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JANET

JANET

: See also: Janet JANET is a British, private, government-funded computer network dedicated to education and research. All further- and higher-education organizations are connected to JANET, as are all the Research Councils and several metropolitan area networks in the UK. The name was originally a contraction of Joint Academic NETwork: as this title excludes the network's connections with education and research, it is now known as JANET in its own right.

History

JANET developed out of a number of local and research networks dating back to the 1970s. In the early 80s a standardization and interconnect effort started, hosted on an expansion of the pioneering SERCnet X.25 research network. The system first went live in April 1983, hosting about 50 sites with line speeds of 9.6 kbit/s. In the mid-80s the backbone was upgraded to a 2 Mbit/s backbone with 64 kbit/s access links, and a further upgrade in the early 1990s sped the backbone to 8 Mbit/s and the access links to 2 Mbit/s, making JANET the fastest X.25 network in the world. The JANET effort resulted in the standarization known as the Coloured Book protocols, which provided the first complete X.25 standard. There had been some talk of moving JANET to OSI protocols in the 1990s, but changes in the networking world meant this never happened. In January 1991 the JANET IP Service (JIPS) was set up as a pilot project to host IP traffic on the existing network. Within ten months the IP traffic had exceeded the levels of X.25 traffic, and the IP support became official in November. Today JANET is primarily a high-speed IP network. In order to address speed concerns, several hardware upgrades have been incorporated into the JANET system. In 1989 SuperJANET was proposed, to re-host JANET on a fibre optic network. Work started in late 1992, and by late 1993 the first 14 sites had migrated to the new 32 Mbit/s ATM system. SuperJANET also moved solely to IP. In 1995 SuperJANET II started, adding 155 Mbit/s ATM backbones and a 10 Mbit/s SMDS network encompassing some of the original JANET nodes. JANET's mandate now included running metropolitan area networks centered on these sites. SuperJANET III created new 155 Mbit/s ATM nodes to fully connect all of the major sites at London, Bristol, Manchester and Leeds, with 34 Mbit/s links to smaller sites around the country. In March 2001 SuperJANET4 was launched. The key challenges for SuperJANET4 was the need to increase network capacity and to strengthen the design and management of JANET to allow it to meet a similar increase in the size of its userbase. SuperJANET4 saw the implementation of a 2.5Gbit/s core backbone from which connections to regional network points of presence were made at speeds ranging between 155Mbit/s to 2.5Gbit/s depending upon the size of the regional network. In 2002 the core SuperJANET4 backbone was upgraded to 10Gbit/s. SuperJANET4 also saw an increase in the userbase of JANET with the inclusion of the Further Education Community and the use of the SuperJANET4 backbone to interconnect schools networks. Work is currently (2005) underway to procure [http://www.ja.net/sj5/ SuperJANET 5], the next generation of the backbone which will include the ability to dedicate connections to specific projects using Wavelength-division multiplexing. This is scheduled to be deployed during 2006. JANET is linked to other European and worldwide NRENs through GEANT, has a private connection to CERNET in China and peers extensively with other ISPs at Internet Exchange Points in the UK. JANET is operated by a consortium known as the United Kingdom Education and Research Networking Association (UKERNA), who are also responsible for the .ac.uk and .gov.uk domains.

External links

- [http://www.ja.net/ JANET and UKERNA website] Category:Education in the United Kingdom Category:Science and technology in the United Kingdom Category:Academic computer network organizations

JANET

History

External links

- [http://www.ja.net/ JANET and UKERNA website] Category:Education in the United Kingdom Category:Science and technology in the United Kingdom Category:Academic computer network organizations

Computer network

A computer network is a system for communication between computers. These networks may be fixed (cabled, permanent) or temporary (as via modems or null modems). Carrying instructions between calculation machines and early computers was done by human users. In September, 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model K at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency ARPA when, in 1962, J.C.R. Licklider was hired and developed a working group he called the 'Intergalactic Network' a precursor to the ARPANet. In 1964 researchers at Dartmouth developed a time sharing system for distributed users of large computer systems. The same year, at MIT, a research group supported by General Electric and Bell Labs used a computer (DEC's PDP-8) to route and manage telephone connections. in 1968 Paul Baran proposed a network system consisting of datagrams or packets that could be used in a packet switching network between computer systems. In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANet network using 50 kbit/s circuits. Networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from researchers and businesses to families and individuals in everyday use.

Categorizing

- Local area network (LAN)
- HomePNA
- Power line communication (HomePlug)
- Metropolitan area network (MAN)
- Wide area network (WAN)

Protocol stacks

Computer networks may be implemented using a variety of protocol stack architectures, computer buses or combinations of media and protocol layers, incorporating one or more of:
- ARCNET
- AppleTalk
- ATM
- Bluetooth
- DECnet
- Ethernet
- FDDI
- Frame relay
- HIPPI
- IEEE 1394 aka FireWire, iLink
- IEEE 802.11
- IEEE-488
- IP
- IPX
- Myrinet
- QsNet
- RS-232
- SPX
- System Network Architecture
- Token Ring
- TCP
- TCP Tuning for discussion of improving performance of same
- USB
- UDP
- X.25 For a list of more see Network protocols. For standards see IEEE 802.

References

- Andrew S. Tanenbaum, "Computer Networks" (ISBN 0133499456).
- Important publications in computer networks

External links

- [http://www.ericdigests.org/pre-921/networking.htm Networking and Microcomputers]
- [http://www.elook.org/computing/network.htm Network – eLook Computing Reference] – defines what a network is and provides leading links
- [http://www.ericdigests.org/1993/k-12.htm Networking: K-12]
- [http://www.pcnineoneone.com/howto/hmnetwk1.html How to set up a home network]
- [http://www.techbooksforfree.com/networking.shtml Open source and non-copyrighted books on networking available for free download]
- Prof. Rahul Banerjee's [http://discovery.bits-pilani.ac.in/rahul/PDFversions/Complete-InetBook-PHI-2003-Secure.pdf free e-book on Internetworking Technologies] deals with the foundations of major internetworking architectures (chapters 4–9)
- [http://www.netfilter.org/documentation/HOWTO//networking-concepts-HOWTO.html Easy Network Concepts] (Linux kernel specific) Category:Information technology Category:Networks zh-min-nan:Tiān-náu bāng-lō· ja:コンピュータ・ネットワーク nb:Datanett simple:Computer network th:เครือข่ายคอมพิวเตอร์

Research Council

The Research Councils of the UK are government agencies responsible for particular areas of science and technology. They are non-departmental government bodies which receive public funds from the Department of Trade and Industry through the Office of Science and Technology. There are currently eight Research Councils:
- Arts and Humanities Research Council
- Biotechnology and Biological Sciences Research Council
- Council for the Central Laboratory of the Research Councils
- Engineering and Physical Sciences Research Council
- Economic and Social Research Council
- Medical Research Council
- Natural Environment Research Council
- Particle Physics and Astronomy Research Council Research Councils UK (RCUK) is a partnership of all the research councils, through which they promote various joint activities and interact with the UK government. The MRC has its head office in central London, CCLRC is based at its Rutherford Appleton Laboratory, in Oxfordshire, the AHRC is based in Bristol and the other five research councils and RCUK operate from a single complex in Swindon.

