Connectivity Framework Annex B: Assessment Template: OPC-UA
B. 6.5 Implementation Viewpoint B. 6.5.1 System Architecture Considerations
Peer-to-Peer vs. Broker:
( Section 4.2.1.1)
Data-Centric vs. Device / App-Centric:( Section 4.2.1.2)
Explicit vs. Implicit Governance:
( Section 4.2.1.3)
B. 6.5.2 Data Considerations
Content-Based Selection( Section 4.2.2.1)
Time-Based Selection( Section 4.2.2.2)
B. 6.5.3 Performance Considerations
Real-Time( Section 4.2.3.1)
Latency and Jitter vs. Throughput( Section 4.2.3.2)
Does the connectivity framework require running a special process or broker?
The OPC-UA specifications are designed to support aggregated servers, which are a type of broker. With an aggregating server, a client connects to the aggregating server and that server acts as a proxy to one or more servers. The information models and address spaces are aggregated.
Does the application code( or business logic) have to be aware of the other endpoints in order to participate in information exchange?
Data is accessible as variables, abstracted away from the physical endpoints. Clients can use OPC-UA discovery to locate which server or servers provides a variable of interest. Aggregated OPC-UA Servers are used to provide applications with a single unified address space and abstract away the physical server providing the variable. Thus, OPC-UA is nodecentric which maps closely to a device-centric approach. Is the governance explicit and shareable?
The OPC-UA service definition and the information model provide governance. Thus, governance is explicit and shareable.
Can a content-filter specify the data subset of interest?
Yes, the data subset of interest can be specified by content. For example, event data is subscribed to using a filter( essentially a stream filter) that compares the content of each event with a set of criteria provided by the client and only sends the subset that matches. Data Subscriptions are also based on filtering. Can sub-sampling specify the data subset of interest? Yes, each client can request its own client specific sampling rate.
Does the connectivity technology support real-time data distribution? Is the latency deterministic( smaller jitter is better)?
Current transport mappings rely on TCP, which is known to have non-deterministic latency. Work is underway to add support for Time Sensitive Networking( TSN), and that is expected to provide deterministic latency and jitter for real-time applications. How does the latency and jitter change with throughput? What limits the throughput? Expected to be similar to that of TCP( see section 7.2.1).
Use of binary protocols and direct client-server connections expected to result in throughput limited only by the network bandwidth and CPU of client and server computers.
IIC: PUB: G5: V1.0: PB: 20170228- 79-