Re: [CCAMP] Yangdoctors last call review of draft-ietf-ccamp-mw-yang-05

"Yemin (Amy)" <amy.yemin@huawei.com> Fri, 08 June 2018 09:37 UTC

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From: "Yemin (Amy)" <amy.yemin@huawei.com>
To: Jan Lindblad <janl@tail-f.com>, "yang-doctors@ietf.org" <yang-doctors@ietf.org>
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Thread-Topic: [CCAMP] Yangdoctors last call review of draft-ietf-ccamp-mw-yang-05
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Subject: Re: [CCAMP] Yangdoctors last call review of draft-ietf-ccamp-mw-yang-05
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Hi Jan,



Thanks very much for the comments. I found them are quiet useful to improve the models.

Please see my reply below in blue.

The draft co-authors may add more reply to your comments.



BR,

Amy

-----Original Message-----
From: CCAMP [mailto:ccamp-bounces@ietf.org] On Behalf Of Jan Lindblad
Sent: Thursday, June 07, 2018 6:18 PM
To: yang-doctors@ietf.org
Cc: ccamp@ietf.org; draft-ietf-ccamp-mw-yang.all@ietf.org; ietf@ietf.org
Subject: [CCAMP] Yangdoctors last call review of draft-ietf-ccamp-mw-yang-05



Reviewer: Jan Lindblad

Review result: Ready with Issues



YD review of draft-ietf-ccamp-mw-yang



I have now reviewed the YANG modules and corresponding examples of the -05 version of this draft. I have not read much of the RFC text, so I can't vouch for how well the text aligns with the model. I find the proposed modules in good shape. Most of my comments below are alternate ways of modeling something that the wg may consider, or a few things where I propose a better option for something that would be acceptable even as it is. There is a single issue that must be fixed IMO, see #8 below.



Let's start with module ietf-microwave-types.



#1) Consider adding structure to related identities



This module consists mostly of a long list of identities based off of coding-modulation. If it makes sense that in the future someone might be interested in doing something with all qam-4096 based identities or all -strong identities, say, it may make sense to model the identities as based on each other in a tree style. E.g.



  identity qam-4096 {

    base coding-modulation;

    description

      "4096 QAM coding and modulation scheme.";

  }



  identity qam-4096-strong {

    base qam-4096;

    description

      "4096 QAM strong coding and modulation scheme.";

  }



  identity qam-4096-light {

    base qam-4096;

    description

      "4096 QAM light coding and modulation scheme.";

  }



Or even go to "multiple inheritance" with multiple bases for identities, e.g.

for qam-4096 and strong. This would allow future applications to filter the identities on such criteria. Just a thought.
[Amy] change to base qam-4096. Multiple bases seem not applicable here.



#2) Convention to use all lowercase in YANG symbols



There are a couple of identities with capitals. Consider changing to all lowercase; that is the YANG convention.



  identity E1 {

  identity STM-1 {
[Amy] will fix it.



Next, let's look at module ietf-interface-protection.



I can't say I understand exactly why this is a separate module. It publishes a single grouping, which is required by ietf-microwave-radio-link, and as far as I understand would probably never be used anywhere else. When the grouping is used a single time in ietf-microwave-radio-link, it is immediately refined.

Would probably reduce the clutter by merging the two modules and resolving the refine.

[Amy] They were in one model. During the WG discussion, comment was raised that the interface protection function could be generic and be used by other technologies in future, so we split the models.

I'm open to discuss about this.



#3) Config true leaf name status



I find it counter-intuitive that a leaf called status (or state) is a configuration item. I had to re-read the model several times to get my head around the fact that this is indeed meant to be config true. Perhaps consider a name change?



      leaf status {

[Amy] status should be config false.



#4) Action external-commands



There is a single action called external-commands (even in plural). It takes a single argument, which is the name of the operation to execute. No output. To me, a more natural modeling would be to make each of the external commands an action, over time possibly with different input and output.

[Amy] add output to describe the action result (success, fail, inprogress). But prefer to use one action.

Change the name to external-command.





Finally, we have module ietf-microwave-radio-link.



#5) Use derived-from when comparing identities



It's more future-proof and more likely to be interoperable if you use proper XPATH functions to determine kinship than using plain equality



  augment "/if:interfaces/if:interface" {

    when "if:type = 'mw-types:radio-link-terminal'";



is better written as



  augment "/if:interfaces/if:interface" {

    when "derived-from-or-self(if:type, 'mw-types:radio-link-terminal')";



This allows future sub-typing (sub-classing) of radio-link-terminal, i.e. new identities that are based on radio-link-terminal to reflect some special kind of RLT. It also improves chances of interoperability.

[Amy] will adopt this.



#6) Blank id reasonable?



Leafs that function as an id usually do not have defaults. Does a blank id make sense here? If it does, maybe it would make more sense to leave it without a default and explain what happens if not set in the description instead? Or mark it as mandatory if it has to be set.



    leaf id {

      type string;

      default "";

[Amy] remove default. Add mandatory.



