Application layer is implemented in ____________

Answer: End system — the application layer runs on end systems (hosts).

• Layers implemented in end systems: application layer, presentation layer, session layer, and transport layer. These layers are part of the host software stack and provide services to user applications.

• Layers implemented on intermediary devices or hardware: the network layer is commonly implemented on routers (which forward packets between networks), while the data link and physical layers are implemented by the network interface card (NIC) and link technologies such as Ethernet.

• Why this matters: the application layer provides end-to-end services to user processes and therefore must run on the end hosts that originate or receive application data. Lower-layer functions (framing, signaling, and packet forwarding) are handled by NICs, link technologies, and routers, not by application software.