice Channels
• 1 Data Channel
• Q.931 Messages

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E1

• ITU-T Specification
• Digital Interface
• CAS Channel Associated Signaling
• 30 Voice Channels
• R2MF
• PRI Primary Rate Interface (D Channel)
• 28 Voice Channels
• 2 Data Channel
• Q.931 Messages

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Connections (Users/Peers/Friends)

• VoIP Connections
• Users -gt connections that authenticate to us
  (phones, etc)
• Peers gt authenticate us (service provider)
• Friends -gtConnections that do both may be defined
  as
• Relationship defined in (sip.conf, iax.conf)

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Dialplan

• "road map" for how Asterisk will work.
• specifies how Asterisk should handle calls.
• consists of a list of instructions or steps that
  Asterisk should follow.
• To successfully set up your own Asterisk system,
  it is absolutely vital that you understand
  dialplans.

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Codec

• Codec Short for Coder/Decoder
• Codecs determine the sustained data bit rate
  which is required for each channel.
• The codec converts the analog voice signal to a
  digitally encoded one that should take less space
• The quality and data bitrate vary from one codec
  to the next.
• Examples
• ulaw, alaw, gsm,g.729, g.723.

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Channels

• Telephony connections to the PBX
• Call Processing in Asterisk Is Centered Around
  Channels
• Drivers for various kinds of connections
• IP (SIP,H.323,IAX,SCCP,MGCP)
• PSTN (Zaptel, PRI, BRI,

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Channel Types

• Channel Types could be Physical or Logical
• Agent ACD Agent channel
• Console Linux console client driver for sound
  cards (using OSS or ALSA)
• H.323 An older VOIP protocol
• IAX and IAX2 Inter-Asterisk Exchange protocol,
  Asterisk's own VOIP protocol
• MGCP Media Gateway Control Protocol, another
  VOIP protocol
• SIP Session Initiation Protocol, the most common
  VOIP protocol
• Skinny A driver for Cisco Skinny Client Control
  Protocol (a VOIP protocol)
• VOFR voice over frame relay Adtran style
• VPB For connecting ordinary telephone and
  telephone lines using Voicetronix cards
• Zap For connecting ordinary telephones and
  telephone lines using Digium cards. Also for
  TDMoE and for Asterisk zaphfc

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Channel Drivers

• Channel drivers offering other technologies can
  be optionally installed
• Bluetooth Allows the use of bluetooth devices to
  change routing - see CVS "chan_btp"
• CAPI ISDN CAPI channel
• mISDN mISDN channel
• vISDN vISDN channel (native BRI channel for HFC
  chipsets)
• SCCP An alternate Skinny/SCCP channel
• Sirrix ISDN BRI for Sirrix cards (with optional
  ISDN encryption)
• UNISTIM Nortel Unistim channel
• Unicall Replacement for zaptel, with R2 support
• SS7 SS7 (ISUP on MTP2/3) channel

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Context

• Named Group of Extensions
• Extensions are Unique only Inside Context
• incoming example of context
• Special Contexts
• globals
• general
• Contexts are Used for Security and to
  Differentiate Services

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Extensions

• Defined Within Context
• An extension is an instruction triggered by an
  incoming call or by digits being dialed on a
  Channel.
• Extensions specify what happens to calls as they
  make their way through the dialplan.
• Traditional Extensions (i.e. extension 153)
• Extensions can be used for much more in Asterisk.
• exten gt (followed by the name of extensions)
• Can be numeric (i.e. regular Extension)
• Alphanumeric (i.e. email address)

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Extensions (More then just a Number)

• An extension is composed of three components
• The name (or number) of the extension
• The priority (each extension can include multiple
  steps the step number is called the priority)
• The application (or command) that performs some
  action on the call
• Example
• exten gt name, priority, application( )
• exten gt 123,1,Answer( )

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Special Extension

• s - extension
• Calls entering a context without a specific
  destination (i.e. ring on FXO line), they are
  handled automatically by the s extension.
• Example
• incoming
• exten gt s,1,Answer( )
• exten gt s,2,Playback(hello-world)
• exten gt s,3,Hangup( )

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Priority

• Defines step number in a multi-step Extension
• Numbered sequentially, starting with 1.
• Unnumbered Priority (Contradiction -))
• n priority, - next
• Takes the number of the previous priority and
  adds 1
• No need to re-number dial plan when changes are
  made.
• Example
• exten gt 123,1,Answer( )
• exten gt 123,n,do something
• exten gt 123,n,do something else
• exten gt 123,n,Hangup( )
• Label Priority
• exten gt 123,n(label),do something
• Executes one Specific Application

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Variables

• Channel Variables
• A channel variable is a variable (such as the
  CallerID number) that is associated only with a
  particular call.
• Predefined channel variables available for use
  within the dialplan,which are explained in the
  README.variables file in the doc subdirectory of
  the
• Channel variables are set via the Set( )
  application
• exten gt 123,1,Set(MAGICNUMBER42)
• Environment variables are a way of accessing Unix
  environment variables from within Asterisk.
• Example ENV(var) var Unix Environment
  Variable
• Global Variables
• globals Special Context
• JOHNZIP/1
• JANESIP/JANE
• exten gt 123,1,SetGlobalVar(JOHNZap/1)

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Applications

• Applications are the workhorses of the dialplan.
• performs a specific action on the current channel
• Types
• Generic (Authenticate, VMAuthenticate,etc)
• Billing (SetAccount, SetAMAFlags)
• Call Processing (Answer, Busy, Dial, Hangup)
• Caller Presentation (SetCallerID,
  SetCallerCIDName)
• Database(DBdel, DBget, DBput)
• Application Interface( AGI, EAGI, PERL, PHP)
• Audio( Playback, Playtones, MusicOnHold)
• Voicemail Conferencing( MeetMe, VoiceMailMain)
• Queue/ACD (AddQueueMember,AgentLogin)

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Macros

• Macros are used to reduce the amount of redundant
  code in the dialplan.
• passing arguments to the macro allows to
  generalize macros
• Single line invocation from dialplan
• Macros are identified in the dialplan by starting
  a context name with "macro-".
• s extension is used within macros since we want
  the actions to be performed automatically
• Arguments in macros are accessed as ARGn

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QA

• Alex Vishnev
• Chief Technical Officer, VoIP
• 13620 Reese Blvd. Ste. 400
• Huntersville, NC 28078
• Office [phone]
• Mobile [phone]
• Fax [phone]
• Email avishnev_at_acninc.com
• Website http//www.acninc.com