[Detnet] AD review of draft-ietf-detnet-oam-framework-08

[John Scudder <[e-mail]>]

Hi Authors, WG,

Thanks for this spec. 

I’ve supplied my questions and comments in the form of an edited copy of the draft. Minor editorial suggestions I’ve made in place without further comment, more substantive questions and comments are done in-line and prefixed with “jgs:”. You can use your favorite diff tool to review them; I’ve attached the iddiff output for your convenience if you’d like to use it. I’ve also pasted a traditional diff below in case you want to use it for in-line reply. 

Thanks,

—John

--- draft-ietf-detnet-oam-framework-08.txt	2023-05-25 15:47:46.000000000 -0400
+++ draft-ietf-detnet-oam-framework-08-jgs-comments.txt	2023-05-26 12:10:44.000000000 -0400
@@ -22,8 +22,8 @@
 
 Abstract
 
-   Deterministic Networking (DetNet), as defined in RFC 8655, is aimed
-   to provide a bounded end-to-end latency on top of the network
+   Deterministic Networking (DetNet), as defined in RFC 8655, aims
+   to provide bounded end-to-end latency on top of the network
    infrastructure, comprising both Layer 2 bridged and Layer 3 routed
    segments.  This document's primary purpose is to detail the specific
    requirements of the Operation, Administration, and Maintenance (OAM)
@@ -139,7 +139,7 @@
    Objectives (SLO), such as in-order packet delivery, packet delay,
    delay variation, and packet loss ratio, assigned to each DetNet flow.
 
-   This document lists the functional requirements toward OAM for DetNet
+   This document lists the functional requirements toward OAM for a DetNet
    domain.  The list can further be used for gap analysis of available
    OAM tools to identify possible enhancements of existing or whether
    new OAM tools are required to support proactive and on-demand path
@@ -176,17 +176,31 @@
 
    *  Maintenance Intermediate Point (MIP): an OAM instance along the
       DetNet flow in the particular sub-layer of the DetNet OAM domain.
-      A MIP MAY respond to an OAM message generated by the MEP at its
+      A MIP may respond to an OAM message generated by the MEP at its
       sub-layer of the same DetNet OAM domain.
+--
+jgs: Do you really want the MAY above? The note in Section 1.3 implies
+you'll only be using RFC 2119 keywords in Section 6, so I've tentatively
+changed it to "may".
+--
 
    *  Control and management plane: the control and management planes
       are used to configure and control the network (long-term).
       Relative to a DetNet flow, the control and/or management plane can
       be out-of-band.
+--
+jgs: I'm not sure what work the parenthetical comment "(long-term)" is
+doing here. Would it do any harm to remove it?
+--
 
    *  Active measurement methods (as defined in [RFC7799]) modify a
       DetNet flow by inserting novel fields, injecting specially
       constructed test packets [RFC2544]).
+--
+jgs: Consider "new", "extra", or "additional" instead of "novel", which 
+is a bit of a trigger word for some reviewers and doesn't seem to be  
+needed here.
+--
 
    *  Passive measurement methods [RFC7799] infer information by
       observing unmodified existing flows.
@@ -216,6 +230,16 @@
    OAM: Operations, Administration, and Maintenance
 
    DetNet: Deterministic Networking
+--
+jgs: "DetNet" is not, strictly speaking, an acronym, it's an
+abbreviation. For that matter, neither is "OAM", it's an initialism,
+since it's read as "oh ay em". "PREOF" is a legit acronym. [*] I was
+going to suggest you consider changing the subsection name to
+"terminology" except you've already used that. I guess you could use
+"definitions".
+
+[*] https://www.rd.com/article/acronym-vs-abbreviation-whats-the-difference/
+--
 
    PREOF: Packet Replication, Elimination and Ordering Functions
 
@@ -228,7 +252,11 @@
 
    SLO: Service Level Objective
 
-   PM: Perfromance Monitoring
+   PM: Performance Monitoring
+--
+jgs: You only use the term "PM" in one place. Consider removing it and just
+writing out "Performance Monitoring" in that place.
+--
 
