Understanding Network Protocols and the OSI Model

Understanding Network Protocol Families

While the OSI model defines a comprehensive reference for network study, not every commercial network fully adopts OSI designs. Instead, many networks are built upon specific technologies and proprietary protocols.

NetWare Family

Manufactured by Novell, NetWare was once among the most widely used network systems worldwide. It was renowned for its high performance and capacity for growth.

NetBEUI Family

Microsoft has developed several operating systems that utilize NetBEUI (NetBIOS Extended User Interface) for communications within local area networks. Originally an IBM protocol introduced in 1985, NetBEUI provides a foundational basis for building peer-to-peer networks.

AppleTalk Family

AppleTalk is the network architecture designed by Apple Computer Corporation for use with Macintosh computers. Its original design aimed to facilitate simple file and printer sharing among network users. Its straightforward configuration allowed even non-expert users to easily benefit from network services.

TCP/IP Family

The UNIX system has widely adopted and popularized a set of protocols that have since spread globally. This technology, known as TCP/IP (Transmission Control Protocol/Internet Protocol), is formally defined in a series of documents called RFCs (Requests for Comments).

The OSI Network Model: Levels and Functions

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. Each layer serves a specific purpose:

Level 1: Physical Layer

The Physical Layer is concerned with defining the mechanical, electrical, functional, and procedural characteristics required to establish and release connections between two computers on a network. As the lowest-level layer, it primarily deals with the transmission of raw bits over a communication medium.

Level 2: Data Link Layer

The function of the Data Link Layer is to establish a communication line that is free of errors, which can then be utilized by the layer immediately above it: the Network Layer.

Level 3: Network Layer

The Network Layer handles subnet control. Its primary function is to choose the most appropriate route for network layer data blocks to reach their destination.

Level 4: Transport Layer

The Transport Layer acts as a crucial transition point between the subnet-oriented layers (Physical, Data Link, Network) and the application-oriented layers (Session, Presentation, Application).

Level 5: Session Layer

The Session Layer enables the establishment, management, and termination of dialogue between sending and receiving applications. It is responsible for setting up and maintaining communication sessions.

Level 6: Presentation Layer

The Presentation Layer deals with the syntax and semantics of the information transmitted. It ensures that data is presented in a format that the application layer can understand, handling data encryption, compression, and translation.

Level 7: Application Layer

The Application Layer is the highest layer, providing network services directly to end-user applications. It enables users to interact with the network.