An office is generally a room or other area where administrative work is done, but may also denote a position within an organization with specific duties attached to it (see officer, office-holder, official); the latter is in fact an earlier usage, office as place originally referring to the location of one's duty. When used as an adjective, the term "office" may refer to business-related tasks. In legal writing, a company or organization has offices in any place that it has an official presence, even if that presence consists of, for example, a storage silo rather than an office. An office is an architectural and design phenomenon; whether it is a small office such as a bench in the corner of a small business of extremely small size (see small office/home office), through entire floors of buildings, up to and including massive buildings dedicated entirely to one company. In modern terms an office usually refers to the location where white-collar workers are employed. As per James Stephenson,"Office is that part of business enterprise which is devoted to the direction and co-ordination of its various activities."

Offices in classical antiquity were often part of a palace complex or a large temple. The High Middle Ages (1000â€"1300) saw the rise of the medieval chancery, which was usually the place where most government letters were written and where laws were copied in the administration of a kingdom. With the growth of large, complex organizations in the 18th century, the first purpose-built office spaces were constructed. As the Industrial Revolution intensified in the 18th and 19th centuries, the industries of banking, rail, insurance, retail, petroleum, and telegraphy dramatically grew, and a large number of clerks were needed, and as a result more office space was required to house these activities. The time and motion study, pioneered in manufacturing by F. W. Taylor led to the “Modern Efficiency Desk” with a flat top and drawers below, designed to allow managers an easy view of the workers. However, by the midpoint of the 20th century, it became apparent that an efficient office required discretion in the control of privacy, and gradually the cubicle system evolved.

The main purpose of an office environment is to support its occupants in performing their job. Work spaces in an office are typically used for conventional office activities such as reading, writing and computer work. There are nine generic types of work space, each supporting different activities. In addition to individual cubicles, there are also meeting rooms, lounges, and spaces for support activities, such as photocopying and filing. Some offices also have a kitchen area where workers can make their lunches. There are many different ways of arranging the space in an office and whilst these vary according to function, managerial fashions and the culture of specific companies can be even more important. While offices can be built in almost any location and in almost any building, some modern requirements for offices make this more difficult, such as requirements for light, networking, and security. The primary purpose of an office building is to provide a workplace and working environment primarily for administrative and managerial workers. These workers usually occupy set areas within the office building, and usually are provided with desks, PCs and other equipment they may need within these areas.

History

The structure and shape of the office is impacted by both management thought as well as construction materials and may or may not have walls or barriers. The word stems from the Latin officium, and its equivalents in various, mainly romance, languages. An officium was not necessarily a place, but rather an often mobile 'bureau' in the sense of a human staff or even the abstract notion of a formal position, such as a magistrature. The relatively elaborate Roman bureaucracy would not be equaled for centuries in the West after the fall of Rome, even partially reverting to illiteracy, while the East preserved a more sophisticated administrative culture, both under Byzantium and under Islam.

Offices in classical antiquity were often part of a palace complex or a large temple. There was usually a room where scrolls were kept and scribes did their work. Ancient texts mentioning the work of scribes allude to the existence of such "offices". These rooms are sometimes called "libraries" by some archaeologists and the general press because one often associates scrolls with literature. In fact they were true offices since the scrolls were meant for record keeping and other management functions such as treaties and edicts, and not for writing or keeping poetry or other works of fiction.

Middle Ages

The High Middle Ages (1000â€"1300) saw the rise of the medieval chancery, which was usually the place where most government letters were written and where laws were copied in the administration of a kingdom. The rooms of the chancery often had walls full of pigeonholes, constructed to hold rolled up pieces of parchment for safekeeping or ready reference, a precursor to the book shelf. The introduction of printing during the Renaissance did not change these early government offices much.

Medieval illustrations, such as paintings or tapestries, often show people in their private offices handling record-keeping books or writing on scrolls of parchment. All kinds of writings seemed to be mixed in these early forms of offices. Before the invention of the printing press and its distribution there was often a very thin line between a private office and a private library since books were read or written in the same space at the same desk or table, and general accounting and personal or private letters were also done there.

It was during the 13th century that the English form of the word first appeared when referring to a position involving duties (ex. the office of the ...). Geoffrey Chaucer appears to have first used the word in 1395 to mean a place where business is transacted in The Canterbury Tales.

As mercantilism became the dominant economic theory of the Renaissance, merchants tended to conduct their business in the same buildings, which might include retail sales, warehousing and clerical work. During the 15th century, population density in many cities reached the point where stand-alone buildings were used by merchants to conduct their business, and there was a developing a distinction between church, government/military and commerce uses for buildings.

Emergence of the modern office

With the growth of large, complex organizations such as the Royal Navy and the East India Company in the 18th century, the first purpose-built office spaces were constructed. The Old Admiralty (Ripley Building) was built in 1726 as a three storey U-shaped brick building and was the first purpose built office building in Great Britain. As well as offices, the building housed a board room and apartments for the Lords of the Admiralty. In the 1770s, many scattered offices for the Royal Navy were gathered into Somerset House, the first block purpose-built for office work.

The East India House was built in 1729 on Leadenhall Street as the headquarters from which the East India Company administered its Indian colonial possessions. The Company developed a very complex bureaucracy for the task, which required thousands of office employees to process the necessary paperwork. The Company recognized the benefits of centralized administration, and required that all workers sign in and out at the central office, daily.

As the Industrial Revolution intensified in the 18th and 19th centuries, the industries of banking, rail, insurance, retail, petroleum, and telegraphy dramatically grew in size and complexity. To transact business, an increasing large number of clerks were needed to handle order-processing, accounting, and document filing, with increasingly specialized office space required to house these activities. Most of the desks of the era were top heavy with paper storage bins extending above the desk-work area, giving the appearance of a cubicle and offering the workers some degree of privacy.

The relatively high price of land in the central core of cities lead to the first multi-story buildings, which were limited to about 10 stories until the use of iron and steel allowed for higher structures. The first purpose-built office block was the Brunswick Building, built in Liverpool in 1841. The invention of the safety elevator in 1852 by Elisha Otis saw the rapid escalation upward of buildings. By the end of the 19th century, larger office buildings frequently contained large glass atriums to allow light into the complex and improve air circulation.

20th century

By 1906, Sears, Roebuck and Co had opened their mail order and headquarters operation in a 3,000,000-square-foot (280,000 m²) building in Chicago, at the time the largest building in the world. The time and motion study, pioneered in manufacturing by F. W. Taylor and later applied to the office environment by Frank and Lillian Gilbreth, led to the idea that managers needed to play an active role in directing the work of subordinates in order to increase the efficiency of the workplace. F.W. Taylor advocated the use of large, open floor plans, and desks that faced supervisors. As a result, in 1915, the Equitable Life Insurance Company in New York City introduced the “Modern Efficiency Desk” with a flat top and drawers below, designed to allow managers an easy view of the workers. This led to a demand for a large square footages per floor in buildings, and a return to the open spaces that were seen in preâ€"industrial revolution buildings.

However, by the midpoint of the 20th century, it became apparent that an efficient office required discretion in the control of privacy, which is needed to combat tedium linked to poor productivity, and to encourage creativity. In 1964, the Herman Miller (office equipment) company engaged Robert Propst, a prolific industrial designer, who came up with the concept of the Action Office which later evolved into the cubicle office furniture system.

Japan 20th century office

Japanese businesses have set themselves apart from their American counterparts by implementing different techniques in the way they handle business. The Japanese office layout improves work productivity, harmony in the office, and holds every employee accountable for the work they produce. The type of office layout used in Japan is called an open plan, and relies on ergonomics to help make employees as productive as possible. The Japanese open office layout allows them to use an organizational structure known as the horizontal structure. In the typical Japanese office there are no walls dividing desks, no cubicles, and no individual offices. Also they are able to implement policies using the ringi-sho consensus.

In order to get group members to work effectively in the open office floor plan the use of island style desks are used. The most dominant feature of the Japanese island style office layout is that each group forms an island. Kageyu Noro, Goroh Fujimaki & Shinsuke Kishi, researches of ergonomics in the work place, stated,” Japanese offices have traditionally adhered to island layouts because these reflect the Japanese style of teamwork and top-down style of management.” The group leader will then sit at the prominent position and ensure productivity.

