Asterisk Jargon

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Asterisk Jargon

• Carl Davis

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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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What is Asterisk?

• Popular Open Source, multi-protocol PBX (Private
  Branch Exchange)
• Provides a library of basic telephony
  applications for use as building blocks for
  advanced functionality
• Includes Common PBX functionality such as
  voicemail, call queuing, conferencing, music on
  hold and more
• 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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Asterisk Architecture
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Network Interfaces

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

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FXS/FXO

• Analog Line Interface
• FXS Foreign Exchange Station
• Generates Dialtone
• Generates Ring
• Connects to Analog Phones (aka Stations)
• FXO Foreign Exchange Office
• Accepts Dialtone from Central Office (CO)
• Provides Connection to the CO

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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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Telephony Channels

• Telephony Connections
• Channels map physical FXO and FXS connections to
  logical Asterisk channels
• Trunkgroups an advanced topic
• Non-Facility Associated Signaling (NFAS)
• Generic Requirement-303 (GR-303)
• These relationships are defined in the
  zapata.conf channel configuration

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Connections (Users/Peers/Friends)

• VoIP Connections
• Users -gt connections that authenticate to us
  (phones, etc)
• Peers gt authenticate us (to a service provider)
• Friends -gtConnections that may do both
• These relationships are defined in the channel
  configuration (sip.conf, iax.conf)

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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 (Analog, PRI, BRI)

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Channel Types

• Channel Types can 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 and SCCP Drivers 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 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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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 bit-rate vary from one codec
  to the next.
• Examples
• ulaw, alaw, gsm, g.723, g.726, g.729

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Dialplan

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

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Contexts

• Named group of Extensions
• Extensions are unique only inside a context
• Example of a context label incoming
• Special Contexts
• globals
• general
• Contexts are used for security and to
  differentiate services

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Extensions

• An extension is an instruction triggered by an
  incoming call or by digits being dialed on a
  Channel.
• Defined Within Context
• Specify what happens to calls as they make their
  way through the dialplan.
• Can be numeric or alphanumeric
• Can be defined using wildcard syntax to provide
  handling for predefined extension groups

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More Extensions

• An extension is composed of three components
• descriptor
• priority (each extension can include multiple
  steps the step number is called the priority)
• application that performs action for the call
• Example
• exten gt 123,1,Answer( )
• extengt _NXX976XXXX,1,Congestion()

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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,n,Playback(hello-world)
• exten gt s,n,Hangup( )

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Priority

• Defines step number in an Extension script
• Numbered sequentially, starting with 1
• Unnumbered Priority
• 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

• A channel variable (such as the CallerID number)
  is associated only with a particular call.
• Predefined channel variables are available for
  use within the dialplan and are explained in the
  README.variables file
• 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)
• Global Variables
• globals Special Context in extensions.conf
• 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 a macro allows
  generalization
• 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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Example Macro

• macro-dialuser
• exten gt s,1,GotoIf(DB_EXISTS(CFD/MACRO_EXTE
  N) 0?checkdnd)
• exten gt s,n,set(CFDDB_RESULT)
• exten gt s,n,set(MYEXTENMACRO_EXTEN)
• exten gt s,n,goto(staff_incoming,CFD,1)
• exten gt s,n(checkdnd),GotoIf(DB_EXISTS(DND/
  MACRO_EXTEN) 0?dialuser,1)
• Tell them we are not all there
• exten gt s,n,Playback(tt-monkeysintro)
• exten gt s,n,Hangup
• exten gt dialuser,1,dial(ARG1,15)
• exten gt dialuser,n,goto(d-DIALSTATUS,1)

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Example Macro (cont)

• exten gt d-NOANSWER,1,Answer
• exten gt d-NOANSWER,n,wait(2)
• exten gt d-NOANSWER,n,Playback(vm-nobodyavail)
• exten gt d-NOANSWER,n,Hangup
• exten gt d-BUSY,1,Answer
• exten gt d-BUSY,n,wait(2)
• exten gt d-BUSY,n,Playback(tt-allbusy)
• exten gt d-BUSY,n,Hangup
• exten gt _d-.,1,Answer
• exten gt _d-.,n,wait(2)
• exten gt _d-.,n,Playback(pbx-invalid)
• exten gt _d-.,n,Hangup

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QA

• Carl Davis
• President Chief Architect
• Stellar System Technologies, Inc
• carl_davis_at_stellarsystech.com
• www.stellarsystech.com
• Executive Director
• High Tech Business Council of Rochester
• www.htbc.org