October 10-13, 2006• San Diego Convention Center, San Diego California
Asterisk Jargon
Carl Davis
Agenda
October 10-13, 2006• San Diego Convention Center, San Diego California
• What is Asterisk?
– PBX Definition and Functionality
– Architecture Overview
• Jargon
– Network Interfaces
– VoIP Connections
– Dial Plan
– Codec
– Channel
– Context
– Extension
– Application
– Variable
– Macro
What is Asterisk?
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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)
Asterisk Architecture
October 10-13, 2006• San Diego Convention Center, San Diego California
Network Interfaces
October 10-13, 2006• San Diego Convention Center, San Diego California
• PSTN
– Analog (FXS/FXO)
– Digital (E1/T1,BRI)
• IP
– SIP
– H.323
– IAX
– SCCP/Skinny
FXS/FXO
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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
T1
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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
E1
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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
Telephony Channels
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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
Connections
(Users/Peers/Friends)
October 10-13, 2006• San Diego Convention Center, San Diego California
• VoIP Connections
– Users -> connections that authenticate to
us (phones, etc)
– Peers –> authenticate us (to a service
provider)
– Friends ->Connections that may do both
• These relationships are defined in the
channel configuration (sip.conf, iax.conf)
Channels
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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)
Channel Types
October 10-13, 2006• San Diego Convention Center, San Diego California
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
Channel Drivers
October 10-13, 2006• San Diego Convention Center, San Diego California
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
Codec
October 10-13, 2006• San Diego Convention Center, San Diego California
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
Dialplan
October 10-13, 2006• San Diego Convention Center, San Diego California
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.
Contexts
October 10-13, 2006• San Diego Convention Center, San Diego California
•
•
•
•
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
Extensions
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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
More Extensions
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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 => 123,1,Answer( )
– exten=> _NXX976XXXX,1,Congestion()
Special Extension
October 10-13, 2006• San Diego Convention Center, San Diego California
• ‘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 => s,1,Answer( )
– exten => s,n,Playback(hello-world)
– exten => s,n,Hangup( )
Priority
October 10-13, 2006• San Diego Convention Center, San Diego California
• 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 => 123,1,Answer( )
• exten => 123,n,do something
• exten => 123,n,do something else
• exten => 123,n,Hangup( )
– Label Priority
• exten => 123,n(label),do something
• Executes one Specific Application
Variables
October 10-13, 2006• San Diego Convention Center, San Diego California
• A channel variable (such as the Caller*ID 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 => 123,1,Set(MAGICNUMBER=42)
• Environment variables are a way of accessing Unix
environment variables from within Asterisk.
– Example: ${ENV(var)}
– Global Variables
• [globals] – Special Context in extensions.conf
– JOHN=ZIP/1
– JANE=SIP/JANE
– exten => 123,1,SetGlobalVar(JOHN=Zap/1)
Applications
October 10-13, 2006• San Diego Convention Center, San Diego California
• Applications are the workhorses of the dialplan.
– performs a specific action on the current channel
• Types
– Generic (Authenticate, VMAuthenticate, etc)
– Billing (SetAccount, SetAMAFlags)
– Call Processing (Answer, Busy, Dial, Hangup)
– Caller Presentation (SetCallerID, SetCallerCIDName)
– Database (DBdel, DBget, DBput)
– Application Interface (AGI, EAGI, PERL, PHP)
– Audio (Playback, Playtones, MusicOnHold)
– Voicemail & Conferencing (MeetMe, VoiceMailMain)
– Queue/ACD (AddQueueMember, AgentLogin)
Macros
October 10-13, 2006• San Diego Convention Center, San Diego California
• Macros are used to reduce the amount of
redundant code in the dialplan.
• Passing arguments to a macro allows
generalization
• Single line invocation from dialplan
• Macros are identified in the dialplan by starting a
context name with "macro-".
• ’s’ extension is used within macros since we
want the actions to be performed automatically
• Arguments in macros are accessed as {ARGn}
Example Macro
October 10-13, 2006• San Diego Convention Center, San Diego California
[macro-dialuser]
exten => s,1,GotoIf($[${DB_EXISTS(CFD/${MACRO_EXTEN})} =
0]?checkdnd)
exten => s,n,set(CFD=${DB_RESULT})
exten => s,n,set(MYEXTEN=${MACRO_EXTEN})
exten => s,n,goto(staff_incoming,${CFD},1)
exten =>
s,n(checkdnd),GotoIf($[${DB_EXISTS(DND/${MACRO_EXTEN}
)} = 0]?dialuser,1)
; Tell them we are not all there
exten => s,n,Playback(tt-monkeysintro)
exten => s,n,Hangup
exten => dialuser,1,dial(${ARG1},15)
exten => dialuser,n,goto(d-${DIALSTATUS},1)
Example Macro (cont)
October 10-13, 2006• San Diego Convention Center, San Diego California
exten => d-NOANSWER,1,Answer
exten => d-NOANSWER,n,wait(2)
exten => d-NOANSWER,n,Playback(vm-nobodyavail)
exten => d-NOANSWER,n,Hangup
exten => d-BUSY,1,Answer
exten => d-BUSY,n,wait(2)
exten => d-BUSY,n,Playback(tt-allbusy)
exten => d-BUSY,n,Hangup
exten => _d-.,1,Answer
exten => _d-.,n,wait(2)
exten => _d-.,n,Playback(pbx-invalid)
exten => _d-.,n,Hangup
Q&A
October 10-13, 2006• San Diego Convention Center, San Diego California
Carl Davis
President & Chief Architect
Stellar System Technologies, Inc
[email protected]
www.stellarsystech.com
Executive Director
High Tech Business Council of Rochester
www.htbc.org