The group leader will assign a task to the group, and each member of the group then receives their individual task to complete. Island style seating also gives the group the benefit of being able to speak to one another at any time, and ask for help if needed. Being in such close proximity to one another in the office gives another advantage to the supervisor in that he can call an uchi-awase. Uchi-awase is an informal meeting in order to get an important message across, and also allows all members of the team to be creative in the office. “The open office layout allows for this because there are hardly any independent rooms or enclosures. If the supervisor stands at his desk he can glance at his associates and easily call them over.”, according to Durlabhji, Subhash, Norton E. Marks, and Scott Roach, authors of Japanese Business Cultural Perspective. Once all individual tasks are complete the group then combines each person’s work and the project is the put together as a wh ole and returned to the supervisor. The work is viewed as a team effort and that each member of the group receives equal credit for being part of a team completing the goal assigned. The group itself holds each member accountable for ensuring that the work is getting done, and that no one individual is doing more work than another. Another motivating factor is that the groups boss is also seated at the same desk, and the effect that this has on the individuals is that they must work hard just like the boss. The role of having an open lay out with island type seating allows the office to be structured so the employees are put together as teams.

The type of organizational structure found within the Japanese office is known as a horizontal structure. According to Andrew, Ghillyer, author of Management Now,” Horizontal structure is an organization structure consisting of two groups: the first composed of senior management responsible for strategic decisions and policies and the second composed of empowered employees working together in different process teams; also known as a team structure.” The benefit of using this type of structure is that hierarchy is flattened to reduce supervision, teams are able to self-manage, team performance, not just the individual is rewarded, and training is highly emphasized amongst all employees. With the heightened sense of empowerment and responsibility workers are motivated to complete objectives in a timely manner. Having the office structured horizontally allows for the easy communication of introducing new policies and ideas amongst the groups.

“Ringisho” refers to the concept of submitting proposals and making decisions off those ideas. By unifying everyone together in the Japanese office it helps to make better informed decisions on policies of the company that all managers and employees have input on. The idea behind this is to get a hold of various thinking individuals to see if there is a good way in writing their policies that come to benefit the company better. Richard Lewis, author of When Cultures Collide, states “Suggestions, ideas and inventions make their way up the company hierarchy by a process of collecting signatures among workers and middle managers. Many people are involved. Top executives take the final step in ratifying items that have won sufficient approval.” With this system in place changes to policies are only passed if there is an overall consensus to pass it. Allowing each group to have a say on which policies should be implemented improves overall job satisfaction and harmony throughou t the office.

The way Japanese offices are structured allow them to be more efficient when conducting business. The efficiency at which they operate has been noticed by such companies General Motors, Ford, Motorola, and Chrysler Company. They continue to look for other ways to be more efficient and productive with the office layout and employee productivity.

Office spaces

The main purpose of an office environment is to support its occupants in performing their jobâ€"preferably at minimum cost and to maximum satisfaction. With different people performing different tasks and activities, however, it is not always easy to select the right office spaces. To aid decision-making in workplace and office design, one can distinguish three different types of office spaces: work spaces, meeting spaces and support spaces. For new, or developing businesses, remote satellite offices and project rooms, Serviced Offices can provide a simple solution and provide all of the former types of space.

Work spaces

Work spaces in an office are typically used for conventional office activities such as reading, writing and computer work. There are nine generic types of work space, each supporting different activities.

Open office: An open work space for more than ten people, suitable for activities which demand frequent communication or routine activities which need relatively little concentration

Team space: A semi-enclosed work space for two to eight people; suitable for teamwork which demands frequent internal communication and a medium level of concentration

Cubicle: A semi-enclosed work space for one person, suitable for activities which demand medium concentration and medium interaction

Private office: An enclosed work space for one person, suitable for activities which are confidential, demand a lot of concentration or include many small meetings

Shared office: An enclosed work space for two or three people, suitable for semi-concentrated work and collaborative work in small groups

Team room: An enclosed work space for four to ten people; suitable for teamwork which may be confidential and demands frequent internal communication

Study booth: An enclosed work space for one person; suitable for short-term activities which demand concentration or confidentiality

Work lounge: A lounge-like work space for two to six people; suitable for short-term activities which demand collaboration and/or allow impromptu interaction

Touch down: An open work space for one person; suitable for short-term activities which require little concentration and low interaction

Meeting spaces

Meeting spaces in an office typically use interactive processes, be it quick conversations or intensive brainstorms. There are six generic types of meeting space, each supporting different activities.

Small meeting room: An enclosed meeting space for two to four persons, suitable for both formal and informal interaction

Large meeting room: An enclosed meeting space for five to twelve people, suitable for formal interaction

Small meeting space: An open or semi-open meeting space for two to four persons; suitable for short, informal interaction

Large meeting space: An open or semi-open meeting space for five to twelve people; suitable for short, informal interaction

Brainstorm room: An enclosed meeting space for five to twelve people; suitable for brainstorming sessions and workshops

Meeting point: An open meeting point for two to four persons; suitable for ad hoc, informal meetings

Support spaces

Support spaces in an office are typically used for secondary activities such as filing documents or taking a break. There are twelve generic types of support space, each supporting different activities.

Filing space: An open or enclosed support space for the storage of frequently used files and documents

Storage space: An open or enclosed support space for the storage of commonly used office supplies

Print and copy area: An open or enclosed support space with facilities for printing, scanning and copying

Mail area: An open or semi-open support space where employees can pick up or deliver their personal mail

Pantry area: An open or enclosed support space where people can get coffee and tea as well as soft drinks and snacks

Break area: A semi-open or enclosed support space where employees can take a break from their work

Locker area: An open or semi-open support space where employees can store their personal belongings

Smoking room: An enclosed support space where employees can smoke a cigarette

Library: A semi-open or enclosed support space for reading of books, journals and magazines

Games room: An enclosed support space where employees can play games (e.g. computer games, pool, darts)

Waiting area: An open or semi-open support space where visitors can be received and can wait for their appointment

Circulation space: Support space which is required for circulation on office floors, linking all major functions

Office structure

There are many different ways of arranging the space in an office and whilst these vary according to function, managerial fashions and the culture of specific companies can be even more important. Choices include, how many people will work within the same room. At one extreme, each individual worker will have their own room; at the other extreme a large open plan office can be made up of one main room with tens or hundreds of people working in the same space. Open plan offices put multiple workers together in the same space, and some studies have shown that they can improve short term productivity, i.e. within a single software project. At the same time, the loss of privacy and security can increase the incidence of theft and loss of company secrets. A type of compromise between open plan and individual rooms is provided by the cubicle desk, possibly made most famous by the Dilbert cartoon series, which solves visual privacy to some extent, but often fails on acoustic separ ation and security. Most cubicles also require the occupant to sit with their back towards anyone who might be approaching; workers in walled offices almost always try to position their normal work seats and desks so that they can see someone entering, and in some instances, install tiny mirrors on things such as computer monitors.

Office buildings

While offices can be built in almost any location and in almost any building, some modern requirements for offices make this more difficult. These requirements can be both legal (e.g. light levels must be sufficient) or technical (e.g. requirements for computer networking). Alongside, other requirements such as security and flexibility of layout, has led to the creation of special buildings which are dedicated only or primarily for use as offices. An office building, also known as an office block or business center is a form of commercial building which contains spaces mainly designed to be used for offices.

The primary purpose of an office building is to provide a workplace and working environment primarily for administrative and managerial workers. These workers usually occupy set areas within the office building, and usually are provided with desks, PCs and other equipment they may need within these areas.

An office building will be divided into sections for different companies or may be dedicated to one company. In either case, each company will typically have a reception area, one or several meeting rooms, singular or open-plan offices, as well as toilets.

Many office buildings also have kitchen facilities and a staff room, where workers can have lunch or take a short break. Many office spaces are now also serviced office spaces, which means that those occupying a space or building can share facilities.

Need to mention all building names with company details

Office and retail rental rates

Rental rates for office and retail space are typically quoted in terms of money per floor-areaâ€"time, usually money per floor-area per year or month. For example, the rate for a particular property may be $29 per square-foot per year ($29/s.f/yr) - $290 per square-meterâ€"year ($290/m²/a), and rates in the area could range $20â€"$50/s.f./yr ($200â€"$500/m²Â·a).

In many countries, rent is typically paid monthly even if usually discussed in terms of years.

Examples:

• A particular 2,000 s.f. space is priced at $15/s.f./yr = (2,000 s.f.) × ($15/s.f./a) / (12 mo/yr) = $2500/month
• A 200 m² space priced at $150/m²Â·a = (200 m²) × ($150/m²Â·a) / (12 mo/a) = $2500/month

In a gross lease, the rate quoted is an all-inclusive rate. One pays a set amount of rent per time and the landlord is responsible for all other expenses such as costs of utilities, taxes, insurance, maintenance, and repairs.

The triple net lease is one in which the tenant is liable for a share of various expenses such as property taxes, insurance, maintenance, utilities, climate control, repairs, janitorial services and landscaping.

Office rents in the United States are still recovering from the high vacancy rates that occurred in the wake of the 2008 depression.

