The basic implementation of an OPC UA Server without IODD (see section 15.4.1) is done on very limited resources, like for example the IO-Link Master itself. A system likely will have several of those simple servers. In addition, an aggregating server implementing the IODD management and interpretation capabilities (see section 15.4.2) as well accesses the simple servers and adds the IODD management and interpretation capabilities on top. As the simple server interface already allows ISDU access, the ISDU logic can be triggered by the aggregating server. This aggregating server typically would have enough resources to manage a large amount of IODDs, potentially even having access to get more IODDs by using tools like the IODD finder. Users would access the aggregating server to get the IODD based information of all connected IO-Link Masters. Figure 27 gives an example for such an architecture.
Several variations of that approach are possible. The aggregating server might, in addition to the OPC UA based sources also proprietarily access IO-Link Masters. There might be several aggregating servers in a system, etc.