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 -