SIP Events: Open Issues

1
SIP EventsOpen Issues

• IETF 51 / SIP Working Group
• Adam Roach
• adam.roach_at_ericsson.com

2
DoS Attacks

• Problem SUBSCRIBE in, RESPONSE plus NOTIFY out
  amplifier.
• No one seems to notice or care. No proposals have
  been made. Similar problems exist with e.g. 100
  and 180 responses to INVITE.
• Proposal move from open issues section to
  security section.

3
Forking

• No technical problems preclude the forking of
  SUBSCRIBE requests.
• Some have voiced philosophical objections,
  although Ive received indications that some of
  the most vocal opponents are softening their
  stance.
• If we disallow it globally, no one can use it,
  even if it works well for some as-yet-undefined
  package. If we let packages allow/disallow it
  according to their needs, and no one ever allows
  it, no harm done.
• Proposal Status Quo describe technical solution
  in base draft, let individual drafts make a
  decision to allow or disallow it.

4
Notification of Expiration

• Expires header in NOTIFY used to convey time
  remaining on subscription.
• This is not really a change from previous drafts
  however, it has recently raised some objections.
• Proposal New header Subscription-Expires for
  this purpose it may contain a reason parameter
  (when set to 0), which aids in subscription
  migration.

5
Leg Correlation

• Original draft described SUB/NOT legs as being
  stand-alone and/or part of INVITE-initiated legs.
• Early objections led to removal of distinction.
• Recently, there have been calls to add
  INVITE-initiated legs back in.
• Proposal I dont care. Lets add it back.

6
Package Name Syntax

• Previously, any token was okay private packages
  were in the form of org.monkeys.foo
• New sub-package syntax uses . to separate
  packages, which causes ambiguity.
• Proposal Drop private name spaces altogether.

7
Complete State vs. Sub-State

• Current draft proposes (although it doesnt
  require) conveying complete state in NOTIFY
  messages.
• To save message space, we can define a mechanism
  to convey complete state immediately following
  SUBSCRIBE, and only state deltas in subsequent
  NOTIFYs.
• CSeq gaps can be used to detect lost NOTIFYs,
  triggering re-subscriptions for full state.

8
Main Changes Since Last Draft

• New section detailing what information is to
  appear in event packages.
• Added concept of sub-packages (including
  supporting syntax changes).
• Added IANA Considerations Section.

9
Main Changes to Next Draft

• Alignment with 2543bis REGISTER handling allow
  Expires to be increased and decreased by
  notifier.
• Output from nits reviewer(s) (thanks, Bert!)
• Further fleshing out of requirements on
  sub-packages.