Grading

The Building Owners and Managers Association (BOMA) classifies office space into three categories: Class A, Class B, and Class C. According to BOMA, Class A office buildings have the "most prestigious buildings competing for premier office users with rents above average for the area". BOMA states that Class A facilities have "high quality standard finishes, state of the art systems, exceptional accessibility and a definite market presence". BOMA describes Class B office buildings as those that compete "for a wide range of users with rents in the average range for the area". BOMA states that Class B buildings have "adequate systems" and finishes that "are fair to good for the area", but that the buildings do not compete with Class A buildings for the same prices. According to BOMA Class C buildings are aimed towards "tenants requiring functional space at rents below the average for the area". The lack of specifics allows considerable room for "fudging" the boundaries of the categor ies. Oftentimes, the above categories are further modified by adding the plus or minus sign to create subclasses, such as Class A+ or Class B-.

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Herman Miller, Inc., based in Zeeland, Michigan, is a major American manufacturer of office furniture, equipment and home furnishings. It is notable as one of the first companies to produce modern furniture and, under the guidance of Design Director George Nelson, is likely the most prolific and influential producer of furniture of the modernist style. Among classic Herman Miller products are the Equa chair, Aeron chair, Noguchi table, Marshmallow sofa, and the Eames Lounge Chair. Herman Miller is credited with the invention of the office cubicle (originally known as th e "Action Office II") in 1968 under then-director of research Robert Propst. Herman Miller holds a unique position among furniture manufacturers for having cultivated the talents of a large number of modernist designers, producing a significant number of pieces that are now considered icons of industrial design.

History

Herman Miller was founded in 1905 as the Star Furniture Co. in Zeeland, Michigan. Initially the company produced high quality furniture, especially bedroom suites, in historic revival styles. In 1909, Dirk Jan De Pree began working for the company as a clerk, and became its president by 1919, when it was renamed The Michigan Star Furniture Co. De Pree and his father-in-law, Herman Miller, purchased 51% of the company stock in 1923 and renamed it the Herman Miller Furniture Company. It became Herman Miller, Inc. in 1960.

Until 1930, the company produced only traditional wood furniture. With the coming of the Great Depression the company was forced to explore new products to survive in a shrinking market and reluctantly hired Gilbert Rohde, a designer who specialized in modernist designs. Rohde turned the company in a totally new direction and in 1933, Herman Miller debuted a line of modern furniture at the Century of Progress exposition in Chicago, Illinois. In 1941, the company opened a showroom in the Merchandise Mart in Chicago, and another in New York City. Under Rohde's supervision Herman Miller entered the contract (office) furniture market in 1942, with the introduction of the "Modular Executive Office" Group (EOG), the first in a long line of office furnishings to be produced by the company. Rohde died in 1944 and was replaced by architect George Nelson, who joined the firm as director of design in 1945. Over the next four decades Nelson was to have an enormous influence upon Herman Miller , not only for his personal design contributions, but also for the talented designers he recruited to its ranks, including; Isamu Noguchi, Charles and Ray Eames, Robert Propst, and textile designer Alexander Girard. Beginning in the late 1940s, the period under Nelson's guidance saw Herman Miller produce some of the world's most iconic pieces of modern furniture, including the Noguchi table, Eames Lounge Chair, Marshmallow sofa, Ball clock (actually produced by Howard Miller Clock Company), and the Sling sofa.

Dirk Jan De Pree continued to serve as Herman Miller CEO until 1961, when he was forced by illness to step-down. He was succeeded by his son, Hugh De Pree. Hugh served as company CEO until the mid-1980s, when he was succeeded by his brother Max De Pree, who held the position until 1990.

In 1961, Herman Miller added the Herman Miller Research Division, based in Ann Arbor, Michigan. This division developed the "Action Office" line in 1964 under the supervision of Robert Propst and with the design assistance of George Nelson's New York design studio,. Though the initial line, known as "Action Office I", was not a success, it led Propst to develop the "Action Office II" line, which introduced the "Office cubicle". The impact of "Action Office II" on the workplace cannot be overstated, as it revolutionized the office environment. In 1978, "Action Office II" was renamed simply Action Office. Herman Miller's line of "Action Office" products has generated sales of over $5 billion to date.

George Nelson's influence at Herman Miller gradually declined during the 1970s and new designers joined the company, including Don Chadwick and Bill Stumpf, who co-designed the Equa chair, and in the 1990s developed the highly successful Aeron chair. In 1981 Herman Miller started to work with the Italian designer Clino T. Castelli on the process of designing physical environments: a so-called Design Primario including CMF Design and Ethospace design concept. Designer Tom Newhouse introduced the "Newhouse group" of free-standing furniture in 1987 and assisted with the "Ethospace" wall panel system for the "Action Office" line. Ray Wilkes designed the "Modular Seating Group", popularly known as the Chicklet Chairs.

Artist Stephen Frykholm is also noted for his contributions to Herman Miller. From 1970 to 1989 Frykholm produced a series of posters for Herman Miller's annual summer picnics, some of which are in the permanent collections of the Museum of Modern Art, and remain highly sought-after art prints.

In July 2014, Herman Miller announced it had reached an agreement to purchase the contemporary retailer Design Within Reach (DWR) for $154 million in a bid to establish itself as a “premier lifestyle brand.”

Workplace

Herman Miller is consistently recognized as one of Fortune Magazine's "Most Admired Companies", having placed at the top of the list for Furniture companies for the past 18 consecutive years.

According to CNN Money, as of March 2011, Herman Miller is ranked as the second most admired company in the Home Equipment, Furnishing division. They also scored first in Innovation, People Management, Use of Corporate Assets, Social Responsibility, and Quality of Products/Services. In Quality of Management they scored second place, third in Long Term Investments, fourth in Financial Soundness, and ninth in Global Competitiveness.

In March 2008, they settled an antitrust lawsuit with the states of New York, Michigan, and Illinois for $750,000. The lawsuit focused on Herman Miller's use of a suggested retail pricing policy, which was found to be within the bounds of the law. Today, many companies employ such policies to avoid price erosion in the internet channel.

Sustainability

Herman Miller has engaged in a number of initiatives to promote sustainability, and many of them have had cost-saving implications for the company. The company has developed a technique of mixing sawdust with chicken manure to produce topsoil. The company also uses a database to track every chemical in each product used by the company, in order to eliminate harmful chemicals from their products. Management of the company has expressed concerns about global warming, and the company was using 27% renewable energy as of 2007. The company also issues a sustainability report.

Herman Miller's driving sustainability initiatives is its "Perfect Vision" goal. This is a broad initiative that sets significant targets for the year 2020. These targets include zero landfill, zero hazardous waste generation, zero air emissions (VOC), zero process water use, 100 percent green electrical energy use, company buildings constructed to a minimum LEED Silver certification, and 100 percent of sales from DfE-approved products.

Many of Herman Miller's products are designed to be ecologically sound, and many are good examples of ecodesign techniques for achieving sustainability include saving materials, energy efficient manufacturing, recycled content, and recyclable content, including design for disassembly. The design process also utilizes life cycle assessment.

Herman Miller helped fund the start of the United States Green Building Council, and hired architect William McDonough + Partners to design a factory incorporating green design principles. The building is known as the Greenhouse and is an example of green building. The building won the following awards:

• AIA Committee on the Environment Top Ten Environmental Buildings, 1997
• Business Week/Architectural Record Good Design Is Good Business Award, 1997
• AIA Central Virginia Honor Award, 1998
• International Development Research Council, Award for Distinguished Service in Environmental Planning, 1995

Notable products

Seating

• Aeron Chair: Designed by Bill Stumpf and Don Chadwick in 1994.
• Eames Aluminum Group Chairs: Designed by Charles and Ray Eames in 1958.
• Eames Lounge Chair and Ottoman: Designed by Charles and Ray Eames in 1956.
• Eames Lounge Chair Wood: Designed by Charles and Ray Eames in 1946.
• Marshmallow sofa: Designed by Irving Harper in 1954.
• Mirra Chair: Designed by Studio 7.5 in 2003.

Tables/desks

• Noguchi table: Designed by Isamu Noguchi in 1948.

References

External links

• Official Herman Miller company website
• CNN'.com: "Cubicles: The great mistake"
• Youtube.com: "Comments on Herman Miller" â€" by designer Yves Béhar.

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Multi is a shortened form of "multiple". It may refer to:

• Alternate character in online gaming
• Multi 2 diamonds, a contract bridge convention
• Multirhyme, a synonym for feminine rhyme used in hip hop music
• Multi (To Heart), a character from the visual novel and anime series To Heart
• Multi-touch display

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Dentistry is a branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, commonly in the dentition but also the oral mucosa, and of adjacent and related structures and tissues, particularly in the maxillofacial (jaw and facial) area. Although primarily associated with teeth among the general public, the field of dentistry or dental medicine is not limited to teeth but includes other aspects of the craniofacial complex including the temperomandibular and other supporting structures. The term dentistry comes from odontology (from Ancient Greek ὀδούς (odoús, "tooth")) â€" the study of the structure, development, and abnormal ities of the teeth. Because of their substantial overlap in concept, dentistry is often also understood to subsume the now largely defunct medical specialty of stomatology (the study of the mouth and its disorders and diseases) for which reason the two terms are used interchangeably in certain regions.