 1.3.  Requirements Language
 
@@ -244,6 +272,10 @@
    DetNet networks expect to provide communications with predictable low
    packet delay and packet loss.  Most critical applications will define
    an SLO to be required for the DetNet flows it generates.
+--
+jgs: You identify bounding delay and loss as primary goals of DetNet, but 
+leave out misordering, which RFC 8655 also identifies as a first-order goal.
+--
 
    To respect strict guarantees, DetNet can use an orchestrator able to
    monitor and maintain the network.  Typically, a Software-Defined
@@ -252,27 +284,38 @@
    the regular operation of the network.  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.
+--
+jgs: the last sentence above doesn't work. Are you using "represents" in
+the sense of "is defined as"? If so, let me implore you not to redefine
+OAM in-line in a single sentence, after all we have an entire RFC (6291,
+which you cite) to do this. It seems to me you can just delete the 
+sentence.
+
+If you're doing something other here than (re)defining "OAM", I
+seriously don't get it, please propose a rewrite or help me understand
+what you mean.
+--
 
    Many legacy OAM tools can be used in DetNet networks, but they are
    not able to cover all the aspects of deterministic networking.
    Fulfilling strict guarantees is essential for DetNet flows, resulting
-   in new DetNet specific functionalities that must be covered with OAM.
+   in new DetNet-specific functionalities that must be covered with OAM.
    Filling these gaps is inevitable and needs accurate consideration of
-   DetNet specifics.  Similar to DetNet flows itself, their OAM needs
+   DetNet specifics.  Similar to DetNet flows themselves, their OAM needs
    careful end-to-end engineering as well.
 
    For example, appropriate placing of MEPs along the path of a DetNet
-   flow is not always a trivial task and may require proper design
+   flow is not always a trivial task and may require proper design,
    together with the design of the service component of a given DetNet
    flow.
 
-   There are several DetNet specific challenges for OAM.  Bounded
+   There are several DetNet-specific challenges for OAM.  Bounded
    network characteristics (e.g., delay, loss) are inseparable service
    parameters; therefore, PM is a key topic for DetNet.  OAM tools are
    needed to prove the SLO without impacting the DetNet flow
-   characteristics.  A further challenge is the strict resource
+   characteristics.  A further challenge is strict resource
    allocation.  Resources used by OAM must be considered and allocated
-   to avoid disturbing DetNet flow(s).
+   to avoid disturbing DetNet flows.
 
 
 
@@ -292,12 +335,12 @@
       network.
 
    OAM mechanisms exist for the DetNet forwarding sub-layer,
-   nonetheless, OAM for the service sub-layer requires new OAM
+   but the service sub-layer requires new OAM
    procedures.  These new OAM functions must allow, for example, to
    recognize/discover DetNet relay nodes, to get information about their
    configuration, and to check their operation or status.
 
-   DetNet service sub-layer functions use a sequence numbers for PREOF.
+   DetNet service sub-layer functions use a sequence number for PREOF.
    That creates a challenge for inserting OAM packets in the DetNet
    flow.
 
@@ -312,13 +355,17 @@
    also control PREOF in those scenarios where DetNet solutions involve
    more than one single central controller.
 
-   DetNet forwarding sub-layer is based on legacy technologies and has a
+   The DetNet forwarding sub-layer is based on preexisting technologies and has
    much better coverage regarding OAM.  However, the forwarding sub-
    layer is terminated at DetNet relay nodes, so the end-to-end OAM
    state of forwarding may be created only based on the status of
    multiple forwarding sub-layer segments serving a given DetNet flow
    (e.g., in case of DetNet MPLS, there may be no end-to-end LSP below
    the DetNet PW).
+--
+jgs: Please write out PW. You could expand on first use instead, but...
+this is the only use.
+--
 
 3.  Operation
 
@@ -326,8 +373,8 @@
    forwarding and routing purposes.
 
