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Re: [Sip] INFO considered harmful
INFO = BEEP-like functionality over SIP :-)?
To amplify one part of what Dean said: Part of the functionality that an
SDP-negotiated channel does not (readily) provide is different degrees
of specificity. In SDP, I have to include a single IP address or an
A-record. In SIP, Contact can be significantly more general, since it
allows different degrees of binding detail and much more resolution
functionality (SRV, NAPTR), including using the same old generic address
that started the session and thus redoing the resolution with every
request. This makes life much easier for sparse sessions with user
mobility (same user, different device). This matters less when you
already have a set of media sessions that need to be re-negotiated
anyway when things change.
Dean Willis wrote:
SIP provides for the establishment of a session (dialog) between two or more
end points, optionally intermediated by proxies, and the exchange of
information between those end points. This information is applied by
applications to provide application functionality. SIP provides several
methods for relaying application information, including relaying a text
message, requesting notification of changes in the state of a named element,
reporting a change in the state of some named element, and so on. It is
either a historical accident that the dialog-initiation request (INVITE) is
non-transparently overloaded with media session negotiation OR that the
media session negotiation method (INVITE) establishes a dialog on which
other requests may be relayed.
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