Dentistry is important to one's overall health. Dental treatments are carried out by the dental team, which often consists of a dentist and dental auxiliaries (dental assistants, dental hygienists, dental technicians, as well as dental therapists). Most dentists either work in private practices (primary care), dental hospitals or (secondary care) institutions (prisons, armed forces bases, etc.).

The history of dentistry is almost as ancient as the history of humanity and civilization with the earliest evidence dating from 7000 BC. Remains from the early Harappan periods of the Indus Valley Civilization (c. 3300 BC) show evidence of teeth having been drilled dating back 9,000 years. It is thought that dental surgery was the first specialization from medicine.

Dental treatment

Dentistry usually encompasses very important practices related to the oral cavity. Oral diseases are major public health problems due to their high incidence and prevalence across the globe with the disadvantaged affected more than other socio-economic groups.

The majority of dental treatments are carried out to prevent or treat the two most common oral diseases which are dental caries (tooth decay) and periodontal disease (gum disease or pyorrhea). Common treatments involve the restoration of teeth, extraction or surgical removal of teeth, scaling and root planing and endodontic root canal treatment.

All dentists in the United States undergo at least three years of undergraduate studies, but nearly all complete a bachelor's degree. This schooling is followed by four years of dental school to qualify as a "Doctor of Dental Surgery" (DDS) or "Doctor of Dental Medicine" (DMD). Dentists need to complete additional qualifications or continuing education to carry out more complex treatments such as sedation, oral and maxillofacial surgery, and dental implants.

By nature of their general training they can carry out the majority of dental treatments such as restorative (fillings, crowns, bridges), prosthetic (dentures), endodontic (root canal) therapy, periodontal (gum) therapy, and extraction of teeth, as well as performing examinations, radiographs (x-rays) and diagnosis. Dentists can also prescribe medications such as antibiotics, sedatives, and any other drugs used in patient management.

Dentists also encourage prevention of oral diseases through proper hygiene and regular, twice yearly, checkups for professional cleaning and evaluation. Conditions in the oral cavity may be indicative of systemic diseases such as osteoporosis, diabetes, or cancer. Many studies have also shown that gum disease is associated with an increased risk of diabetes, heart disease, and preterm birth. The concept that oral health can affect systemic health and disease is referred to as "oral-systemic health".

Education and licensing

Dr. John M. Harris started the world's first dental school in Bainbridge, Ohio, and helped to establish dentistry as a health profession. It opened on 21 February 1828, and today is a dental museum. The first dental college, Baltimore College of Dental Surgery, opened in Baltimore, Maryland, USA in 1840. The second in the United States was the Philadelphia College of Dental Surgery, established in 1852. In 1907, Temple University accepted a bid to incorporate the school.

Studies showed that dentists graduated from different countries, or even from different dental schools in one country, may have different clinical decisions for the same clinical condition. For example, dentists graduated from Israeli dental schools may recommend more often for the removal of asymptomatic impacted third molar (wisdom teeth) than dentists graduated from Latin American or Eastern European dental schools.

In the United Kingdom, the 1878 British Dentists Act and 1879 Dentists Register limited the title of "dentist" and "dental surgeon" to qualified and registered practitioners. However, others could legally describe themselves as "dental experts" or "dental consultants". The practice of dentistry in the United Kingdom became fully regulated with the 1921 Dentists Act, which required the registration of anyone practising dentistry. The British Dental Association, formed in 1880 with Sir John Tomes as president, played a major role in prosecuting dentists practising illegally.

In Korea, Taiwan, Japan, Finland, Sweden, Brazil, Chile, the United States, and Canada, a dentist is a healthcare professional qualified to practice dentistry after graduating with a degree of either Doctor of Dental Surgery (DDS) or Doctor of Dental Medicine (DMD). This is equivalent to the Bachelor of Dental Surgery/Baccalaureus Dentalis Chirurgiae (BDS, BDent, BChD, BDSc) that is awarded in the UK and British Commonwealth countries. In most western countries, to become a qualified dentist one must usually complete at least four years of postgraduate study; within the European Union the education has to be at least five years. Dentists usually complete between five and eight years of post-secondary education before practising. Though not mandatory, many dentists choose to complete an internship or residency focusing on specific aspects of dental care after they have received their dental degree.

Specialties

Some dentists undertake further training after their initial degree in order to specialize. Exactly which subjects are recognized by dental registration bodies varies according to location. Examples include:

• Dental public health â€" The study of epidemiology and social health policies relevant to oral health
• Conservative dentistry and endodontics: The art and science of restoring the tooth form and function when destructed by carious and non carious lesions affecting the teeth, before involvement of pulp or root canal is termed as conservative dentistry. When the root canal are involved, the speciality is known as endodontics. This speciality degree is awarded in India
• Endodontics (also called endodontology) â€" Root canal therapy and study of diseases of the dental pulp and periapical tissues.
• Forensic odontology â€" The gathering and use of dental evidence in law. This may be performed by any dentist with experience or training in this field. The function of the forensic dentist is primarily documentation and verification of identity.
• Geriatric dentistry or Geriodontics â€" The delivery of dental care to older adults involving the diagnosis, prevention, and treatment of problems associated with normal aging and age-related diseases as part of an interdisciplinary team with other health care professionals.
• Oral and maxillofacial pathology â€" The study, diagnosis, and sometimes the treatment of oral and maxillofacial related diseases.
• Oral and maxillofacial radiology â€" The study and radiologic interpretation of oral and maxillofacial diseases.
• Oral and maxillofacial surgery (also called oral surgery) â€" Extractions, implants, and surgery of the jaws, mouth and face.
• Oral biology â€" Research in dental and craniofacial biology
• Oral Implantology â€" The art and science of replacing extracted teeth with dental implants.
• Oral medicine â€" The clinical evaluation and diagnosis of oral mucosal diseases
• Orthodontics and dentofacial orthopedics â€" The straightening of teeth and modification of midface and mandibular growth.
• Pediatric dentistry (also called pedodontics) â€" Dentistry for children
• Periodontology (also called periodontics) â€" The study and treatment of diseases of the periodontium (non-surgical and surgical) as well as placement and maintenance of dental implants
• Prosthodontics (also called prosthetic dentistry) â€" Dentures, bridges and the restoration of implants. Some prosthodontists further their training in "oral and maxillofacial prosthodontics", which is the discipline concerned with the replacement of missing facial structures, such as ears, eyes, noses, etc.
• Special needs dentistry (also called special care dentistry) â€" Dentistry for those with developmental and acquired disabilities.
• Veterinary dentistry, a speciality of veterinary medicine â€" The field of dentistry applied to the care of animals.

History

Tooth decay was low in pre-agricultural societies, the growth in farming society about 10,000 years ago correlated with an increase with the rate of cavities. An infected tooth from Italy partially cleaned with flint tools, between 13,820 and 14,160 years old, represents the oldest known dentistry. The Indus Valley Civilization (IVC) has yielded evidence of dentistry being practised as far back as 7000 BC. An IVC site in Mehrgarh indicates that this form of dentistry involved curing tooth related disorders with bow drills operated, perhaps, by skilled bead crafters. The reconstruction of this ancient form of dentistry showed that the methods used were reliable and effective. The earliest dental filling, made of beeswax, was discovered in Slovenia and dates from 6500 years ago.

An ancient Sumerian text describes a "tooth worm" as the cause of dental caries. Evidence of this belief has also been found in ancient India, Egypt, Japan, and China. The legend of the worm is also found in the writings of Homer, and as late as the 14th century AD the surgeon Guy de Chauliac still promoted the belief that worms cause tooth decay.

Recipes for the treatment of toothache, infections and loose teeth are spread throughout the Ebers Papyrus, Kahun Papyri, Brugsch Papyrus, and Hearst papyrus of Ancient Egypt. The Edwin Smith Papyrus, written in the 17th century BC but which may reflect previous manuscripts from as early as 3000 BC, discusses the treatment of dislocated or fractured jaws. In the 18th century BC, the Code of Hammurabi referenced dental extraction twice as it related to punishment. Examination of the remains of some ancient Egyptians and Greco-Romans reveals early attempts at dental prosthetics. However, it is possible the prosthetics were prepared after death for aesthetic reasons.