    It is worth noting that the test and data packets are expected to
-   follow the same path, i.e., the connectivity verification has to be
-   conducted in-band without impacting the data traffic.  It is expected
+   follow the same path, i.e., connectivity verification has to be
+   conducted in-band without impacting data traffic.  It is expected
    that test packets share fate with the monitored data traffic without
    introducing congestion in normal network conditions.
 
@@ -371,7 +418,7 @@
 3.2.  Continuity Check
 
    Continuity check is used to monitor the continuity of a path, i.e.,
-   that there exists a way to deliver the packets between two MEP A and
+   that there exists a way to deliver packets between MEP A and
    MEP B.  The continuity check detects a network failure in one
    direction, from the MEP transmitting test packets to the remote
    egress MEP.  Continuity check in a DetNet OAM domain monitors the
@@ -381,11 +428,21 @@
 3.3.  Connectivity Verification
 
    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
+   connectivity.  This verification considers additional
+   constraints, e.g., the absence of misconnection.  The misconnection
    error state is entered after several consecutive test packets from
-   other DetNet flows are received.  The definition of the conditions of
-   entry and exit for misconnection error state is outside the scope of
+   other DetNet flows are received.  The definition of the conditions for
+   entry and exit of misconnection error state is outside the scope of
+--
+jgs: Above I changed "i.e." to "e.g.", since I *think* you mean "for
+example", and not "in other words".
+
+On the other hand if you really did mean "i.e." then I guess it's not 
+"additional constraints" but "an additional constraint", singular, and 
+you should revert my edit and make that edit instead, for agreement in
+number. (In that case you could also remove "i.e." entirely without 
+loss of clarity.)
+--
 
 
 
@@ -396,40 +453,48 @@
 
    this document.  Connectivity verification in a DetNet OAM domain
    monitors the DetNet forwarding sub-layer and thus is not affected by
-   PREOF that operates at the DetNet service sub-layer ([RFC8655].
+   PREOF that operates at the DetNet service sub-layer ([RFC8655]).
 
 3.4.  Route Tracing
 
    Ping and traceroute are two ubiquitous tools that help localize and
-   characterize a failure in the network using echo request/reply
+   characterize a failure in the network using an echo request/reply
    mechanism.  They help to identify a subset of the list of routers in
    the route.  However, to be predictable, resources are reserved per
+--
+jgs: Would it be correct to rewrite as "They help to identify a subset of
+the routers in the path"? (If not, why not?)
+--
    flow in DetNet.  Thus, DetNet needs to define route tracing tools
-   able to track the route for a specific flow.  Also, tracing can be
+   able to trace the route for a specific flow.  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.
 
    DetNet is not expected to use Equal-Cost Multipath (ECMP) [RFC8939].
-   As the result, DetNet OAM in ECMP environment is outside the scope of
+   As the result, DetNet OAM in an ECMP environment is outside the scope of
    this document.
 
 3.5.  Fault Verification/Detection
 
    DetNet expects to operate fault-tolerant networks.  Thus, mechanisms
-   able to detect faults before they impact the network performance are
+   able to detect faults before they impact network performance are
    needed.
 
-   The network has to detect when a fault occurred, i.e., the network
+   The network has to detect when a fault has occurred, i.e., the network
    has deviated from its expected behavior.  Fault detection can be
-   based on pro-active OAM protocols like continuity check or on-demand
+   based on proactive OAM protocols like continuity check or on-demand methods
    like ping.  While the network must report an alarm, the cause may not
    be identified precisely.  For instance, the end-to-end reliability
    has decreased significantly, or a buffer overflow occurs.
+--
+jgs: Would it be right to replace "For instance" with "Examples of such 
+alarms are"?
+--
 
 3.6.  Fault Localization and Characterization
 
-   An ability to localize the network defect and provide its
+   An ability to localize a network defect and provide its
    characterization are necessary elements of network operation.
 
       Fault localization, a process of deducing the location of a
@@ -437,7 +502,7 @@
       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.
+      interleaved sessions monitoring path continuity.
 
