计算机网络与因特网论文.doc

1、计算机网络与因特网论文作 者：学 号：院 系： 专 业： 题 目： 指导者： 评阅者： CataloguePreface3Basics5Ultra-High-frequency communication (100 MHz)5Home networking (LAN)6Internet access (broadband over powerlines)8Medium frequency (kHz)10Low-speednarrow-band communication11High-speed narrow-band powerline communication distribution l

2、ine carrier13Transmitting radio programs14Utility applications15Low frequency (kHz)16Broadband over power line (BPL)17notching out and dynamic adaptation to contention18Interference issue remains a challenge to PLC systems19Automotive uses21Failure Scenarios21IEEE P1901, ITU G.hn home grids22Standar

3、ds organizations24Small and medium-sized enterprise office LAN construction scheme25Personal feeling30Reference directory32PrefaceThis article is now in its fourth edition. Each edition has corresponded to a different phase in the way computer networks were used. When the first edition appeared in 1

4、980, networks were an academic curiosity. When the second edition appeared in 1988, networks were used by universities and large businesses. When the third edition appeared in 1996, computer networks, especially the Internet, had become a daily reality for millions of people. The new item in the fou

5、rth edition is the rapid growth of wireless networking in many forms. The networking picture has changed radically since the third edition. In the mid-1990s, numerous kinds of LANs and WANs existed, along with multiple protocol stacks. By 2003, the only wired LAN in widespread use was Ethernet, and

6、virtually all WANs were on the Internet. Accordingly, a large amount of material about these older networks has been removed. However, new developments are also plentiful. The most important is the huge increase in wireless networks, including 802.11, wireless local loops, 2G and 3G cellular network

7、s, Bluetooth, WAP, i-mode, and others. Accordingly, a large amount of material has been added on wireless networks. Another newly-important topic is security, so a whole chapter on it has been added. Many people helped me during the course of the fourth edition. I would especially like to thank the

8、following people: Ross Anderson, Elizabeth Belding-Royer, Steve Bellovin, Chatschik Bisdikian, Kees Bot, Scott Bradner, Jennifer Bray, Pat Cain, Ed Felten, Warwick Ford, Kevin Fu, Ron Fulle, Jim Geier, Mario Gerla, Natalie Giroux, Steve Hanna, Jeff Hayes, Amir Herzberg, Philip Homburg, Philipp Hosch

9、ka, David Green, Bart Jacobs, Frans Kaashoek, Steve Kent, Roger Kermode, Robert Kinicki, Shay Kutten, Rob Lanphier, Marcus Leech, Tom Maufer, Brent Miller, Shivakant Mishra, Thomas Nadeau, Shlomo Ovadia, Kaveh Pahlavan, Radia Perlman, Guillaume Pierre, Wayne Pleasant, Patrick Powell, Thomas Robertaz

10、zi, Medy Sanadidi, Christian Schmutzer, Henning Schulzrinne, Paul Sevinc, Mihail Sichitiu, Bernard Sklar, Ed Skoudis, Bob Strader, George Swallow, George Thiruvathukal, Peter Tomsu, Patrick Verkaik, Dave Vittali, Spyros Voulgaris, Jan-Mark Wams, Ruediger Weis, Bert Wijnen, Joseph Wilkes, Leendert va

11、n Doorn, and Maarten van Steen. Special thanks go to Trudy Levine for proving that grandmothers can do a fine job of reviewing technical material. Shivakant Mishra thought of many challenging end-of-chapter problems. Andy Dornan suggested additional readings for Chap. 9. Jan Looyen provided essentia

12、l hardware at a critical moment. Dr. F. de Nies did an expert cut-and-paste job right when it was needed. My editor at Prentice Hall, Mary Franz, provided me with more reading material than I had consumed in the previous 7 years and was helpful in numerous other ways as well. Finally, we come to the

13、 most important people: Suzanne, Barbara, and Marvin. To Suzanne for her love, patience, and picnic lunches. To Barbara and Marvin for being fun and cheery all the time (except when complaining about awful college textbooks, thus keeping me on my toes). BasicsAll power line communications systems op

14、erate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC

15、power, in conventional use, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications. A new discovery called E-Line that allows a single power conductor on an overhead power line to operat

16、e as a waveguide to provide low attenuation propagation of RF through microwave energy lines while providing information rate of multiple Gbps is an exception to this limitation.Data rates over a power line communication system vary widely. Low-frequency (about 100-200kHz) carriers impressed on high

17、-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at

18、 millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.Ultra-High-frequency communication (100 MHz)The highest information rate transmissions over power line use RF through microwave frequencies transmitted via a transver

19、se mode surface wave propagation mechanism that requires only a single conductor (US patent 7,567,154). An implementation of this technology called E-Line has been demonstrated using a single power line conductor. These systems have demonstrated symmetric and full duplex communication well in excess

20、 of 1 Gbit/s in each direction. Multiple WiFi channels with simultaneous analog television in the 2.4 and 5.3 GHz unlicensed bands have been demonstrated operating over a single medium voltage line conductor. Because the underlying propagation mode is extremely broadband, it can operate anywhere in

21、the 20MHz - 20GHz region. Also since it is not restricted to 80 MHz, as is the case for high-frequency BPL, these systems can avoid the need to share spectrum with other licensed or unlicensed services and can completely avoid the interference issues associated with use of shared spectrum while offe

22、ring complete flexibility for modulation and protocols of a RF-microwave system.High frequency communication may (re)use large portions of the radio spectrum for communication, or may use select (narrow) band(s), depending on the technologyHome networking (LAN)A LAN is a system of computers and asso

