Electronic Communications
Executive Summary Business data communications and networking could possibly be one of the fastest growing technologies in today’s society. This report aims to examine a fundamental building block of computer networks The Open System Interconnection Reference Model. The report provides a definition and description of the Transport Layer, Network Layer, Data Link Layer, Physical layer and the difference between Logical and Physical path. A further more detailed description about the Transport layer is also incorporated 1.1 Introduction The Open Systems Interconnection (OSI) Reference Model is a structure for determining how messages in a network system communicate with one another. The creation of the OSI model initiated during the late 70’s by the International Organisation for standards (OSI) and the International Telegraph and Telephone Consultative Committee. In 1983 both organisations combined their efforts to compose a document detailing the Reference Model for Open Systems Interconnection. The purpose of the OSI Model is that the process of communication between computers within a network can be separated into seven smaller and more amenable layers each layer having a distinguished set of interconnected functions. The OSI Model also guides product implementors in developed greater compatible and interoperable network system. The higher layers: Transport, Session, Presentation and Application. The four layers of the OSI model primary objective is to provide services to users of end systems, which consequently constitute the end-to-end portion of the model. The CCITT and ISO use several principles to determine the number and nature of the layers. Below states five of them: Black (1989) P1: For simplicity, keep the number of layers within a small limit P2: Create layer boundaries that minimise layer interactions and the description of services P3: Separate layers so that different functions are separated from each other. Also, layers that use different kinds of technology should be separated P4: Similarly, place similar functions in the same layer P5: Select layer boundaries that past experience shows have functioned successfully 1.2 The Transport Layer The transport layer’s primary function is to accept data from the session layer. Separate it into smaller units or packets if needed, pass these on to the network layer and ensure that packets have arrived in sequence, error free with no losses or duplications. Furthermore packets are reassembled back into the original message.