Describe the OSI model layers and their functions.

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Layer 1: Physical Layer – This layer deals with the physical hardware (e.g. hubs, routers, cables, etc.) and the physical connections between the nodes in a network. It provides the mechanism for sending and receiving raw bits across the physical medium.

Layer 2: Data Link Layer – This layer provides the link between different nodes, including the addressing and control of the physical hardware, and allows for local packet delivery.

Layer 3: Network Layer – This layer provides the logical connections and routing between hosts, and works to ensure that a packet arrives at the correct destination. This layer is also responsible for packet fragmentation and reassembly.

Layer 4: Transport Layer – This layer is responsible for end-to-end communication between applications, and provides reliable data transport with flow control, segmentation, and error recovery.

Layer 5: Session Layer – This layer provides a session between applications, allowing them to communicate in an organized manner (e.g. for logging in and out).

Layer 6: Presentation Layer – This layer takes data from the application layer and formats it into a common or standard format (e.g. one network might use X.25 packets while another might use TCP/IP).

Layer 7: Application Layer – This layer provides the interfaces and services necessary for application programs to access the network, such as FTP, Telnet, and HTTP.

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