RE: Yangdoctors last call review of draft-ietf-teas-yang-te-topo-08

[Xufeng Liu <[e-mail]>]

Hi Mahesh,

Thank you much for the review. We have submitted an updated draft (https://tools.ietf.org/html/draft-ietf-teas-yang-te-topo-09) to address these issues. More detailed explanations are put below inline. 

If the responses and updates are satisfactory, we are ready for the last call.

Best regards,
- Xufeng

> -----Original Message-----
> From: Mahesh Jethanandani [mailto:[e-mail]]
> Sent: Wednesday, May 24, 2017 11:44 AM
> To: [e-mail]
> Cc: [e-mail]; [e-mail]; [e-mail]
> Subject: Yangdoctors last call review of draft-ietf-teas-yang-te-topo-08
> 
> Reviewer: Mahesh Jethanandani
> Review result: Ready with Issues
> 
> Document reviewed: draft-ietf-teas-yang-te-topo-08
> 
> Status: Ready with Issues
> 
> I am not an expert in Traffic Engineering. This review is looking at the draft from
> a YANG perspective. With that said, I have marked it as “Ready with Issues”
> because of some of the points discussed below.
> 
> Summary:
> 
> This document defines a YANG data model for representing, retrieving and
> manipulating TE Topologies. The model serves as a base model that other
> technology specific TE Topology models can augment.
> 
> Comments:
> 
> Almost all the containers in the model are presence containers. Is there a reason
> why they have to be presence containers? Note, that presence containers are
> containers whose existence itself represents configuration data. What particular
> configuration data is each container representing in itself?
[Xufeng] Containers that use “presence” are:
	- Container “underlay”
	  o  We have changed 13 occurrences of such containers to be not presence container. 
	- Container “te” under augmentation
	  o  To indicate that “TE” is enabled (configuration data)
	  o  Also used to do augmentation. The “presence” statement can prevent the mandatory child from affecting augmented base model.
	- /nw:networks/nw:network/nw:network-types/te-topology!
	  o  A mechanism required by I2RS topology model to specify the topology type.

> 
> It is difficult to co-relate the diagram with the model itself because of different
> terms being used to define different parts of the model.
> There is “TE Topology Model” and then there is “Generic TE Topology Model”.
> Are these one and the same models? If so, a common term for both of them
> would be helpful.
[Xufeng] Yes. These two terms are the same. Figure 12, Figure 13, and relevant descriptions have been updated to make the document consistent.

> 
> There is extensive use of groupings in the document. However, not all instances
> of groupings are used multiple number of times. Where they are not being
> repeated, it would be better to move the grouping directly where the uses
> statement resides. Case in point the grouping connectivity-label-restriction-list.
[Xufeng] We have removed the following groupings
    te-link-augment
    te-node-augment
    te-termination-point-augment
    te-topologies-augment
    te-topology-augment
    te-link-state-underlay-attributes
    te-node-state-derived-notification
    te-topology-type

The remaining groupings have been kept so that we can:
	- Share the groupings in this model
	- Prepare to be shared by a model augmenting this model
	- Prevent a grouping or configuration section from being too long
	- Improve readability

> 
> The split between config and state containers does not seem to follow any
> particular pattern. 
[Xufeng] The pattern is clear:
For each manageable entity (object), there is a config container and state container. The configurable properties go into the config container and state properties go into the state container. Such objects are identified by a list item or a presence container so that the “create”, “delete”, and “modify” operations can be performed on them. The non-presence containers do not represent configuration data so they do not introduce such objects.

> It is neither a top level split, as is the case with existing IETF
> models, 
[Xufeng] We could not do top level split because the base I2RS network topology model (https://tools.ietf.org/html/draft-ietf-i2rs-yang-network-topo-12) that we augment does not have the top-level split (for its own reasons).

> nor do they follow the OpenConfig style of splitting config and state
> under each relevant leaf, 
[Xufeng] The pattern is consistent with this style in principle, with some adjustments to fit to our multiple levels of hierarchy.

