Re: [rtcweb] Ben Campbell's Yes on draft-ietf-rtcweb-fec-08: (with COMMENT)
Justin Uberti <juberti@google.com> Sat, 23 February 2019 01:17 UTC
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From: Justin Uberti <juberti@google.com>
Date: Fri, 22 Feb 2019 17:17:20 -0800
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To: Ben Campbell <ben@nostrum.com>
Cc: The IESG <iesg@ietf.org>, RTCWeb IETF <rtcweb@ietf.org>, rtcweb-chairs@ietf.org, draft-ietf-rtcweb-fec@ietf.org
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Subject: Re: [rtcweb] Ben Campbell's Yes on draft-ietf-rtcweb-fec-08: (with COMMENT)
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On Fri, Feb 22, 2019 at 4:57 PM Ben Campbell <ben@nostrum.com> wrote: > Thanks for the response. Comments below: > > On Feb 22, 2019, at 6:31 PM, Justin Uberti <juberti@google.com> wrote: > > Thanks for your comments. See below: > > On Wed, Feb 20, 2019 at 9:56 AM Ben Campbell <ben@nostrum.com> wrote: > > > […] > > ---------------------------------------------------------------------- >> >> Thanks for this effort. I am balloting "yes", but have some minor >> comments: >> >> §8: >> - "Given this, WebRTC implementations SHOULD consider using RTX or >> flexfec retransmissions instead of FEC when RTT is low," >> >> "consider" seems vague for a normative requirement. Can you describe >> concrete >> requirements? Otherwise I suggest descriptive language. >> > > Perhaps "prefer" rather than "consider" would be less squishy. > > > Prefer is better, thanks. > > >> Can you give guidance on what RTT would be reasonable to consider as >> "low"? >> > > This is somewhat application-dependent, but ~100 ms would be a reasonable > threshold. > > > Would it make sense to say that the threshold for “low” is application > dependent, but that would be a reasonable number for “typical” applications? > > > >> - "Note that when probing bandwidth, i.e., speculatively sending extra >> data to determine if additional link capacity exists, FEC SHOULD be >> used in all cases." >> >> I assume the point of this is the redundant FEC data should _be_ that >> extra >> data. But one could read this to mean that, if you are already sending >> extra >> data, you should also use FEC. >> > > I see what you mean, agree this could be clarified. > > > Thanks > > >> §9, 2nd paragraph: >> >> I'm by no means an expert in this, and leave it to the crypto experts to >> know >> if this matters, but does the additional redundancy of FEC have any >> impact on >> SRTP encryption? >> > > My understanding is that the fact that FEC is sent as its own stream with > its own IV means that even if the data was identical to the primary > payload, there would be no issue. > > > Is that true for the case of in-band FEC at the codec level? > In the RFC 2198 case, SRTP is once again run over a new packet, again with a new IV (from a new sequence number), and a new primary payload, so the cipher state will be entirely different when the previous data is re-encrypted. In the codec in-band case, you have a new bitstream, so there are no repeated bytes. > > But given that no new mechanisms are being proposed in this document, it's > probably covered elsewhere. > > > I can accept that argument. > > Thanks! > > Ben. >
- [rtcweb] Ben Campbell's Yes on draft-ietf-rtcweb-… Ben Campbell
- Re: [rtcweb] Ben Campbell's Yes on draft-ietf-rtc… Justin Uberti
- Re: [rtcweb] Ben Campbell's Yes on draft-ietf-rtc… Ben Campbell
- Re: [rtcweb] Ben Campbell's Yes on draft-ietf-rtc… Justin Uberti
- Re: [rtcweb] Ben Campbell's Yes on draft-ietf-rtc… Ben Campbell