По ответить на вопросы.текст внизу
1. who runs the internet?
2. what are the levels of the internet?
3. what are main differences between circuit-switching and packet-switching technologies?
4. what type of switching technology should be used for nuclear power station control? why?
5. what type of switching will be more reliable if part of network infrastructure is destroyed?
structure of the internet
the internet is a loose amalgamation of computer networks run by many different organizations in over seventy countries. most of the technological decisions are made by small committees of volunteers who set standards for interoperability. the us portion of the internet is best thought of as having three levels. at the bottom are local area networks (lans); for example, campus networks. usually the local networks are connected to a regional, or mid-level network. the mid-levels connect to one or more backbones. a backbone is an overarching network to which multiple regional networks connect, and which generally does not serve directly any local networks or end-users. the u.s. backbones connect to other backbone networks around the world. there are, however, numerous exceptions to this structure.
most backbone and regional network traffic moves over leased phone lines. however, there is a fundamental distinction in how the lines are used by the internet and the phone companies. the internet provides connectionless packet-switched service whereas telephone service is circuit-switched. the difference may sound arcane, but it has vastly important implications for pricing and the efficient use of network resources.
phone networks use circuit switching: an end-to-end circuit must be set up before the call can begin. a fixed share of network resources is reserved for the call, and no other call can use those resources until the original connection is closed. this means that a long silence between two teenagers uses the same resources as an active negotiation between two fast-talking lawyers. one advantage of circuit-switching is that it enables performance guarantees such as guaranteed maximum delay, which is essential for real-time applications like voice conversations.
the internet uses “packet-switching” technology. the term “packets” refers to the fact that the data stream from your computer is broken up into packets of about 200 bytes (on average), which are then sent out onto the network. each packet contains a “header” with information necessary for routing the packet from origination to destination. thus each packet in a data stream is independent. the main advantage of packet-switching is that it permits “statistical multiplexing” on the communication lines. that is, the packets from many different sources can share a line, allowing for very efficient use of the fixed capacity.
read the text again and answer the following questions.
1 задание
1
Если говорится о единственном в мире предмете
The sun is in the sky.
Солнце находится на небе.
2
Когда говорится о предмете (или лице), единственном в данной обстановке
The teacher is in theclassroom.
Учитель в классе. (В данном классе находится только один учитель)
3
Когда о данном предмете уже упоминалось в разговоре или повествовании
"I’ve got a very interesting book," says Mike.
"Please show me the book," says Nick.
«У меня есть интересная книга», — говорит Майк.
«Покажи мне эту книгу», — говорит Ник.
4
С существительным, перед которым стоит порядковое числительное
We are on the fourth floor.
Мы на пятом этаже.
5
С существительным, перед которым стоит прилагательное в превосходной степени
He is the best student in our group.
Он лучший студент в нашей группе.
6
Если говорится об определенном (по контексту) количестве вещества, например tea чай, milk молоко, bread хлеб и т. п.
Is the milk on the table?
Молоко на столе? (т. е. именно молоко (в определённой упаковке / в определённом объёме и т. д.), подразумеваемое по контексту, а не просто молоко как вещество)
7
Перед названиями морей, горных массивов, островов, рек, пустынь, кораблей, гостиниц, кинотеатров, театров; перед словами country за городом, seaморе, seaside у моря, mountains горы (и при обобщении)
I’m taking a trip to themountains next week.
На следующей неделе я еду в горы.
Did you go to the Black Sea or to the Volga?
Вы ездили на Черное море или на Волгу?
8
Перед существительным в единственном числе, обозначающим целый класс предметов, людей (т. е. при обобщении)
The whale is a mammal, not a fish.
Кит — это млекопитающее, а не рыба.
9
После слов one of один (из), some of некоторые (из), many of многие (из),each of каждый (из),most of большинство (из) (часто после слов all все, both of оба)
Most of the stories are very interesting.
Большинство рассказов очень интересны.
Give me one of the books.
Дайте мне одну из (этих) книг.
10
Перед названиями четырех сторон света
the Northern part of our country —
север нашей страны
11
Перед фамилией во множественном числе (при обозначении всех членов семьи)
The Petrovs are at home.
Петровы дома.
2 задание
грамматическое образование:
noun+verb2(окончание ~ed)
I went to school yesterday; He cooked a cake
слова индикаторы:
yesterday, the day before yesterday, last day, week..., ... days ago