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This document aims to propose a hop-by-hop mechanism for improved network feedback in case of failures, requiring configuration of the first relay for the initial deployment. It discusses the benefits, challenges, and scenarios of implementing this mechanism in MSRP applications.
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MSRP Hop-by-Hop Mechanism draft-levin-simple-msrp-review-00 SIMPLE WG Interim Meeting May 24th, 2004, Bedford MA MSRP Hop-by-hop Mechanism
Two Distinct Mechanisms • Application Layer: End-to-end • For application use • Network Layer: Hop-by-hop • For improved feedback (to application layer) in case of network failure • Require configuration of the first relay (only) • The very first deployment will use RELAYs • Don’t build interim solutions for one hop only • End-to-end abstraction MUST be provided even over a single hop • Applications need to be exposed to the end-to-end view ONLY MSRP Hop-by-hop Mechanism
Hop-by-Hop Mechanism • Added Value • Automatic negative feedback in case of TCP link failure without additional application logic: requires state information (at least per MSRP connection) in relays • Ability to specify (with high probability) messages that have been affected by the failure – requires per message state + 200 OK • Improved timing for “stalled” TCP connections – requires “per something” state + “200 OK” + timer • Issues • Specific message information can be misleading • OVERHEAD for BIG deployments ( > 25%, easily 50%) • Lack of throttling manageability for MUXing and CONFERENCING MSRP Hop-by-hop Mechanism
MUX and Conferencing Scenario MCU RELAY Send 200 OK TCP connection Send MSRP Hop-by-hop Mechanism
Eliminating Hop-by-hopResponses per Message • Negative Feedback by Network Layer - alternatives • None: can be implemented end-to-end by application with timer • By network layer per MSRP session: state implementation in relays • By network layer per message: state + timer + 200 OK • Bilateral agreement between service providers • Over a single TCP hop • For all connections, sessions, messages • Application signaling • Per instant message in a session • End-to-end “bit” inspected by relays MSRP Hop-by-hop Mechanism