Bus / Ethernet Star Switched Ring

1) In this configuration, the central computer performs all processing and control functions. All access devices are linked directly to the central computer. The configuration has two major limitations. First of all, the remote devices are unable to communicate directly. Instead, they must communicate via the central computer only. Secondly, the network is very susceptible to failure, either in the central computer or the transmission links.

2) The central device, which could be a telephone exchange, is used to connect different devices on the network directly. Once the link is established, the two devices communicate as though they were directly linked without interference from any other device. At the end of the session, the connection is closed, freeing capacity for other users and allowing access to other devices. Multiple switches can be used to create alternative transmission routes.

3) Each device is attached to a network shaped as a continuous loop. Data proceeds in only one direction and at a constant speed round the loop. Devices may send information only when they are in control of the 'token'. The token is a package of data which indicates which device has control. The receiving device picks up the token, then clears it for another's use once it has received the message. Only one device may send data at any given moment, and each device must be working for the network to function.

4) This network consists of one piece of cable terminated at each end to which all devices are connected. In such a network, each device is able to broadcast a message when it has detected silence for a fixed period of time. All devices receive the broadcast and determine from the content of the message whether it was intended for them. The only problem occurs when two devices try to send at the same time. When a sending device detects another's transmission, it aborts its own.

Task 9. Read the text and choose the correct words.

What's the difference between the Web and the Internet?

Some people think that the Internet and the Web are the same thing, but in fact they are different. The Internet (often called simply "the net") is a global (1) network/ net of interconnected computers. These computers communicate with each other (2) over / through existing telecommunications networks – principally, the telephone system. The Word Wide Web (usually known as just "the Web") is the billions of web pages that are stored on large computers called web (3) servers / services.

To (4) see / access the web, you may need a computer and a modem. You then connect over your telephone line to an Internet Service (5) Port / Provider (ISP), which sends your request to view a particular web page to the correct web server.

Websites are not the only service available on the Internet. It is also used for many other functions, including sending and receiving e-mail, and connecting to newsgroups and (6) discussion / talking groups.

You could say that the Internet is a system of roads, and web pages and e-mails are types of traffic that travel on those roads.

Task 10. Choose the correct word to complete each sentence. You may change some words slightly. Consult the Appendix for confusable words.

Describe, proscribe, inscribe, prescribe

1. The name of the National hero was _______ on the memorial plaque.

2. The medicine was made as the doctor had _______.

3. The word alphanumeric is used to _______data that contains numbers and letters.

4. Bringing food and drinks into computer laboratories is strictly __________.