[MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)

Flemming Andreasen <fandreas@cisco.com> Tue, 19 March 2013 06:24 UTC

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Date: Tue, 19 Mar 2013 02:24:27 -0400
From: Flemming Andreasen <fandreas@cisco.com>
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Subject: [MMUSIC] Connection Data Capability (ccap) and IP-addresses (draft-ietf-mmusic-sdp-miscellaneous-caps-04)
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As you may have seen, there has recently been some list discussion on 
the "connection data capability" defined in 
draft-ietf-mmusic-sdp-miscellaneous-caps-04 (see e.g. thread in 

To recap, the connection data capability ("ccap") provides capability 
negotiation capabilities for what amounts to the "c=" line in regular 
SDP, and as such enables negotiation of network type (such as "IN") and 
IP-address information (v4 and v6 addresses). The Standards Track 
mechanism for negotiating and determining alternative IP-address 
information today is ICE, and hence the draft currently includes the 
following wording:
The 'ccap' capability attribute is intended to
    be used only when there is no other mechanism available for
    negotiating alternative connection address information, such as when
    the <nettype> is different among the alternative addresses (e.g.
    "IN" and "PSTN").  The 'ccap' attribute MUST NOT be used in
    situations where an existing mechanism (such as Interactive
    Connectivity Establishment (ICE) [RFC5245]) can be used to select
    between different connection addresses (e.g.  "IP4" and "IP6" or
    different IP addresses within the same IP address family).

The above text has led to some confusion as to exactly when and what 
"ccap" can be used for. More specifically, is it/should it ever be 
allowed to use "ccap" to convey an IP4 or IP6 address, and if so, under 
what circumstances ?

If you have an opinion, please let us know.

A couple of points to keep in mind:
- The current document has been WGLC'ed without comment ~6 months ago.
- 3GPP has a dependency on the document (however I'm not sure if that 
dependency includes the above "IN" feature)
- The connection data capability is defined in a general manner to be 
generally useful in line with the overall capability negotiation 
framework (as opposed to targeted at one specific use case with one 
specific value)
- There are scenarios where ICE cannot be used, even if implemented 
(e.g. ice-mismatch).
- RFC 6849 (media loopback) provides for NAT traversal in the absence of 
ICE support


-- Flemming