GRUU Mechanism

1
GRUU Mechanism

• Jonathan Rosenberg

2
Status

• Draft-rosenberg-sipping-gruu-reqs-01 defines the
  problem
• Draft-rosenberg-sip-gruu submitted with proposed
  solution
• Needed for
• App interaction
• Consultative transfer
• Presence

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Mechanism Summary

• Obtaining a GRUU
• REGISTER request has Supported gruu
• Each Contact in the response has a gruu parameter
  with GRUU
• Using a GRUU
• Place into Contact URI of INVITE/200
• Include Supported gruu

Registrar
REGISTER Supported gruu
200 OK Contact Sipa_at_b gruuc_at_d
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Open Issues

• GRUU lifecycle definition
• Dialog reuse
• Locally generated GRUU

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GRUU Lifecycle Management

• Can GRUU change during a registration? N
• What happens if gruu parameter is placed in REG
  request? ignored
• What happens if registrar changes gruu in
  response? not allowed
• Implication registrar has to remember gruu for
  lifetime of registration
• Can be different across different registrations
  of the same contact
• GRUU is not randomized across transactions
  privacy implications?

6
Dialog Reuse

• GRUU can allow us to eliminate dialog reuse
• Many problems with it
• Underspecified in RFC3261
• Bad idea
• Do we have GRUU spec say that you should not do
  dialog reuse if your peer supports GRUU?
• Will need to fix REFER for that to work or except
  REFER
• Or do we live with the mistake?

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Locally Generated GRUU

• Putting a GRUU in the Contact will end direct
  signaling
• A UA can try to generate its own local GRUU and
  use that
• But how does it know that it is reachable at that
  GRUU?
• Proposed solution ICE

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ICE Approach
Proxy
INVITE Contact sipa_at_domain altsipa_at_ip-addr
Callee
Caller
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ICE Approach
Proxy Doesnt RR
Proxy
INVITE Contact sipa_at_domain altsipa_at_ip-addr
Callee
Caller
10
ICE Approach
Proxy
200 OK Contact sipb_at_domain altsipb_at_ip-addr2
Callee
Caller
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ICE Approach
Proxy
200 OK Contact sipb_at_domain altsipb_at_ip-addr2
Callee
Caller
12
ICE Approach
Proxy
Callee
Caller
OPTIONS b_at_ip-addr2
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ICE Approach
Proxy
B knows that A was able to Reach him
_at_ip-addr2 So he can now Re-invite to update
Contact
Callee
Caller
200 OK
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ICE Approach
Proxy
INVITE Contact sipb_at_ipaddr2
Callee
Caller
15
ICE Approach
Proxy
INVITE Contact sipb_at_ipaddr2
Callee
Caller
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ICE Approach
Proxy
200 OK Contact sipa_at_domain sipa_at_ip-addr
Callee
Caller
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ICE Approach
Proxy
200 OK Contact sipa_at_domain sipa_at_ip-addr
Callee
Caller
18
ICE Approach
Proxy
Callee
Caller
OPTIONS a_at_ip-addr
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ICE Approach
Proxy
Callee
Caller
200 OK
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Caveats

• A and B both have to OPTIONS separately
• Connectivity must be tested in each direction
• OPTIONS is not on the same dialog as INVITE
• Need to have randomization on OPTIONS to avoid
  glare
• Doesnt work if a proxy record-routed INVITE
• Connectivity check would need to be from
  outermost proxy to UA no easy way to do this
• Source routing would reuse dialog route headers
  not allowed

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Proposal

• Add this as an optional mechanism to the draft
• Recommend that this is the ONLY way you can use
  locally generated GRUU