Asterisk Jargon Alex Vishnev Chief Technical Office, VoIP ACN

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 voic , 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 )

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

Asterisk Architecture

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

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

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

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

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

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.

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.

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,

Channel Types Channel Types could be Physical or Logical Agent: ACD Agent channelAgent Console: Linux console client driver for sound cards (using OSS or ALSA)Console H.323: An older VOIP protocolH.323 IAX and IAX2: Inter-Asterisk Exchange protocol, Asterisk's own VOIP protocolIAXIAX2 MGCP: Media Gateway Control Protocol, another VOIP protocolMGCP SIP: Session Initiation Protocol, the most common VOIP protocolSIP Skinny: A driver for Cisco Skinny Client Control Protocol (a VOIP protocol)Skinny VOFR: voice over frame relay Adtran styleVOFRAdtran VPB: For connecting ordinary telephone and telephone lines using Voicetronix cardsVPB Zap: For connecting ordinary telephones and telephone lines using Digium cards. Also for TDMoE and for Asterisk zaphfcZapTDMoEAsterisk zaphfc

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"Bluetooth CAPI: ISDN CAPI channelCAPI mISDN: mISDN channelmISDN vISDN: vISDN channel (native BRI channel for HFC chipsets)vISDN SCCP: An alternate Skinny/SCCP channelSCCP Sirrix: ISDN BRI for Sirrix cards (with optional ISDN encryption)Sirrix UNISTIM: Nortel Unistim channelUNISTIM Unicall: Replacement for zaptel, with R2 supportUnicall SS7: SS7 (ISUP on MTP2/3) channelSS7

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

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 => (followed by the name of extensions) –Can be numeric (i.e. regular Extension) –Alphanumeric (i.e. address)

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 => name, priority, application( ) –exten => 123,1,Answer( )

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,2,Playback(hello-world) –exten => s,3,Hangup( )

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 => 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 Channel Variables A channel variable is a variable (such as the Caller*ID 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 => 123,1,Set(MAGICNUMBER=42) 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 –JOHN=ZIP/1 –JANE=SIP/JANE –exten => 123,1,SetGlobalVar(JOHN=Zap/1)

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) –Voic & Conferencing( MeetMe, Voic Main) –Queue/ACD (AddQueueMember,AgentLogin)

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}

Q&A Alex Vishnev Chief Technical Officer, VoIP Reese Blvd. Ste. 400 Huntersville, NC Office (704) Mobile (704) Fax (704) Website