OT & CSDM - WIIMLT - part I

[Fabian Kunzke]

Why is it modeled like that? This question often comes up in CSDM workshops. This series of small articles will dive into some specific modeling practices related to not just CSDM but also Service Mapping.

Today we are going to jump into foreign waters (for some of you readers) and look into OT. Here we can see a completely new modeling approach which seems to be unaligned with CSDM. But - is it really? Or is it just the same in new clothing? Let's take a deeper look - from an IT perspective. In a part II we will then look deeper into the OT side of things.

The model

The ISA95 model is the standard when integrating ERP systems with manufacturing. It was created to better bridge IT and OT. It standardizes the terminology, modeling and exchange between most of the aspects. At its core the model tries to achieve the same thing as CSDM does:

standardize to make sure the understanding and thus the support remains transparent.

So how does it align with CSDM? Or does it even align?

This is an article, so we won't dive deep into every aspect. But lets focus on the most important one and start off with something CSDM does not actually portray: The ISA95 hierarchy:

Source: https://cdn.ai-forall.com/ifa_dev_media/Exploring_ISA_95_Standards_in_Manufacturing_1_54746907c1.jpg

The hierarchy of the model separates the detail of what is going on in OT. It strictly sorts types of entities into levels and with that also dictates how these levels can interact. At its core each Level can only communicate with the Level directly above and below. Level 2 won't communicate with Level 0. But with Level 3 and 1. This allows for a clear differentiation on what is actually needed and how communication must be allowed & separated. It is also important to understand this from a CMDB perspective.

With the focus on Security & Operations from an IT perspective first, most OT CMDBs drive for Level 3 and Level 2 transparency - sometimes even Level 1. Why? Because Level 3 - Operations platforms - are interconnected and must be able to communicate with ERP systems. They reach the internet. Level 2 sometimes must have direct access to these platforms and thus could also be exposed to the internet. Down from Level 2, everything should be in separated, local & exclusive networks. These devices only need to communicate with the local network or even just parts of it. So when we are looking at OT from an IT perspective, we do not care about that Level (Note: OT management of course does!).

So how can this be aligned with CSDM? Well, outside of the OT management - which we will cover in another article - the perspective of Level 3 and Level 2 interacting with the ERP layer is pretty straight forward. For the start, it is mostly enough to make sure devices of the same site & same layer are represented through dynamic CI groups. We aim to understand the impact: Which ERP does my production depend on.

For OT this results in a funny perspective - an upside-down one. The Level 3 & Level 2 dynamic CI groups will depend on the ERP system - and Level 2 will depend on Level 3. This is by design in CSDM and through an IT perspective it does make sense. But on an OT side, it may not (Hint: This is what part II of this article will be about).

The key principle

From an IT perspective, the ISA95 model can be aligned pretty straight forward with CSDM. From an OT perspective this results in an up-side-down view. But again, as before, with CSDM we are modeling impact. So for us, this is fine.

However, for OT, this is unnatural. Its not how the world works there. This is why the OT-M plugin from ServiceNow runs with its own specific model. And within that model, things look slightly different. Something we will cover in part II.

If you have any CSDM related example where you want insights on "why is it modeled like that?", feel free to drop a reply and I will look to add it to this series.