> nor do they follow the new guidelines as suggested by
> the new datastore model draft (https://tools.ietf.org/html/draft-dsdt-nmda-
> guidelines-01.html).
> Since there recommendation for all new models is to follow the new datastore
> guidelines, would suggest that the state containers be removed and any non-
> duplicate leafs within state be moved under a single container. I am told that the
> change in ietf-te-topology from the current draft to NMDA style is about 175
> lines and for te-types it is 24 line diff (thanks Robert). As such, the change is not
> major and can be done easily. See the diffs at the end of this review.
[Xufeng] The changes are simple, but the implications are not:
	o  Need to re-open the discussions for the I2RS network topology model (https://tools.ietf.org/html/draft-ietf-i2rs-yang-network-topo-12), which currently does not have the state branch, and is the base model that this model augments.
	o  Need to re-discuss the issues of cross referencing between config branch and state branch (which was brought up by I2RS model and has no good solution currently).
	o  Need to modify existing and on-going implementations with no functional benefits.
	o  Will delay publishing both the I2RS base network topology model and this document.

This proposed model currently has multiple on-going implementations. Implementers wish for advancing this document without unnecessary delays, and before the final NETCONF/RESTCON protocol support which is expected to be available in a year. 

The authors and contributes have discussed the adoption of the NMDA style, and currently prefer the following strategy:
	o  Publish the document with the current model style without structure changes, allowing the on-going implementations to continue, supporting necessary operational states before the NMDA protocol specification is updated and supporting implementations are available. 
	o  Follow this up ASAP with an NMDA-compatible model draft (WG could adopt this right away). This was suggested by Kent, and is considered to fit our situation the best, allowing the implementations to migrate to the long term approach without interruption.

