Лекция: Text 6. Computer Networks

A network is a group of computers that are connected to each other for the purpose of communication. A computer network allows computers to communicate with many other computers and to share resources (such as printers and CDs), exchange files. The computers on a network may be linked through cables, telephone lines, radio waves, satellites. You can connect one computer to another. This can be done using their serial ports. This is possible because almost every computer has a serial port. The solution is to use a central object that the computers and other resources can connect to, and then this object becomes responsible to “distribute” or manage network traffic.

The most regularly used types of network distributors are the hub, the router, and the switch.

Hub. A hub is a rectangular box that is used as the central object on which computers and other devices are connected. To make this possible, a hub is equipped with small holes called ports. Depending on its type, a hub can be equipped with 4, 5, 12, or more ports. In most cases for a home-based or a small business network, you may not need a hub.

Routers: wired or Wireless. Router is another type of device that acts as the central point among computers and other devices that are part of a network. A router functions a little differently than a hub. Like a hub, the computers and other devices are connected to a router using network cables. To make this possible, a router is equipped with holes, called ports, in the back. There are wireless routers. With this type the computers and devices connect to the router using microwaves.

Network cables. A cable is used to connect computers. Although we may use wireless networking, you should always have cables with you. The most commonly used cable is referred to as Category 5 cable RJ-45. You can purchase this cable in a computer store.

Network cards. In order to connect to a network, a computer must be equipped with a device called a network card. If you buy a computer from one of those popular stores or big companies on the Internet, most of their computers have a network card tested and ready. If you have a computer that doesn’t have a network card, you can install one.

Networks are classified:

· Depending on their scale and purpose: as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN), campus Area Network (CAN);

· According to the network topology upon which the network is based: bus, star, tree (hierarchical), ring, mesh, linear. The network topology defines the ways in which computers, printers and other devices are connected, physically and logically.

Local Area Network. LAN is a computer network covering a small physical area, like a home, office or a small group of buildings, such as a school or an airport. The defining characteristics of LANs, in contrast to WANs, include their higher data transfer rates, smaller geographic range and lack of a need for leased communication lines. Computers connected to a network are broadly categorized as servers or workstations. Servers are generally not used by humans directly, but rather run continuously to provide “services” to the other computers and their human users) on the network. Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network’s resources, and many others. On a single LAN computers and servers may be connected by cables or wirelessly. Wireless access to a wired network is possible by wireless access points (WAPs). Nearly always servers will be connected by cables to the network, because the cable connections remain the fastest.

Wide area Network. WAN is a computer network that covers a broad geographic area. The most well-known and best example of a WAN is the Internet which is a network comprised of many smaller networks. The Internet is considered to be the largest network in the world. An example of this is a multinational business that uses a Wan to interconnect their offices in different countries. A WAN involves communication through the use of a wide range of different technologies. These technologies include Point-to Point WANs such as Point-to-Point Protocol (PPP) and High-Level data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network).

Metropolitan Area Network. A MAN is a network that is too large for even the largest of LAN’s but is not on the scale of a WAN. In other words, it is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the town/city.

Personal Area Network. A PAN is a computer network used for communication among computer devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners and even video game consoles. Such a network may include wired and wireless connections between devices.

Campus Area Network. A CAN is a computer network made up of interconnected LANs within a limited geographical area. A CAN is larger than a LAN but smaller than a Wan. The main aim of a CAN is to facilitate students and professors accessing the Internet and university resources.