OPC UA modern architecture in SCADA systems - Step-by-Step Execution

Process Flow - OPC UA modern architecture

Client Request

↓

Secure Channel Setup

↓

Session Establishment

↓

Service Request

↓

Server Processes Request

↓

Response Sent

↓

Session Close

↓

Secure Channel Close

This flow shows how a client connects securely to an OPC UA server, establishes a session, sends requests, receives responses, and then closes the session and secure channel.

Execution Sample

SCADA systems

Client -> Server: Open Secure Channel
Client -> Server: Create Session
Client -> Server: Send Read Request
Server -> Client: Send Data Response
Client -> Server: Close Session
Client -> Server: Close Secure Channel

This sequence shows the main steps of communication between an OPC UA client and server in a modern architecture.

Process Table

Step	Action	Details	Result
1	Client sends Open Secure Channel request	Client initiates secure communication	Secure Channel established
2	Client sends Create Session request	Client requests a session for communication	Session created and acknowledged
3	Client sends Read Request	Client asks for data from server	Server processes request
4	Server sends Data Response	Server returns requested data	Client receives data
5	Client sends Close Session request	Client ends the session	Session closed
6	Client sends Close Secure Channel request	Client ends secure communication	Secure Channel closed

💡 Communication ends after secure channel is closed

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6
Secure Channel	Not established	Established	Established	Established	Established	Established	Closed
Session	None	None	Created	Created	Created	Closed	Closed
Data Request	None	None	None	Sent	Processed	Processed	Processed
Data Response	None	None	None	None	Received	Received	Received

Key Moments - 3 Insights

Why do we need to open a Secure Channel before creating a Session?

The Secure Channel ensures all communication is encrypted and safe. Without it, the Session cannot be securely established. See execution_table step 1 and 2.

What happens if the Session is not closed properly?

If the Session remains open, resources on the server stay allocated, which can cause issues. Step 5 shows the proper closing of the Session.

Why does the client close the Secure Channel last?

The Secure Channel protects all communication including session close messages. Closing it last ensures all messages are securely sent. See steps 5 and 6.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the Session created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Check the 'Action' column for 'Create Session' in the execution_table.

According to variable_tracker, what is the state of the Secure Channel after Step 6?

A Closed

B Established

C Not established

D Created

💡 Hint

Look at the 'Secure Channel' row under 'After Step 6' in variable_tracker.

If the client sends a Read Request before opening the Secure Channel, what would happen?

A Request is processed normally

B Session is created automatically

C Communication fails due to no secure channel

D Data response is sent immediately

💡 Hint

Refer to the concept_flow where Secure Channel setup is the first step before any requests.

Concept Snapshot

OPC UA modern architecture uses a Secure Channel for encrypted communication.
A Session is created inside this channel for client-server interaction.
Clients send service requests (like Read) within the session.
Server processes requests and sends responses.
Sessions and Secure Channels must be properly closed to free resources.

Full Transcript

OPC UA modern architecture starts with the client opening a Secure Channel to ensure encrypted communication. Then, the client creates a Session to interact with the server. Within this session, the client sends service requests such as reading data. The server processes these requests and sends back responses. Finally, the client closes the Session and then the Secure Channel to end communication securely. This flow ensures safe, organized, and efficient data exchange between client and server in industrial systems.