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56 lines
2.3 KiB
Plaintext
Executable File
56 lines
2.3 KiB
Plaintext
Executable File
Inter-Asterisk eXchange Protocol
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================================
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Usage:
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======
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The format for the dialing string on Asterisk is:
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IAX/[user@]peer[:exten[@context]]
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(Note, []'s denote optional fields). The peer is either an IP address
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or a peer as specified in the /etc/asterisk/iax.conf file. Exten is
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an optional requested extension (otherwise "s" will be used), and
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"context" is an optional context to request. The user is an optional
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username specified in the peer's iax.conf. If the user is not specified,
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the peer will select one.
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Protocol and rationale:
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=======================
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IAX is a simple, low overhead and low bandwidth VoIP protocol designed to
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allow multiple Asterisk PBX's to communicate with one another without
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the overhead of more complex protocols like H.323. Payload is sent with
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a header overhead of only 4 octets. Control functions (and one payload packet
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per minute or so) is sent with a more complex header of 12 octets.
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IAX is slightly stateful.
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IAX contains two kinds of packets: The full header packet type, which
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contains much information about the frame, in addition to its contents,
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and the mini header type, which is used only for non-reliable voice
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packet delivery.
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All packets are immediately transmitted. Packets are received, but not
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delivered to the actual channels until a given time quantum has passed, in
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order to try to eliminate jitter.
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All full header packets must be ackd (except, obviously for the ACK packets
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themselves and not so obviously for hangup packets). The "timestamp" field of
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ack packets is not the normal offset, but rather a quote of the timestamp as
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included with the original packet that you're acking, and likewise the
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seqno field is the seqno of the packet you're acking, not your own seqno,
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and you do not increment your own sequence number. ACKing is based on the
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sequence number.
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See iax.h for a description of the frame formats.
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IAX internal frames use the AST_FRAME_IAX type. The subclass of these
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frames is the IAX control number, as seen in iax.h. The first frame sent
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must be an AST_FRAME_IAX with the control AST_IAX_CONTROL_NEW.
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The AST_IAX_CONTROL_NEW establishes a new connection.
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The first frame sent MUST be an AST_CONTROL_NEW to start a connection.
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IAX connnections may require authentication using either simple plaintext
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passwords or an md5 challenge/response pair.
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