Re: [secdir] Secdir review of draft-ietf-dart-dscp-rtp-07

"Black, David" <> Thu, 16 October 2014 17:45 UTC

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From: "Black, David" <>
To: Tina TSOU <>, "" <>
Thread-Topic: Secdir review of draft-ietf-dart-dscp-rtp-07
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Subject: Re: [secdir] Secdir review of draft-ietf-dart-dscp-rtp-07
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> IMHO, the document is almost ready. I just have minor comments:

Thank you for the review - the RFC 6274 pointer was particularly useful.

Comments inline @ "David>"


From: Tina TSOU []
Sent: Thursday, October 16, 2014 9:21 AM
Subject: Secdir review of draft-ietf-dart-dscp-rtp-07

Dear all,

I have reviewed this document as part of the security directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written primarily for the benefit of the security area directors. Document editors and WG chairs should treat these comments just like any other last call comments.

IMHO, the document is almost ready. I just have minor comments:

** Technical **

* Page 6:

For IPv6, addition of the flow label [RFC6437] to network 5-tuples
results in network 6-tuples, but in practice, use of a flow label is
unlikely to result in a finer-grain traffic subset than the
corresponding network 5-tuple (e.g., the flow label is likely to
represent the combination of two ports with use of the UDP

The flow label is different in each direction. Hence, if anything, you
should talk about 7-tuples rather than 6-tuples.

David> Yes, but many of the UDP flows involved are unidirectional.  I'll add a parenthetical "(or 7-tuples for bidirectional flows)."

* Page 6, Section 2.2:

What about the drawbacks of multiplexing? -- You don't describe any.
What about Head of Line blocking?

David> The primary purpose of the section is to explain why one would want to do this multiplexing from an RTP
David> perspective - there are plenty of drawbacks described elsewhere in the draft, but if there's something specific
David> that belongs in this section, please suggest text ;-).

David> UDP does not exhibit TCP-like Head of Line blocking problems.

* Page 13, Section 5.1:

When a protocol that provides reliable delivery receives a packet
other than the next expected packet, the protocol usually assumes
that the expected packet has been lost and respond with a
retransmission request for that packet.

Note: There is no "retransmission request" in TCP. Additionally:

David> Definitely a concern in general, and one that was also caught by another reviewer - thank you for noticing.  New wording:
David> "the protocol usually assumes that the expected packet has been lost and updates the peer, which often causes a retransmission."

* Page 13, Section 5.1:

This should not be done for current transport protocols within a
single network 5-tuple, with the exception of UDP and UDP-Lite.

This text is rather confusing. Maybe rephrase as "This should not be
done for transport protocol instances of current protocols, except of
UDP and UDP-Lite"?

David> The 5-tuple concept should not be dropped, as the resulting text is easy to mis-read.
David> Reorganized to: "This should not be done within a single network 5-tuple for current transport protocols, with the important exception of UDP and UDP-Lite.."

* Security considerations section

Maybe Section 3.3 of RFC 6274 wuld be of use here?

David> It's not as if the draft doesn't have enough references already :-).
David> Seriously, Section of RFC 6274 is definitely relevant - I'll add a pointer to that and the RFC 6274 reference, thanks for the suggestion.

** Nits/Editorial **

* Page 2:

The results of using multiple DSCPs to obtain different QoS
treatments within a single network 5-tuple (e.g., reordering) have
transport protocol interactions, particularly with congestion
control functionality.

Please "(e.g., reordering)" right after "treatments".

David> I prefer not to do that, as "within a single network 5-tuple" is an important modification to the scope of "different QoS  treatments."

* Page 2:


David> Fixed, thanks.

* Page 3:
Please add references for VP8 and H264

David> Ok, I'll go look for these.

* Page 5:

RTP is usually carried over a datagram protocol, such as
UDP[RFC0768], UDP-Lite [RFC3828] or DCCP [RFC4340]; UDP is most
commonly used, but a non-datagram protocol (e.g., TCP) may also be

Add missing space in "UDP[RFC0768]".

David> Fixed, thanks.

* Page 6:

When TURN selects use of TCP, the entire real-time communications
session is carried over a single TCP 5-tuple.


David> Good suggestion, changed to "TCP connection (i.e., 5-tuple)."

* Page 8, Section 3:

The DiffServ architecture[RFC2475] maintains distinctions among:

Please add the missing space

David> Fixed, thanks.  The way that XXE displays citations makes it easy to miss these ...

* Page 8:

David> "loading" is ok, prefer to leave as-is.

* Page 11, Section 3.2:

Better results may be achieved when DSCPs are used to spread traffic
among a smaller number of DiffServ-based traffic subsets or
aggregates, see [I-D.geib-tsvwg-diffserv-intercon] for one proposal.

Please put the "see [I-D..]" within parenthesis.

David> will change comma before "see" to a semicolon instead.

* Page 13, Section 5.1:

Reordering also affects other forms of congestion control, such as
techniques for RTP congestion control that were under development
when this memo was published, see [I-D.ietf-rmcat-cc-requirements]
for requirements.

Please put the "see [I-D..." within parethesis -- i.e. "(see [I-D..)".

David> Same change as previous comment (',' -> ';').

* Page 17, section 5.4:


Please expand this acronym.

David> Already done when acronym first used in Section 2.1.
David> The actual expansion is "Synchronization SouRCe," which seems unhelpful to provide in camel-case.

* Page 18, Section 6:

, see Section 5.2 above.

Please put this text within parenthesis.

David> Done, and also for several other occurrences of similar text.

Thank you,