draft-macdonald-simple-opaque-path-00

1
draft-macdonald-simple-opaque-path-00

• Derek MacDonald derek_at_counterpath.com
• Hadriel Kaplanhkaplan_at_acmepacket.com

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The Problem

• MSRP messages contain User Agent IP/port info in
  To-Path/From-Path
• Exposes user PC address to any peer
• Affects NAT traversal
• MSRP Relays dont scale
• Done at an application layer like a SIP proxy,
  instead of transport relay
• SDP syntax is different from Comedia
• Yet more app-specific rules for SDP, complicating
  ICE, cap-neg, etc.

3
The Proposed Solution

• Stop putting IPport in MSRP message headers
  how?
• Use anonymous MSRP path URI at UA
• Example
• apathmsrp//msrp.invalid.com0000/jshA7weztastc
  popaquef7jey483rydfhkyerky3
• New opaque uri-param provides unique cookie
  to tie MSRP connection to socket
• Opaque param is unique per UA, per connection
  connection sharing is done with same param value

4
TCP Connection handling

• Use Comedia-style SDP syntax
• c-line for address, m-line for port, setup
  attribute for active/passive, connection attrib,
  etc.
• MSRP connection binding model
• The SEND request with From-Path is already sent
  by the active node in MSRP, binding the TCP
  connection to the MSRP session
• The whole URI including opaque param would be
  used for connection binding

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New SIP Option Tag

• Defined a new option tag msrp-opaque
• MUST be included in Require header if anonymous
  URI used
• Request will fail if far-end doesnt support it,
  but thats appropriate (MSRP would fail anyway)
• NOTE some nodes will reject a SIP request
  without this option tag, because they will demand
  the UAs implement this

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Example

• Alice Bob
• 
  
• ------INVITE-------gt
• lt------200----------
• -------ACK---------gt
• cIN IP4 192.168.0.100
• mmessage 12454 TCP/MSRP
• apathmsrp//msrp.invalid.com0000/jshA7weztastc
  popaquef7jey483rydfhkyerky3
• cIN IP4 192.168.0.200
• mmessage 27784 TCP/MSRP
• apathmsrp//msrp.invalid.com0000/kjhd37s2s20w2a
  tcpopaquea6ghr7yv6egw33r
• MSRP d93kswow SEND
• To-Path msrp//msrp.invalid.com0000/jshA7weztas
  tcpopaque

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MSRP Relays

• Current opaque proposal does not work with RFC
  4976 Relays
• Are there any?? Are they used?
• By not work we mean the UA can fallback or
  choose, but cant use both at the same time
• It will work with TURN Relays, MSRP B2BUAs, SIP
  B2BUAs, SBCs, and things that go bump in the
  night
• We may be able to make it work with MSRP Relays,
  if Relays can change too, but is it worth it?

8
Open Issues

• Relays a horse we need to ride, or a unicorn?
• Need to specify the shared-connection behavior
• Question is the WG interested in this topic?