Geometry may possibly be a rather specialist use of an English language term. The usage here is not colloquial.
Picking an online dictionary at random… (The American Heritage® Dictionary of the English Language, 5th Edition) adjective 1. Corresponding; congruous 4. Possessing congruity; suitable; agreeing; corresponding. 6. Corresponding in character Further, as indicated in the draft, this term is used (and defined) in RFC 6669. The concept of “congruent routes” is found in RFC 2362, and congruent topologies in RFC 2796 and RFC 4257/8. There are many other RFCs that talk about congruent topologies, and I don’t think any of them means, “Of the same shape or connectivity so that one could be mapped to the other through an isomorphic transposition.” Notwithstanding this, if Greg finds this word to be confusing we should assume that other readers of similar education may be similarly confused. I think the best solution is to include a careful definition of “congruent”. Cheers, Adrian From: Greg Mirsky <[email protected]> Sent: 05 June 2025 01:41 To: Matthew Bocci (Nokia) <[email protected]> Cc: Andrew G. Malis <[email protected]>; Ops Area WG <[email protected]>; Carlos Pignataro <[email protected]> Subject: [OPSAWG]Re: RFC 5085/PALS/PWE3 (RE: Re: WG LAST CALL: Guidelines for Charactering "OAM" Hi Matthew, In another email thread related to this draft, Tal and I discussed <https://mailarchive.ietf.org/arch/msg/opsawg/isseTIy5uTZYl-K-oVAoV_yf5iE/> a similar scenario in which proactive defect detection for a multi-CoS flow utilizes a single OAM session. As in the discussed example of ETH-CC, using VCCV-BFD at higher CoS might create false positives for the lower CoS sub-flows since there is no definition of what constitutes a "short bursts of congestion" and when such bursts must be handled as a loss of connectivity for the particular CoS. Also, I'm confused by the colloquial use of "congruent", which is not consistent with the definition of the term: Geometry (of figures) identical in form; coinciding exactly when superimposed. As I understand it, "superimposed" includes transformations such as shift, flip, and rotate. For example, semi-circles are congruent, but that is not what is required for an OAM packet. Would you agree? That re-definition of the fundamental term in geometry is inappropriate, and I consider "in-band" a clearer term for demonstrating the required topological equivalency between the path traversed by an OAM packet and the data packet of the monitored flow. Regards, Greg On Wed, Jun 4, 2025 at 8:49 PM Matthew Bocci (Nokia) <[email protected] <mailto:[email protected]> > wrote: Hi Med My interpretation and experience of this is that in-band means that the encapsulation is such that the OAM packets flow on the same tunnel and PW as the user data of that PW. This means that the paths are congruent from an MPLS / PWE3 perspective (same P and PE routers). I am not sure that it is strictly correct to conflate in-band with congruent. If VCCV packets are sent in-band then they are congruent with the PW user data, but in general the term congruent does not imply they are in-band. RFC6669 was written from an MPLS-TP perspective where bidirectional paths were intended to be congruent (see RFC5921). I believe that text quoted below from RFC6669 really meant that the OAM packets are sent in-band to achieve congruency. I don’t think it means the QoS treatment *must* always be the same between VCCV and user data on a given PW. For example, there are cases such as VCCV-BFD where you are doing a continuity check that should not be affected by short bursts of congestion that might affect the user packets (which would be measured by some other OAM such as PM) but must nonetheless follow the same PW. Best regards Matthew From: [email protected] <mailto:[email protected]> <[email protected] <mailto:[email protected]> > Date: Wednesday, 4 June 2025 at 09:48 To: Andrew G. Malis <[email protected] <mailto:[email protected]> >, Stewart Bryant <[email protected] <mailto:[email protected]> >, Matthew Bocci (Nokia) <[email protected] <mailto:[email protected]> > Cc: Ops Area WG <[email protected] <mailto:[email protected]> >, Carlos Pignataro <[email protected] <mailto:[email protected]> >, Greg Mirsky <[email protected] <mailto:[email protected]> > Subject: RFC 5085/PALS/PWE3 (RE: [OPSAWG]Re: WG LAST CALL: Guidelines for Charactering "OAM" Hi Andy/Stewart/Matthew, I hope you are doing well. I’m soliciting your feedback on this text which is included in draft-ietf-opsawg-oam-characterization: An example of "Path-Congruent OAM" is the Virtual Circuit Connectivity Verification (VCCV), described is Section 6 of [RFC5085] as "The VCCV message travels in-band with the Session and follows the exact same path as the user data for the session". Thus, the term "in-band" in [RFC5085] refers to using the same path as the user data. This term is also used in Section 2 of [RFC6669] with the same meaning, and the word "congruent" is mentioned as synonymous. Do you see any disconnect between this text and RFC5085? FWIW, draft-ietf-opsawg-oam-characterization defines “Path-Congruent OAM” as follows: The OAM information follows the exact same path as the observed data traffic. This was sometimes referred to as "in-band". Thank you. Cheers, Med PS: Please see below for more context. De : Greg Mirsky <[email protected] <mailto:[email protected]> > Envoyé : mercredi 4 juin 2025 07:32 À : Carlos Pignataro <[email protected] <mailto:[email protected]> > Cc : Ops Area WG <[email protected] <mailto:[email protected]> > Objet : [OPSAWG]Re: WG LAST CALL: Guidelines for Charactering "OAM" Hi Carlos, please find my notes below tagged GIM2>>. Regards, Greg On Tue, Jun 3, 2025 at 1:21 AM Carlos Pignataro < <mailto:[email protected]> [email protected]> wrote: Greg: While I’ll defer to Tal for a detailed response, I’ve provided three key points inline. See “CMP:” below On Jun 1, 2025, at 7:49 PM, Greg Mirsky < <mailto:[email protected]> [email protected]> wrote: Hi Tal, thank you for explaining updates. Please find my follow-up notes below tagged GIM>>. Regards, Greg On Thu, May 29, 2025 at 5:59 PM Tal Mizrahi < <mailto:[email protected]> [email protected]> wrote: Hi Greg, Thanks again for reviewing the draft. Your comments for the previous versions have helped in improving the draft. Please see my responses to the latest comments that you have sent to the authors off-list when you kindly reviewed an intermediate version of the draft. On Tue, May 13, 2025 at 8:38 PM Greg Mirsky < <mailto:[email protected]> [email protected]> wrote: > > Hi Tal, > > Thank you for your work on addressing my comments. I reviewed the working > version of the draft and have some comments and questions, which are below. > Section 2: > > It is noted that "A frequently encountered case is the use of "in-band" to > mean either in-packet or on-path." If that is the case, and there are many > IETF documents that use these interpretations of "in-band," it seems like it > would be easy to provide several references in support of that assumption. [TM] Following your comment we have focused the following two paragraphs. The following paragraph demonstrates the use of the term "in-band" in the context of path-congruent OAM: Connectivity Verification (VCCV), described is Section 6 of [RFC5085] as "The VCCV message travels in-band with the Session and follows the exact same path as the user data for the session". Thus, the term "in-band" in [RFC5085] refers to using the same path as the user data. This term is also used in Section 2 of [RFC6669] with the same meaning, and the word "congruent" is mentioned as synonymous. GIM>> I don't think that your interpretation of "in-band" in RFC 5085 is accurate. The VCCV message not only traverses the same path as a data packet because the same labels are applied along the path, but it also receives the same forwarding treatment by the network because the same Traffic Class is used for the VCCV message as for the data packet. Thus, it is in-band with the monitored data flow, and topological equivalence is only one element, while it must be complemented by the QoS equivalence. CMP: As an author of RFC 5085, I can confirm that you are completely wrong on this. GIM2>> That is your personal opinion, not the opinion of other authors, and even less the opinion of PWE3 (later PALS) WG. As the PALS WG is winding down, the MPLS WG may be the community to provide a more authoritative interpretation of RFC 5085. CMP: That said, you do not need to be an author to know this, you can actually **read** the RFC, where it says: CMP: "in-band (i.e., following the same data-plane faith as PW data).” CMP: “ travels in-band with the Session and follows the exact same path as the user data for the session" CMP: Let’s not make up ‘interpretations’. ____________________________________________________________________________________________________________ Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration, Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci. 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