Ancient Greek scholars Hippocrates and Aristotle wrote about dentistry, including the eruption pattern of teeth, treating decayed teeth and gum disease, extracting teeth with forceps, and using wires to stabilize loose teeth and fractured jaws. Some say the first use of dental appliances or bridges comes from the Etruscans from as early as 700 BC. In ancient Egypt, Hesi-Re is the first named "dentist" (greatest of the teeth). The Egyptians bound replacement teeth together with gold wire. Roman medical writer Cornelius Celsus wrote extensively of oral diseases as well as dental treatments such as narcotic-containing emollients and astringents. The earliest dental amalgams were first documented in a Tang Dynasty medical text written by the Chinese physician Su Kung in 659, and appeared in Germany in 1528.

Historically, dental extractions have been used to treat a variety of illnesses. During the Middle Ages and throughout the 19th century, dentistry was not a profession in itself, and often dental procedures were performed by barbers or general physicians. Barbers usually limited their practice to extracting teeth which alleviated pain and associated chronic tooth infection. Instruments used for dental extractions date back several centuries. In the 14th century, Guy de Chauliac invented the dental pelican (resembling a pelican's beak) which was used to perform dental extractions up until the late 18th century. The pelican was replaced by the dental key which, in turn, was replaced by modern forceps in the 20th century.

The first book focused solely on dentistry was the "Artzney Buchlein" in 1530, and the first dental textbook written in English was called "Operator for the Teeth" by Charles Allen in 1685.

In the United Kingdom there was no formal qualification for the providers of dental treatment until 1859 and it was only in 1921 that the practice of dentistry was limited to those who were professionally qualified. The Royal Commission on the National Health Service in 1979 reported that there were then more than twice as many registered dentists per 10,000 population in the UK than there were in 1921.

Modern dentistry

It was between 1650 and 1800 that the science of modern dentistry developed. The English physician Thomas Browne in his A Letter to a Friend (c. 1656 pub. 1690) made an early dental observation with characteristic humour:

The Egyptian Mummies that I have seen, have had their Mouths open, and somewhat gaping, which affordeth a good opportunity to view and observe their Teeth, wherein 'tis not easie to find any wanting or decayed: and therefore in Egypt, where one Man practised but one Operation, or the Diseases but of single Parts, it must needs be a barren Profession to confine unto that of drawing of Teeth, and little better than to have been Tooth-drawer unto King Pyrrhus, who had but two in his Head.

The French surgeon Pierre Fauchard became known as the "father of modern dentistry". Despite the limitations of the primitive surgical instruments during the late 17th and early 18th century, Fauchard was a highly skilled surgeon who made remarkable improvisations of dental instruments, often adapting tools from watch makers, jewelers and even barbers, that he thought could be used in dentistry. He introduced dental fillings as treatment for dental cavities. He asserted that sugar derivate acids like tartaric acid were responsible for dental decay, and also suggested that tumors surrounding the teeth and in the gums could appear in the later stages of tooth decay.

Fauchard was the pioneer of dental prosthesis, and he discovered many methods to replace lost teeth. He suggested that substitutes could be made from carved blocks of ivory or bone. He also introduced dental braces, although they were initially made of gold, he discovered that the teeth position could be corrected as the teeth would follow the pattern of the wires. Waxed linen or silk threads were usually employed to fasten the braces. His contributions to the world of dental science consist primarily of his 1728 publication Le chirurgien dentiste or The Surgeon Dentist. The French text included "basic oral anatomy and function, dental construction, and various operative and restorative techniques, and effectively separated dentistry from the wider category of surgery".

After Fauchard, the study of dentistry rapidly expanded. Two important books, Natural History of Human Teeth (1771) and Practical Treatise on the Diseases of the Teeth (1778), were published by British surgeon John Hunter. In 1763 he entered into a period of collaboration with the London-based dentist James Spence. He began to theorise about the possibility of tooth transplants from one person to another. He realised that the chances of an (initially, at least) successful tooth transplant would be improved if the donor tooth was as fresh as possible and was matched for size with the recipient. These principles are still used in the transplantation of internal organs. Hunter conducted a series of pioneering operations, in which he attempted a tooth transplant. Although the donated teeth never properly bonded with the recipients' gums, one of Hunter's patients stated that he had three which lasted for six years, a remarkable achievement for the period.

Major advances were made in the 19th century, and dentistry evolved from a trade to a profession. The profession came under government regulation by the end of the 19th century. In the UK the Dentist Act was passed in 1878 and the British Dental Association formed in 1879. In the same year, Francis Brodie Imlach was the first ever dentist to be elected President of the Royal College of Surgeons (Edinburgh), raising dentistry onto a par with clinical surgery for the first time.

Priority patients

UK NHS priority patients include patients with congenital abnormalities (such as cleft palates and hypodontia), patients who have suffered orofacial trauma and those being treated for cancer in the head and neck region. These are treated in a multidisciplinary team approach with other hospital based dental specialities orthodontics and maxillofacial surgery. Other priority patients include those with infections (either third molars or necrotic teeth) or avulsed permanent teeth, as well as patients with a history of smoking or smokeless tobacco with ulcers in the oral cavity.

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A telephone exchange is a telecommunications system used in the public switched telephone network or in large enterprises. An exchange consists of electronic components and in older systems also human operators that interconnect (switch) telephone subscriber lines or virtual circuits of digital systems to establish telephone calls between subscribers.

In historical perspective, telecommunication terms have been used with different semantics over time. The term telephone exchange is often used synonymously with central office (CO), a Bell System term. Often, a central office is defined as a building used to house the inside plant equipment of potentially several telephone exchanges, each serving a certain geographical area. Such an area has also been referred to as the exchange. Central office locations may also be identified in North America as wire centers, designating a facility from which a telephone obtains dial tone. For business and billing purposes, telephony carriers also define rate centers, which in larger cities may be clusters of central offices, to define specified geographical locations for determining distance measurements.

In the United States and Canada, the Bell System established in the 1940s a uniform system of identifying central offices with a three-digit central office code, that was used as a prefix to subscriber telephone numbers. All central offices within a larger region, typically aggregated by state, were assigned a common numbering plan area code. With the development of international and transoceanic telephone trunks, especially driven by direct customer dialing, similar efforts of systematic organization of the telephone networks occurred in many countries in the mid-20th century.

For corporate or enterprise use, a private telephone exchange is often referred to as a private branch exchange (PBX), when it has connections to the public switched telephone network. A PBX is installed in enterprise facilities, typically collocated with large office spaces or within an organizational campus to serve the local private telephone system and any private leased line circuits. Smaller installations might deploy a PBX or key telephone system in the office of a receptionist.

History

In the era of the electrical telegraph, post offices, railway stations, the more important governmental centers (ministries), stock exchanges, very few nationally distributed newspapers, the largest internationally important corporations and wealthy individuals were the principal users of such telegraphs. Despite the fact that telephone devices existed before the invention of the telephone exchange, their success and economical operation would have been impossible on the same schema and structure of the contemporary telegraph, as prior to the invention of the telephone exchange switchboard, early telephones were hardwired to and communicated with only a single other telephone (such as from an individual's home to the person's business).

A telephone exchange is a telephone system located at service centers (central offices) responsible for a small geographic area that provided the switching or interconnection of two or more individual subscriber lines for calls made between them, rather than requiring direct lines between subscriber stations. This made it possible for subscribers to call each other at homes, businesses, or public spaces. These made telephony an available and comfortable communication tool for everyday use, and it gave the impetus for the creation of a whole new industrial sector.

One of the first to propose a telephone exchange was Hungarian Tivadar Puskás in 1877 while he was working for Thomas Edison. The first experimental telephone exchange was based on the ideas of Puskás, and it was built by the Bell Telephone Company in Boston in 1877. The world's first commercial telephone exchange opened on November 12, 1877 in Friedrichsberg close to Berlin. George W. Coy designed and built the first commercial US telephone exchange which opened in New Haven, Connecticut in January, 1878. The switchboard was built from "carriage bolts, handles from teapot lids and bustle wire" and could handle two simultaneous conversations. Charles Glidden is also credited with establishing an exchange in Lowell, MA. with 50 subscribers in 1878.

In Europe other early telephone exchanges were based in London and Manchester, both of which opened under Bell patents in 1879. Belgium had its first International Bell exchange (in Antwerp) a year later.

In 1887 Puskás introduced the multiplex switchboard..

Later exchanges consisted of one to several hundred plug boards staffed by switchboard operators. Each operator sat in front of a vertical panel containing banks of ¼-inch tip-ring-sleeve (3-conductor) jacks, each of which was the local termination of a subscriber's telephone line. In front of the jack panel lay a horizontal panel containing two rows of patch cords, each pair connected to a cord circuit.