External links

- [http://www.ahrc.ac.uk/ Arts and Humanities Research Council]
- [http://www.bbsrc.ac.uk/ Biotechnology and Biological Sciences Research Council]
- [http://www.cclrc.ac.uk/ Council for the Central Laboratory of the Research Councils]
- [http://www.epsrc.ac.uk/ Engineering and Physical Sciences Research Council]
- [http://www.esrc.ac.uk/ Economic and Social Research Council]
- [http://www.mrc.ac.uk/ Medical Research Council]
- [http://www.nerc.ac.uk/ Natural Environment Research Council]
- [http://www.pparc.ac.uk/ Particle Physics and Astronomy Research Council]
- [http://www.rcuk.ac.uk/ Research Councils UK] Category:Science and technology in the United Kingdom Category:Public bodies and task forces of the United Kingdom government

Kbit/s

A kilobit per second (kbps or kbit/s) is a unit of data transmission speed equal to 1,000 bits per second. Most audio applications are measured in kbit/s: (These values vary depending on audio data compression schemes)
- 4 kbit/s – minimum necessary for recognizable speech (using special-purpose speech codecs)
- 8 kbit/s – telephone quality
- 32 kbit/s – MW quality
- 96 kbit/s – FM quality
- 192 kbit/s – "CD quality" for an mp3
- 1,411 kbit/s – CD audio (at 16-bits and 44.1 kHz)

Related units

Another unit of data transmission is the kilobyte per second (kB/s or kbyte/s), which is 8 times the size of a kilobit per second: : 1 kilobyte/s = 8 kilobit/s Another related unit is the kibibit per second:

Mbit/s

A megabit per second (Mbps or Mbit/s) is a unit of data transmission equal to 1,000 kilobits per second or 1,000,000 bits per second. The bandwidth of consumer broadband internet services are often rated in Mbit/s. Most video applications are measured in Mbit/s:
- 32 kbit/s – videophone quality (minimum necessary for a recognizable talking head)
- 2 Mbit/s – VHS quality
- 8 Mbit/s – DVD quality
- 55 Mbit/s – HDTV quality

Megabyte per second

Another unit of data transmission is the megabyte per second (MBps or MB/s), which is 8 times a megabit per second: : 1 megabyte/s = 8 megabit/s Many computer data interfaces are rated in MB/s:
- PATA 33-133 MB/s
- SATA 150-300 MB/s
- PCI 133-533 MB/s

Confusion

One megabit per second should not be confused with one mebibit per second:

Open systems interconnect

The Open Systems Interconnection (usually abbreviated to OSI) was a new effort in networking started in 1982 by the International Organization for Standardization (ISO), along with the ITU-T. Prior to OSI, networking was completely vendor-developed and proprietary, with protocol standards such as SNA and DECnet. OSI was a new industry effort, attempting to get everyone to agree to common network standards to provide multi-vendor interoperability. It was common for large networks to support multiple network protocol suites, with many devices unable to talk to other devices because of a lack of common protocols between them. The OSI reference model (which actually predates the OSI protocol work, dating to 1977) was the most important advance in the teaching of network concepts. It promoted the idea of a common model of protocol layers, defining interoperability between network devices and software. However, the actual OSI protocol stack that was specified as part of the project was considered by many to be too complicated and to a large extent unimplementable. Taking the "forklift upgrade" approach to networking, it specified eliminating all existing protocols and replacing them with new ones at all layers of the stack. This made implementation difficult, and was resisted by many vendors and users with significant investments in other network technologies. In addition, the OSI protocols were specified by committees filled with differing and sometimes conflicting feature requests, leading to numerous optional features. Because so much was optional, many vendors' implementations simply could not interoperate, negating the whole effort. The OSI approach was eventually eclipsed by the Internet's TCP/IP protocol suite. TCP/IP's pragmatic approach to computer networking and two independent implementations of simplified protocols made it a practical standard. For example, the definition for OSI's X.400 e-mail standards took up several large books, while the Internet e-mail (SMTP) definition took only a few dozen pages in RFC-821. It should be noted, however, that over time there have been numerous RFCs which extended the original SMTP definition, so that its complete documentation finally takes up several large books as well. Many of the protocols and specifications in the OSI stack are long-gone or have been superseded, such as token-bus media, CLNP packet delivery, FTAM file transfer, and X.400 e-mail. Some still survive, often in significantly simplified forms. The X.500 directory structure still remains with significant usage, mainly because the original unwieldy protocol has been stripped away and effectively replaced with LDAP. IS-IS also continues as a network routing protocol used by larger telecommunications companies, having been adapted for use with the Internet Protocol. Many legacy SONET systems still use TARP (TID Address Resolution Protocol - utilizes CLNP and IS-IS) to translate Target Identifier of a SONET node. Often protocols and specifications in the OSI stack remain in use in legacy systems, unless or until such legacy systems are eventually upgraded, replaced or decomissioned. The collapse of the OSI project in 1996 severely damaged the reputation and legitimacy of the organizations involved, especially ISO. The worst part was that OSI's backers took too long to recognize and accommodate the dominance of the TCP/IP protocol suite.

Reference

- ISO 7498:1984 Open Systems Interconnection - Basic Reference Model Category:ITU-T recommendations

Fibre optic

An optical fiber (also spelled fibre) is a transparent thin fiber, usually made of glass or plastic, for transmitting light. Fiber optics is the branch of science and engineering concerned with such optical fibers.

