1. Message Sessions Draft-campbell-simple-im-sessions-01 Ben Campbell (bcampbell@dynamicsoft.com)

2. History We've been may places – MESSAGE dialogs – IMTP proposal – Cpimmsg-sessions with COMEDIA (most recent) – And now...MSRP

3. 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.

4. 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.

5. 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.

6. 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

7. 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.

8. Direct Connection 1. Offer (i-am:A, u-b:B) 2. VISIT (B) 3. Answer (i-am:B) 4. SEND (A or B)

9. One Relay Host Visit or Relay 1. BIND 2. VISIT 3. SEND

10. Two Relays Host Visit or Relay 1 1. BIND 2. BIND 3. SEND Relay 2 3. SEND

11. 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.

12. 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.

13. 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.