When a calling party lifted the receiver, the local loop current lit a signal lamp near the jack. The operator responded by inserting the rear cord (answering cord) into the subscriber's jack and switched her headset into the circuit to ask, "Number, please?" For a local call, the operator inserted the front cord of the pair (ringing cord) into the called party's local jack and started the ringing cycle. For a long distance call, she plugged into a trunk circuit to connect to another operator in another bank of boards or at a remote central office. In 1918, the average time to complete the connection for a long-distance call was 15 minutes.

Early manual switchboards required the operator to operate listening keys and ringing keys, but by the late 1910s and 1920s, advances in switchboard technology led to features which allowed the call to be automatically answered immediately as the operator inserted the answering cord, and ringing would automatically begin as soon as the operator inserted the ringing cord into the called party’s jack. The operator would be disconnected from the circuit, allowing her to handle another call, while the caller heard an audible ringback signal, so that that operator would not have to periodically report that she was continuing to ring the line.

In the ringdown method, the originating operator called another intermediate operator who would call the called subscriber, or passed it on to another intermediate operator. This chain of intermediate operators could complete the call only if intermediate trunk lines were available between all the centers at the same time. In 1943 when military calls had priority, a cross-country US call might take as long as 2 hours to request and schedule in cities that used manual switchboards for toll calls.

On March 10, 1891, Almon Brown Strowger, an undertaker in Kansas City, Missouri, patented the stepping switch, a device which led to the automation of telephone circuit switching. While there were many extensions and adaptations of this initial patent, the one best known consists of 10 levels or banks, each having 10 contacts arranged in a semicircle. When used with a rotary telephone dial, each pair of digits caused the shaft of the central contact "hand" of the stepping switch to first step (ratchet) up one level for each pulse in the first digit and then to swing horizontally in a contact row with one small rotation for each pulse in the next digit.

Later stepping switches were arranged in banks, the first stage of which was a linefinder. If one of up to a hundred subscriber lines had the receiver lifted "off hook", a linefinder connected the subscriber's line to a free first selector, which returned the subscriber a dial tone to show that it was ready to receive dialed digits. The subscriber's dial pulsed at about 10 pulses per second, although the speed depended on the standard of the particular telephone administration.

Exchanges based on the Strowger switch were eventually challenged by other exchange types and later by crossbar technology. These exchange designs promised faster switching and would accept pulses faster than the Strowger's typical 10 ppsâ€"typically about 20 pps. At a later date many also accepted DTMF "touch tones" or other tone signaling systems.

A transitional technology (from pulse to DTMF) had converters to convert DTMF to pulse, to feed to older Strowger, panel, or crossbar switches. This technology was used as late as mid-2002.

Technologies

Many terms used in telecommunication technology differ in meaning and usage in various regions of the world among English speaking regions. For the purpose of this article the following definitions are made:

• Manual service is a condition in which a human operator routes calls inside an exchange without the use of a dial.
• Dial service is when an exchange routes calls by a switch interpreting dialed digits.
• A telephone switch is the switching equipment of an exchange.
• A concentrator is a device that concentrates traffic, be it remote or co-located with the switch.
• An off-hook condition is a tip condition or describes a circuit that is in use, e.g., when a phone call is in progress.
• An on-hook condition represents an idle circuit, i.e. no phone call is in progress.
• A wire center is the area served by a particular switch or central office.

Central office originally referred to switching equipment and its operators, it is also used generally for the building that houses switching and related inside plant equipment. In United States telecommunication jargon, a central office (C.O.) is a common carrier switching center Class 5 telephone switch in which trunks and local loops are terminated and switched. In the UK, a telephone exchange means an exchange building, and is also the name for a telephone switch.

Manual service exchanges

With manual service, the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number. Provided that the number is in the same central office, and located on the operator's switchboard, the operator connects the call by plugging the ringing cord into the jack on the switchboard corresponding to the called customer's line. If the called party's line is on a different switchboard in the same office, or in a different central office, the operator plugs into the trunk for the destination switchboard or office and asks the operator answering (known as the "B" operator) to connect the call.

Most urban exchanges provided common-battery service, meaning that the central office provided power to the subscriber telephone circuits for operation of the transmitter, as well as for automatic signaling with rotary dials. In common-battery systems, the pair of wires from a subscriber's telephone to the exchange carry 48V (nominal) DC potential from the telephone company end across the conductors. The telephone presents an open circuit when it is on-hook or idle.

When a subscriber's phone is off-hook, it presents an electrical resistance across the line which causes current to flow through the telephone and wires to the central office. In a manually operated switchboard, this current flowed through a relay coil, and actuated a buzzer or a lamp on the operator's switchboard, signaling the operator to perform service.

In the largest cities, it took many years to convert every office to automatic equipment, such as a panel switch. During this transition period, once numbers were standardized to the 2L-4N or 2L-5N format (two-letter exchange name and either four or five digits), it was possible to dial a number located in a manual exchange and be connected without requesting operator assistance. The policy of the Bell System stated that customers in large cities should not need to be concerned with the type of office, whether they were calling a manual or an automatic office.

When a subscriber dialed the number of a manual station, an operator at the destination office answered the call after seeing the number on an indicator, and connected the call by plugging a cord into the outgoing circuit and ringing the destination station. For example, if a dial customer calling from TAylor 4725 dialed a number served by a manual exchange, e.g., ADams 1383-W, the call was completed, from the subscriber’s perspective, exactly as a call to LEnnox 5813, in an automated exchange. The party line letters W, R, J, and M were only used in manual exchanges with jack-per-line party lines.

In contrast to the listing format MAin 1234 for an automated office with two capital letters, a manual office, having listings such as Hillside 834 or East 23, was recognizable by the format in which the second letter was not capitalized.

Rural areas, as well as the smallest towns, had manual service and signaling was accomplished with magneto telephones, which had a crank for the signaling generator. To alert the operator, or another subscriber on the same line, the subscriber turned the crank to generate ringing current. The switchboard responded by interrupting the circuit, which dropped a metal tab above the subscriber's line jack and sounded a buzzer. Dry cell batteries, normally two large N°. 6 cells in the subscriber's telephone, provided the direct current for the transmitter. Such magneto systems were in use in the US as late as 1983, as in the small town, Bryant Pond, Woodstock, Maine.

Many small town magneto systems featured party lines, anywhere from two to ten or more subscribers sharing a single line. When calling a party, the operator used code ringing, a distinctive ringing signal sequence, such as two long rings followed by one short ring. Everyone on the line could hear the signals, and could pick up and monitor other people's conversations.

Early automatic exchanges

Automatic exchanges, or dial service, came into existence in the early 20th century. Their purpose was to eliminate the need for human switchboard operators who completed the connections required for a telephone call. Automation replaced human operators with electromechanical systems and telephones were equipped with a dial by which a caller transmitted the destination telephone number to the automatic switching system.

A telephone exchange automatically senses an off-hook condition of the telephone when the user removes the handset from the switchhook or cradle. The exchange provides dial tone at that time to indicate to the user that the exchange is ready to receive dialed digits. The pulses or DTMF tones generated by the telephone are processed and a connection is established to the destination telephone within the same exchange or to another distant exchange.

The exchange maintains the connection until one of the parties hangs up. This monitoring of connection status is called supervision. Additional features, such as billing equipment, may also be incorporated into the exchange.

The Bell System dial service implemented a feature called automatic number identification (ANI) which facilitated services like automated billing, toll-free 800-numbers, and 9-1-1 service. In manual service, the operator knows where a call is originating by the light on the switchboard jack field. Before ANI, long distance calls were placed into an operator queue and the operator asked the calling party's number and recorded it on a paper toll ticket.

Early exchanges were electromechanical systems using motors, shaft drives, rotating switches and relays. Some types of automatic exchanges were the Strowger switch or step-by-step switch, All Relay, X-Y, panel switch and the crossbar switch.

Electromechanical signaling

Circuits interconnecting switches are called trunks. Before Signalling System 7, Bell System electromechanical switches in the United States communicated with one another over trunks using a variety of DC voltages and signaling tones. It would be rare to see any of these in use today.

Some signalling communicated dialed digits. An early form called Panel Call Indicator Pulsing used quaternary pulses to set up calls between a panel switch and a manual switchboard. Probably the most common form of communicating dialed digits between electromechanical switches was sending dial pulses, equivalent to a rotary dial's pulsing, but sent over trunk circuits between switches.

In Bell System trunks, it was common to use 20 pulse-per-second between crossbar switches and crossbar tandems. This was twice the rate of Western Electric/Bell System telephone dials. Using the faster pulsing rate made trunk utilization more efficient because the switch spent half as long listening to digits. DTMF was not used for trunk signaling.

Multi-frequency (MF) was the last of the pre-digital methods. It used a different set of tones sent in pairs like DTMF. Dialing was preceded by a special keypulse (KP) signal and followed by a start (ST). Variations of the Bell System MF tone scheme became a CCITT standard. Similar schemes were used in the Americas and in some European countries including Spain. Digit strings between switches were often abbreviated to further improve utilization.

