Asterisk Douglas E. Warner and Brady Alleman

Telco Terms ● FXO: Foreign Exchange Office – A port that handles accepting calls from a POTS line – you would plug your phone line from your telephone company in here ● FXS: Foreign Exchange Subscriber – A port that provides a POTS-like interface with dial tone and ring generation – for devices like Fax machines, analog phones, or terminal gateways

Telco Terms ● POTS: Plain Ol' Telephone Service ● Channel/Trunk: A device (physical or virtual) that handles an audio call (ex: FXO/FXS port, SIP/IAX channel)

VoIP Terms ● Protocols – SIP: Session Initiation Protocol – HTTP-like; very common among hardware phones; problems traversing NAT devices without a proxy – IAX: Asterisk-proprietary protocol; good at traversing NAT devices – H.323: ITU standard for audio; very common among enterprise hardware

VoIP Terms ● Protocols (cont.) – RTP: Real-time Transport Protocol – used for transporting audio over the Internet and reconstructing packets (used by other protocols such as SIP and H.323 for transmitting the audio) – MGCP: Media Gateway Transport Protocol – used by some enterprise-class devices for better support traversing NAT devices

VoIP Terms ● Codecs: – uLaw, aLaw: high-quality, high-bandwidth (64kbps) – GSM: medium-quality, low bandwidth (~13kbps) – same codec used for cell-phones – ILBC (Internet Low Bitrate Vocoder): medium- quality, low-bandwith (~15kbps) – subjectively better quality than GSM

VoIP Terms ● Codecs (cont.) – G.729: medium-quality, low-bandwith (~8kbps) – very common among enterprise hardware – non-free license

VoIP Features ● Unregulated: you can pretty much do whatever you want to with it ● Make free calls ● Set your own caller-id ● Make your phone number usable from anywhere

VoIP Problems ● Unregulated: no guarantees on service ● e911 is difficult (location identification is all but impossible) ● QoS/reliability problems

What Asterisk Is ● Open-Source PBX – capable of advanced call routing – multiple channel drivers (POTS, T1/PRI, SIP, IAX, H.323, etc) – highly extensible through dynamic modules (DSOs) or AGI (Asterisk Gateway Interface)

Asterisk Alternatives ● yate ● FreeSWITCH ● OpenPBX ● Avaya Communications Manager ● Cisco CallManager

Examples ● Multi-ring: have one inbound number that rings you at your home, cell phone, office, etc ● Re-writing caller id ● Blacklisting ● Privacy Screening for unknown callers

Intermission

Demo ● Setup software SIP client ● Setup extensions and dial between two clients

Q&A