Re: [rtcweb] Default proto transport in JSEP

[Roman Shpount <[e-mail]>]

On Mon, Nov 19, 2018 at 6:08 PM Justin Uberti <[e-mail]> wrote:

> Pretty clear that the 0.0.0.0/9 behavior being proposed violates 5245
> <https://tools.ietf.org/html/rfc5245#section-5.1>:
>
>    The agent will proceed with the ICE procedures defined in this
>    specification if, for each media stream in the SDP it received, the
>    default destination for each component of that media stream appears
>    in a candidate attribute.  For example, in the case of RTP, the IP
>    address and port in the c and m lines, respectively, appear in a
>    candidate attribute and the value in the rtcp attribute appears in a
>    candidate attribute.
>
> Ergo, I don't think this proposal will fly. Of the three options being
> considered (below), only #1 avoids violating 5245 while simultaneously
> minimizing busywork.
>
> 1) (current) Match IP and port, but stipulate an exact proto value
> 2) Match IP, port and proto
> 3) Set IP, port, and proto to fixed values
>
> If we think avoiding ice-mismatch when interacting with 5245 endpoints is
> not important, that point needs to be made clearly. Otherwise, I think the
> easiest path is to update ice-sip-sdp to permit #1 as a legacy interop
> behavior (and it can continue to recommend #3 for interop with 8445
> clients).
>

The RFC 5245 does not define any candidate transports except UDP, so it
does not seem to mention protocol in most of the examples. I believe that
language in 5245 that you are quoting actually specifies that default
address, port and protocol foundation in c= and m= line must match.

Specifically it says that  "for each media stream in the SDP it received,
the default destination for each component of that media stream appears in
a candidate attribute."

If we look the term definitions,in
https://tools.ietf.org/html/rfc5245#section-3 it says:

Default Destination/Candidate: *The default destination for a component of
a media stream is the transport address that would be used by an agent that
is not ICE aware. *For the RTP component, the default IP address is in the
c line of the SDP, and the port is in the m line. For the RTCP component,
it is in the rtcp attribute when present, and when not present, the IP
address is in the c line and 1 plus the port is in the m line. A default
candidate for a component is one whose transport address matches the
default destination for that component.

Transport Address: The combination of an IP address and transport protocol
(such as UDP or TCP) port.

>From this  it looks like the document simply assumes that port has type
which is UDP or TCP and in order for port to match both its value and type
must match.

Furthermore, without protocol foundation candidate default destination is
ambiguous and cannot be used without ICE.  So, 1, as proposed will likely
to cause ICE mismatch with existing implementations and will not be RFC
5245 compatible.

2 is the only RFC 5245 compatible option.

Regards,
_____________
Roman Shpount