 
 
@@ -464,11 +529,14 @@
       of Active Methods and Passive Methods.
 
    A hybrid measurement method may produce metrics as close to passive,
+--
+jgs: I don't know what you mean by "as close to passive"
+--
    but it still alters something in a data packet even if that is the
    value of a designated field in the packet encapsulation.  One example
    of such a hybrid measurement method is the Alternate Marking method
    (AMM) described in [RFC8321].  As with all on-path telemetry methods,
-   AMM in a DetNet domain with the IP data plane is natively in-band in
+   AMM in a DetNet domain with the IP data plane is natively in-band with
    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
@@ -478,26 +546,34 @@
 
 4.  Administration
 
-   The ability to expose a collection of metrics to support an operator
-   making proper decisions is essential.  Following perfromance metrics
+   The ability to expose a collection of metrics to support an operator's
+   decision-making is essential.  The following performance metrics
    are useful:
 
-   *  Queuing Delay: the time elapsed between a packet enqueued and its
+   *  Queuing Delay: the time elapsed between enqueuing a packet and its
       transmission to the next hop.
 
    *  Buffer occupancy: the number of packets present in the buffer, for
       each of the existing flows.
 
-   *  Per a DetNet flow to measure the end-to-end performance for a
+   *  Per DetNet flow, a measure of the end-to-end performance for a
       given flow.  Each of the paths has to be isolated in multipath
       routing strategies.
+--
+jgs: I'm not sure my proposed edit correctly captures your meaning,
+please check.
+--
 
-   *  Per path to detect misbehaving path(s) when multiple paths are
-      used for the service protection.
+   *  Per path, detection of misbehaving path(s) when multiple paths are
+      used for service protection.
 
-   *  Per device to detect misbehaving device, when it relays the
+   *  Per device, detection of a misbehaving device, when it relays the
       packets of several flows.
-
+--
+jgs: Same above. Also, I don't understand what work "when it relays the
+packets of several flows" is doing. Is it OK for a device to misbehave when
+it relays the packets of only a single flow?
+--
 
 
 
@@ -514,6 +590,15 @@
    Periodic and event-triggered collection information characterizing
    the state of a network is an example of of of mechanisms to achieve
    the optimization.
+--
+jgs: I'm not entirely sure what the first sentence above means, but I
+suspect the "important operational function" text is muddling things
+up. Perhaps,
+
+It is important to optimize the volume and frequency of statistics/
+measurement collection, whether the mechanisms are distributed, 
+centralized, or both.
+--
 
 4.2.  Worst-case metrics
 
@@ -530,7 +615,25 @@
    Service protection (provided by the DetNet Service sub-layer) is
    designed to cope with simple network failures and mitigates the
    DetNet Controller Plane's immediate reaction to network events.  In
-   the face of events that impact the network operation (e.g., link up/
+--
+jgs: I don't understand what you mean by "mitigates the DetNet
+Controller Plane's immediate reaction". Are you trying to say
+that it mitigates the inevitable latency between a network event,
+and the Controller Plane's ability to respond to it, analogous
+to the relationship between IPFRR and traditional routing 
+protocols?
+
+On the assumption that's what you're getting at, perhaps something
+like,
+
+"... designed to mitigate simple network failures more rapidly
+than the expected response time of the DetNet Controller Plane."
+
+If you wanted to you could even add the analogy to the relationship
+between IPFRR and the IP control plane, but this might just be 
+clutter.
+--
+   the face of events that impact network operation (e.g., link up/
    down, device crash/reboot, flows starting and ending), the DetNet
    Controller Plane needs to perform repair and re-optimization actions
    in order to permanently ensure the SLO of all active flows with
@@ -541,6 +644,17 @@
 
       the cost of the sub-optimality: resources may not be used
       optimally (e.g., a better path exists).
+--
+jgs: I'm trying to think of an example where resources are not used 
+optimally but no better path exists. I guess it depends on exactly
+how one defines "better" and "optimal" but essentially, it seems to me that
+"resources used optimally" is equivalent to "there exists no better
+path" and therefore "resources not used optimally" must mean "there does
+exist a better path".
+
+Which, if you agree, means either the "e.g." should be an "i.e.", or
+the parenthetical comment should go away.
+---
 
