draft-hoeneisen-sip-proxy-supported-00

1
draft-hoeneisen-sip-proxy-supported-00

• Table of Contents
• Motivation of Proxy-Supported
• Differences Proxy-Supported vs. Proxy-Require
• Issues
• Questions and discussion

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Motivation of Proxy-Supported

• Define a SIP extension that allows UAs to query
  in an INITIAL request the capabilities of all
  record-routing proxy servers.
• The (proxy-)supported capabilities can then be
  used in SUBSEQUENT requests. These include
• New methods that require special handling in
  proxy servers
• Selecting a suitable call leg after (parallel)
  forking
• No error responses when a capability is not
  supported session establishment can continue
  undisturbed.

Note This proposal assumes Route header
specifies strict source routing.
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Differences to Proxy-Require

• Using Proxy-Supported

• ...a request goes through even if any of the
  intermediate proxy servers doesn't support an
  indicated extension, whereas Proxy-Require
  results in a 420 error response in the proxy
  server.

• ...only Record-Routing proxy servers are queried,
  whereas Proxy-Require concerns all proxy servers
  in a signalling path.

• the features are used only in subsequent
  requests, whereas features in Proxy-Require can
  be used also in the first request.

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Issues
From the SIP mailing list

• Concerns, that only few features can be
  negotiated with Proxy-Supported, as most need
  support in the initial request.
• Are there further use cases?
• A more generic solution, which also allows UAs to
  query, whether at least one proxy server supports
  a certain feature, might be considered as well.
• Technical solution could be somewhat simpler
• More?

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Questions and Discussion

• Is there a general interest for this proposal?
• How to continue?
• Additional comments to the technical solution?

• Thank you!