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Communications Networks and their Types

Communications Networks

Communications channels and hardware may have different layouts or networks, varying in size from large to small: wide area networks (WANs), metropolitan area networks (MANs), and local networks.

Features of networks are hosts, nodes, downloading, and uploading.

Networks allow users to share peripheral devices, programs, and data; to have better communications; to have more secure information; and to have access to databases.

A network, or com­munications network, is a system of interconnected computers, telephones, or other communications devices that can communicate with one another and share applications and data. Here let us consider the following:

· Types of networks—wide area, metropolitan area, and local

· Some network features

· Advantages of networks

Types of Networks: Wide Area, Metropolitan Area, & Local

Networks are categorized principally in the following three sizes:

· Wide area networks: A wide area network (WAN) is a communications network that covers a wide geographical area, such as a state or a country. The international pathway Internet links together hundreds of computer WANs. Most telephone systems—long-distance and local—are WANs.

· Metropolitan area network: A metropolitan area network (MAN) is a communica-tions network covering a geographic area the size of a city or suburb. The purpose of a MAN is often to bypass local telephone compa­nies when accessing long-distance services. Cellular phone systems are often MANs.

· Local network: A local network is a privately owned communications network that serves users within a confined geographical area. The range is usually within a mile—perhaps one office, one building, or a group of buildings close together, as a college campus. Local networks are of two types: private branch exchanges (PBXs) and local area networks (LANs), as we discuss shortly.

All of these networks may consist of various combinations of computers, storage devices, and communications devices.

Some Features: Hosts & Nodes, Downloading & Uploading

Many computer networks, particularly large ones, are served by a host com­puter. A host computer, or simply a host, is the main computer—the cen­tral computer that controls the network. On a local area network, some or all of the functions of the host may be performed by a computer called a server. A server is a computer shared by several users in a network.

A node is simply a device that is attached to a network. A node may be a microcomputer, terminal, or some peripheral device (a peripheral device is any piece of hardware that is connected to a computer).

As a network user you can download and upload files. Download means that you retrieve files from another computer and store them in your com­puter. Upload means that you send files from your computer to another computer.

Local Networks

Local networks may be private branch exchanges (PBXs) or local area networks (LANs).

LANs may be client/server or peer-to-peer and include components such as cabling, network interface cards, an operating system, other shared devices, and bridges and gateways.



The topology, or shape, of a network may take four forms: star, ring, bus and hybrid.

Although large networks are useful, many organizations need to have a local network—an in-house network—to tie together their own equipment. Here let's consider the following aspects of local networks:

· Types of local networks—PBXs and LANs

· Types of LANs—client/server and peer-to-peer

· Components of a LAN

· Topology of LANs—star, ring, bus, hybrid.

· Impact of LANs

Types of Local Networks: PBXs & LANs

The most common types of local networks are PBXs and LANs.

· Private branch exchange (PBX). A private branch exchange (PBX) is a private or leased telephone switching system that connects telephone extensions in-house. It also connects them to the outside phone system.

A public telephone system consists of "public branch exchanges"— thousands of switching stations that direct calls to different "branches" of the network. A private branch exchange is essentially the old-fashioned company switchboard. You call in from the outside, the switchboard oper­ator says "How may I direct your call?" and you are connected to the extension of the person you wish to talk to.

Newer PBXs can handle not only analog telephones but also digital equipment, including computers. However, because older PBXs use exist­ing telephone lines, they may not be able to handle the volume of elec­tronic messages found in some of today's organizations. These companies may be better served by LANs.

· Local area network PBXs may share existing phone lines with the telephone system. Local area networks usually require installation of their own communication channels, whether wired or wireless. Local area networks (LANs) are local networks consisting of a communications link, network operating system, microcomputers or workstations, servers, and other shared hardware. Such shared hardware might include printers, scan­ners, and storage devices. Unlike larger networks, LANs do not use a host computer.

Many LANs mix elements from client/server and peer-to-peer models.

The word peer denotes one who is equal in standing with another. A peer-to-peer LAN is one in which all microcomputers on the network com­municate directly with one another without relying on a server. Peer-to-peer networks are less expensive than client/server networks and work effectively for up to 25 computers. Beyond that they slow down under heavy use. They are thus appropriate for networking in small groups, as for workgroup computing

 


Date: 2015-04-20; view: 848


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