       the reconfiguration cost: the DetNet Controller Plane needs an
       ability to trigger some reconfigurations.  For this transient
@@ -604,6 +718,10 @@
    2.   It MUST be possible to initialize a DetNet OAM session from
         using any of DetNet Controller Plane solution, e.g., centralized
         controller.
+--
+jgs: I don't understand what the above means. Please explain/propose a 
+rewrite. Possibly you mean "initiate" instead of "initialize"?
+--
 
    3.   DetNet OAM MUST support proactive OAM monitoring and measurement
         methods.
@@ -649,11 +767,11 @@
        the DetNet OAM instance performing continuity checking.
 
    3.  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.
+       for a particular DetNet flow.  Such resources include but are not
+       limited to buffer utilization and scheduler transmission calendar.
 
-   4.  DetNet OAM MUST support monitoring any sub-set of paths traversed
-       through the DetNet domain by the DetNet flow.
+   4.  DetNet OAM MUST support monitoring any subset of paths traversed
+       through the DetNet domain by a DetNet flow.
 
 6.2.  Requirements on OAM for DetNet Service Sub-layer
 
@@ -680,21 +798,47 @@
    3.  DetNet OAM MUST support the discovery of Packet Replication,
        Elimination, and Order preservation sub-functions locations in
        the domain.
+--
+jgs: Probably that should be "sub-function" singular. Also, this is the
+rare case where I suggest inserting an acronym -- since we talk about
+"PREOF" so much in DetNet, it probably would be worth adding "(PREOF)"
+here.
+--
 
-   4.  DetNet OAM MUST support the collection of the DetNet service sub-
+   4.  DetNet OAM MUST support the collection of DetNet service sub-
        layer specific (e.g., configuration/operation/status) information
        from DetNet relay nodes.
+--
+jgs: I'm willing to accept that there *might* be sub-layer specific info
+other than configuration, operation, and status, but I sure don't know 
+what it is. So I wonder if the "e.g." can/should be dropped.
+--
 
-   5.  DetNet OAM MUST support excercising functionality of Packet
+   5.  DetNet OAM MUST support exercising functionality of Packet
        Replication, Elimination, and Order preservation sub-functions in
        the domain.
+--
+jgs: again it might be worth adding "(PREOF)". One reason for this is to
+accommodate people doing text search within the document for relevant
+requirements.
+--
 
    6.  DetNet OAM MUST work for DetNet data planes - MPLS and IP.
 
    7.  DetNet OAM MUST support defect notification mechanism, like Alarm
-       Indication Signal.  Any DetNet relay node within the given DetNet
+       Indication Signal.  Any DetNet relay node within a given DetNet
        flow MAY originate a defect notification addressed to any subset
        of DetNet relay nodes within that flow.
+--
+jgs: there needs to be some article before "defect notification mechanism",
+I'm not sure which to propose, but maybe "a", as in "... must support a
+defect notification mechanism, like Alarm Indication Signal".
+
+Also, are relay nodes "within" a flow? I would think they are "along" a 
+flow or possibly "providing service for" a flow.
+
+The MAY seems a little funny in this context but I think it is OK.
+--
 
    8.  DetNet OAM MUST be able to measure metrics (e.g. delay) inside a
        collection of OAM sessions, specially for complex DetNet flows,
@@ -703,13 +847,13 @@
 7.  IANA Considerations
 
    This document has no actionable requirements for IANA.  This section
-   can be removed before the publication.
+   can be removed before publication.
 
 8.  Security Considerations
 
    This document lists the OAM requirements for a DetNet domain and does
    not raise any security concerns or issues in addition to ones common
-   to networking and those specific to a DetNet discussed in Section 9
+   to networking and those specific to DetNet discussed in Section 9
    of [RFC9055].
 
 9.  Acknowledgments