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The OPC UA systems architecture models Clients and Servers as interacting partners. Each system may contain multiple Clients and Servers. Each Client may interact concurrently with one or more Servers, and each Server may interact concurrently with one or more Clients. An application may combine Server and Client components to allow interaction with other Servers and Clients as described in 6.3.7.
Clients and Servers are described in the sub-clauses 6.2 and 6.3. Figure 3 illustrates the architecture that includes a combined Server and Client.
