[NMOP] SIMAP Issue 88 and 109: Italo Busi, Sergio Belotti, Daniele Ceccarelli - Topology Layer Definition

[Olga Havel <[e-mail]>]

Italo,

I merged your comment for issue 109 into the issue 88, so we can discuss together.

Best regards,
Olga

From: Olga Havel
Sent: Tuesday, December 23, 2025 3:01 PM
To: Italo Busi <[e-mail]>; Belotti, Sergio (Nokia - IT) <[e-mail]>; 'Daniele Ceccarelli (dceccare)' <[e-mail]>; [e-mail]
Subject: SIMAP Issue 88: Italo Busi, Sergio Belotti, Daniele Ceccarelli - Topology Layer Definition

Hi Italo, Sergio and Daniele,

The following is the proposed change for the Issue 88 opened for your comments:
Italo: The difference between the service layer and the top layer is not fully clear. I thought the service layer was the topmost level in SIMAP. I am not sure OSPF, IS-IS or BGP can be considered a "layer"
Sergio: Not clear what "top layer" is representing wrt the service layer
Daniele: The draft’s language about “service layer” vs “top layer” is confusing; at one point it sounds like the service layer is the topmost layer, elsewhere it implies a separate “top” layer concept.
Would it be possible to define topology layers as a level of abstraction or technology domain represented as a topology instance. Examples: physical layer (L0/L1), L2, L3, optical WSON, transport layers, and service layer (customer-facing logical services — VPNs, slices, overlay services) ?

The top layer is just mentioned once, in the terminology. I suggest the following changes, please let me know if this addresses your comments and if I can close the issue:

OLD:
      Some topology layers represent the control aspects of Layer 3,
      like OSPF, IS-IS, or BGP.

NEW:
      Some topology layers represent the control aspects of Layer 3,
      like IGP (for OSPF and IS-IS) or EGP (for iBGP and eBGP).


OLD:
      The top layer represents the application/flow view of Service
      connectivity.

NEW:
      The application/flow layer represents the view of Service data flows
      for the different classes of service - video, voice and data traffic.

      The layers may differ depending on the solution, so the bottom and
      top layers may not be the same across all solutions. We can illustrate
      the concept of topology layers by listing the common set — e.g.,

  *   physical: L1, one or multiple layers, if fully modelling different

         optical layers. Used for WSON, OTN optical, OTN digital),

  *   data‑link: L2 for Ethernet, LAGs and VLAN,
  *   network: L3 for IPv4 and IPv6,
  *   IGP/EGP: for routing inside or between ASs, different layers for
              underlay and overlay, for ISIS, OSPF, iBGP. eBGP,

  *   tunnel: for transport tunnels and paths, for MPLS and SRv6,
  *   service: for different overlay services, like L2 VPNs, L3 VPNs,
            slices, SD-WAN

  *   application: for video, voice and data traffic flows.

      However, this list is illustrative only; it is not a prescriptive requirement.
      Different solutions may adopt alternative layering schemes or combine layers
      differently. Therefore, we will present the above as an example of one possible
      solution, while keeping the definition flexible enough to accommodate flexible
      layering.


Best Regards,
Olga