Optical description

Optical fiber is a cylindrical structure that transmits light along its axis. The fiber consists of a core surrounded by a cladding layer. Like other glasses, the glass used in optical fiber has a refractive index of about 1.5. For the fiber to guide the optical signal the refractive index of the core must be slightly higher than that of the cladding, though typically the difference is less than one per cent. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber. graded-index fiber Fiber with large core diameter, called multi-mode fiber (from the electromagnetic analysis, see below), may be analyzed by geometric optics. In a step-index fiber, rays of light are guided along the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary) are completely reflected. The minimum angle for total internal reflection is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the core into the cladding, where they are not useful for conveying light along the fiber. In this way, the minimum angle for total internal reflection determines the acceptance angle of the fiber, often reported as a numerical aperture. A high numerical aperture makes it easier to efficiently couple a transmitter or receiver to the fiber. However, by allowing light to propagate down the fiber in rays both close to the axis and at various angles, a high numerical aperture also increases the amount of multi-path spreading, or dispersion, that affects light pulses in the fiber. In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This reduces multi-path dispersion because the high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. Index grading also causes light rays to bend smoothly as they approach the cladding, rather than reflect abruptly from the core-cladding boundary. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. This ideal index profile is very close to a parabolic relationship between the index and the distance from the axis. Fiber with a core diameter narrower than a few wavelengths of the light carried, is analyzed as an electromagnetic structure. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. The optical fiber is seen as a cylindrical dielectric wave guide. This wave guide supports one or more confined transverse modes by which light can propagate along its axis. Fiber supporting only one mode is called single-mode or mono-mode fiber, while fiber that supports more than one mode is called multi-mode fiber. By the waveguide analysis, it is seen that the light energy in the fiber is not completely confined in the core, but, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave. bound mode The common type of single-mode fiber, as described in Federal Standard 1037C, has a core diameter of 8 to 10 micrometres. It is notable that the mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with a core diameter of 50 µm, 62.5 µm, or larger. Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber designed to suppress whispering gallery mode propagation. Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses are used for longer-wavelength infrared applications. At high optical powers, above one watt, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second ^,^,. The open fiber control system, which ensures laser eye safety in the event of a broken fiber, can also effectively halt propogation of the fiber fuse . In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "Fiber fuse" protection device at the transmitter can break the circuit to prevent damage.

Optical fiber communication

The optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. Although fibers can be made out of either transparent plastic or glass, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical attenuation. Both multi-mode and single-mode fibers are used in communications, with multi-mode fiber used mostly for short distances (up to 500 m), and single-mode fiber used for longer distance links. Because of the tighter tolerances required to couple light into and between single-mode fibers, single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode components. The light used is typically infrared light, at wavelengths near to the minimum absorption wavelength of the fiber in use. The fiber absorption is minimal for 1550 nm light and dispersion is minimal at 1310 nm making these the optimal wavelength regions for data transmission. A local minimum of absorption is found near 850 nm, a wavelength for which low cost transmitters and receivers can be designed, and this wavelength is often used for short distance applications. Fibers are generally used in pairs, with one fiber of the pair carrying a signal in each direction. For modern glass optical fiber, the maximum transmission distance is limited not by attenuation but by dispersion, or spreading of optical pulses as they travel along the fiber. Dispersion in optical fibers is caused by a variety of factors. Intermodal dispersion, caused by the different axial speeds of different transverse modes, limits the performance of multi-mode fiber. Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated. For single-mode fiber performance is limited by chromatic dispersion, which occurs because the index of the glass varies slightly depending on the wavelength of the light, and light from real optical transmitters has nonzero spectral width. Polarization mode dispersion, which can limit the performance of single-mode systems, occurs because although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations. Dispersion limits the bandwidth of the fiber because the spreading optical pulse limits the rate that pulses can follow one another on the fiber and still be distinguishable at the receiver. Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its bandwidth-distance product, often expressed in units of MHz×km. This value is a product of bandwidth and distance because there is a tradeoff between the bandwidth of the signal and the distance it can be carried. For example, a common multimode fiber with bandwidth-distance product of 500 MHz×km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km. In single-mode fiber systems, both the fiber characteristics and the spectral width of the transmitter contribute to determining the bandwidth-distance product of the system. Typical single-mode systems can sustain transmission distances of 80 to 140 km (50 to 87 miles) between regenerations of the signal. By using an extremely narrow-spectrum laser source, data rates of up to 40 gigabits per second are achieved in real-world applications. Using Wavelength division multiplexing (WDM), the bandwidth carried by a single fiber can be increased into the range of terabits per second. This is accomplished by transmitting many wavelengths at once on the fiber. Wavelength division multiplexers and demultiplexers are used to combine and split up the wavelengths at each end of the link. In coarse WDM (CWDM) only a few wavelengths are used. One use of CWDM is to allow bidirectional communications over one fiber. Recent advances in fiber technology have reduced losses so far that no amplification of the optical signal is needed over distances of hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly over undersea spans where the cost reliability of amplifiers is one of the key factors determining the performance of the whole cable system. In the past few years several manufacturers of submarine cable line terminal equipment have introduced upgrades that promise to quadruple the capacity of older submarine systems installed in the early to mid-1990s. These advances have been the result of increased investigation into two different fields. One is dispersion management, which seeks to balance the effects of dispersion against nonlinearity. The other is solitons. The range of long-range systems is extended by the use of optical amplifiers, typically made by doping a length of fiber with the rare-earth mineral erbium, and pumping it with light from a laser with a shorter wavelength than the communications signal.

Comparison with electrical transmission

The choice between optical fiber and electrical (or "copper") transmission for a particular system is made based on a number of trade-offs. Optical fiber is generally chosen for systems with higher bandwidths, spanning longer distances, than electrical cabling can provide. The main benefits of fiber are its exceptionally low loss, allowing long distances between amplifiers or repeaters; and its inherently high data-carrying capacity, such that thousands of electrical links would be required to replace a single high bandwidth fiber. One further benefit of fiber is that even when run alongside each other for long distances, fiber cables experience effectively no crosstalk, in contrast to some types of electrical transmission lines. In short distance and relatively low bandwidth applications, electrical transmission is often preferred because of its
- Lower material cost, when cabling is not required.
- Lower cost of transmitters and receivers.
- Ease of splicing.
- Capability to carry electrical power as well as signals. Because of these benefits of electrical transmission, optical communication is not common in short box-to-box, backplane, or chip-to-chip applications; however, optical systems on those scales have been demonstrated in the laboratory. In certain situations fiber may be used even for short distance or low bandwidth applications, due to other important features:
- Immunity to electromagnetic interference, including nuclear electromagnetic pulses (although fiber can be damaged by alpha and beta radiation).
- High electrical resistance, making it safe to use near high-voltage equipment or between areas with different earth potentials.
- Low weight, important in aircraft.
- No sparks, important in flammable or explosive gas environments.
- Not electromagnetically radiating, and difficult to tap without disrupting the signal, important in high-security environments.

