[Detnet] Comments on ip-over-tsn, mpls-over-tsn, tsn-vpn-over-mpls

Lou Berger <lberger@labn.net> Tue, 13 October 2020 23:21 UTC

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To: DetNet WG <detnet@ietf.org>
From: Lou Berger <lberger@labn.net>
Cc: draft-ietf-detnet-mpls-over-tsn@ietf.org, draft-ietf-detnet-tsn-vpn-over-mpls@ietf.org, draft-ietf-detnet-ip-over-tsn@ietf.org
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Subject: [Detnet] Comments on ip-over-tsn, mpls-over-tsn, tsn-vpn-over-mpls
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     As I mentioned on the LC thread, I have some comments on these 
drafts as Shepherd that I think should be addressed before passing the 
documents along to the IESG.

Major comment:

In reviewing the other DetNet data plane documents, some members of the 
IESG asked what unique protocol processing was defined in those 
documents that justified those documents being on the Standards Track vs 
Informational.  I reviewed the three TSN related documents with this in 
mind. (FWIW my view of goes in a standard can be found in 
https://trac.ietf.org/trac/teas/wiki/PSGuidelines , albeit a bit dated.)

I found that, as written, both draft-ietf-detnet-ip-over-tsn-03 and 
draft-ietf-detnet-mpls-over-tsn-03 say basically the same thing: That an 
mpls or ip over TSN node behaves as a TSN unaware talker combined with 
an internal TSN-relay.  This is covered in section 4.2 and Figure 3 of 
each document.

The text of these section do have conformance language, but the language 
relates to TSN standardized operation. So, for me use of IETF 
conformance language is not appropriate.  As far as I read it, there is 
no protocol processing defined beyond what is in the referenced TSN 
documents.  For this reason, I think these documents should be revised 
to remove conformance language and be published as BCPs (or even 
informational) .  I'd like to confer with our AD to see if she has a 
preference on which.

draft-ietf-detnet-tsn-vpn-over-mpls-03 is in a slightly different 
position.  This document also contains some TSN-specific conformance 
language that should be removed (e.g., see section 5.1), but it also 
defines TSN over MPLS specific behaviors in section 5.2.  I think this 
definition as a PS is pretty thin and basically comes down to saying TSN 
Steams are mapped to DetNet AppFlows.  This said, there is a real 
interoperability issue being addressed as without even this thin 
definition, different implementations would not necessarily 
interoperate.    I recommend that this document also be revised to

(a) ensure it is not using conformance language for any TSN behaviors  
-- describing what an IEEE reference requires is fine, but that's just 
informative text, and

(b) clearly define what processing/protocol behavior is required, and 
what management/controller information must be supported, to be 
conformant the the new proposed standard.

Minor comments:

- All the documents state that there are required mappings between 
DetNet and TSN management and control planes, but no details are given.  
Rather then make unsubstantiated comments, I suggest stating that such 
mappings are out of scope of the document.

- All three documents repeat/summarize behaviors from the other data 
plane documents in overview sections.  I suggest deleting these and just 
point the readers and these normative documents.

- somewhat related, conformance language from the detnet-mpls is 
partially repeated in section 5.3 of tsn-vpn-over-mpls.  It would be 
better to just point to required processing in detnet-mpls than do a 
partial repetition.

I'm happy to work with the authors, on list or in an informal meeting 
announced on the list,to review these comments and any proposed changes 
they may propose to resolve these  comments. (I'll also provide some 
additional less important nits.)


(as doc Shepherd)