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85 lines
3.3 KiB
TeX
85 lines
3.3 KiB
TeX
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\subsection{Introduction}
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This section is intended as an introduction to the Inter-Asterisk
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eXchange v2 (or simply IAX2) protocol. It provides both a theoretical
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background and practical information on its use.
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\subsection{Why IAX2?}
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The first question most people are thinking at this point is "Why do you
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need another VoIP protocol? Why didn't you just use SIP or H.323?"
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Well, the answer is a fairly complicated one, but in a nutshell it's like
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this... Asterisk is intended as a very flexible and powerful
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communications tool. As such, the primary feature we need from a VoIP
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protocol is the ability to meet our own goals with Asterisk, and one with
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enough flexibility that we could use it as a kind of laboratory for
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inventing and implementing new concepts in the field. Neither H.323 or
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SIP fit the roles we needed, so we developed our own protocol, which,
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while not standards based, provides a number of advantages over both SIP
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and H.323, some of which are:
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\begin{itemize}
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\item Interoperability with NAT/PAT/Masquerade firewalls
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\begin{itemize}
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\item IAX seamlessly interoperates through all sorts of NAT and PAT
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and other firewalls, including the ability to place and
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receive calls, and transfer calls to other stations.
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\end{itemize}
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\item High performance, low overhead protocol
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\begin{itemize}
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\item When running on low-bandwidth connections, or when running
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large numbers of calls, optimized bandwidth utilization is
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imperative. IAX uses only 4 bytes of overhead
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\end{itemize}
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\item Internationalization support
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\begin{itemize}
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\item IAX transmits language information, so that remote PBX
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content can be delivered in the native language of the
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calling party.
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\end{itemize}
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\item Remote dialplan polling
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\begin{itemize}
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\item IAX allows a PBX or IP phone to poll the availability of a
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number from a remote server. This allows PBX dialplans to
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be centralized.
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\end{itemize}
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\item Flexible authentication
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\begin{itemize}
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\item IAX supports cleartext, md5, and RSA authentication,
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providing flexible security models for outgoing calls and
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registration services.
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\end{itemize}
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\item Multimedia protocol
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\begin{itemize}
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\item IAX supports the transmission of voice, video, images, text,
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HTML, DTMF, and URL's. Voice menus can be presented in both
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audibly and visually.
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\end{itemize}
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\item Call statistic gathering
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\begin{itemize}
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\item IAX gathers statistics about network performance (including
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latency and jitter, as well as providing end-to-end latency
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measurement.
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\end{itemize}
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\item Call parameter communication
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\begin{itemize}
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\item Caller*ID, requested extension, requested context, etc are
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all communicated through the call.
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\end{itemize}
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\item Single socket design
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\begin{itemize}
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\item IAX's single socket design allows up to 32768 calls to be
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multiplexed.
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\end{itemize}
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\end{itemize}
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While we value the importance of standards based (i.e. SIP) call handling,
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hopefully this will provide a reasonable explanation of why we developed
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IAX rather than starting with SIP.
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\subsection{Configuration}
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For examples of a configuration, please see the iax.conf.sample in
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your the /configs directory of you source code distribution.
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