Other uses of optical fibers

- Fibers can be used as light guides in medical and other applications where bright light needs to be brought to bear on a target without a clear line-of-sight path.
- Lasers and optical amplifiers can use doped optical fiber as a gain medium.
- Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters.
- Bundles of fibers are used along with lenses for long, thin imaging devices called endoscopes, which are used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy). Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach, such as jet engine interiors.
- In some high-tech buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics).
- Optical fibers have many decorative applications, including signs and art, artificial Christmas trees, and lighting.
- The German company Sennheiser developed a microphone working with a laser and optical fibers.

Manufacture

Optical fiber is made by first constructing a large-diameter preform, with a carefully controlled refractive index profile, and then pulling the preform to form the long, thin optical fiber. The preform is commonly made by three chemical vapor deposition methods: inside vapor deposition, outside vapor deposition, and vapor axial deposition. In inside vapor deposition, a hollow glass tube approximately 40 cm in length known as a "preform" is placed horizontally and rotated slowly on a lathe, and gases such as silicon tetrachloride (SiCl₄) or germanium tetrachloride (GeCl₄) are injected with oxygen in the end of the tube. The gases are then heated by means of an external hydrogen burner, bringing the temperature of the gas up to 1900 kelvin, where the tetrachlorides react with oxygen to produce silica or germania (germanium oxide) particles. When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume, in contrast to earlier techniques where the reaction occurred only on the glass surface, this technique is called modified chemical vapor deposition. The oxide particles then agglomerate to form large particle chains, which subsequently deposit on the walls of the tube as soot. The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as thermophoresis). The torch is then traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the end of the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient amount of material has been deposited. For each layer the composition can be varied by varying the gas composition, resulting in precise control of the finished fiber's optical properties. In outside vapor deposition or vapor axial deposition, the glass is formed by flame hydrolysis, a reaction in which silicon tetrachloride and germanium tetrachloride are oxidized by reaction with water (H₂O) in an oxyhydrogen flame. In outside vapor deposition the glass is deposited onto a solid rod, which is removed before further processing. In vapor axial deposition, a short seed rod is used, and a porous preform, whose length is not limitted by the size of the source rod, is built up on its end. The porous preform is consolidated into a transparent, solid perform by heating to about 1800 kelvin. The preform, however constructed, is then placed in a device known as a drawing tower, where the perform tip is heated and the optic fiber is pulled out as a string. By measuring the resultant fiber width, the tension on the fiber can be controlled to maintain the fiber thickness.

Optical fiber cables

In practical fibers, the cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic. These layers add strength to the fiber but do not contribute to its optical wave guide properties. For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer (e.g. Kevlar) strength members, in a lightweight plastic cover to form a simple cable. Each end of the cable may be terminated with a specialized optical fiber connector to allow it to be easily connected and disconnected from transmitting and receiving equipment. For use in more strenuous environments, a much more robust cable construction is required. In loose-tube construction the fiber is laid helically into semi-rigid tubes, allowing the cable to stretch without stretching the fiber itself. This protects the fiber from tension during laying and due to temperature changes. Alternatively the fiber may be embedded in a heavy polymer jacket. These fiber units are commonly attached to additional steel strength members, again with a helical twist to allow for stretching. Another critical concern in cabling is to protect the fiber from contamination by water, because its component hydrogen and hydroxyl ions can diffuse into the fiber, reducing the fiber's strength and increasing the optical attenuation. Water is kept out of the cable by use of solid barriers such as copper tubes, or water-repellant jelly surrounding the fiber. Finally, the cable may be armored to protect it from environmental hazards, such as construction work or gnawing animals. Undersea cables are more heavily armored in their near-shore portions to protect them from boat anchors, fishing gear, and even sharks, which may be attracted to the electrical power signals that are carried to power amplifiers or repeaters in the cable. Modern fiber cables can contain up to a thousand fibers in a single cable, so the performance of optical networks easily accommodate even today's demands for bandwidth on a point-to-point basis. However, unused point-to-point potential bandwidth does not translate to operating profits, and it is estimated that no more than 1% of the optical fiber buried in recent years is actually 'lit'. Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, installation in conduit, lashing to aerial telephone poles, submarine installation, or insertion in paved streets. In recent years the cost of small fiber-count pole mounted cables has greatly decreased due to the high Japanese and South Korean demand for Fiber to the Home (FTTH) installations.

History

The history of dielectric optical lightguides goes back to Victorian times, when the total internal reflection principle was used to illuminate streams of water in elaborate public fountains. Later development, in the early-to-mid twentieth century, focussed on the development of fiber bundles for image transmission, with the primary application being the medical gastroscope. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed. Basil Hirschowitz In 1965, Charles K. Kao and George A. Hockham of the British Post Office were the first to recognize that attenuation of contemporary fibers was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. They demonstrated that optical fiber could be a practical medium for communication, if the attenuation could be reduced below 20 dB per kilometer (Hecht, 1999, p. 114). By this measure, the first practical optical fiber for communications was invented in 1970 by researchers Robert D. Maurer, Donald Keck, Peter Schultz, and Frank Zimar working for American glass maker Corning Glass Works. They manufactured a fiber with 17 dB optic attenuation per kilometer by doping silica glass with titanium. The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by eliminating the need for optical-electrical-optical repeaters, was invented by David Payne of the University of Southampton, in 1987. The first transatlantic telephone cable to use optical fiber was TAT-8, which went into operation in 1988. In the late 1990s through 2000, the fiber optics industry became associated with the dot-com stock-market bubble. Industry promoters predicted vast increases in demand for communications bandwidth due to increased use of the Internet, and commercialization of various bandwidth-intensive consumer services, such as video on demand. Internet protocol data traffic was said to be increasing exponentially, and at a faster rate than integrated circuit complexity had increased under Moore's Law. Since the bust of the dot-com bubble, however, the main trend in the industry has been consolidation of firms and offshoring of manufacturing to reduce costs.