#7) Use derived-from when comparing identities (again)



    leaf-list carrier-terminations {

      type if:interface-ref;

      must "/if:interfaces/if:interface[if:name = current()]"

         + "/if:type = 'mw-types:carrier-termination'" {



is better written as



      must "derived-from-or-self(/if:interfaces/if:interface[if:name =

      current()]"

         + "/if:type, 'mw-types:carrier-termination')" {



It is possible to write this in a more compact way, but there's nothing wrong with the above.



      must "derived-from-or-self(deref(current())/.."

         + "/if:type, 'mw-types:carrier-termination')" {

[Amy] will adopt this.



#8) Badly broken frequency duplex config



If you read the descriptions in these related leafs:



    leaf tx-frequency {

      type uint32;

      units "kHz";

      mandatory true;

      description

        "Selected transmitter frequency.";

    }

   leaf rx-frequency {

      type uint32;

      units "kHz";

      description

        "Selected receiver frequency.

         Overrides existing value in duplex-distance.

         Calculated from tx-frequency and duplex-distance if

         only duplex-distance is configured.

         Must match duplex-distance if both leaves are

         configured in a single operation.";

    }



    leaf duplex-distance {

      type uint32;

      units "kHz";

      description

        "Distance between Tx & Rx frequencies.

         Used to calculate rx-frequency when

         rx-frequency is not specifically configured.

         Overrides existing value in rx-frequency.

         Calculated from tx-frequency and rx-frequency if only

         rx-frequency is configured.

         Must match rx-frequency if both leaves are configured

         in a single operation.";

    }



It appears that the author intends the system to fill in the value for one of these leaves based on the value set for the other. This is a big no-no. A system should never alter its own configuration, or automation flows (which is the whole purpose with YANG and NETCONF, remember) will break. Also, the validity of the configuration should not depend on how many operations are used to inject it.



I find this a serious flaw that must be fixed before the module can be released.



I propose fixing it like this:



    leaf tx-frequency {

      type uint32;

      units "kHz";

      mandatory true;

      description

        "Selected transmitter frequency.";

    }

    choice freq-or-distance {

      leaf rx-frequency {

        type uint32;

        units "kHz";

        description

          "Selected receiver frequency."

      }

      leaf duplex-distance {

        type uint32;

        units "kHz";

        description

          "Distance between Tx & Rx frequencies."

      }

    }



If you would like to have read-only computed values accessible in the model, maybe you could add:



    leaf actual-rx-frequency {

      type uint32;

      units "kHz";

      description

        "Computed receiver frequency."

      config false;

    }

    leaf actual-duplex-distance {

      type uint32;

      units "kHz";

      description

        "Computed distance between Tx & Rx frequencies."

      config false;

    }



Many other ways of doing this properly are also possible. Let me know if you'd like to discuss options.
[Amy] I think choice is a good way to model those leafs. I suggest to use it.
That's the real value of YANG doctors! Thanks.



#9) Check that lower threshold is less than upper threshold



Would it make sense to add a must statement checking that the lower threshold is less than (or equal?) to the upper threshold?



    leaf atpc-lower-threshold  {

      when "../power-mode = 'atpc'";

      type power {

        range "-99..-30";

      }

      units "dBm";

      mandatory true;

      description

        "The lower threshold for the input power at far-end

         used in the ATPC mode.";

      reference "ETSI EN 302 217-1";

    }

    leaf atpc-upper-threshold  {
[Amy] can add the must statement.



#10) Choice more convenient



There are a few leafs that act as discriminators for when clauses in other leafs. Such constructs might be a little smoother when modeled as a choice instead. I'll take one and show as an example. This power-mode construct:



    leaf power-mode {

      type enumeration {

        enum rtpc {

          description

            "Remote Transmit Power Control (RTPC).";

          reference "ETSI EN 302 217-1";

        }



        enum atpc {

          description

            "Automatic Transmit Power Control (ATPC).";

          reference "ETSI EN 302 217-1";

        }

      }

      mandatory true;

      description

        "A choice of Remote Transmit Power Control (RTPC)

         or Automatic Transmit Power Control (ATPC).";

    }



    leaf maximum-nominal-power {

      type power {

        range "-99..40";

      }

      units "dBm";

      mandatory true;

      description

        "Selected output power in RTPC mode and selected

         maximum output power in ATPC mode. Minimum output

         power in ATPC mode is the same as the system

         capability, available-min-output-power.";

      reference "ETSI EN 302 217-1";

    }



    leaf atpc-lower-threshold  {

      when "../power-mode = 'atpc'";

      type power {

        range "-99..-30";

      }

      units "dBm";

      mandatory true;

      description

        "The lower threshold for the input power at far-end

         used in the ATPC mode.";

      reference "ETSI EN 302 217-1";

    }

    leaf atpc-upper-threshold  {

      when "../power-mode = 'atpc'";

      type power {

        range "-99..-30";

      }

      units "dBm";

      mandatory true;

      description

        "The upper threshold for the input power at far-end

         used in the ATPC mode.";

      reference "ETSI EN 302 217-1";