For example, one switch might send only the last four or five digits of a telephone number. In one case, seven digit numbers were preceded by a digit 1 or 2 to differentiate between two area codes or office codes, (a two-digit-per-call savings). This improved revenue per trunk and reduced the number of digit receivers needed in a switch. Every task in electromechanical switches was done in big metallic pieces of hardware. Every fractional second cut off of call set up time meant fewer racks of equipment to handle call traffic.

Examples of signals communicating supervision or call progress include E and M signaling, SF signaling, and robbed-bit signaling. In physical (not carrier) E and M trunk circuits, trunks were four wire. Fifty trunks would require a hundred pair cable between switches, for example. Conductors in one common circuit configuration were named tip, ring, ear (E) and mouth (M). Tip and ring were the voice-carrying pair, and named after the tip and ring on the three conductor cords on the manual operator's console.

In two-way trunks with E and M signaling, a handshake took place to prevent both switches from colliding by dialing calls on the same trunk at the same time. By changing the state of these leads from ground to -48 volts, the switches stepped through a handshake protocol. Using DC voltage changes, the local switch would send a signal to get ready for a call and the remote switch would reply with an acknowledgment to go ahead with dial pulsing. This was done with relay logic and discrete electronics.

These voltage changes on the trunk circuit would cause pops or clicks that were audible to the subscriber as the electrical handshaking stepped through its protocol. Another handshake, to start timing for billing purposes, caused a second set of clunks when the called party answered.

A second common form of signaling for supervision was called single-frequency or SF signaling. The most common form of this used a steady 2,600 Hz tone to identify a trunk as idle. Trunk circuitry hearing a 2,600 Hz tone for a certain duration would go idle. (The duration requirement reduced falsing.) Some systems used tone frequencies over 3,000 Hz, particularly on SSB frequency division multiplex microwave radio relays.

On T-carrier digital transmission systems, bits within the T-1 data stream were used to transmit supervision. By careful design, the appropriated bits did not change voice quality appreciably. Robbed bits were translated to changes in contact states (opens and closures) by electronics in the channel bank hardware. This allowed direct current E and M signaling, or dial pulses, to be sent between electromechanical switches over a digital carrier which did not have DC continuity.

Sounds

A characteristic of electromechanical switching equipment is that the maintenance staff could hear the mechanical clattering of Strowgers, panel switches or crossbar relays. Most Bell System central offices were housed in reinforced concrete buildings with concrete ceilings and floors.

In rural areas some smaller switching facilities, such as community dial offices (CDOs), were housed in prefabricated metal buildings. These facilities almost always had concrete floors. The hard surfaces reflected sounds.

During heavy use periods, it could be difficult to converse in a central office switch room due to the clatter of calls being processed in a large switch. For example, on Mother's Day in the US, or on a Friday evening around 5pm, the metallic rattling could make raised voices necessary. For wire spring relay markers these noises resembled hail falling on a metallic roof.

On a pre-dawn Sunday morning, call processing might slow to the extent that one might be able to hear individual calls being dialed and set up. There were also noises from whining power inverters and whirring ringing generators. Some systems had a continual, rhythmic "clack-clack-clack" from wire spring relays that made reorder (120 ipm) and busy (60 ipm) signals.

Bell System installations typically had alarm bells, gongs, or chimes to announce alarms calling attention to a failed switch element. A trouble reporting card system was connected to switch common control elements. These trouble reporting systems punctured cardboard cards with a code that logged the nature of a failure. Reed relay technology in stored program control exchange finally quieted the environment.

Maintenance tasks

Electromechanical switching systems required sources of electricity in form of direct current (DC), as well as alternating ring current (AC), which were generated on-site with mechanical generators. In addition, telephone switches required adjustment of many mechanical parts. Unlike modern switches, a circuit connecting a dialed call through an electromechanical switch had DC continuity within the local exchange area via metallic conductors.

The design and maintenance procedures of all systems involved methods to avoid that subscribers experienced undue changes in the quality of the service or that they noticed failures. A variety of tools referred to as make-busys were plugged into electromechanical switch elements upon failure and during repairs. A make-busy identified the part being worked on as in-use, causing the switching logic to route around it. A similar tool was called a TD tool. Delinquent subscribers had their service temporarily denied (TDed). This was effected by plugging a tool into the subscriber's office equipment on Crossbar systems or line group in step-by-step switches. The subscriber could receive calls but could not dial out.

Strowger-based, step-by-step offices in the Bell System required continuous maintenance, such as cleaning. Indicator lights on equipment bays in step offices alerted staff to conditions such as blown fuses (usually white lamps) or a permanent signal (stuck off-hook condition, usually green indicators). Step offices were more susceptible to single-point failures than newer technologies.

Crossbar offices used more shared, common control circuits. For example, a digit receiver (part of an element called an Originating Register) would be connected to a call just long enough to collect the subscriber's dialed digits. Crossbar architecture was more flexible than step offices. Later crossbar systems had punch-card-based trouble reporting systems. By the 1970s, automatic number identification had been retrofitted to nearly all step-by-step and crossbar switches in the Bell System.

Electronic switches

Electronic switching systems gradually evolved in stages from electromechanical hybrids with stored program control to the fully digital systems. Early systems used reed relay-switched metallic paths under digital control. Equipment testing, phone numbers reassignments, circuit lockouts and similar tasks were accomplished by data entry on a terminal.

Examples of these systems included the Western Electric 1ESS switch, Northern Telecom SP1, Ericsson AKE, Philips PRX/A, ITT Metaconta, British GPO/BT TXE series and several other designs were similar. Ericsson also developed a fully computerized version of their ARF crossbar exchange called ARE. These used a crossbar switching matrix with a fully computerized control system and provided a wide range of advanced services. Local versions were called ARE11 while tandem versions were known as ARE13. They were used in Scandinavia, Australia, Ireland and many other countries in the late 1970s and into the 1980s when they were replaced with digital technology.

These systems could use the old electromechanical signaling methods inherited from crossbar and step-by-step switches. They also introduced a new form of data communications: two 1ESS exchanges could communicate with one another using a data link called Common Channel Interoffice Signaling, (CCIS). This data link was based on CCITT 6, a predecessor to SS7. In European systems R2 signalling was normally used.

Digital switches

Digital switches work by connecting two or more digital circuits, according to a dialed telephone number or other instruction. Calls are set up between switches. In modern networks, this is usually controlled using the Signalling System 7 (SS7) protocol, or one of its variants. Many networks around the world are now transitioning to voice over IP technologies which use Internet-based protocols such as the Session Initiation Protocol (SIP). These may have superseded TDM and SS7 based technologies in some networks.

The concepts of digital switching were developed by various labs in the United States and in Europe from the 1930s onwards. The first prototype digital switch was developed by Bell Labs as part of the ESSEX project while the first true digital exchange to be combined with digital transmission systems was designed by LCT (Laboratoire Central de Telecommunications) in Paris. The first digital switch to be placed into a public network was the Empress Exchange in London, England which was designed by the General Post Office research labs. This was a tandem switch that connected three Strowger exchanges in the London area. The first commercial roll-out of a fully digital local switching system was Alcatel's E10 system which began serving customers in Brittany in Northwestern France in 1972.

Prominent examples of digital switches include:

• Ericsson's AXE telephone exchange is the most widely used digital switching platform in the world and can be found throughout Europe and in most countries around the world. It is also very popular in mobile applications. This highly modular system was developed in Sweden in the 1970s as a replacement for the very popular range of Ericsson crossbar switches ARF, ARM, ARK and ARE used by many European networks from the 1950s onwards.
• Alcatel-Lucent inherited three of the world's most iconic digital switching systems : Alcatel E10, 1000-S12, and the Western Electric 5ESS.

Alcatel developed the E10 system in France during the late 1960s and 1970s. This widely used family of digital switches was one of the earliest TDM switches to be widely used in public networks. Subscribers were first connected to E10A switches in France in 1972. This system is used in France, Ireland, China, and many other countries. It has been through many revisions and current versions are even integrated into All IP networks.

Alcatel also acquired ITT System 12 which when it bought ITT's European operations. The S12 system and E10 systems were merged into a single platform in the 1990s. The S12 system is used in Germany, Italy, Australia, Belgium, China, India, and many other countries around the world.

Finally, when Alcatel and Lucent merged, the company acquired Lucent's 5ESS and 4ESS systems used throughout the United States of America and in many other countries.

• Nokia Siemens Networks EWSD originally developed by Siemens, Bosch and DeTeWe for the German market is used throughout the world.
• Nortel now Genband DMS100 is very popular with operators all over the world.
• NEC NEAX used in Japan, New Zealand and many other countries.
• Marconi System X originally developed by GPT and Plessey is a type of digital exchange used by BT Group in the UK public telephone network.

