Implicit Subscriptions Jonathan Rosenberg Cisco Systems

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

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

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

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

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