    }



could be modeled as:



    choice power-mode {

      container rtpc {

        description

          "Remote Transmit Power Control (RTPC).";

        reference "ETSI EN 302 217-1";

        leaf maximum-nominal-power {

          type power {

            range "-99..40";

          }

          units "dBm";

          mandatory true;

          description

            "Selected output power.";

          reference "ETSI EN 302 217-1";

        }

      }

      container atpc {

        description

          "Automatic Transmit Power Control (ATPC).";

        reference "ETSI EN 302 217-1";



        leaf maximum-nominal-power {

          type power {

            range "-99..40";

          }

          units "dBm";

          mandatory true;

          description

             "Selected maximum output power. Minimum output

             power is the same as the system

             capability, available-min-output-power.";

          reference "ETSI EN 302 217-1";

        }



        leaf atpc-lower-threshold  {

          type power {

            range "-99..-30";

          }

          units "dBm";

          mandatory true;

          description

            "The lower threshold for the input power at far-end

             used in the ATPC mode.";

          reference "ETSI EN 302 217-1";

        }

        leaf atpc-upper-threshold  {

          type power {

            range "-99..-30";

          }

          units "dBm";

          mandatory true;

          description

            "The upper threshold for the input power at far-end

             used in the ATPC mode.";

          reference "ETSI EN 302 217-1";

        }

      }

      mandatory true;

      description

        "A choice of Remote Transmit Power Control (RTPC)

         or Automatic Transmit Power Control (ATPC).";

}


[Amy] Choice is a better way. Is it possible to further refine your proposal?
Since maximum-nominal-power will be used by both RTPC and ATPC, how about to move it out of the choice, then use maximum-nominal-power in the choice? Like this:
        leaf maximum-nominal-power {
          type power {
            range "-99..40";
          }
          units "dBm";
         mandatory true;
          description
             "Selected maximum output power. Minimum output
             power is the same as the system
             capability, available-min-output-power.";
          reference "ETSI EN 302 217-1";
        }

    choice power-mode {
      container rtpc {
        description
          "Remote Transmit Power Control (RTPC).";
        reference "ETSI EN 302 217-1";

        use maximum-nominal-power;
      }
      container atpc {
        description
          "Automatic Transmit Power Control (ATPC).";
        reference "ETSI EN 302 217-1";

        use maximum-nominal-power;

        leaf atpc-lower-threshold  {
          type power {
            range "-99..-30";
          }
          units "dBm";
          mandatory true;
          description
            "The lower threshold for the input power at far-end
             used in the ATPC mode.";
          reference "ETSI EN 302 217-1";
        }
        leaf atpc-upper-threshold  {
          type power {
            range "-99..-30";
          }
          units "dBm";
          mandatory true;
          description
            "The upper threshold for the input power at far-end
             used in the ATPC mode.";
          reference "ETSI EN 302 217-1";
        }
      }
      mandatory true;
      description
        "A choice of Remote Transmit Power Control (RTPC)
         or Automatic Transmit Power Control (ATPC).";
    }





#11) Choice more convenient (again)



Same thing again for



    leaf coding-modulation-mode {

[Amy] will update it.



#12) Unusual exponential notation



Do you really mean 10e-9 (=10*10^-9 =10^-8), or do you mean the more traditional notation 1e-9?



      leaf ber-alarm-threshold {

        type enumeration {

          enum "10e-9" {

[Amy] should be 1e-9. Need to confirm with the co-authors.



#13) Separate module with grouping, used a single time with refine



Module ietf-interface-protection defines a grouping (protection-groups), which is used a single time, yet is refined when it is used below. As noted before comment #3, I find this way of laying out the YANG unnecessarily hard to read and understand, for no clear benefit.



  container radio-link-protection-groups { ....

    uses ifprot:protection-groups {



      refine protection-group/members {

        must "/if:interfaces/if:interface[if:name = current()]"

           + "/if:type = 'mw-types:carrier-termination'" {



Also, as noted in comment #7, the must statement is better written using derived-from-or-self. This applies regardless of the current refine statement is kept, or if the must statement moves to the actual leaf-list it applies to.

[Amy] Will update the must statement.



Appendix A.1 & A.2



Besides the actual YANG modules, there are also a couple of examples in Appendix A.1 and A.2. I tried to use them and uncovered a couple of issues.



#14) Config false leaf in config example



Both examples list



        "tx-oper-status": on



This is a config false item, which could never be part of a configuration message (and it also lacks comma at the end).

[Amy] will remove it.



#15) Wrong type in example



Both examples list



        "coding-modulation-mode": 0,



0 not a legal value, should be "single" to match the rest of the example data.

[Amy] will fix it.



#16) Missing mandatory parameter



Both examples lacks leaf maximum-nominal-power, which is mandatory according to the YANG, so the transaction fails to validate.

[Amy] will add it.



#17) Examples perhaps a tad basic



The examples are demonstrating only a small part of the module functionality. A bigger example, e.g. including xpic with interface pointers might be useful.



Feel free to reach out to me to discuss any of this. Thank you.

[Amy] will add additional example.



/jan





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