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SIP [1] provides the necessary protocol mechanisms so that end systems
and proxy servers can provide services:
* call forwarding, including
* the equivalent of 700-, 800- and 900- type calls;
* call-forwarding no answer;
* call-forwarding busy;
* call-forwarding unconditional;
* other address-translation services;
* callee and calling ``number'' delivery, where numbers can be any
(preferably unique) naming scheme;
* personal mobility, i.e., the ability to reach a called party under
a single, location-independent address even when the user changes
terminals;
* terminal-type negotiation and selection: a caller can be given a
choice how to reach the party, e.g., via Internet [2] telephony,
mobile phone, an answering service, etc.;
* terminal capability negotiation;
* caller and callee authentication;
* blind and supervised call transfer;
* invitations to multicast conferences.
Extensions of SIP [3] to allow third-party signaling (e.g., for
click-to-dial services, fully meshed conferences and connections to
multipoint control units (MCU [4]s), as well as mixed modes and the
transition between those) are available.
SIP [5] addresses users by an email-like address and re-uses some of
the infrastructure of electronic mail delivery such as DNS [6] MX
records or using SMTP [7] EXPN [8] for address expansion. SIP [9]
addresses (URL [10]s) can also be embedded in web pages. SIP [11] is
addressing-neutral, with addresses expressed as URL [12]s of various
types such as SIP [13], H.323 [14] or telephone (E.164 [15]).
SIP [16] can also be used for signaling Internet [17] real-time fax
delivery. This requires no major changes. Fax might be carried via RTP
[18], TCP [19] (e.g., the protocols discussed in the Internet [20] fax
WG) or other mechanisms.
SIP [21] is independent of the packet layer and only requires an
unreliable datagram service, as it provides its own reliability
mechanism. While SIP [22] typically is used over UDP [23] or TCP [24],
it could, without technical changes, be run over IPX [25], or carrier
pigeons, frame relay, ATM [26], AAL5 [27] or X.25 [28], in rough order
of desireability.
Links:
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[1] http://melbournewireless.org.au/?SIP
[2] http://melbournewireless.org.au/?Internet
[3] http://melbournewireless.org.au/?SIP
[4] http://melbournewireless.org.au/?MCU
[5] http://melbournewireless.org.au/?SIP
[6] http://melbournewireless.org.au/?DNS
[7] http://melbournewireless.org.au/?SMTP
[8] http://melbournewireless.org.au/?EXPN
[9] http://melbournewireless.org.au/?SIP
[10] http://melbournewireless.org.au/?URL
[11] http://melbournewireless.org.au/?SIP
[12] http://melbournewireless.org.au/?URL
[13] http://melbournewireless.org.au/?SIP
[14] http://melbournewireless.org.au/?H.323
[15] http://melbournewireless.org.au/?E.164
[16] http://melbournewireless.org.au/?SIP
[17] http://melbournewireless.org.au/?Internet
[18] http://melbournewireless.org.au/?RTP
[19] http://melbournewireless.org.au/?TCP
[20] http://melbournewireless.org.au/?Internet
[21] http://melbournewireless.org.au/?SIP
[22] http://melbournewireless.org.au/?SIP
[23] http://melbournewireless.org.au/?UDP
[24] http://melbournewireless.org.au/?TCP
[25] http://melbournewireless.org.au/?IPX
[26] http://melbournewireless.org.au/?ATM
[27] http://melbournewireless.org.au/?AAL5
[28] http://melbournewireless.org.au/?X.25
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