References

- Gambling, W. A., "The Rise and Rise of Optical Fibers", IEEE Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6, pp. 1084-1093, Nov./Dec. 2000
- Gowar, John, Optical Communication Systems, 2 ed., Prentice-Hall, Hempstead UK, 1993 (ISBN 0136387276)
- Hecht, Jeff, City of Light, The Story of Fiber Optics, Oxford University Press, New York, 1999 (ISBN 0195108183)
- Nagel S. R., MacChesney J. B., Walker K. L., "An Overview of the Modified Chemical Vapor Deposition (MCVD) Process and Performance", IEEE Journal of Quantum Mechanics, Vol. QE-18, No. 4, April 1982 # # # # #

External links

- [http://www.siemon.com/us/standards/13-14_optical_fiber_cabling.asp Optical Fiber Cabling Standards]
- [http://www.thefoa.org/ The Fiber Optic Association]
- [http://www.jimhayes.com/lennielw/ Lennie Lightwave's Guide To Fiber Optics] Category:Fiber optics Category:Telecommunications equipment Category:Signal cables ja:光ファイバー

SMDS

SMDS, which stands for Switched Multi-megabit Data Services, was a connectionless service used to connect LANs, MANs and WANs to exchange data. SMDS was based on the IEEE 802.6 DQDB standard. SMDS fragmented its datagrams into smaller "cells" for transport, and can be viewed as a technological precursor of ATM. Increases in raw data rates removed the need for fragmentation into cells, and SMDS' niche market position ensured that it remained a high-priced service. As a result, SMDS has been supplanted by IP-based and Ethernet-based services and MPLS.

External links

- [http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/smds.htm Cisco guide to SMDS]

London

London is the capital city of the United Kingdom and of England. As Europe's richest city, London produces 17% of the UK's GDP, and is one of the world's major business and financial centres. The capital of the former global empire, London is a leader in culture, communications, politics, finance, entertainment and the arts and has considerable influence worldwide. arts]] arts] London is the most populous city in the European Union, with an estimated population on 1 January 2005 of 7,500,000 and a metropolitan area population of between 12 and 14 million. London's population includes an extremely diverse range of peoples, cultures, and religions, making it one of the most cosmopolitan, vibrant and energetic cities on earth. A resident of London is referred to as a Londoner. Over 300 languages are spoken in London, making it the most linguistically diverse city in the world. Initially it was a Roman city and known as Londinium and then as Lunnainn, Llundain and Londain in the Scottish, Welsh and Irish languages respectively. London is known by these names in other languages. London is the home of many global organisations, institutions and companies, and as such retains its leading role in global affairs. A city where cutting-edge meets tradition, London is a major tourist destination and transport hub. It has a great number of important buildings and iconic landmarks, including world-famous museums, theatres, concert halls, galleries, airports, sports stadia and palaces. London is one of the world's major global cities (along with New York City, Tokyo and Paris).

Defining London

Today, "London" usually refers to the conurbation known as Greater London, which is divided into thirty-two London Boroughs and the City of London and forms the London region of England. Historically, "London" referred to the square mile of the City of London at the conurbation's heart, from which the city grew. Between 1889 and 1965 it referred to the former County of London which covered the area now known as Inner London. There are other definitions of "London" which cover varying areas, such as the London postal district; the area covered by the telephone area code 020; the area accessible by public transport using a Transport for London Travelcard; the area delimited by the M25 orbital motorway; the Metropolitan Police district; and the London commuter belt. The coordinates of the centre of London (traditionally considered to be Charing Cross, near the junction of Trafalgar Square, the Strand, Whitehall and the Mall) are approximately . The Romans marked the centre of Londinium with the London Stone in the City.

Geography and climate

London Stone, with Green Park and St. James's Park to its right]] Greater London covers an area of 609 square miles (1,579 km²). London is a port on the Thames, a navigable river. The river has had a major influence on the development of the city. London was founded on the north bank of the Thames and there was only a single bridge, London Bridge, for many centuries. As a result, the main focus of the city was on the north side of the Thames. When more bridges were built in the 18th century, the city expanded in all directions as the mostly flat or gently rolling countryside around the Thames floodplain presented no obstacle to growth. There are some hills in London, examples being Parliament Hill and Primrose Hill, but these provided fine prospects of the city centre without significantly affecting the directions of the spread of the city and London is therefore roughly circular. The Thames was once a much broader, shallower river than it is today. It has been extensively embanked, and many of its London tributaries now flow underground. The Thames is a tidal river, and London is vulnerable to flooding. The threat has increased over time due to a slow but continuous rise in high water level and the slow 'tilting' of Britain (up in the north and down in the south) caused by post-glacial rebound. The Thames Barrier was constructed across the Thames at Woolwich in the 1970s to deal with this threat, but in early-2005 it was suggested that a ten-mile-long barrier further downstream might be required to deal with the flood risk in the future [http://news.bbc.co.uk/1/hi/england/london/4162905.stm]. London has a temperate climate, with warm but seldom hot summers, cool but rarely severe winters, and regular but generally light precipitation throughout the year. Summer temperatures rarely rise much above 33°C (91°F), though higher temperatures have become more common recently. The highest temperature ever recorded in London was 38.1°C (100.6°F), measured at Kew Gardens during the European Heat Wave of 2003. Heavy snowfalls are almost unknown. In recent winters, snow has rarely settled to more than an inch (25 mm). London's average annual precipitation of less than 24 inches (600 mm) is lower than that of Rome or Sydney. London's large built-up area creates a microclimate, with heat stored by the city's buildings: sometimes temperatures are 5°C (9°F) warmer in the city than in the surrounding areas.

History

microclimate bombings of London]] The name London is commonly thought to have come from the Latin name Londinium, as London was founded by the Romans during their reign over the land, around 43AD – although there is some slight evidence of pre-Roman settlement. The [http://www.bbc.co.uk/history/timelines/england/rom_roman_invasion.shtml BBC History website], however, claims that the name Londinium is actually "Celtic, not Latin, and may originally have referred to a previous farmstead on the site"; the root is 'Lond' meaning 'wild' (i.e. overgrown or forested) place. This fortified Roman settlement was the capital of the province of Britannia. According to findings displayed in London Museum, the initial language of London was Latin with much Greek spoken due to the presence of Greek speaking Roman soldiers and businessmen. Another suggestion for where the name of the city comes from could be that of the mythical leader, King Lud. It was said that Lud laid out the first set of roads in the city. His statue can be seen hidden at the church of St Dunstan's In The West, Fleet Street. Around AD 61 the Iceni tribe of Celts lead by Queen Boudica stormed London and took the city from the Romans. The Celts burnt the relatively new Roman town to the ground, and archaeological digs have revealed a layer of red ash beneath the City of London, which is believed to be the burnt remains of the old Roman town. After the fall of the Roman Empire, Londinium was abandoned and a Saxon town named Lundenwic was established approximately one mile to the west in what is now Aldwych, in the 7th century. The old Roman city was then reoccupied during the late-9th or early-10th century. Westminster was once a distinct town, and has been the seat of the English royal court and government since the mediæval era. Eventually, Westminster and London grew together and formed the basis of London, becoming England's largest – though not capital – city (Winchester was the capital city of England until the 12th century). London has grown steadily over centuries, surrounding and making suburbs of neighbouring villages and towns, farmland, countryside, meadows and woodlands, spreading in every direction. From the 16th to the early-20th century, London flourished as the capital of the British Empire. In 1666, the Great Fire of London swept through and destroyed a large part of the City of London. Rebuilding took over 10 years, but London's growth accelerated in the 18th century, and, by the early-19th century, it was the largest city in the world. London's local government system struggled to cope with this rapid growth, especially in providing the city with adequate infrastructure. In 1855 the Metropolitan Board of Works was created to provide London with infrastructure to cope with its growth. In 1889 the MBW was abolished, and the County of London was created which was administered by the London County Council, the first elected London-wide administrative body. Probably the most significant changes to London in the last 100 years were as a result of the Blitz and other bombing by the German Luftwaffe that took place during World War II. The bombing killed over 30,000 Londoners and flattened large tracts of housing and other buildings across London. The rebuilding during the 1950s, 1960s and 1970s was characterised by a wide range of architectural styles and has resulted in a lack of unity in architecture that has become part of London's character. Until their 1997 ceasefire, London was regularly a target for IRA bombers seeking to pressurise the British government into negotiations with Sinn Féin on Northern Ireland. On 7 July 2005, there was a series of coordinated bomb attacks by Islamic extremist suicide bombers on three underground stations and a bus. The explosions came less than 24 hours after London was awarded the 2012 Summer Olympics and as the G-8 summit was underway in Gleneagles, Scotland. A series of explosions also took place on 21 July 2005; however, in the latter incident, there were no fatalities.

