Which layer divides each message into packets at the source and reassembles…

Concept: In layered networks, the transport layer provides end-to-end, process-to-process delivery above the network layer. TCP treats application data as a byte stream, divides it into sequenced segments, and reconstructs the stream at the receiving endpoint; UDP carries independent datagrams without delivery, ordering, or reassembly guarantees. The network layer separately forwards IP datagrams and may fragment and reassemble an IP datagram, which is not the same as rebuilding the original application message.

Application: This question describes source-to-destination division and reconstruction of a message, so the layer being asked about is the Transport layer. The stem uses “packet” loosely for a piece into which the message is divided; the precise transport terms are TCP segment and UDP datagram. For this UGC NET 2022 source item, the official NTA final answer key maps Question ID 354 to Option ID 1414, the Transport layer value.

• Network layer: routes and forwards data hop-by-hop between networks using logical (IP) addressing, and may fragment a datagram to fit a link's MTU — but it never assembles pieces back into the original application message end-to-end.

• Data link layer: frames bits for transmission across a single physical link and checks for link-level errors; its scope is one hop, not source-to-destination.

• Physical layer: transmits raw bits as electrical, optical, or radio signals, with no concept of a message being divided or reassembled at all.

Answer: Transport layer.