| Summary: |
Early Media is the ability of two SIP user agents to communicate
before a SIP call is actually established. Support for early media is
important largely for interoperability with the PSTN. Unfortunately,
many SIP devices are providing this capability today without a
well-documented, consistent, and complete solution. We define the
problem of early media, document and describe the difficulties with
the current approach used in SIP UAs, and present a more formal
protocol mechanism that resolves these difficulties.
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