[Detnet] Fwd: review DetNet OAM framework draft
Greg Mirsky <gregimirsky@gmail.com> Tue, 11 May 2021 13:11 UTC
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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Tue, 11 May 2021 06:10:41 -0700
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Subject: [Detnet] Fwd: review DetNet OAM framework draft
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Now to the list Regards, Greg ---------- Forwarded message --------- From: Greg Mirsky <gregimirsky@gmail.com> Date: Sun, May 9, 2021 at 12:12 PM Subject: Re: review DetNet OAM framework draft To: Pascal Thubert (pthubert) <pthubert@cisco.com> Cc: draft-ietf-detnet-oam-framework@ietf.org < draft-ietf-detnet-oam-framework@ietf.org>, detnet@ietf.org <detnet@ietf.org> Hi Pascal, I much appreciate your thorough review and the most helpful comments. Please find my notes in-lined below under the tag GIM>>. Regards, Greg On Thu, Apr 29, 2021 at 6:07 AM Pascal Thubert (pthubert) < pthubert@cisco.com> wrote: > Dear authors and all > > > > I do support this document but do not see that in its present shape it is > ready for WGLC. Please find some review comments below. > > > > - Sadly RFC 8655 does not define either “latency” or “delay”. Reading this > draft, I now see it as an oversight. I’d suggest that we define them in the > terminology section. it is my sense that RFC 8655 uses “delay” with the > meaning of incremental flight duration, and uses “latency” for the total > time end-to-end time across the network, IOW, minimal_latency + delay <= > bounded_latency. > GIM>> Thank you, Pascal, for bringing this to the discussion. I agree with you and I strongly believe that it is utterly important to set the dictionary so that we can discuss technology and use cases based on the common understanding of terms. I like your suggestion to provide definitions of "latency" and "delay" in the Terminology section. Before going into definitions, I'd like us to define the scope of these terms. Would it be for the draft and all DetNet OAM documents or it can serve as the clarification of the terminology used in DetNet in general since RFC 8655? About the definitions. Do you think that the interpretation of "delay" is close to the definition of the residence time (RFC 8169): Residence time is the sum of the difference between the time of receipt at an ingress interface and the time of transmission from an egress interface for each node along the network path from an ingress node to an egress node. Also, in RFC 8169 we've assumed that the e2e delay, i.e., e2e latency consists of two parts - fixed propagation delay determined by the link speed and variable portion, i.e., residence time. In your opinion, could this model be applied to DetNet? > > > > > - Their work -> that work ? > > GIM>> Yes, you're right. Thank you. > > > - the abstract and the introduction indicate that the document is a problem statement / functional requirement draft, and indeed the text reads like a requirement document. But the title says framework. Which is it? > > > > - same question about the intended status (std track). Is that really what we want here? > > GIM>> Thank you for pointing this out. Switched to Informational track. > > > - “It is critical for the > > quality of information obtained using an active method that > > generated test packets are in-band with the monitored data flow. > > ”. this duplicates text in 3.3 and does not belong in a terminology. Remove? > > GIM>> I agree with you. Text in Section 3.3 is stronger but seems out of place in that section. I think moving it up into Section 3 might be appropriate. What do you think? > > > - “ OAM represents the > > essential elements of the network operation and necessary for OAM > > resources that need to be accounted for to maintain the network > > operational. > > ” does not parse too well > > GIM>> I propose the following update: OLD TEXT: OAM represents the essential elements of the network operation and necessary for OAM resources that need to be accounted for to maintain the network operational. NEW TEXT: Because OAM is an essential element of the network operation, resources, necessary for OAM, need to be accounted for in addition to DetNet flows. Does the update read better? > > > - “information about the state of the network being > > collected > > ” is being? Maybe remove that text ? it seems to repeat the first sentence of the paragraph. > > GIM>> The purpose of the sentence is in the final part "... and sent to the controller".Would the following update make it better: OLD TEXT: In either way, information about the state of the network being collected and sent to the controller. NEW TEXT: In either way, information is collected and sent to the controller. > > > - “ Also, we can characterize methods of transporting OAM information > > relative to the path of data. For instance, OAM information may be > > transported out-of-band or in-band with the data flow. > > ” this deserves its own subsection with some more explanation and possibly some references to relevant IETF work > > GIM>> Thank you for highlighting this question. I propose adding references to work at the IPPM WG. Here's the updated text: NEW TEXT: Also, we can characterize methods of transporting OAM information relative to the path of data. For instance, OAM information may be transported in-band or out-of-band with the data flow. In case of the former, the telemetry information uses resources allocated for the monitored DetNet flow. If an in-band method of transporting telemetry is used, the amount of generated information needs to be carefully analyzed, and additional resources must be reserved. [I-D.ietf-ippm-ioam-data] defines the in-band transport mechanism