Modern London

2005 Today Greater London comprises the City of London and the 32 London boroughs (including the City of Westminster). 12 of these boroughs are defined as Inner London, the remaining 20 defined as Outer London. The dominant centre of activity in London is the City of Westminster (including the West End) which is the main cultural, entertainment and shopping district, the location of most of London's major corporate headquarters outside of the financial services sector, and the centre of the UK's national government. The City of London (also known as the "Square Mile") is at the centre of international finance, and is Europe’s main business centre. The headquarters of more than 100 of Europe’s 500 largest companies are all in London. The London foreign exchange market is the largest in the world, with an average daily turnover of $504 billion, more than the New York and Tokyo exchanges combined. While very busy during the working week, most parts of the City tend to be quiet at weekends, since it is primarily a non-residential area. London is one of the most visited cities on earth. Tourist attractions are located mainly in Central London, comprising the historic City of London; the West End with its many cinemas, bars, clubs, theatres, shops and restaurants; the City of Westminster with Westminster Abbey, the Royal palaces of Buckingham Palace, Clarence House etc., the Royal Borough of Kensington and Chelsea with its museums (the Science Museum, Natural History Museum, and Victoria and Albert Museum) and Hyde Park. Other important tourist attractions include St Paul's Cathedral, the National Gallery; the South Bank and Bankside areas of Southwark with the Globe Theatre and the Tate Modern; London Bridge, Tower Bridge, the Tower of London, and the Tate Britain on the Embankment; and the British Museum in Bloomsbury. There are many other places of interest across the city.

Culture

:Main article: Culture of London. London is an international centre of culture in all its forms - music, theatre, arts, museums, festivals and much more.

London Districts

See also: Inner London, Outer London.

Central London

City of London

Outer London]] The City of London is the principal financial district of the United Kingdom, and is one of the most important in the world. It is governed by the Corporation of London, an ancient body headed by the Lord Mayor of London. The City also has its own police force, the City of London police. Once dominated by the dome of St Paul's Cathedral, it is now home to many skyscrapers, including Tower 42 (formerly, and popularly still, known as the NatWest Tower) and 30 St Mary Axe (popularly known as the "Gherkin", built in 2003). The City has only a small (c. 7,000) resident population, but a daytime working population of more than 300,000. Its primacy as the chief financial district has been directly challenged in recent years by Canary Wharf in East London.

The West End

Canary Wharf.]] The West End is the most popular shopping and entertainment district in London. Trafalgar Square is the most prominent landmark. Oxford Street is one of the best-known shopping streets in the world. Running from Charing Cross Road in the east to Marble Arch in the west, via Oxford Circus where it crosses Regent Street, it is home to many large department stores and shops (Selfridges, John Lewis, Marks and Spencer). Tottenham Court Road runs north from the eastern end of Oxford Street towards the north of the city centre, and is best known for its plethora of hi-fi, computer and electronics stores. West of the City, Covent Garden is home to the Avenue of Stars, London's version of Hollywood's Walk of Fame. South of Oxford Street's eastern end is Soho, a network of small streets crowded with restaurants, pubs, clubs, smaller shops and boutiques, and theatres and cinemas, as well as media companies and film, advertising and post-production companies. Soho is also well known for its very lively club and bar scene, the notorious sex industry and as the major "gay quarter" of the city. Piccadilly is an elegant thoroughfare running from Piccadilly Circus in the east to Hyde Park Corner in the west. It is adjacent to Mayfair, and Green Park. Regent Street and Bond Street are important thoroughfares.

East London

East London saw much of London's early industrial development and much of it now is being extensively redeveloped as part of the Thames Gateway. It was also key to London's successful bid to host the 2012 Olympics, and is now scheduled to undergo extensive regeneration in the run-up to the games. This is the second time in modern history that East London has seen large-scale rebuilding: it took the full force of the Blitz in World War Two, with post-war reconstruction leaving a legacy of bleak housing estates and tower blocks in several areas.

The East End

tower block The East End of London is closest to the original Port of London, and tended for that reason to be the area of the city where immigrants arriving into the port would settle first. Successive waves of immigrants include the French, the Huguenots, Belgians, Jews, Gujaratis, Pakistanis, Bangladeshis and many other groups. The East End extends from the eastern side of the City of London and includes areas such as Whitechapel, Mile End, Bethnal Green, Hackney, Bow, Millwall and Poplar. The area has many places of interest including many of London's markets, (for example Columbia Road Flower Market, Spitalfields Market, Brick Lane Market, Petticoat Lane Market), and several museums, including the Geffrye Museum and the Museum of Childhood in Bethnal Green.

