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Asterisk Jargon

Asterisk Jargon. Carl Davis. Agenda. 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?.

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Asterisk Jargon

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  1. Asterisk Jargon Carl Davis

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

  3. 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)

  4. Asterisk Architecture

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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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)

  11. 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)

  12. 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

  13. 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

  14. 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

  15. 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.

  16. 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

  17. 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

  18. 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()

  19. 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( )

  20. 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

  21. 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)

  22. 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)

  23. 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}

  24. 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)

  25. 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

  26. Q&A Carl Davis President & Chief Architect Stellar System Technologies, Inc carl_davis@stellarsystech.com www.stellarsystech.com Executive Director High Tech Business Council of Rochester www.htbc.org

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