23、ciated peripherals such as Printers that are physically connected by cable within a limited geographical area-typically in an office building or on a college campus. The topology of the network may be ring, star or bus. LANs use fiber optics or coaxial cable to connect computers, and each computer m

24、ust have special communications software installed oil its hard disk. Software has been developed that allows computers with different platforms to coexist and exchange data on the same LAN. Power line communications can also be used in a home to interconnect home computers (and networked peripheral

25、s), as well as any home entertainment devices (including TVs, Blu-ray players, game consoles and Internet video boxes such as Apple TV, Roku, Kodak Theatre, etc.) that have an Ethernet port. Consumers can buy powerline adapter sets at most electronics retailers and use those to establish a wired con

26、nection using the existing electrical wiring in the home. The powerline adapters plug into a wall outlet (or into an extension cord or power strip, but not into any unit with surge suppression and filtering, as this may defeat the signal) and then are connected via CAT5 to the homes router. Then, a

27、second (or third, fourth, fifth) adapter(s) can be plugged in at any other outlet to give instant networking and Internet access to an Ethernet-equipped Blu-ray player, a game console (PS3, Xbox 360, etc.) a laptop or an Internet TV (also called OTT for Over-the-Top video) box that can access and st

28、ream video content to the TV.The most established and widely deployed powerline networking standard for these powerline adapter products is from the HomePlug Powerline Alliance. HomePlug AV is the most current of the HomePlug specifications (HomePlug 1.0, HomePlug AV and the new HomePlug Green PHY f

29、or smart grid comprise the set of published specifications) and it has been adopted by the IEEE P1901 group as a baseline technology for their standard, due to be published and ratified in September or October of 2010. HomePlug estimates that over 45 million HomePlug devices have been deployed world

30、wide. Other companies and organizations back different specifications for power line home networking and these include the Universal Powerline Association, the HD-PLC Alliance and the ITU-Ts G.hn specification.Internet access (broadband over powerlines)Broadband over power lines (BPL), also known as

31、 power-line Internet or powerband, is the use of PLC technology to provide broadband Internet access through ordinary power lines. A computer (or any other device) would need only to plug a BPL modem into any outlet in an equipped building to have high-speed Internet access. International Broadband

32、Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives.BPL may offer benefits over regular cable or DSL connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relati

33、vely little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up. Cost of running wires such as ethernet in many buildings can be prohibitive; Relying on wireless has a number of pred

34、ictable problems including security, limited maximum throughput and inability to power devices efficiently.But variations in the physical characteristics of the electricity network and the current lack of IEEE standards mean that provisioning of the service is far from being a standard, repeatable p

35、rocess. And, the amount of bandwidth a BPL system can provide compared to cable and wireless is in question. The prospect of BPL could motivate DSL and cable operators to more quickly serve rural communities. 1PLC modems transmit in medium and high frequency (1.6 to 80 MHz electric carrier). The asy

36、mmetric speed in the modem is generally from 256 kbit/s to 2.7 Mbit/s. In the repeater situated in the meter room the speed is up to 45 Mbit/s and can be connected to 256 PLC modems. In the medium voltage stations, the speed from the head ends to the Internet is up to 135 Mbit/s. To connect to the I

37、nternet, utilities can use optical fiber backbone or wireless link.Deployment of BPL has illustrated a number of fundamental challenges, the primary one being that power lines are inherently a very noisy environment. Every time a device turns on or off, it introduces a pop or click into the line. En

38、ergy-saving devices often introduce noisy harmonics into the line. The system must be designed to deal with these natural signaling disruptions and work around them. For these reasons BPL can be thought of as a halfway between wireless transmission (where likewise there is little control of the medi

39、um through which signals propagate) and wired transmission (but not requiring any new cables).Broadband over power lines has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Power distribution uses step-down transformers to redu

40、ce the voltage for use by customers. But BPL signals cannot readily pass through transformers, as their high inductance makes them act as low-pass filters, blocking high-frequency signals. So, repeaters must be attached to the transformers. In the U.S., it is common for a small transformer hung from

41、 a utility pole to service a single house or a small number of houses. In Europe, it is more common for a somewhat larger transformer to service 10 or 100 houses. For delivering power to customers, this difference in design makes little difference for power distribution. But for delivering BPL over

42、the power grid in a typical U.S. city requires an order of magnitude more repeaters than in a comparable European city. On the other hand, since bandwidth to the transformer is limited, this can increase the speed at which each household can connect, due to fewer people sharing the same line. One po

43、ssible solution is to use BPL as the backhaul for wireless communications, for instance by hanging Wi-Fi access points or cellphone base stations on utility poles, thus allowing end-users within a certain range to connect with equipment they already have.The second major issue is signal strength and

44、 operating frequency. The system is expected to use frequencies of 10 to 30 MHz, which has been used for many decades by amateur radio operators, as well as international shortwave broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and wil

45、l act as antennas for the signals they carry, and have the potential to interfere with shortwave radio communications. Modern BPL systems use OFDM modulation, which allows them to mitigate interference with radio services by removing specific frequencies used. A 2001 joint study by the American Radi

46、o Relay League (ARRL) and HomePlug Powerline Alliance showed that for modems using this technique in general that with moderate separation of the antenna from the structure containing the HomePlug signal that interference was barely perceptible at the notched frequencies and interference only happen

47、ed when the antenna was physically close to the power lines (however other frequencies still suffer from interference).Medium frequency (kHz)Power line communications technology can use the household electrical power wiring as a transmission medium. This is a technique used in home automation for re

48、mote control of lighting and appliances without installation of additional control wiring.Typically home-control power line communication devices operate by modulating in a carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individuall