Docklands

Bethnal Green]] The London Docklands, on the Isle of Dogs along the Thames in the East End, has developed enormously since the early-1980s. For a period in the early-1980s, many warehouse buildings in Wapping had been occupied and used as artists studios and low-cost loft living spaces. This inevitably drew the attention of property developers who gradually (and then not so gradually) moved in to take over. The London Docklands Development Corporation (LDDC) was set up in 1981 to accelerate the process, and the first phases of major development started to reshape the area, culminating in Canary Wharf, whose best-known feature is the 1 Canada Square office tower (which is often incorrectly called "Canary Wharf"), which has been the UK's tallest skyscraper since 1991. A massive-scale development within the last three or four years has added a great many more skyscrapers, and many large businesses (investment banks, law firms, etc.) have moved in. A new headquarters for HSBC and Barclays as well as the European headquarters of Citigroup, have now been completed, and are in use. Attracted by this growth, restaurants, bars and nightclubs have opened, there are three interconnected shopping malls beneath the Canary Wharf structure, and a cinema complex has opened in the area. The Docklands Light Railway (DLR) serves the area, connecting to the London Underground at Bank, Shadwell, Canning Town and Stratford stations. There has also been a great deal of gentrification and residential development in the area: North of the Thames around Limehouse Basin and toward Wapping, as well as south of the Thames in Rotherhithe where former wharfs and the old docks have been converted into high-priced loft apartments for a community of bankers, software developers and others working in the financial service industries in and around Docklands. Further east in the London Borough of Newham are London City Airport and the ExCeL Exhibition Centre.

West London

West London includes many of the traditionally fashionable and expensive residential areas such as Notting Hill, made better known in 1999 by a film of the same name starring Hugh Grant and Julia Roberts. Within the district is the famous antique market at Portobello Road. Kensington and Chelsea are the most expensive places to live in the country. The area is also famous for the Kings Road, a distinguished and attractive shopping street and thoroughfare. Further to the west, at White City, near Shepherd's Bush, is the principal operating centre for the BBC, while in the extreme west, in the London Borough of Hillingdon, lies Heathrow Airport. Considered more south-west than West London on account of its being the only London borough to straddle the River Thames, Richmond upon Thames includes the attractive riverside districts of Richmond and Twickenham. This corner of London is home to Richmond Park, London's largest, and Twickenham, the home of English rugby union.

North London

North London includes suburbs such as Hampstead and Highgate, which retain a village atmosphere. North London is more hilly than the south, and many of the hills give excellent views across the city. Large parks include Hampstead Heath, which includes Parliament Hill, noted for its fine views over the city, and the Hampstead bathing ponds; and Alexandra Park, site of Alexandra Palace. Many areas have significant minority populations including Stamford Hill, home to a significant community of Orthodox Jews, the Green Lanes area of Harringay and the Finsbury Park area have large Turkish and Greek communities. Islington is considered one of the more affluent areas in London, due to large scale gentrification, although it is in fact one of the most deprived boroughs in the country; it is also home to Arsenal football club. North London's other world-famous football team, Tottenham Hotspur, play in nearby Tottenham.

South London

South London contains such diverse districts as Wimbledon (famous as the home of the major tennis Wimbledon Championships), Bermondsey, and Dulwich. Redevelopment of the Elephant and Castle, a road intersection and district close to the centre, is due to start in 2006. Greenwich is on the banks of the Thames where the river broadens into a wide meandering reach of muddy water. It is an historic neighbourhood and boasts a fine park and the Royal Greenwich Observatory. It is also has a popular market. Brixton, Camberwell and Peckham are home to many families (and their descendants) who immigrated to London from the West Indies during the 1950s, 1960s and 1970s, sometimes known as Afro-Caribbeans.

Demographics

Afro-Caribbeans London had about 860,000 people in 1801 (in comparison, Paris had about 670,000 in 1802), and the population of Edo (modern-day Tokyo, Japan), at the time the largest city in the world, has been estimated at 1 million to 1.25 million people. London was the most populous city in the world from 1825 until 1925, when it was overtaken by New York. Residents of London are known as Londoners. The city and the 32 boroughs (some 1,579 km² or 610 square miles) had an estimated 7,421,228 inhabitants in 2004, making London the most populous city in Europe alongside Moscow. Subsequent reviews suggested that the returns were understated, and that the population on Census Day was closer to 7.29 million. The official estimate of London's population in mid-2003 is 7,387,900 [http://www.statistics.gov.uk/statbase/Expodata/Spreadsheets/D8561.xls] In the 2001 census, 76% of these seven million people classed their ethnic group as white (classified as British White, Irish White or "Other White" in the 2001 census), 10% as Indian, Bangladeshi or Pakistani, 5% as black African, 5% as black Caribbean, 3% as mixed race and 1% as Chinese. The largest religious groupings are Christian (58.2%) and No Religion (15.8%). 21.8% of inhabitants were born outside the European Union. The Irish are the largest foreign-born group in London (numbering approximately 200,000). European Union] Unlike many other countries, the UK does not provide national metropolitan area population figures based on commuter percentages and economic influence. This is left up to each individual city to define. This has created much confusion when comparing London's true metropolitan area region with others around the world. It is helped even less by confusion of the term "Greater London" with the political entity of the City of London, which is often confused with the metropolitan area. Without a specific national reference to London's metropolitan area, many different sources provide alternate definitions. One widely regarded definition describes the London metropolitan area (6,267 square miles, 16,043 km²) with a population of 13,945,000 — larger than the combined populations of Scotland, Wales and Northern Ireland. (External references: [http://www.demographia.com/dm-lonarea.htm], [http://www.lbwf.gov.uk/demography/census/london/london_boroughs_census2001.pdf]) If this definition is followed, then London is the largest metropolitan area of Europe, along with Moscow (whose metropolitan area has somewhere around 14 million people), and above Paris (11.5 million people in the metropolitan area in 2004). In 2004, the Greater London Authority defined a metropolitan region centred on London with a population of 18 million. This region extends to cover the commuter belt, and much of South East England and East of England, for example including the cities of Brighton and Oxford. (External references:[http://www.london.gov.uk/mayor/strategies/sds/london_plan/lon_plan_all.pdf],[http://www.london.gov.uk/mayor/strategies/sds/london_plan/lon_plan_1.pdf],[http://www.london.gov.uk/mayor/strategies/sds/draft_london_plan/dlp_ch1.pdf])