where telemetry information is collected in the data packet on which information is generated. Two tracing methods are described - end- to-end, i.e., from the ingress and egress nodes, and hop-by-hop, i.e., like end-to-end with additional information from transit nodes. [I-D.ietf-ippm-ioam-direct-export] and [I-D.mirsky-ippm-hybrid-two-step] are examples of out-of-band telemetry transport. In the former case, information is transported by each node traversed by the data packet of the monitored DetNet flow in a specially constructed packet. In the latter, information is collected in a sequence of follow-up packets that traverse the same path as the data packet of the monitored DetNet flow. In both methods, transport of the telemetry can avoid using resources allocated for the DetNet domain. > > > > “ Similarly, the destination does not receive packets from different > > flows through its interface. > > ” sorry I do not get the intended meaning > > GIM>> We're pointing to the distinction between the Continuity Check (CC) and Connectivity Verification (CV). The former only verifies that a path between two systems exists, while the latter, in addition to that path, verifies that the system does not receive packets from any flow other than one being monitored. Associated with the CV, is a misconnection error state and conditions of raising and clearing it. I propose removing the paragraph with that sentence and update the first paragraph as follows: OLD TEXT: In addition to the Continuity Check, DetNet solutions have to verify the connectivity. This verification considers additional constraints, i.e., the absence of misconnection. NEW TEXT: In addition to the Continuity Check, DetNet solutions have to verify the connectivity. This verification considers additional constraints, i.e., the absence of misconnection. The misconnection error state is entered after several consecutive test packets from other DetNet flows received. The definition of the conditions of entry and exit for misconnection error state is outside the scope of this document. > > > - section 3.3 –“It is worth noting that the test and data packets MUST follow the > > same path, i.e., the connectivity verification has to be conducted > > in-band without impacting the data traffic.” > > there appears to be a tension between the bandwidth that is reserved for the flow and the extra bandwidth that the OAM needs . > > Do we need to know in advance how much OAM there will be? Must that be included in the reservation? > > GIM>> Yes, the impact of OAM, whether active or hybrid, must be evaluated and accounted for when reserving resources in the DetNet domain. The update above is intended to clarify that: Because OAM is an essential element of the network operation, resources, necessary for OAM, need to be accounted for in addition to DetNet flows. > > > > > > - section 3.4. What do we do for PREOF? > > GIM>> Excellent question, thank you! I think of two updates: - in Section 3.4: Also, tracing can be used for the discovery of the Path Maximum Transmission Unit or location of elements of PREOF for the particular route in the DetNet domain. - in Section 6: DetNet OAM MUST support the discovery of PREOF along a route in the given DetNet domain. > > - “The network has isolated and identified the cause of the fault.” > > Again I fail to understand the intention. > > GIM>> Indeed. How about we change this text as the following: OLD TEXT: The network has isolated and identified the cause of the fault. For instance, the replication process behaves not as expected to a specific intermediary router. NEW TEXT: An ability to localize the network defect and provide its characterization are necessary elements of network operation. * Fault localization, a process of deducing the location of a network failure from a set of observed failure indications, might be achieved, for example, by tracing the route of the DetNet flow in which the network failure was detected. Another method of fault localization can correlate reports of failures from a set of interleaving sessions monitoring path continuity. * Fault characterization is a process of identifying the root cause of the problem. For instance, misconfiguration or malfunction of PREOF elements can be the cause of erroneous packet replication or extra packets being flooded in the DetNet domain. > > > -“ One of the advantages of the use of > > AMM in a DetNet domain with the IP data plane is that the marking is > > applied to a data flow, thus ensuring that measured metrics are > > directly applicable to the DetNet flow. > > ” isn’t this the case for IPPM in general? Isn’t the benefit of AMM more related to conciseness? > > GIM>> You are right. Do you think that the update below makes the text better: OLD TEXT: One of the advantages of the use of AMM in a DetNet domain with the IP data plane is that the marking is applied to a data flow, thus ensuring that measured metrics are directly applicable to the DetNet flow. NEW TEXT: As with all on-path telemetry methods, AMM in a DetNet domain with the IP data plane is natively in-band in respect to the monitored DetNet flow. Because the marking is applied to a data flow, measured metrics are directly applicable to the DetNet flow. AMM minimizes the additional load on the DetNet domain by using nodal collection and computation of performance metrics in combination with optionally using out-of-band telemetry collection for further network analysis. > > > - Maybe we should discuss the tension between RFC 8939 and the capability to use separate packets for OAM, since the flow is routed on the 5/6 tuple. Does that mean that only in-situ is feasible with RFC 8939 (ref draft-ietf-ippm-ioam-ipv6-options)? > > GIM>> I agree, that