tyulegenevapolina

06.03.2020 16:20

Английский язык

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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.