draftkisssips100rel

1
draft-kiss-sip-s100rel
Krisztian Kiss, Bernie Höneisen, Markus Isomäki

• Defines an alternative for PRACK for providing
  reliability for provisional responses.
• The new method is called SPRACK.
• The aim is to reduce the number of messages
  needed to establish a session.
• Requires a special kind of transaction model (no
  response), and thus support from Proxies.
• Either Proxy-Supported or Proxy-Require could be
  used for this. Feasibility depends whether
  Record-Routing is strict or loose.

2
SPRACK vs. PRACK
INVITE
INVITE
183
183
Resource Reservation
PRACK
PRACK
Resource Reservation
200
200
COMET
COMET
Default Proxy Behaviour
3
SPRACK vs. PRACK
INVITE
INVITE
183
183
Resource Reservation
SPRACK
SPRACK
Resource Reservation
COMET
COMET
SPRACK-specific Proxy Behaviour
4
Mailing List Discussion

• Messes up the SIP transaction model
• True, some additional logic needed, default
  transaction does not apply.
• Not backwards compatible needs Proxy support
• True, but there is a fallback scheme with
  Proxy-Supported.
• Achieves only minimum benefit compared to the
  cost
• It's two messages, the other one overlaps with
  resource reservation.
• With PRACK-200 message sizes the calculations
  show there is some benefit in narrowband wireless
  systems (specifically GERAN). If compression is
  used, benefit is smaller.
• Is there any interest for this in SIP WG?