Connectivity Framework Annex B: Assessment Template: OPC-UA
B. 6.4 Functional Viewpoint B. 6.4.2 Core Transport Layer Functions
Messaging Protocol( Section 5.1.1)
Communication Modes( Section 5.1.2)
Endpoint Addressing
( Section 5.1.3)
Connectedness( Section 5.1.4)
Prioritization( Section 5.1.5)
Timing & Synchronization
( Section 5.1.6)
Message Security( Section 5.1.7)
Does it require UDP or TCP? What are the salient aspects of the messaging protocol? What are the message size limitations? What are the usage assumptions? Is it optimized for certain message requirements?
OPC-UA specifies the use of two alternative protocols:
• OPC-UA Binary: A binary protocol on top of TCP
• An XML-based protocol on top of HTTP( which runs on top of TCP)
• Web Sockets( in progress)
There are no explicit message-size limits in OPC-UA when using the TCP protocol. Which communication modes does it support? Current OPC-UA transport mappings rely on unicast over TCP.
Future versions of OPC-UA plan to include mappings for UDP and multicast UDP. Describe the transport endpoints. How are the endpoints addressed? What are the limitations, if any, on the number of endpoints?
Endpoints are the OPC-Server and the OPC-Client. OPC-Clients initiate requests to OPC- Servers.
The specification relies on the endpoint-addressing scheme provided by the underlying transport mapping. For current transport mappings, an IP address and a port number identify an endpoint. Does it require a connected circuit between the endpoints? Summarize the salient aspects.
The OPC-UA specification does not require a connection-oriented transport. Secure sessions are established above the transport layer.
Current technology mappings rely on a connection-oriented transport( TCP).
Future version of OPC-UA will also support connectionless UDP transport. Does it provide a means to prioritize messages? Summarize the salient aspects.
No, prioritization is not supported in the specification. However, a OPC-UA Server implementation could easily prioritize the processing of requests. For example, a OPC-UA Server may give certain clients( possibly based on credentials) priority over others. Or, for example, a OPC-UA-Server may process subscription advise requests at a higher priority than browse requests. Does it provide the ability to synchronize time? Summarize the salient aspects.
No, timing and synchronization services are not currently provided. However, work is underway to provide timing and synchronization services through Time Sensitive Networking( TSN) support. Does it provide mechanisms for message security? Summarize the salient aspects.
OPC-UA was architected from the beginning with security as a top priority requirement. Current mappings use TLS( or HTTPS) for message security.
IIC: PUB: G5: V1.0: PB: 20170228- 78-