Unit 22 laNs and waNs reading material

T E X T A

Task

a) Try to answer these questions.

1. What is a computer network?

2. What are the benefits of connecting computers and peripherals in a network?

b) Read the text and match the technical terms on the left with the explanations on the right.

LAN Network architecture Nodes Protocol Transceiver Token Gateway

the hardware that emits and receives signals in a computer network; a network contained in a relatively small area; the arrangement of nodes in a communication system (i.e. the distribution of elements in a network); a device that translates protocols between different types of networks (e.g. it can link networks of PCs and Macs to mainframes and minicomputers); a special unit of data which acts as a key on a Token Ring network; only the machine in possession of this piece of software can transmit on the network; a set of rules that allows the exchange of information over a network; computer devices interconnected in a network.

Network configurations

A network is a group of devices (PCs, printers, etc.) or 'nodes' connected by communications circuits so that users can share not only data, programs but also hardware like printers and other computer resources such as fax. A network has two main elements: the physical structure that links the equipment and the software that allows communication.

The physical distribution of nodes and their circuits is known as network 'topology' or 'architecture'. The software consists of the protocols, i.e. the rules which determine the formats by which information may be exchanged between different systems. We could say that cables and transceivers (the architecture) allow computers to 'hear' one another, while the software is the 'language' that they use to 'talk' to one another over the network.

As regards the cables, they consist essentially of the transceiver – the hardware that sends and receives network signals. At present the most widely used transceivers are Token Ring, Ethernet and LocalTalk. Token Ring is the most common method of connecting PCs and IBM mainframes. Most Token Ring adapters transmit data at a speed of 16 megabits per second. With Ethernet, data is transmitted at 100 Mbits/sec. The newest version, Gigabit Ethernet, supports data rates of 1Gb per second. Ethernet provides a very robust, trouble-free architecture with good levels of performance. In this regard, Ethernet is the best solution for fast and intensive activity.

LocalTalk transceivers are the cheapest of all because they are directly included in each Macintosh. However, they're a bit slow, which is why most Macs come with built-in Ethernet.

As for protocols, these are rules which describe things like transmission speed and physical interfaces. The Token Ring protocol avoids the possibility of collisions. To transmit data, a workstation needs a token, and as there is only one token per network, holding one guarantees sole use of the network. With Ethernet there are other options, of which TCP/IP (Transmission Control Protocol/Internet Protocol) is perhaps the most useful since it allows different operating systems to communicate with each other. With regard to LocalTalk networks, they use AppleTalk protocols. The Macintosh operating system includes the AppleTalk manager and a set of drivers that let programs on different Macs exchange information.

LANs can be interconnected by gateways. These devices help manage communications and control traffic on large networks. They change the data to make it compatible with the protocols of different networks.

Most networks link computers within a limited area – within a department, an office, or a building. These are called Local Area Networks, or LANs. But networks can link computers across the world, so you can share information with someone on the other side of the world as easily as sharing with a person at the next desk. When networks are linked together in this way, they are called Wide Area Networks, or WANs.

Networks increase productivity by allowing workers to share information easily without printing, copying, telephoning, or posting. They also save money by sharing peripherals such as printers.

Network topology

Topology refers tо the shape of a network. There are three basic physical topologies.

• Star: there is a central device to which all the workstations are directly connected. The central position can be occupied by a server or a hub, a connection point of the elements of a network that redistributes the data.

• Bus: every workstation is connected to a main cable called a bus.

• Ring: the workstations are connected to one another in a closed loop configuration.

• There are also mixed topologies like the tree, a group of stars connected to a central bus.

Ex. 1. Read these descriptions of different physical topologies of communication networks and match them with the terms in the text “Network topology”.

1. All the devices are connected tо a central station.

2. In this type of network there is a cable to which all the computers and peripherals are connected.

3. Two or more star networks connected together; the central computers are connected to a main bus.

4. Alt devices (computers, printers, etc.) are connected to one another forming a continuous loop.

Ex. 2. Which topologies do these statements refer to?

1. If one of computers fails, the whole network will be affected.

2. If we remove a computer from the network, it won’t affect the other computers.

3. If the main cable fails, the whole networks will fail.

4. If the central server fails, the whole network will fail.

5. If a cable breaks, the whole network will be affected.

6. If a computer fails, it won’t affect the other computers.