Which OSI layer provides end-to-end communication between processes using port numbers?

• A. Data Link Layer
• B. Application Layer
• C. Transport Layer
• D. Network Layer

Answer: (C)

The transport layer is responsible for end-to-end communication between processes on different hosts, and it uses port numbers to identify which process on each host should receive the data. This layer multiplexes multiple applications on the same device by assigning each a unique port, so data can be delivered to the correct socket across the network. It can offer reliable, connection-oriented delivery (as with TCP) or best-effort datagram delivery (as with UDP), depending on the protocol in use.

Data Link Layer handles communication between devices on the same network segment and uses MAC addresses, not port numbers. Network Layer handles routing between networks and uses IP addresses to reach the correct host. Application Layer provides services to software applications but relies on the transport layer to perform end-to-end delivery and port-based process identification.