Re: [bfcpbis] AD Review of draft-ietf-bfcpbis-rfc4583bis-24

[Roman Shpount <[e-mail]>]

Hi Adam,

On Mon, Sep 10, 2018 at 4:41 PM, Adam Roach <[e-mail]> wrote:

>
> §4 (BLOCKING):
>
> >  This document defines five values for the proto field: TCP/BFCP,
> >  TCP/DTLS/BFCP, TCP/TLS/BFCP, UDP/BFCP, and UDP/TLS/BFCP.
>
> Generally, having more ways to do the same things in a protocol leads to
> less
> interoperability rather than more. While the rationale for the four-way
> split
> caused by TLS-versus-plaintext and UDP-versus-TCP is pretty self evident,
> there
> appears to be no rationale in this document for having both TCP/DLTS/BFCP
> and
> TCP/TLS/BFCP; more importantly, the document offers no guidance to
> implementors
> regarding which to use. This is likely to lead to some implementations
> choosing
> one encoding and others choosing the other somewhat arbitrarily. This
> decreases
> the chances of the protocol interoperating.
>
> Minimally, please include guidance regarding which of these two variations
> implementations should use, and under which conditions. On a first glance,
> it
> would appear that the guidance might be that non-ICE uses should use
> TCP/TLS/BFCP for maximal compatibility with RFC 4583 implementations, and
> that
> ICE uses need to use TCP/DTLS/BFCP, as outlined in section 9.
>

You are correct, the reason there are two protocols is that TCP/TLS/BFCP
needs to be supported for legacy interop with RFC4583 but it does not work
with ICE. Since  ICE is designed as being able to switch between ICE
candidates, including UDP and TCP based candidates, without disrupting the
higher level protocol, any ICE transport, including ICE-TCP, should be
treated as packet-based unreliable transport. As a result, ICE can only
work with UDP/TLS/DTLS/BFC for UDP candidates or TCP/DTLS/BFCP for TCP
candidates. Both of these protocols treat underlying transport as
unreliable with DTLS responsible for packet re-transmission. On the other
hand,  TCP/TLS/BFCP relies on the underlying transport for reliable
in-order delivery, which is not provided by ICE. Furthermore, ICE is not
supported by plain UDP/BFC either, or you will end up with TCP/UDP/BFCP
(different from TCP/BFCP) which everyone found to be even more confusing. I
think some explanation of this would be helpful.

Regards,
_____________
Roman Shpount