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Message Sessions Draft-campbell-simple-im-sessions-01 Ben Campbell (firstname.lastname@example.org) History ● We've been may places – MESSAGE dialogs – IMTP proposal – Cpimmsg-sessions with COMEDIA (most recent) – And now...MSRP Message Session Relay Protocol (MSRP) ● Attempts to solve COMEDIA related problems in previous drafts. ● Design effort from Paul Kyzivat, Robert Sparks,Jonathan Rosenberg, and Ben Campbell. ● Builds on work from message sessions design team discussed in Atlanta. Message Session Relay Protocol ● Similar to cpim-msg approach: – Congestion-safe, connection-oriented transports. – Arbitrary MIME payloads (including message/cpim.) ● But different: – No COMEDIA dependency – Supports 1 and 2 NAT scenarios – Supports common firewall policies – Connections may carry multiple sessions. The Trouble with COMEDIA ● Limited support for bidirectional connections – No good way to associate an inbound connection with a session – Cannot use source address/port to identify connections due to NATs. Relay Support ● Explicit support for zero or one relay ● At least one endpoint must have a pre- existing relationship with the relay ● Implicit support for dual relay scenario MSRP Structure ● Primitives – BIND (RELEASE) -- establishes session state at a relay – VISIT (LEAVE) -- associates a connection with a session – SEND -- sends a message ● Host/Visitor endpoint concept – Visitor connects to Host... – ...or to a relay operating on behalf of the Host. Open Issues ● ACK related Bug in offer/answer handling – May be able to handle with UPDATE ● Do we need a refresh mechanism for BIND state? ● Race condition when tearing down a session. Open Issues ● Need to fully define MSRP: URI scheme. ● SDP encoding mechanism requires the host and visitor temp URIs to share the same domain. – Probably ok, since both represent resources at the same host device. Open Issues ● Additional work needed for security – Digest authentication on BIND not fully specified. – Do we need an msrps: URI scheme? – Needs more work on end-to-end security ● Session key exchange using MIKEY ● Fitting in S/MIME ● Protection across CPIM gateways.
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