STP VS UTP OF TWISTED PAIR

Twisted pair
Twisted pair cabling is a form of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from Unshielded Twisted Pair (UTP) cables, and crosstalk between neighboring pairs

A)Unshielded Twisted Pair
Twisted pair cables were first used in telephone systems by Alexander Graham Bell in 1881. By 1900, the entire American telephone line network was either twisted pair or open wire with similar arrangements to guard against interference. Today, most of the millions of kilometres of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers.
UTP cables are found in many ethernet networks and telephone systems. For indoor telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T. A typical subset of these colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables.
For urban outdoor telephone cables containing hundreds or thousands of pairs, the cable is divided into smaller but identical bundles. Each bundle consists of twisted pairs that have different twist rates. The bundles are in turn twisted together to make up the cable. Pairs having the same twist rate within the cable can still experience some degree of crosstalk. Wire pairs are selected carefully to minimize crosstalk within a large cable.Short for Unshielded Twisted Pair cable, UTP cable is a popular type of cable used in computer networking that consists of two shielded wires twisted around each other.

B)Shielded Twisted Pair
Shielded Twisted Pair Cable is used to eliminate inductive and capacitive coupling. Twisting cancels out inductive coupling, while the shield eliminates capacitive coupling. Most applications for this cable are between equipment, racks and buildings. Shielding adds usually some attenuation to the cable (compared to unshielded), but usually not because in the case of balanced transmission, the complementing signals will effectively cancel out any shield currents, so shield current losses are negligible.
The noise pickup characteritics of twisted pair cable is determined by the following cable characteristics: number of twists per meter (generally more twists per meter gives better performance), uniform cable construction, capacitance balance (less capacitance difference to groud, the better), cable diameter (less are between wires is better) and the amount of shielding (more shielding, the better).

ADVANTAGES AND DISADVANTAGES

(A)Twisted Pair
Advantages :
1. Cheaper and far easier to splice.
2. Less susceptible to electrical interference caused by nearby equipment or wires.
3. In turn are less likely to cause interference themselves
.4. Because it is electrically "cleaner", STP wire can carry data at a faster speed.
Disadvantages :
1. STP wire is that it is physically larger and more expensive than twisted pairwire.
2. STP is more difficult to connect to a terminating block.

(B)Coaxial Pair
Advantages :
1. Coaxial cable can support greater cable lengths between network devices than twisted pair cable.
2. Thick coaxial cable has an extra protective plastic cover that help keep moistureaway.
Disadvantages :
1. Thick coaxial is that it does not bend easily and is difficult to install.

(C)Fiber Optic
Advantages :
1. One single mode fiber can replace a metal of time larger and heavier.
2. Multi-mode optical cable has a larger diameter and can be used to carry signalover short distance.
Disadvantages :
1. Fiber optic versus metal cable is that it is difficult to make connections tofiber optic cable.
2. The optical fiber must be highly polished to allow light to pass with little loss.

B2B,B2C AND C2C..

B2B
B2B (business-to-business), also known as e-biz, is the exchange of products, services, or information between businesses rather than between businesses and consumers.
B2C
A transaction that occurs between a company and a consumer, as opposed to a transaction between companies (called B2B). The term may also describe a company that provides goods or services for consumers.
C2C
Consumer-to-consumer (C2C) (or citizen-to-citizen)electronic commerce involves the electronically-facilitated transactions between consumers through some third party. A common example is the online auction, in which a consumer posts an item for sale and other consumers bid to purchase it; the third party generally charges a flat fee or commission. The sites are only intermediaries, just there to match consumers. They do not have to check quality of the products being offered.

