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 __________.

Export, deport, report, import

5. Oil and gas are the main _______ of Russia.

6. The notorious spy was _______ from the country.

7. If there is an attempt of an unauthorised access, the security system ________ to an administrator.

8. DTP software can ________ text and graphics from another application.

Express, oppress, impress, depress

9. He was really _______ by his failure in the exam.

10. I must _______ my thanks for your help.

11. I was hoping to _______ my new boss with my computer skills.

12. The rural poor were _______ by the land-owners.

Writing and Translation

Task 11. Make the written translation into Russian (3,000 characters).

The OSI Reference Model

The Open System Interconnection (OSI) reference model describes how information from a software application in one computer moves through a network medium to a software application in another computer. The OSI model divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. This enables the solutions offered by one layer to be updated without affecting the other layers.

The application layer (Layer 7) is the OSI layer that is closest to the user; it provides network services to the user’s applications. It differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs. The application layer establishes the availability of intended communication partners, synchronizes and establishes agreement on procedures for error recovery and control of data integrity.

The presentation layer (Layer 6) ensures that the information that the application layer of one system sends out is readable by the application layer of another system. If necessary, the presentation layer translates between multiple data formats by using a common format.

As its name implies, the session layer (Layer 5) establishes, manages, and terminates sessions between two communicating hosts. The session layer provides its services to the presentation layer. It also synchronizes dialogue between the two hosts' presentation layers and manages their data exchange. In addition to session regulation, the session layer offers provisions for efficient data transfer, class of service, and exception reporting of session layer, presentation layer, and application layer problems.

The transport layer (Layer 4) segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system. The transport layer attempts to provide a data transport service that shields the upper layers from transport implementation details. In providing communication service, the transport layer establishes, maintains, and properly terminates virtual circuits. In providing reliable service, transport error detection-and-recovery and information flow control are used.

The network layer (Layer 3) is a complex layer that provides connectivity and path selection between two host systems that may be located on geographically separated networks.

The data link layer (Layer 2) provides reliable transit of data across a physical link. In so doing, the data link layer is concerned with physical (as opposed to logical) addressing, network topology, network access, error notification, ordered delivery of frames, and flow control.

The physical layer (Layer 1) defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other, similar, attributes are defined by physical layer specifications.

(From CISCO Networking Academy)

A handy way to remember the seven layers of the OSI reference model is the sentence All people seem to need data processing. The beginning letter of each word corresponds to a layer.

• All Application layer

• People Presentation layer

• Seem Session layer

• To Transport layer

• Need Network layer

• Data Data link layer

• Processing Physical layer

Task 12. Read the text and choose the correct words.

Bank transfer:payment can be made (1) by / from ordering a home bank to transfer money to an overseas account. The Society for Worldwide Interbank Financial Communications (SWIFT) offers facilities for a 24-hour transfer of money (2) in / to a beneficiary on its computer systems.

Bill of exchange: the seller prepares a bill of exchange in the name of the buyer. The bill states (3) that / what the buyer will pay the seller an amount within a stated time, e.g. 30 days. The bill is sent to the buyer either by post, or through a bank, and the buyer signs (accepts) the bill before the goods are sent. Shipping documents usually accompany bills when the bank acts (4) as / how an intermediary in overseas transactions.

Letter of credit (L/C): letters of credit (or documentary credits, as banks refer to them) have to be applied for from the buyer's bank, by filling out a form giving details of the type of credit (i.e. revocable, which can be cancelled, or irrevocable, which cannot be cancelled), the beneficiary (the person receiving the money), the amount, (5) when / how long the credit will be available for (i.e. valid until...), the documents involved (bill of lading, insurance, invoice, etc.), and a description of the goods. The money will be credited to the supplier's account as soon as confirmation of shipment is made. This is done (6) when / if the documents are lodged with the customer's bank.

Notes:

beneficiary (N) – бенефициар (получатель платежа)

bill of exchange (N) –переводной вексель, тратта

bill of lading (N) – коносамент, накладная на груз

insurance (N) – страховка invoice (N) – счет-фактура

letter of credit (N) –аккредитив

lodge (V) – помещать, класть (в банк) overseas (A) - зарубежный

revocable (A) – отзывный, irrevocable (A) – безотзывный

shipment (N) – отправка товаров, поставка

Task 13.Read the text and fill in the table.

	Ex-works	F.O.R.	F.A.S.	F.O.B.	C.& F.	C.I.F.
Cost of goods	+
Delivery to the nearest railway station	-
Loading goods aboard	-
Shipping to the destination	-
Insurance	-