What is the primary function of Layer 3 in the OSI model?

• A. Data exchange between applications
• B. End-to-end communications and flow control
• C. Packet transport across independent networks
• D. Linking and isolating network hosts

Answer: (C)

The primary function of Layer 3 in the OSI model is indeed the transport of packets across independent networks. This layer, known as the Network layer, is responsible for routing data from the source to the destination through potentially multiple networks. It encompasses the methods and protocols used for addressing, transferring, and forwarding packets independently of the physical data transmission methods utilized in the lower layers of the OSI model.

At Layer 3, devices such as routers operate to ensure that packets are directed correctly according to their destination addresses. This layer handles logical addressing (such as IP addresses), allowing for communication between devices that are not on the same local network. It facilitates the creation of paths through the network infrastructure, making it fundamental for Internet functionality and the communication of data across diverse networks.

In contrast, other layers serve different purposes: the Application layer focuses on data exchange between applications, while the Transport layer manages end-to-end communications and flow control. The Data Link layer isolates and links network hosts, but it deals with local connections rather than routing packets over broader networks. Thus, Layer 3's specialized function in network layer processing differentiates its critical role in enabling complex inter-network communications.