What is the difference between functional and non-functional requirements? What is requirement validation?

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. Its primary purpose is to allow different systems to communicate by adhering to a common set of protocols and interfaces.

The seven layers of the OSI model and their functions are as follows:

• 7. Application Layer: This is the layer closest to the end user. It provides services directly to user applications, allowing them to communicate with other applications over the network. Examples include web browsers, email clients, and file transfer applications. Protocols include HTTP, FTP, SMTP, DNS.
• 6. Presentation Layer: This layer is responsible for translating data between the application layer and the network format. It handles data encryption, decryption, compression, and decompression to ensure data is presented in a format that the application layer can understand. Examples include ASCII, EBCDIC, JPEG, MPEG.
• 5. Session Layer: The session layer establishes, manages, and terminates communication sessions between applications. It synchronizes dialogue between presentation layer services and manages token passing and synchronization points. Examples include NetBIOS, PPTP.
• 4. Transport Layer: This layer provides end-to-end communication between devices and ensures reliable data transfer. It handles segmentation, reassembly, error control, and flow control. The two main protocols are TCP (Transmission Control Protocol) for reliable, connection-oriented communication and UDP (User Datagram Protocol) for unreliable, connectionless communication.
• 3. Network Layer: The network layer is responsible for logical addressing (IP addressing) and routing data packets across different networks. It determines the best path for data to travel from source to destination. Key protocols include IP (Internet Protocol) and ICMP (Internet Control Message Protocol).
• 2. Data Link Layer: This layer provides reliable data transfer across a physical link. It handles physical addressing (MAC addressing), error detection and correction for frames, and flow control. It is often divided into two sub-layers: Logical Link Control (LLC) and Media Access Control (MAC). Protocols include Ethernet, PPP, HDLC.
• 1. Physical Layer: This is the lowest layer of the OSI model, dealing with the physical transmission of raw bit streams over a physical medium. It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link. It specifies things like cable types, connectors, voltage levels, and data rates. Examples include cables (fiber optic, twisted pair), connectors (RJ45), radio frequencies.