IETF Last Call Review of draft-ietf-nmop-simap-concept-12
review-ietf-nmop-simap-concept-12-genart-lc-bryant-2026-07-25-00

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Document: draft-ietf-nmop-simap-concept-12
Reviewer: Stewart Bryant
Review Date: 2026-07-25
IETF LC End Date: None
IESG Telechat date: Not scheduled for a telechat

Summary: A well written and informative document that is ready for approval. I
have a few comments listed under nits that the authors may wish to consider.

Major issues:None

Minor issues:None

Nits/editorial comments:

Early in the document it talks about simulation prior to change and then at
later talks about simulation at varying degrees of abstraction. Only much later
in the document does it formally talk about the digital twin concept. Now it
may be industry convention, but given that unless you simulate at the quantum
level all digital twinning is based on abstraction I am surprised the concept
is not introduced earlier and in conjunction with the higher levels of
abstraction,

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214           There are several types of topologies: point-to-point, bus, ring,
215           star, tree, mesh, hybrid, and daisy chain.

SB> Nit: I think there should be a for example preceding the above list so as
not to limit it.

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217           Topologies may be unidirectional (all links unidirectional) or
218           bidirectional (all links bidirectional), or contain combination of
219           unidirectional and bidirectional links.

SB> Do you need to consider co-routing here?
=========

250           Some topology layers may relate closely to OSI layers, like Layer
251           1 topology for physical topology, Layer 2 for link topology and
252           Layer 3 for IPv4 and IPv6 topologies.

SB> Does there need to be a comment about the cross layer operation of the
Internet which is not as “pure” as the OSI model? For example the IP layer
carries transport layer type which some have argued is a layer violation.
Normally this is of no significant consequence but needs to be thought about in
formal hierarchical models like this/

Maybe that is addressed by "closely"?
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278           *  tunnel: for transport tunnels and paths, for MPLS and SRv6,

SB> I am not sure SRv6 is a tunnel, and the designation of MPLS as a tunnel
causes confusion until you understand what is really happening. MPLS can be
thought of as a full blown network layer in its own right and SRv6 in some
applications is a novel network layer constructed using IPv6 infrastructure. A
GRE, IPSec or pseudowire might be a better examples.

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Reading section 3.1.1

SB> I am caused to wonder what happens in cases where you are not allowed to
know the physics of the underlay. Presumably you support the abstraction of
those concepts into a higher layer?

561        The service placement feasibility check application will be able to
562        retrieve the topology at any layer from the SIMAP server via the

SB> Should that be any visible layer? I would have thought that there would
still be layer hiding for security and commercial reasons.
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755     3.8.1.  Types of Network Simulation
SB> Presumably we will eventually have quantum simulation where it explores all
network conditions simultaneously.

SB> My thought on section 3.10 in response to the notes on
[I-D.irtf-nmrg-network-digital-twin-arch] SB> That is the IRTF view, but I
would have thought that some of the methods celled up in this document would
have been considered a digital twin. I imagine it depends on where DT needs to
sit on the abstraction-reality line, and different points seem appropriate for
different levels of congruence between the physics and the analysis.

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