Government

Greater London Authority meets here]] Greater London is divided into the 32 London boroughs and the City of London. The boroughs are the most important unit of local government in London, and are responsible for running most local services in their respective areas. The City of London is run not by a conventional local authority, but by the historical Corporation of London. The Greater London Authority (GLA) is the London-wide body responsible for co-ordinating the boroughs, strategic planning, and running some London-wide services such as policing, the fire service and transport. The GLA consists of the Mayor of London and the London Assembly. The mayor is elected by the Supplementary Vote system while the assembly is elected by the Additional Member System. The incumbent Mayor of London, Ken Livingstone, was elected as an independent candidate in the 2000 election. Despite opposition from all the main political parties and the press, his popularity with Londoners has remained high. Livingstone was expelled from the Labour Party when he opposed the official Labour candidate Frank Dobson in the 2000 Mayoral election. Readmitted by that party in 2004, he was re-elected as Mayor as an official Labour candidate in the election later that year. The GLA was created in 2000 as a replacement body for the former Greater London Council (GLC) which was created in 1965 and abolished in 1986 after political disputes between the GLC (then led by Ken Livingstone) and the Conservative government of Margaret Thatcher. Previous London wide administrative bodies were the Metropolitan Board of Works (MBW) from 1855 to 1889; the London County Council (LCC) from 1889 to 1965; and the Greater London Council (GLC) from 1965 to 1986. When the GLC was abolished, most of its functions were devolved to the London boroughs, while others were taken over by joint-boards or other unelected bodies. The boroughs thus enjoyed "unitary status" and a degree of autonomy when the GLC was abolished, and although losing some powers which have been repatriated to the GLA they still retain many areas they did not control under the GLC. London is represented in Parliament by 74 MPs. For a list of London constituencies see List of Parliamentary constituencies in Greater London. The territorial police force for the 32 London boroughs is the Metropolitan Police Service, more commonly referred to as the Metropolitan Police, or simply "the Met". The City of London has its own police force, the City of London Police. Health services in London are managed by the national government via the National Health Service (NHS). Greater London is divided into five Strategic Health Authorities [http://www.nhs.uk/england/authoritiestrusts/sha/MapSearch.aspx?rg=Y21].

Transport and infrastructure

For main article see Transport and infrastructure in London Transport and infrastructure in London Transport is one of the four areas of policy administered by the Mayor of London, but the mayor's financial control is limited. The executive agency which runs London's transport system is Transport for London (TfL). The public transport network is one of the most extensive in the world, but faces congestion and reliability issues. The network is one of the most complex transit systems in the world with just over 1 billion journeys used every year on the underground alone. London is most famous for its AEC Routemaster buses which have been in service in the capital since 1956. Routemasters will be phased out of service from TfL's main bus routes, with the last routemaster service being operated on the 9 December 2005 on Route 159. Two 'heritage' routes are planned for service to maintain Routemasters on London's streets. 2005]] The networks for transport in London include: Underground (commonly known as the tube); Bus; River Services; Docklands Light Railway (DLR); Croydon Tramlink; National Rail; Thameslink. As of mid-2005, in preparation for the 2012 London Olympic Games a total of £7 billion ($12 billion) will be spent on refurbishment and expansion of city links, mainly on the London Underground. Although the main reason for this is because of the increased traffic flow that will be caused by the 2012 Olympics, the work would still be completed if London had not won the games. By 2013 a new service called Crossrail is due to be opened. Also in planning is the Cross River Tram (CRT). It will depart in the south suburbs, cross the River Thames, through to the City of London (the financial district), and continue its journey to the northern suburbs. It is speculated that it will be the world's longest tram. The main Olympic arenas will be sited close to Stratford International station, which is currently being constructed as part of the Channel Tunnel Rail Link. The new high-speed line, due to open in 2007, will be used by the regular 'Olympic Javelin' service with a journey time of 7 minutes between Stratford and St Pancras. This service was a key part of the Olympic bid and will provide access from northern areas of the UK via King's Cross and Euston.
Education
Main Article: Education in London London is home to a diverse number of universities, colleges and schools, and is a leading centre of research and development. This includes prominemnt universities such as Imperial College, London and the London School of Economics

Media

The British media is concentrated in London and is sometimes accused of having a "London bias". All the major television networks are headquartered in London including the BBC, which remains one of the world's most influential media organisations. Partly to counter complaints about London bias, the BBC announced in June 2004 that some departments (BBC Sport, CBBC, Cbeebies, BBC Three and BBC Radio Five Live) are to be relocated to Manchester. Other major networks include ITV, Channel 4, Five and BSkyB - all based in London. Like the BBC, these produce some programmes elsewhere in the UK, but London is their main production centre. There is a huge choice of radio stations available in London. Local city-wide stations include music-based stations such as Capital FM, Heart 106.2 and Kiss 100 and popular news/talk stations include BBC London, LBC 97.3 and LBC News 1152. The London newspaper market is dominated by national newspapers, all of which are edited in London. Until the 1970s, most of the national newspapers were concentrated in Fleet Street, but in the 1980s they relocated to new premises with automated printing works. Most of these are in East London, most famously the News International plant at Wapping. The move was resisted strongly by the printing trade union SOGAT 82, and strike action at Wapping in 1986 led to violent skirmishes. The last major news agency in Fleet Street, Reuters, moved to Canary Wharf in 2005, but Fleet Street is still commonly used as a collective term for the national press. Regional Editions of most national newspapers are available, including editions for northern England, Scotland and Wales. London has three daily newspaper titles - the popular Evening Standard, plus two free titles, Metro and Standard Lite (published by the Evening Standard) which are distributed every morning at London tube and railway stations. The independent weekly listings guide Time Out Magazine has been providing concert, film, theatre and arts information since 1968. London is at the centre of British film and television production industries, with major studio facilities on the western fringes of the conurbation and a large post-production industry centred in Soho. London is one of the two leading centres of English-language publishing alongside New York. Globally important media companies based in London range from publishing group Pearson, to the information agency Reuters, to the world's number two advertising business WPP Group. There are a vast number of local newspapers in the London area, often covering a small section of the vast city.

Religion

local newspapers When Pope Gregory the Great sent St. Augustine to bring England into the Catholic fold in 597, it was intended that the envoy should become "Archbishop of London", as the city was remembered as the capital of Roman Britain. In the event, the saint received his most hospitable reception in the Kingdom of Kent, and the archiepiscopal see was founded at Canterbury. Nonetheless London has been at the centre of England's religious life for much of its history, and each Archbishop of Canterbury has traditionally spent much of his time in London, where he has an official residence at Lambeth Palace. London's two Anglican bishops are the Bishop of London, whose see is London north of the Thames, and whose throne is in London's grandest church, the baroque St Paul's Cathedral (designed by Sir Christopher Wren), and the Bishop of Southwark, who tends to Anglicans south of the river. Important national and royal ceremonies are divided between St Paul's and Westminster Abbey, a gothic church on the scale of a cathedral. As in the rest of the UK, religious attendance in London is low, and the Church of England has borne the brunt of this decline. The Roman Catholic Archbishop of Westminster is generally regarded as the leader of the Catholic Church in England and Wales. Other traditional Protestant denominations whose headquarters are in London include the United Reformed Church and the Quakers. Many of Lo

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