the definition of the DetNet IP flow is an important aspect when considering the applicability of IOAM in a DetNet domain. That may be discussed in this document, though, as I think of it, that discussion seems also in place in draft-ietf-detnet-ip-oam <https://datatracker.ietf.org/doc/draft-ietf-detnet-ip-oam/>. What do you think? > > > Section 4. This section needs more thoughts. For instance there are packets like PTP packets for which it is important to know the transit duration in each hop. Isn’t that true for DetNet as well? > > GIM>> We can discuss if and how RFC 8169 <https://datatracker.ietf.org/doc/rfc8169/> may be applicable. Perhaps in a new discussion thread. > Radio links have numerous metrics that can be reported (think RFC 8175), we need to know that information per hop as opposed to per path/circuit. We need to know if the hop does store-and-forward or passthrough – e.g., in the former case using smaller frames / packets / segments / fragments and/or network coding may improve the latency. Maybe we could dump the WG collective mind with a dedicated thread? > > GIM>> I agree, a new discussion thread will certainly help. I've been thinking of per node metrics too. I think that to be useful, per node metrics might as well be for the given ordered pair of ingress-egress interfaces. I understand that blows the amount of information we generate and collect, but by doing on-node PM calculations exported will be median, percentiles values. Definetely needs discussion. > > > - “ DetNet needs to implement a self-healing and self-optimization > > approach.” > > Though I agree with the intention and the next sentences, I’m not sure this is the best wording. Those words are classical for routing protocols that > > (re)compute a path, which is disruptive or consecutive to a disruption. We do not want disruptions in DetNet. There must be enough PREOF to ensure the SLO > > without repairing. The RAW problem is actually NOT to use all the redundancy at all times in order to save battery and spectrum. I’d rather say that > > ” in the face of events that impact the network operation (e.g., link up/down, node crash/reboot, flows starting and ending) > > the DetNet Controller need to perform repair and re-optimization actions in order to permanently ensure the SLO of all active flows > > with minimal waste of resources”. > > GIM>> Pascal, thank you for the suggested text. Accepted with gratitude > > > - section 5.2: Is it the intention to include the repair action in OAM work? > > GIM>> Thank you for the question. Thinking of it, OAM role is the detection of a performance metric degradation. Restorative actions, in my opinion, are taken by the control or management plane. Since the detection of performance monitoring and SLO are discussed in other sections, the value of Section 5.2 may be not sufficient to keep it in the document. What do you think? > > > - section 6. Why only MPLS data plane? It seems that the requirement are not dependent on the underlying technology. > > GIM>> That is my cut'n'paste mistake. > > > - I’m not sure about requirement 5, 6, 10, 11, and of the use of “excellent” in 16. > > GIM>> Let's remove the "excellent" :) GIM>> The intention of listing OAM functionality in that particular manner as requirements is to provide the check list for the gap analysis and defining extensions. Are you concerned wth the described OAM functions or the manner requirements are expressed? > > > - I read requirement 16 as the only service assurance requirement. A very important requirement in my view, and I think we want more. We also want to ensure that a scheduled transmission happens as scheduled/when, that the guaranteed resources like buffers are available per reservation.. > > GIM>> Thank you for the suggestion. I've tried to capture these resource reservation parameters in the new requirement: NEW TEXT: 18. DetNet OAM MUST support monitoring levels of resources allocated for the particular DetNet flow. Such resources include but not limited to buffer utilization, scheduler transmission calendar. > > > > Many thanks to the authors for all the great work! > > GIM>> Many thanks for your great review, much appreciated! > > > Pascal > > > > > > *From:* detnet <detnet-bounces@ietf.org> *On Behalf Of *Janos Farkas > *Sent:* jeudi 29 avril 2021 0:28 > *To:* detnet@ietf.org > *Subject:* [Detnet] review DetNet OAM framework draft > > > > WG, > > > > Please review the DetNet OAM framework draft: > https://datatracker.ietf.org/doc/draft-ietf-detnet-oam-framework/. > > > > The authors consider the draft in a pretty good shape, do not see any > major piece missing. > > > > WG review and comments would be great in order to develop the draft > towards WG Last Call. > > > > Please send your comments to the list before the next informal OAM > discussion on May 11 or bring it to the informal meeting: > https://ietf.webex.com/ietf/j.php?MTID=m27bb8ee31f025670e4071bfdfcd47432. > (More details on the OAM informal meetings: > https://mailarchive.ietf.org/arch/msg/detnet/4ik3tI-E3uhOFNaKhpkZiWwyiZc/ > .) > > > > Regards, > > Janos > > >
- [Detnet] review DetNet OAM framework draft Janos Farkas
- Re: [Detnet] review DetNet OAM framework draft Pascal Thubert (pthubert)
- [Detnet] Fwd: review DetNet OAM framework draft Greg Mirsky
- Re: [Detnet] Fwd: review DetNet OAM framework dra… Pascal Thubert (pthubert)
- Re: [Detnet] review DetNet OAM framework draft - … Pascal Thubert (pthubert)
- Re: [Detnet] review DetNet OAM framework draft - … Pascal Thubert (pthubert)
- Re: [Detnet] review DetNet OAM framework draft - … gregory.mirsky
- Re: [Detnet] review DetNet OAM framework draft - … Balázs Varga A
- Re: [Detnet] review DetNet OAM framework draft - … BRUNGARD, DEBORAH A