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Peter Saint-Andre 2006-10-31 20:45:34 +00:00
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]]></example>
</section2>
<section2 topic='Exchanging Address Information' anchor='protocol-addresses'>
I'll use the example of a voice chat (only one content type) to simplify .... (1) I send you a session request with (say) one description and two transports and (2) if you want to proceed, you provisionally accept the request (IQ result), then (3) we both start exchanging possible transport candidates as quickly as possible because end users hate to wait for the voice chat to start; (4) as soon as you find a candidate that will work, you send me a session-accept and we start sending mediate over that candidate; (5) if later on we discover a better candidate, we do a transport-modify or content-modify in order to switch to the better candidate
<p>Once the session is provisionally accepted, each entity SHOULD send one &TRANSPORT; element in a transport-info meessage, containing exactly one &CANDIDATE; element per channel, whose 'ip' and 'port' attributes specify the IP address and port number of the candidate that the initiator has reason to believe will be most likely to succeed for that channel. This is not necessarily the initiator's preferred address for communication, but instead is the "address most likely to succeed", i.e., the address that is assumed to be reachable by the vast majority of target entities. To determine reachability, the client needs classify ahead of time the permissiveness of the NAT or firewall it is behind, if any. If the NAT is symmetric (not permissive), the candidate SHOULD specify a relay address. Otherwise it SHOULD be an address derived via prior discovery using &rfc3489;, which will be an address on the outside of the firewall or NAT.</p>
<p>Note: The Raw UDP candidate is equivalent to the "in-use" candidate as described in &ice;. (In older versions of XEP-0166, this was referrred to as the "default candidate".)</p>
<example caption="Address Exchange Example"><![CDATA[