Re: [CCAMP] Question about identities with multiple bases

["Rob Wilton (rwilton)" <[e-mail]>]

Hi,

Apologies for the delayed reply.

Tom, I would be interested if you can provide your feedback on the quirks in the English.  It would be useful to get them fixed/tweaked now rather than later in the process.

Some thoughts of the main question regarding multiple base identities:

I think that you might be using base identities in two different ways here.  One of those seems reasonable, the other, I'm not so sure about.

The first way, that I think is reasonable, is if you want to tag a subset of identities that all derive from a common base as having the same property.
E.g. if you have lots of identities that derive from "client-signal", then it might be reasonable to group a subset of them as also deriving from the "Ethernet" base identity.  In this scenario, the set of identities that derive from "Ethernet" would be a subset of identities that derive from "client-signal".  I have no issues with this approach and have considering using this formulation myself.  

The second way, that I'm not convinced by, is where I think that you are trying to share the same identity in different sets (e.g. client-signal vs coding-func).  In this case, I think that it would be much better to define separate identities, either by prefixing the name of the set in the identity name (to make the names unique), or perhaps more cleanly by putting them in separate YANG source files, where the module name/prefix can be used to use the same textual identity name different scoped names.

Further discussion, perhaps involving the YANG doctors' alias might be helpful.

Thanks,
Rob



-----Original Message-----
From: tom petch <[e-mail]> 
Sent: 05 June 2020 12:11
To: Italo Busi <[e-mail]>; Rob Wilton (rwilton) <[e-mail]>
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: Question about identities with multiple bases

From: CCAMP <[e-mail]> on behalf of Italo Busi <[e-mail]>
Sent: 19 May 2020 17:49

Hi Rob,

We have discussed an open issue with the ietf-l1csm which is impacting the ietf-layer1-types YANG model, for which we are addressing CCAMP WG LC comments

See slides 3 and 4 of the attached presentation made during the CCAMP WG virtual meeting last week

Since we have not much experience with identities having multiple bases, we would like to get a feedbacks from you about whether the proposed solution would work
<tp>
Italo

I have not seen a response to your question.  I had a look and it seems ok but like you I do not see much of this construct in IETF modules.

So while it may be ok, that does make me wonder; is this approach too complicated?  If you and I are uncertain about it, then what about future users - will they be comfortable with it?  I had to look up which Boolean operator applied with multiple bases!

Separately, having persuaded my obstructionist ESP to let me send an e-mail, I see a number of quirks in the English of layer1-types.  Are you interested in hearing about them? (assuming that my ESP lets me:-)

Tom Petch



You can check initial changes to ETH-1GbE, FICON-4G and STM-1 identities in github:

https://github.com/haomianzheng/IETF-ACTN-YANG-Model/pull/65

Let me report here the key ones:

  identity ETH-1Gb {
    base client-signal;
    description
      "Client signal type of 1GbE";
    reference "RFC7139/ITU-T G.709";
  }

  identity FICON-4G {
    base client-signal;
    description
      "Client signal type of Fibre Connection 4G";
    reference "RFC4328/RFC7139";
  }

  identity ETH-1000X {
    base "coding-func";
    base Ethernet;
    description
      "1000BASE-X PCS clause 36 coding function.";
    reference "MEF63: Subscriber Layer 1 Service Attributes";
  }

  identity STM-1 {
    base client-signal;
    base "coding-func";
    base SDH;
    description
      "STM-1 client signal;
       STM-1 G.707 (N=1) coding function.";
    reference
      "RFC7139/ITU-T G.709
       MEF63: Subscriber Layer 1 Service Attributes";
  }

              leaf client-signal {
                type identityref {
                  base "l1-types:client-signal";
                }
                mandatory true;
                description
                  "The client signal being used at the UNI";
              }

Then ETH-1GbE, FICON-4G and STM-1 would be valid configuration for the client-signa leaf, while ETH-1000X will not be valid

    leaf coding {
      type identityref {
        base "l1-types:coding-func";
      }
      must 'derived-from(../coding, ../protocol)';
      mandatory true;
      description "The coding function being used at the UNI.";
    }

Then:
- ETH-1000X would be valid configuration of the coding leaf, if Ethernet is configured, otherwise it is invalid;
- STM-1 would be valid configuration of the coding leaf, if SDH is configure as protocol, otherwise it is invalid;
- ETH-1GbE and FICON-4G would never be valid configuration of the coding leaf

Before applying these changes to a lot of identities, it would be good to check that our understanding is correct

What do you think?

Thanks in advance

Italo

Italo Busi
Principal Optical Transport Network Research Engineer

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