www.itexpo.com October 10-13, 2006• San Diego Convention Center, San Diego California Asterisk Jargon Carl Davis
Www.itexpo.com October 10-13, 2006 San Diego Convention Center, San Diego California Asterisk Jargon Carl Davis.
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www.itexpo.com
October 10-13, 2006• San Diego Convention Center, San Diego California
Asterisk Jargon
Carl Davis
www.itexpo.com
October 10-13, 2006• San Diego Convention Center, San Diego California
Agenda
• What is Asterisk?– PBX Definition and Functionality– Architecture Overview
– Network Interfaces– VoIP Connections– Dial Plan– Codec– Channel
• Jargon– Context– Extension– Application– Variable– Macro
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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
Asterisk Architecture
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October 10-13, 2006• San Diego Convention Center, San Diego California
Network Interfaces
• PSTN– Analog (FXS/FXO)– Digital (E1/T1,BRI)
• IP– SIP– H.323– IAX– SCCP/Skinny
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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
Connections (Users/Peers/Friends)
• 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)
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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
Channel TypesChannel 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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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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October 10-13, 2006• San Diego Convention Center, San Diego California
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 => 123,1,Answer( )– exten=> _NXX976XXXX,1,Congestion()
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October 10-13, 2006• San Diego Convention Center, San Diego California
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 => s,1,Answer( )– exten => s,n,Playback(hello-world)– exten => s,n,Hangup( )
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October 10-13, 2006• San Diego Convention Center, San Diego California
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 => 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
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October 10-13, 2006• San Diego Convention Center, San Diego California
Variables• 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: ${ENV(var)}– Global Variables
• [globals] – Special Context in extensions.conf– JOHN=ZIP/1– JANE=SIP/JANE– exten => 123,1,SetGlobalVar(JOHN=Zap/1)
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October 10-13, 2006• San Diego Convention Center, San Diego California
Applications
• Applications are the workhorses of the dialplan.– performs a specific action on the current channel
• Types– Generic (Authenticate, VMAuthenticate, etc)– Billing (SetAccount, SetAMAFlags)– Call Processing (Answer, Busy, Dial, Hangup)– Caller Presentation (SetCallerID, SetCallerCIDName)– Database (DBdel, DBget, DBput)– Application Interface (AGI, EAGI, PERL, PHP)– Audio (Playback, Playtones, MusicOnHold)– Voicemail & Conferencing (MeetMe, VoiceMailMain)– Queue/ACD (AddQueueMember, AgentLogin)
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October 10-13, 2006• San Diego Convention Center, San Diego California
Macros
• Macros are used to reduce the amount of redundant code in the dialplan.
• Passing arguments to a macro allows generalization
• Single line invocation from dialplan• Macros are identified in the dialplan by starting a
context name with "macro-".• ’s’ extension is used within macros since we
want the actions to be performed automatically• Arguments in macros are accessed as {ARGn}
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October 10-13, 2006• San Diego Convention Center, San Diego California
Example Macro[macro-dialuser]
exten => s,1,GotoIf($[${DB_EXISTS(CFD/${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)
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October 10-13, 2006• San Diego Convention Center, San Diego California
Example Macro (cont)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
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October 10-13, 2006• San Diego Convention Center, San Diego California
Q&A
Carl Davis
President & Chief Architect
Stellar System Technologies, Inc
www.stellarsystech.com
Executive Director
High Tech Business Council of Rochester
www.htbc.org
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