Intended Learning Outcomes

At the end of this chapter, you are expected to:

1. 
   define the basic of data communication;
   
2. 
   identify data communication components;
   
3. 
   describe data communication modules of operation
   
4. 
   define what a protocol and network protocol is;
   
5. 
   define Open Systems Interconnections and its layer;
   

From the early days of networking, LAN and WAN communications have been generally guided by a network communications model called the Open Systems Interconnection (OSI) reference model. Importance of studying OSI model.

• Choose the best equipment for the job at hand

• Create the most effective network designs

• Design networks that will communicate with other networks

• Troubleshoot network problems more effectively

Developed in the 1970s, the OSI model applies to LAN and WAN communications and represents an effort to standardize network software and hardware implementation. Over the years, the OSI model has facilitated the growth in network communications by accomplishing the following:

• Enabling communications between different types of LANs, MANs, CANs, and WANs

• Providing standardization of network equipment so that equipment from one vendor communicates with equipment from another vendor

• Helping customers to retain their investment by enabling older network equipment to communicate with newer equipment, reducing the need for equipment replacement when new devices are installed

• Enabling software and hardware to be developed using common interfaces for communicating within and between networks

• Making possible worldwide network communications, with the Internet as a prime example
The OSI model consists of seven distinct layers stacked on one another: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer handles specific communication tasks and uses specific types of protocols to communicate with the next layer in the stack. Communications between two network devices go up and down the layered stack at each device. For example, when a workstation communicates with a server, communication starts at the workstation’s Application layer. It then formats specific information through the lower layers until the data reaches the Physical layer and is transmitted over the network to the server.

The server picks up the data at the Physical layer of its stack and sends it up each layer for interpretation until it reaches the Application layer. Each layer is called by its actual name or by its placement in the stack. For example, the bottom layer is called either the Physical layer or Layer 1.