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Implicit Subscriptions

This article discusses the challenges faced in implementing implicit subscriptions in SIP, including issues related to NAT, SBCs, and unsolicited NOTIFY messages. It also proposes a solution that couples subscriptions with registrations to improve efficiency and reduce messaging volume.

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Implicit Subscriptions

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  1. Implicit Subscriptions Jonathan Rosenberg Cisco Systems

  2. A Trend • IETF and SIP WG are (for the better) recognizing that industry usage doesn’t match specifications in several areas • NAT (behave) • SBCs (voipeer, sipping SBC work) • But, there are others • Unsolicited NOTIFY

  3. Why is it common? • Perceived high cost of subscription maintenance at client • Refreshes, dialog for entire registration interval • Perceived high cost of subscription maintenance at server • One for EVERY user that is logged in • Perceived high cost of messaging compared to frequency of events • Not like presence • Assumption of endpoint interest • “Self” cases – unlike presence • There is a real engineering issue here

  4. Other Problems • Avalanche restart: Metropolitan power outage and reboot • Endpoint messaging • SUBSCRIBE config-pkg • REGISTER • SUBSCRIBE for • MWI • Reg-event • Presence-list • Winfo • Dialog-event (BLA) • 13 SIP transactions! • Time to recover and potential scope of load directly proportional to this

  5. Requirements • Reduce messaging volume • Ideally: 1 transaction (REGISTER) • Allow event servers to have a finite number of dialogs • Preserve compatibility with RFC3265 mechanisms

  6. Proposed Solution • Couple a subscription with a registration • Subscription lifetime bound to registration lifetime • Create subscription as a side effect of registration • Tunnel dialog identifiers through REGISTER request and response

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