[Detnet] Benjamin Kaduk's No Objection on draft-ietf-detnet-tsn-vpn-over-mpls-06: (with COMMENT)
Benjamin Kaduk via Datatracker <noreply@ietf.org> Wed, 17 February 2021 18:36 UTC
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Date: Wed, 17 Feb 2021 10:36:29 -0800
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Subject: [Detnet] Benjamin Kaduk's No Objection on draft-ietf-detnet-tsn-vpn-over-mpls-06: (with COMMENT)
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Benjamin Kaduk has entered the following ballot position for draft-ietf-detnet-tsn-vpn-over-mpls-06: No Objection When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-detnet-tsn-vpn-over-mpls/ ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- While I could easily imagine a document like this being an Informational document, I don't object to the requested Proposed Standard status. (FWIW, the only strong new normative requirement I remember seeing is that aggregation of TSN flows into DetNet flows "SHALL be supported".) I didn't take the time to sign up for an IEEE account to use the "IEEE Get" program and pull the external references, but what is described from them seems to make sense just from the standalone descriptions here. I just have a couple of (barely) substantive comments, followed by some editorial/nit-level remarks that need no reply. Section 7 Given that this documents calls for flooding of TSN frames in some scenarios, it seems like a caution against the risk of L2 loops would not be out of place (though I would hope no one would be surprised about it). Section 10.2 I think the IEEE references need to be normative; we say that DetNet Edge Node acts as a TSN entity and so compliance with the TSN specs is mandatory. And the editorial stuff: Section 4.1 MPLS DetNet nodes and transit nodes include DetNet forwarding sub-layer functions, support for notably explicit routes, and resources allocation to eliminate (or reduce) congestion loss and jitter. nits: I think this is better as "notably, support for explicit routes and resource allocation to eliminate (or reduce) congestion loss and jitter". Section 4.2 My understanding is that each column in figure 3 is intended to represent a distinct TSN Stream/App-flow; it might be useful to confirm that somewhere (e.g., with a note about showing three example flows in the figure). In the figure, "Application" indicates the application payload carried by the TSN network. "MPLS App-Flow" indicates that the TSN Stream is the payload from the perspective of the DetNet MPLS data plane defined in [RFC8964]. [...] nit: the figure seems to say "App-Flow for MPLS" rather than the "MPLS App-Flow" in the quoted prose. Section 5 Description of Edge Nodes procedures and functions for TSN over DetNet MPLS scenario follows the concept of [RFC3985] and covers the Edge Nodes components shown on Figure 1. In this section the following procedures of DetNet Edge Nodes are described: some nits here; maybe NEW: > The description of Edge Node procedures and functions for TSN over > DetNet MPLS scenarios follows the concepts from [RFC3985], and covers > the Edge Node components shown in Figure 1. In this section the > following procedures of DetNet Edge Nodes are described: Section 5.1 TSN specific functions are executed on the data received by the DetNet Edge Node from the connected CE before forwarded to connected CE(s) or presentation to the DetNet Service Proxy function for transmission across the DetNet domain. [...] nit: there's a type of speech mismatch between "forwarded" and "presentation" (and "forwarded" would need to be "being forwarded" in order to be grammatical), so the list doesn't have a parallel structure. I'd suggest "before being forwarded to connected CE(s) or presented to the DetNet Service Proxy function", but there are plenty of other valid options. When a TSN entity of the PE receives a packet from the DetNet Service Proxy, it first checks via Stream Identification (see Clause 6. of IEEE 802.1CB [IEEE8021CB] and IEEE P802.1CBdb [IEEEP8021CBdb]) whether the packet belongs to a configured TSN Stream. If no Stream ID is matched, then packet is dropped. [...] nit: s/then packet/then the packet/ Section 5.2 When a DetNet Service Proxy receives a packet from the TSN Entity it MUST check whether such an App-flow is present in its mapping table. If present it associates the internal DetNet flow-ID to the packet and MUST forward it to the DetNet Service and Forwarding sub-layers. If no matching statement is present it MUST drop the packet. (nit) this seems to be the only place I could find that uses the term "statement" to refer to an entry in the DetNet flow mapping table; I'd suggest using a phrasing like "if no match is found". The management or control function that provisions flow mapping SHALL ensure that adequate resources are allocated and configured to provide proper service requirements of the mapped flows. nit: I think we'd say "provider proper service that meets the requirements" or "to fulfil the service requirements"; just "providing service requirements" doesn't seem to match up to the intended meaning. Due to the (intentional) similarities of the DetNet PREOF and TSN FRER functions service protection function interworking is possible between the TSN and the DetNet domains. Such service protection interworking scenarios MAY require to copy sequence number fields from TSN (L2) to PW (MPLS) encapsulation. However, such interworking is out-of-scope in this document and left for further study. This feels more like a descriptive "may" or "might" than a normative "MAY" to me. Section 5.3 sequence number are not valid outside the DetNet network. MPLS (DetNet) Edge node terminates all related information elements encoded in the MPLS labels. nit: missing article for "MPLS Edge node", but I'd suggest converting to the plural "Edge nodes terminate" to avoid the issue. Section 6 For example, it may be not trivial to locate the egress point/interface of a TSN Streams with a multicast destination MAC address. nit: singular/plural mismatch "a TSN Streams" (it looks like using the singular "Stream" is the minimal change to resolve).
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