Need to clarify the topology-role

[italobusi]

https://github.com/ietf-ccamp-wg/draft-ietf-ccamp-client-signal-yang/blob/96fbf3e2ecd8e306813716bbab6a1ae7e10715c5/ietf-eth-tran-service.yang#L637-L644

It is not clear from the description and location within the tree whether this attribute represents:

1. the topology of the service (E-Line/any-to-any, E-LAN/any-to-any or E-Tree/hub-and-spoke)
2. the topology of the underlay tunnels (full-mesh or hub-and-spoke)
3. the role of the service end-point (any-to-any, hub/root or spoke/leaf)

In case 1 (topology of the service), this attribute belongs to the service and not to the service end-point and it provides duplicated information with the etht-svc-type attribute

In case 2 (topology of the underlay tunnels), this attribute belongs the underlay container and not to the service end-point. More discussion is also needed since the list of tunnels should anyhow be explicitly configured and more complex topologies could also be required.

In case 3 (role of the service end-point), this attribute belongs to the service end-point but more discussion is needed since the configuration of the split-horizon groups could also be used to configure E-Tree services.

In any case:

• the description needs further clarification;
• the option to define a enum instead of an identityref should be considered