n system that accommodates multiple sources of information,and allows each source to send to a separate destination. It may seem that communication in such a system is straightforward.Each source needs a mechanism to gather the information,prepare the information for transmission ,and transmit the information across the shared physical medium.Similarly, a mechanism is needed that extracts the information for the destination and delivers the information. Figure 2.1 illustrates the simplistic view.
Figure 2.1
2.2 The basic types of Multiplexing
There are four basic approaches to multiplexing that each have a set of variationgs and implementions.
•Frenquency Division Multiplexing
•Wavelength Division Multiplexing
•Time Division Multiplexing
•Code Division Multiplexing
Time and frequency division multiplexing are widely used. Wavelength division multiplexing is a form of frenquency division multiplexing used for optical fiber. Code division multiplexing is a mathematical approach used in cell phone mechanisms.
2.3Access and interconnection technologies
A variety of technologies are used to provide Internet access.They can be divided into two broad categories based on the data rate they provide:
•Narrowband
•Broadband
Chapter 3 Packet switching and network technologies summary
3.1 LAN concepts
LAN is dispersed within a limited geographical area multiple computers connected through the transmission medium of communication networks, through full-featured networksoftware to achieve communication between computers and share resources with each other.LAN is usually in the tens of meters to a few kilometers within a local area network can accommodate several to several thousand computers.Now look at the characteristics according to the LAN, local area network has the following features:
LAN distributed in relatively small geographic range.Because it uses a different transmission capacity of transmission media, so the LAN transmission distance is also different.
LANs are often used for a particular group.For example, a company, a unit of a block of flats,certain schools.
3.2 LAN topology
3.2.1Star topology
A star topology resembles a wheel with the network itself corresponding to a central hub, and the link to individual computers corresponding to spokes.
3.2.2 A bus topology
A bus topology consists of a single, shared cable to which many computers attach. When it uses a bus, a computer transmits a signal that all other computers attached to the bus receive.
3.2.3 A ring topology
A ring topology consists of computers connected in a closed loop. The first computer connects to the second, the second connects to the third, and so on, until the last computer connects back to the first.
A star topology resembles a wheel with the network itself corresponding to a central
3.3 WAN tecnology
WAN------wide area network, is a set of packet switches are interconnected to form a wide area network. A switch usually has multiple I/O connectors, making it possible to form many different topologies and connect multiple computers. WAN also called remote nets. Usually jumper great physical limits, the coverage range from a few tens of kilometers to thousands of kilomet
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