RFC 3263:Session Initiation Protocol (SIP): Locati...
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SCTP


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... transport protocols, including TCP, UDP, and SCTP. SIP can also use TLS. ...


... specification defines D2U for UDP, D2T for TCP, and D2S for SCTP. We also establish an IANA registry for NAPTR ...


... UDP SIP+D2S SCTP (RFC 2960prop) ...



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