ISA Certified Automation Professional (CAP) program

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CAP question

“Translation of data between a networking service and an application, including character encoding, data compression, and encryption/decryption” is the responsibility of which layer of the open system interconnection (OSI) model?

A. application
B. presentation
C. session
D. transport

CAP Answer

The correct answer is B, presentation. The presentation layer for protocols used in control systems provides the translation of data received into a usable format, such as binary data from a programmable logic controller into floating point data for presentation in a distributed control system data table.

The application layer addresses high-level application programming interfaces, including resource sharing, remote file access, directory services, and virtual terminals. The session layer deals with continuous exchange of information transactions between two nodes. This layer is often not required in instrumentation bus protocols. The transport layer provides reliable transmission of data segments between points on a network, such as TCP and UDP.


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