Digital switches encode the speech going on, in 8,000 time slices per second. At each time slice, a digital PCM representation of the tone is made. The digits are then sent to the receiving end of the line, where the reverse process occurs, to produce the sound for the receiving phone. In other words, when someone uses a telephone, the speaker's voice is "encoded" then reconstructed for the person on the other end. The speaker's voice is delayed in the process by a small fraction of one second â€" it is not "live", it is reconstructed â€" delayed only minutely. (See below for more info.)

Individual local loop telephone lines are connected to a remote concentrator. In many cases, the concentrator is co-located in the same building as the switch. The interface between remote concentrators and telephone switches has been standardised by ETSI as the V5 protocol. Concentrators are used because most telephones are idle most of the day, hence the traffic from hundreds or thousands of them may be concentrated into only tens or hundreds of shared connections.

Some telephone switches do not have concentrators directly connected to them, but rather are used to connect calls between other telephone switches. These complex machines (or a series of them) in a central exchange building are referred to as "carrier-level" switches or tandem switches.

Some telephone exchange buildings in small towns now house only remote or satellite switches, and are homed upon a "parent" switch, usually several kilometres away. The remote switch is dependent on the parent switch for routing and number plan information. Unlike a digital loop carrier, a remote switch can route calls between local phones itself, without using trunks to the parent switch.

Telephone switches are usually owned and operated by a telephone service provider or carrier and located in their premises, but sometimes individual businesses or private commercial buildings will house their own switch, called a PBX, or Private branch exchange.

The switch's place in the system

Telephone switches are a small component of a large network. A major part, in terms of expense, maintenance, and logistics of the telephone system is outside plant, which is the wiring outside the central office. While many subscribers were served with party-lines in the middle of the 20th century, it was the goal that each subscriber telephone station was connected to an individual pair of wires from the switching system.

A typical central office may have tens of thousands of pairs of wires that appear on terminal blocks called the main distribution frame (MDF). A component of the MDF is protection: fuses or other devices that protect the switch from lightning, shorts with electric power lines, or other foreign voltages. In a typical telephone company, a large database tracks information about each subscriber pair and the status of each jumper. Before computerization of Bell System records in the 1980s, this information was handwritten in pencil in accounting ledger books.

To reduce the expense of outside plant, some companies use "pair gain" devices to provide telephone service to subscribers. These devices are used to provide service where existing copper facilities have been exhausted or by siting in a neighborhood, can reduce the length of copper pairs, enabling digital services such as Integrated Services Digital Network (ISDN) or Digital Subscriber Line (DSL).

Pair gain or digital loop carriers (DLCs) are located outside the central office, usually in a large neighborhood distant from the CO. DLCs are often referred to as Subscriber Loop Carriers (SLCs), after a Lucent proprietary product.

DLCs can be configured as universal (UDLCs) or integrated (IDLCs). Universal DLCs have two terminals, a central office terminal (COT) and a remote terminal (RT), that function similarly. Both terminals interface with analog signals, convert to digital signals, and transport to the other side where the reverse is performed.

Sometimes, the transport is handled by separate equipment. In an Integrated DLC, the COT is eliminated. Instead, the RT is connected digitally to equipment in the telephone switch. This reduces the total amount of equipment required.

Switches are used in both local central offices and in long distance centers. There are two major types in the Public switched telephone network (PSTN), the Class 4 telephone switches designed for toll or switch-to-switch connections, and the Class 5 telephone switches or subscriber switches, which manage connections from subscriber telephones. Since the 1990s, hybrid Class 4/5 switching systems that serve both functions have become common.

Another element of the telephone network is time and timing. Switching, transmission and billing equipment may be slaved to very high accuracy 10 MHz standards which synchronize time events to very close intervals. Time-standards equipment may include Rubidium- or Caesium-based standards and a Global Positioning System receiver.

Switch design

Long distance switches may use a slower, more efficient switch-allocation algorithm than local central offices, because they have near 100% utilization of their input and output channels. Central offices have more than 90% of their channel capacity unused.

Traditional telephone switches connected physical circuits (e.g., wire pairs) while modern telephone switches use a combination of space- and time-division switching. In other words, each voice channel is represented by a time slot (say 1 or 2) on a physical wire pair (A or B). In order to connect two voice channels (say A1 and B2) together, the telephone switch interchanges the information between A1 and B2. It switches both the time slot and physical connection. To do this, it exchanges data between the time slots and connections 8,000 times per second, under control of digital logic that cycles through electronic lists of the current connections. Using both types of switching makes a modern switch far smaller than either a space or time switch could be by itself.

The structure of a switch is an odd number of layers of smaller, simpler subswitches. Each layer is interconnected by a web of wires that goes from each subswitch, to a set of the next layer of subswitches. In most designs, a physical (space) switching layer alternates with a time switching layer. The layers are symmetric, because in a telephone system callers can also be callees.

A time-division subswitch reads a complete cycle of time slots into a memory, and then writes it out in a different order, also under control of a cyclic computer memory. This causes some delay in the signal.

A space-division subswitch switches electrical paths, often using some variant of a nonblocking minimal spanning switch, or a crossover switch.

Switch control algorithms

Fully connected mesh network

One way is to have enough switching fabric to assure that the pairwise allocation will always succeed by building a fully connected mesh network. This is the method usually used in central office switches, which have low utilization of their resources.

Clos's nonblocking switch algorithm

The scarce resources in a telephone switch are the connections between layers of subswitches. The control logic has to allocate these connections, and most switches do so in a way that is fault tolerant. See nonblocking minimal spanning switch for a discussion of the Charles Clos algorithm, used in many telephone switches, and a very important algorithm to the telephone industry.

Fault tolerance

Composite switches are inherently fault-tolerant. If a subswitch fails, the controlling computer can sense it during a periodic test. The computer marks all the connections to the subswitch as "in use". This prevents new calls, and does not interrupt old calls that remain working. As calls in progress end, the subswitch becomes unused, and new calls avoid the subswitch because it's already "in use." Some time later, a technician can replace the circuit board. When the next test succeeds, the connections to the repaired subsystem are marked "not in use", and the switch returns to full operation.

To prevent frustration with unsensed failures, all the connections between layers in the switch are allocated using first-in-first-out lists (queues). As a result, if a connection is faulty or noisy and the customer hangs up and redials, they will get a different set of connections and subswitches. A last-in-first-out (stack) allocation of connections might cause a continuing string of very frustrating failures.

Fire and disaster recovery

In July 1951, during massive flooding in Kansas and Missouri, a manual switchboard in Manhattan, Kansas was abandoned as water levels rose in the central office; operators regained access to the town's four trunk lines from a local filling station on higher ground to send emergency messages and radiotelephone was used to bypass damaged facilities.

On February 27, 1975 a fire at New York Telephone's building at 204 Second Avenue (at East 13th Street) in Manhattan destroyed the main distribution frame and damaged much of the underground cabling, disconnecting 170,000 subscribers. This office connects many circuits to Brooklyn which were disrupted. Equipment was redirected from other Bell System operating companies in multiple US states to establish temporary service and rebuild the destroyed exchange.

In 1978, a central office fire in Mebane, North Carolina knocked out every one of the small community's 3900 phones.

In May 1988, a central office fire in the Chicago suburb of Hinsdale, Illinois knocked out 35,000 local subscribers, broke the link between the FAA and air traffic control at Chicago O'Hare International Airport (then the world's busiest) and disrupted the Midwest's ability to communicate with the rest of the country. The office had a fire alarm but no automatic fire suppression equipment. The facility was unattended and monitored remotely by an Illinois Bell technician in Springfield; it took an hour to notify firefighters of the blaze as the distant technician's attempts to call the fire department in Hinsdale did not get through. The fire had already knocked out the phone lines.

In 1991, all twenty-eight exchanges serving Kuwait were out of service in the wake of a 1990 invasion by Iraq; equipment had been looted and central offices destroyed. Service was initially restored via satellite.

On September 11, 2001 a terrorist attack destroyed a central office in the World Trade Center in New York City and heavily damaged an adjacent exchange. The Verizon Building at 140 West Street was restored by 3500 workers at a cost of $1.2 billion, after 200,000 voice lines and three million data circuits had been knocked out of operation.

The central exchange, due to the system's design, is almost always a single point of failure for local calls. As the capacity of individual switches and the optical fibre which interconnects them increases, potential disruption caused by destruction of one local office will only be magnified. Multiple fibre connections can be used to provide redundancy to voice and data connections between switching centres, but careful network design is required to avoid situations where a main fibre and its backup both go through the same damaged central office as a potential common mode failure.

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