INTRODUCTION TO NETWORKS

Introduction to Networks

Introduction to Networks

Advantages of Open System Interconnection (OSI) Model

The Open System Interconnection (OSI) model is a set of protocols that attempt to define and standardize the data communications process. (Piscitello, Chapin, 1993) The OSI model is set by the International Standards Organization (ISO). The OSI model has the support of most major computer and network vendors, many large customers, and most governments, including the United States. (Piscitello, Chapin, 1993)

Figure: OSI Protocol Suite Maps to All Layers of the OSI Reference Model

The OSI model is not a single definition of how data communications takes place. It states how the processes should be divided and offers several options. In addition to the OSI protocols, as defined by ISO, networks can use the TCP/IP protocol suite, the IBM Systems Network Architecture (SNA) suite, and others. TCP/IP and SNA roughly follow the OSI structure (www.cisco.com).

Functionality of Seven Layers of OSI Model

Although each layer of the OSI model provides its own set of functions, it is possible to group the layers into two distinct categories. The first four layers physical, data link, network, and transport—provide the end-to-end services necessary for the transfer of data between two systems. (Piscitello, Chapin, 1993)

Figure: Seven Layers of OSI Model

The top three layers—the application, presentation, and session layers— provide the application services required for the exchange of information. That is, they allow two applications, each running on a different node of the network, to interact with each other through the services provided by their respective operating systems. The following is a description of just what each layer does.

The Physical layer provides the electrical and mechanical interface to the network medium (the cable). This layer gives the data-link layer (layer 2) its ability to transport a stream of serial data bits between two communicating systems; it conveys the bits that move along the cable. (www.how2pass.com)

The Data-Link layer handles the physical transfer, framing (the assembly of data into a single unit or block), flow control and error-control functions (and retransmission in the event of an error) over a single transmission link; it is responsible for getting the data packaged and onto the network cable.

The Network layer establishes, maintains, and terminates logical and/or physical connections. The network layer is responsible for translating logical addresses, or names, into physical addresses.

The Transport layer ensures data is successfully sent and received between the two computers. If data is sent incorrectly, ...