RADIO CORPORATION OF AMERICA(RCA)

RADIO CORPORATION OF AMERICA (RCA)
U.S. RADIO COMPANY

In 1919, General Electric (GE) formed a privately owned corporation to acquire the assets of the wireless radio company American Marconi from British Marconi. The organization, known as the Radio Corporation of America or RCA, was formally incorporated on 17 October of that year. Shortly thereafter, American Telephone and Telegraph (AT and T) and Westinghouse acquired RCA assets and became joint owners of RCA. In 1926, RCA formed a new company, the National Broadcasting Company (NBC), to oversee operation of radio stations owned by RCA, General Electric, Westinghouse and AT and T.
In the early 1930's, the Justice Department filed an antitrust suit against the company. In a 1932 consent decree, the organization's operations were separated and GE, AT and T, and Westinghouse were forced to sell their interests in the company. RCA retained its patents and full ownership of NBC. Shortly after becoming an independent company, RCA moved into new headquarters in the Rockefeller Center complex in New York City, into what later became known as Radio City.
While other American companies were cutting back on research expenditures during the depression years, David Sarnoff, President of RCA since 1930, was a staunch advocate of technological innovation. He expanded RCA's technology research division, devoting increased resources to television technology. Television pioneer Vladimir Zworykin was placed in charge of RCA's television research division. RCA acquired competing and secondary patents related to television technology, and once the organization felt that the technology had attained an appropriate level of refinement, it pushed for commercialization of the new medium.
In 1938, RCA persuaded the Radio Manufacturers Association (RMA) to consider adoption of its television system for standardization. The RMA adopted the RCA version, a 441 line, 30 pictures per second system, and presented the new standard to the FCC on 10 September 1938. Upon the recommendation of the RMA, the Federal Communications Commission (FCC) scheduled formal hearings to address the adoption of standards. The hearings, however, did not take place until January 1940.
In the interim, RCA began production of receivers and initiated a limited schedule of television programming from the New York transmitters of the National Broadcasting Corporation (NBC) basing their service upon the RMA-RCA standards. The service was inaugurated in conjunction with the opening of the New York World's Fair on 30 April 1939 and continued throughout the year. At the commission's hearing addressing standards on 15 January 1940, opposition to the proposed RMA standards emerged. The two strongest opponents of the standard were DuMont Laboratories and Philco Radio and Television. One of the criticisms voiced by both organizations was the assertion that the 441 line standard did not provide sufficient visual detail and definition. Given the lack of a clear industry consensus, the Commission did not act on the proposed RMA standards. Despite the absence of official approval, RCA continued to employ the RMA standards and announced plans in early 1940 to increase production of television receivers, cut the price to consumers by one-third, and double their programming schedule. While some commentators saw this as a reasonable and progressive action, the Commission perceived it as a step towards prematurely freezing the standards in place, and as a consequence, scheduled another set of public hearings for 8 April 1940. At these hearings, opponents argued that the action taken by RCA was stifling research and development into other alternative standards. As a result of the hearings, the Commission eliminated commercial broadcasting until further development and refinement had transpired. Furthermore, the Commission asserted that commercialization of broadcasting would not be permitted until there was industry consensus and agreement on one common system. To marshal industry wide support for a single standard, the RMA formed the National Television System Committee (NTSC). The NTSC standards, a 525 line, 60 fields per second system, were approved by the FCC in 1941.
Several years later, RCA also became a major participant in the establishment of color television standards. In 1949, the organization proposed to the FCC that its dot sequential color system, which was compatible with existing black and white receivers, be adopted as the new color standard. Citing shortcomings in the compatible systems offered by RCA and other organizations, the FCC opted to formally adopt an incompatible color system offered by the Columbia Broadcasting System as the color standard. RCA appealed this decision all the way to the Supreme Court, while simultaneously refining their color system. A second NTSC was formed to examine the color issue. In 1953, the FCC reversed itself and endorsed a modified version of the RCA dot sequential system compatible color system offered by the NTSC.
In the 1950s, RCA continued the military and defense work in which it had been heavily engaged during World War II. In the late 1950s and early 1960s, the company became involved with both satellite technology and the space program. During the 1960s, RCA began to diversify as the company acquired such disparate entities as the publishing firm Random House, and the car rental company Hertz. Throughout the 1970s and early 1980s, RCA began to divest itself of many of its acquired subsidiaries. In June 1986, RCA was acquired by General Electric, the organization that had originally established it as a subsidiary. GE retained the brand name RCA, established NBC as a relatively autonomous unit, and combined the remainder of RCA's businesses with GE operations.

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