Re: [Detnet] [RTG-DIR] Rtgdir last call review of draft-ietf-detnet-mpls-04

[Balázs Varga A <[e-mail]>]

Hi Sasha,
Thanks for pointing to this topic.
We will discuss how to make “in-order” and “out-of-order” much more clear and update the text.
Thanks
Bala’zs


From: Alexander Vainshtein <[e-mail]>
Sent: Tuesday, December 24, 2019 3:35 PM
To: Stewart Bryant <[e-mail]>; Carlos Pignataro <[e-mail]>
Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: RE: [RTG-DIR] Rtgdir last call review of draft-ietf-detnet-mpls-04

Stewart, Carlos and all,
I understand the concerns with the 16-bit space for sequence numbers and the skip-zero approach taken by RFC 4385 (presumably, for compatibility with the early Martini drafts that have already been implemented). And it was quite convenient to turn off sequencing in PWs simply by setting SN to zero,

(The TDM PWs that MUST use sequence numbers because they MUST detect lost packets and compensate the lost payload use the entire 16-bit SN space).

But  I think that the draft should clearly articulate these considerations and also provide a definition of in-order and out-of-order packets. I have not found any of these things in the draft – did I miss something?

Regards,
Sasha

Office: [phone]
Cell:      [phone]
Email:   [e-mail]<mailto:[e-mail]>

From: rtg-dir <[e-mail]<mailto:[e-mail]>> On Behalf Of Stewart Bryant
Sent: Tuesday, December 24, 2019 4:26 PM
To: Carlos Pignataro <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [RTG-DIR] Rtgdir last call review of draft-ietf-detnet-mpls-04



On 24 Dec 2019, at 00:03, Carlos Pignataro via Datatracker <[e-mail]<mailto:[e-mail]>> wrote:


3.1.  Layers of DetNet Data Plane

  The DetNet control word (d-CW)
  conforms to the Generic PW MPLS Control Word (PWMCW) defined in
  [RFC4385].

Yes, but why not the Preferred CW?

Hi Carlos

Thanks for the review. Just picking up a couple of points at this stage,

The PCW only supports a 16bit sequence number and it has the skip zero auto-signalling of active S/N feature.

This was a problem for DetNet because:

- We were worried about S/N rollover frequency in some applications and so we wanted the option of a larger S/N.

- We wanted to have the option to propagate the S/N from the payload to the transport to simplify the implementation in some cases. These applications have a non-skip zero S/N. Skip zero is an irritation to implement and we should probably have signalled in in PWs.

As you note in is only a preferred design for PWs, DetNet is not constrained by that and there were good reasons to adopt this alternate approach,



4.1.  DetNet Over MPLS Encapsulation Components

  The LSP used to forward the DetNet packet may be of any type (MPLS-
  LDP, MPLS-TE, MPLS-TP [RFC5921], or MPLS-SR
  [I-D.ietf-spring-segment-routing-mpls]).

I am not sure of the value of this statement for an "MPLS Dataplane" document.
Further, are these "LSP Types" and if so where are the different types
ennumerated? Does this mean that static binding LSPs and BGP signaled cannto be
used? T-LDP does not work? "SDN Assigned"? I recommend removing this, since it
can confuse and does not add much.

I think it just needs a “for example” and I think that it needs to be made clear that the design is not restricted to a single method of establishing an LSP nor to the characteristics and constraints that go with those LSPs.


4.3.  OAM Indication

It is important to have the OAM Indication, but what type of OAM packets can
run on top of this AcH? I found it interesting that for example there is not
reference or citation to RFC 8029.

Work has started on OAM, for example draft-mirsky-detnet-mpls-oam-00

The OAM for DetNet will be more complex than the OAM for a classical P2P or P2MP LSP (or PW) because of the PREOF function. There is nothing in the data plane that precludes us using on of the existing OAM indicators (GAL or 0001 ACH), but I think that it is important to thing through the subtleties. Thus I think it is OK to make progress on the elements of the data plane that we can nail down, and leave. The OAM as follow-up work.




Also, outdated reference: draft-ietf-spring-segment-routing-mpls has been
published as RFC 8660

This will get picked up on the next resin as part of the Nits check.

Best regards

Stewart

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