Re: [bfcpbis] Eric Rescorla's Discuss on draft-ietf-bfcpbis-rfc4583bis-26: (with DISCUSS and COMMENT)

[Roman Shpount <[e-mail]>]

Hi Eric,

Since I have helped with ICE related sections of this draft, I can provide
answers to some of your comments:

On Wed, Oct 24, 2018 at 3:23 PM Eric Rescorla <[e-mail]> wrote:

> S 9.
> >      transport is used for the default candidate, then the 'm' line proto
> >      value MUST be 'UDP/TLS/BFCP'.  If TCP transport is used for the
> >      default candidate, the 'm' line proto value MUST be 'TCP/DTLS/BFCP'.
> >
> >         Note: Usage of ICE with protocols other than UDP/TLS/BFCP and
> >         TCP/DTLS/BFCP is outside of scope for this specification.
>
> this is very different from any other use of ICE, and I'm not sure
> it's interoperable, unless you require that only TCP or only UDP
> candidates be offered (which you do not seem to). The reason is that
> with ICE you can flip between different candidates as part of the
> negotiation. So what happens if I initially get a UDP candidate and
> then via aggressive nomination settle on TCP (or vice versa). DTLS and
> TLS aren't really interoperable in that way. It would be far better to
> do what WebRTC does and when you do ICE, always do DTLS even if it's
> over TCP.
>
>
When ICE is used, DTLS is always used exactly for the reasons you mention.
End points only allowed to use 'UDP/TLS/BFCP', which is DTLS over UDP, or
'TCP/DTLS/BFCP', which is DTLS over TCP. DTLS over UDP is only named
'UDP/TLS/BFCP' instead of  'UDP/DTLS/BFCP' for legacy interop reasons,
since some implementations apparently already added support for this.
Please note that naming of BFCP over DTLS over UDP  as 'UDP/TLS/BFCP'  is
similar to naming RTP over DTLS over UDP as "UDP/RTP/TLS/SAVP".


> S 5.5.
> >      'bfcpver' attribute in offers and answers.  The attribute value, if
> >      present, MUST be in accordance with the definition of the Version
> >      field in [I-D.ietf-bfcpbis-rfc4582bis].  If the attribute is not
> >      present, endpoints MUST assume a default value in accordance with
> >      [I-D.ietf-bfcpbis-rfc4582bis]: when used over a reliable transport
> >      the default attribute value is "1", and when used over an unreliable
>
> Just for clarity: UDP over TURN-TCP is an unreliable transport, right?
>
>
UDP/BFCP, UDP/TLS/BFCP, and TCP/DTLS/BFCP are all unreliable transports,
even if TURN-TCP or TURN-TLS is used. Only TCP/BFCP and TCP/TLS/BFCP
transports are considered reliable. Do you think it should be explicitly
spelled out?

Regards,
_____________
Roman Shpount