> 
> A pyang compilation of the model with —ietf and —lint option was clean.
> 
> A idnits run of the draft reveals some issues with spacing and references, but
> they are parts of the diagram, which confuses idnits.
> 
> te-types.diff
> —————
> 507,509c507,509
> <   grouping explicit-route-hop_config {
> <     description
> <       "The explicit route subobject grouping";
> ---
> >   grouping explicit-route-hop {
> >     description "Explicit route hop grouping";
> >
> 595,609d594
> <     }
> <   }
> <
> <   grouping explicit-route-hop {
> <     description "Explicit route hop grouping";
> <     container config {
> <       description
> <         "Configuration parameters for the explicit route hop";
> <       uses explicit-route-hop_config;
> <     }
> <     container state {
> <       config false;
> <       description
> <         "State parameters for the explicit route hop";
> <       uses explicit-route-hop_config;
> 
> te-topology.diff
> ——————-
> 264a265
> >       config false;
> 323a325
> >       config false;
> 327a330
> >       config false;
> 357a361
> >       config false;
> 361a366
> >       config false;
> 733,744c738,739
> <       container config {
> <         description
> <           "Configuration data.";
> <         uses te-link-config;
> <       } // config
> <       container state {
> <         config false;
> <         description
> <           "Operational state data.";
> <         uses te-link-config;
> <         uses te-link-state-derived;
> <       } // state
> ---
> >       uses te-link-config;
> >       uses te-link-state-derived;
> 780,781c775,776
> <                 path "../../../../../../nw:node[nw:node-id = "
> <                   + "current()/../../../../../nt:source/"
> ---
> >                 path "../../../../../nw:node[nw:node-id = "
> >                   + "current()/../../../../nt:source/"
> 792,793c787,788
> <                 path "../../../../../../nw:node[nw:node-id = "
> <                   + "current()/../../../../../nt:destination/"
> ---
> >                 path "../../../../../nw:node[nw:node-id = "
> >                   + "current()/../../../../nt:destination/"
> 841c836
> <         path "../../../../../te/templates/link-template/name";
> ---
> >         path "../../../../te/templates/link-template/name";
> 1087a1083
> >       config false;
> 1092a1089
> >       config false;
> 1106a1104
> >       config false;
> 1113a1112
> >       config false;
> 1128a1128
> >       config false;
> 1267,1279c1267,1268
> <       container config {
> <         description
> <           "Configuration data.";
> <         uses te-node-config;
> <       } // config
> <       container state {
> <         config false;
> <         description
> <           "Operational state data.";
> <
> <         uses te-node-config;
> <         uses te-node-state-derived;
> <       } // state
> ---
> >       uses te-node-config;
> >       uses te-node-state-derived;
> 1297,1309c1286,1287
> <         container config {
> <           description
> <             "Configuration data.";
> <           uses te-node-tunnel-termination-attributes;
> <         }
> <         container state {
> <           config false;
> <           description
> <             "Operational state data.";
> <
> <           uses te-node-tunnel-termination-attributes;
> <           uses geolocation-container;
> <         } // state
> ---
> >         uses te-node-tunnel-termination-attributes;
> >         uses geolocation-container;
> 1406c1384
> <         path "../../../../../te/templates/node-template/name";
> ---
> >         path "../../../../te/templates/node-template/name";
> 1473,1474c1451
> <               path "../../../../../../../nt:termination-point/"+
> <                 "nt:tp-id";
> ---
> >               path
> "../../../../../../nt:termination-point/nt:tp-id";
> 1485,1486c1462
> <               path "../../../../../../../nt:termination-point/"+
> <                 "nt:tp-id";
> ---
> >               path
> "../../../../../../nt:termination-point/nt:tp-id";
> 1577a1554
> >       config false;
> 1583a1561
> >       config false;
> 1595a1574
> >       config false;
> 1738c1717
> <             path "../../../../../../nt:termination-point/nt:tp-id";
> ---
> >             path "../../../../../nt:termination-point/nt:tp-id";
> 1753c1732
> <     uses te-types:explicit-route-hop_config;
> ---
> >     uses te-types:explicit-route-hop;
> 1773,1779c1752,1754
> <       container config {
> <         description
> <           "Configuration data.";
> <         uses te-termination-point-config;
> <       } // config
> <       container state {
> <         config false;
> ---
> >       uses interface-switching-capability-list;
> >       leaf inter-layer-lock-id {
> >         type uint32;
> 1781,1784c1756,1765
> <           "Operational state data.";
> <         uses te-termination-point-config;
> <         uses geolocation-container;
> <       } // state
> ---
> >           "Inter layer lock ID, used for path computation in a TE
> >            topology covering multiple layers or multiple regions.";
> >         reference
> >           "RFC5212: Requirements for GMPLS-Based Multi-Region and
> >            Multi-Layer Networks (MRN/MLN).
> >            RFC6001: Generalized MPLS (GMPLS) Protocol Extensions
> for
> >            Multi-Layer and Multi-Region Networks (MLN/MRN).";
> >       }
> >
> >       uses geolocation-container;
> 1787,1802d1767
> <   grouping te-termination-point-config {
> <     description
> <       "TE termination point configuration grouping.";
> <     uses interface-switching-capability-list;
> <     leaf inter-layer-lock-id {
> <       type uint32;
> <       description
> <         "Inter layer lock ID, used for path computation in a TE
> <          topology covering multiple layers or multiple regions.";
> <       reference
> <         "RFC5212: Requirements for GMPLS-Based Multi-Region and
> <          Multi-Layer Networks (MRN/MLN).
> <          RFC6001: Generalized MPLS (GMPLS) Protocol Extensions
> <          for Multi-Layer and Multi-Region Networks (MLN/MRN).";
> <     }
> <   } // te-termination-point-config
> 1879,1890c1844,1845
> <       container config {
> <         description
> <           "Configuration data.";
> <         uses te-topology-config;
> <       } // config
> <       container state {
> <         config false;
> <         description
> <           "Operational state data.";
> <         uses te-topology-config;
> <         uses geolocation-container;
> <       } // state
> ---
> >       uses te-topology-config;
> >       uses geolocation-container;
> 
> 
>