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Piggyback model (current draft). Proxies insert policies into INVITE transaction. Policy MFOs are inserted in the message containing the SDP. Preconditions used to avoid “ghost rings” if UAC CANCELs because of policies. Pro’s: call setup delay independent of number of proxies; small number of messages. Con’s: policies traverse entire network (encryption to hide them). Re-direct model. Proxies use INVITE transaction to tell UAs to retrieve policies. UAC: proxy rejects INVITE and provides policy URI. UAS: proxy inserts policy URI in INVITE. UAs submit MIOs to policy server and retrieve policies. Pro’s: policies for local UAs stay in local network; reuse session-independent mechanisms. Con’s: reject cascade with multiple proxies; increased setup delay. Session-Specific Policies – Models |