Implicit Subscriptions

1
Implicit Subscriptions

• Jonathan Rosenberg
• Cisco Systems

2
A Trend

• IETF and SIP WG are (for the better) recognizing
  that industry usage doesnt 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