Subject: [MMUSIC] NAT traversal in draft-loreto-mmusic-sctp-sdp

From: Gonzalo Camarillo <[email-masked]>
Date: Tue, 12 Apr 2011 15:00:28 +0300

Folks,

[with my individual contributor hat on]

In our session in Prague, we discussed whether or not the following
draft needs to specify an ICE-based NAT traversal mechanism, which would
include support for UDP-encapsulated SCTP traffic.

https://datatracker.ietf.org/doc/draft-loreto-mmusic-sctp-sdp/

SCTP has its own association establishment and address management
mechanisms. SCTP supports, among other things, multihomed endpoints. It
is clear that while some SCTP associations may be established using SDP
(as described in the draft above), many SCTP associations will be
established and managed without using SDP.

Defining SDP-based ICE procedures for SCTP would require the
specification of extensions to SCTP (e.g., a UDP encapsulation of SCTP
or how to perform initial connectivity checks when the UDP encapsulation
is not used). Additionally, even if we defined SDP-based ICE procedures
for SCTP, they would need to be redefined for SCTP associations that are
established without using SDP anyway.

Therefore, I believe we should not be including ICE procedures in the
draft above at this point. If the SCTP community decides to include ICE
procedures in SCTP itself in the future, specifying how to use them in
SDP will be easy enough, though.

With respect to whether or not the draft above needs to specify a way to
describe SCTP over UDP streams, this discussion is related to the DCCP
over UDP discussion also on this mailing list. I also believe we should
stick to ICE instead of defining a new specific attribute.

In summary, I would leave the draft above as is. It would only define
the 'SCTP' and 'SCTP/DTLS' protocol identifiers for SDP. In this way,
the mechanism for establishing an SCTP association would be identical to
the mechanism used to establish a regular SCTP association. Address
management would be performed by SCTP, and not at the SDP level, as in
any regular SCTP association. If or when the SCTP community decides to
extend SCTP to support UDP encapsulation (there is a draft on that) or
ICE-based procedures, we can add SDP-based support if needed.

Cheers,

Gonzalo