CERTIFIED-IN-CYBERSECURITY Question #133: Real Exam Question with Answer & Explanation

Question

At which of the OSI layers do TCP and UDP work?

Options

• APhysical Layer
• BTransport Layer
• CSession Layer
• DApplication Layer

Explanation

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both transport layer protocols, which operate at the fourth layer of the OSI (Open Systems Interconnection) model (see ISC2 Study Guide, chapter 4, module 1). The transport layer (also known as "Layer 4") ensures that data is delivered reliably and efficiently between different devices on a network. TCP is a connection-oriented protocol which establishes a dedicated end-to-end connection. UDP is a connectionless protocol, and therefore does not establish a reliable connection before transmitting data. The choice between using TCP or UDP is typically based on tradeoffs between requirements of reliability and speed. The physical layer ("Layer 1") is responsible for transmitting raw data over a physical medium, such as a copper wire or fiber optic cable. The session layer ("Layer 5") is responsible for establishing, maintaining and terminating connections between different devices on a network. The application layer ("Layer 7") is the highest layer of the OSI model, and is responsible for enabling communication between applications, as well as for providing services to the user.

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