COMMUNICATION TECHNOLOGIES

Archive for the ‘Data Transmission’ Category

Data communication consists of primary source, a transmission medium and destination. The primary source is the source of the information and secondary destination is the user of the information. The primary host is a mainframe computer. It is connected to many local terminals. The data is given from host to DTE or vice versa. The data terminal equipment is the interface between user computer and DCE or modem. And the data communication equipment it is modem. It converts digital signals to analog signals. The terminal equipment is interfaced to transmission medium through DEC. To establish the data transmission between the computers / terminals of different manufactures, there was a need to develop some common minimum standards.
International standards organization develops standards for graphics, document exchange and related technologies. Consultative committee for international telephony and telegraphy develops the standards for telephone and telegraph communications. CCITT has developed V series for modems and interface. X series for data communications and I & Q series for ISDN.

Composite video signal consists of camera signal corresponding to the desired picture information, blanking pulses and synchronizing pulses. The blanking and sync pulses are added during retrace intervals with amplitude of 75% and 100% levels, to obtain higher efficiency of picture transmission. A horizontal sync pulse is needed at the end of each active line period, whereas a vertical sync pulse is required after each field is scanned. The composite video signal of three different levels each corresponding to a different brightness level of the scene. During the forward scan, the video signal level changes between black and white levels occupying intermediate grey level also, depending upon the picture brightness in the scanned areas.Thus the picture information may vary between 12.5 percent to about 67.5 percent of the composite video signal. The picture details about white areas are placed in lower amplitudes, and the dark areas are placed in higher amplitudes.

Dear all! Finding a well reputed real estate Company for all your real estate needs is not an easy task. For people in and around South Carolina, I can give a feasible solution which is nothing but making your deals with Chapin Real Estate.

I can say that this Lexington SC Real Estate is completely dedicated to their customers and work towards their satisfaction. It’s so pleasant spending the vacation near Lake Murray, which can be accomplished by Chapin Homes. For more details, log onto www.lexingtonsconline.com to know about the locations, prices and much more about their properties.

Dear friends! Health insurance plans are also known as mediclaim policy offered by leading insurance companies. Not only you can select the best product but also select the product that suits your specific need and save money comparing plans. There are loads of companies offering insurance plans but which is the best one is the common question. Their various plans include individual health plan, family floater plan and lot more. It is an agreement of paying certain amount as premium for the insurance between the insurer and insured. Nowadays you can get online quotes for your health insurance plans, select the best plan among the various plans.

My advice to save your money is to make research plans online and then speak with the agents or brokers. CA Health Insurance Plans and Quotes from KaiserQuotes.com is one of the best. Comparison plans online can be easy if you find the right plans. Health insurance plans are very helpful if there may be any case of surgery which is more expensive. If your health is insured you need not worry about the hospital bills because your insurance company will face those problems on behalf of you. Health coverages may differ depending upon their plans. Get the best plans and enjoy benefits of health insurance plans.

Absorption loss is related to the material composition and fabrication process of the fiber. Absorption loss is caused by three different mechanisms. They are absorption by atomic defects in the glass composition, extrinsic absorption by impurity atoms in the glass material and intrinsic absorption by the basic constitute atoms of the fiber material. Now let us discuss about the absorption by atomic defects. Atomic defects are imperfections in the atomic structure of the fiber material such as missing molecules high- density clusters of atom groups or oxygen defects in the glass structure. These absorption losses are negligible compared with intrinsic and impurity absorption effects. The radiation damages in the internal structure of the fiber.

The damage effects depend on the energy of the ionizing particles or rays, the radiation flux and the fluency. The total dose a material receives is expressed in rad(si), which is measure of radiation absorbed in bulk silicon. Attenuation is increased due to ionizing radiations causes attenuation centers that absorb optical energy. There are two types of absorption namely extrinsic absorption and intrinsic absorption. Extrinsic absorption is caused due to impurities in the fiber material. The impurities are transition metal impurities and OH ions. Intrinsic absorption occurs when material is in absolutely pure state with no density variations, impurities and material in homogeneities. Thus intrinsic absorption sets the fundamental lower limit on absorption for any particular material.

Composite video signal consists of camera signal corresponding to the desired picture information, blanking pulses and synchronizing pulses. The blanking and sync pulses are added during retrace intervals with amplitude of 75% and 100% levels, to obtain higher efficiency of picture transmission. A horizontal sync pulse is needed at the end of each active line period, whereas a vertical sync pulse is required after each field is scanned. The composite video signal of three different levels each corresponding to a different brightness level of the scene. During the forward scan, the video signal level changes between black and white levels occupying intermediate grey level also, depending upon the picture brightness in the scanned areas.

Thus the picture information may vary between 12.5 percent to about 67.5 percent of the composite video signal. The picture details about white areas are placed in lower amplitudes, and the dark areas are placed in higher amplitudes. The lowest 10 percent of the voltage range is not used, to minimize noise effects. Average brightness means, the average of value of brightness variation of horizontal lines in one frame. The distance between average brightness and blanking level is called pedestal height. Similarly the distance between zero level and the average brightness is called DC level. The higher amplitude composite video signal represents dark picture and lower amplitude represents bright picture.

A transmission lines is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission. Types of transmission line include wires, coaxial cables, dielectric slabs, strip lines, optical fibers electric power lines, and waveguides. Coaxial lines confine the electromagnetic wave to the area inside the cable, between the center conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.

In radio-frequency applications up to a few gigahertz, the wave propagates in the transverse electric and magnetic mode (TEM) only, which means that the electric and magnetic fields are both perpendicular to the direction of propagation. Waveguides are rectangular or circular metallic tubes inside which an electromagnetic wave is propagated and is confined by the tube. Waveguides are not capable of transmitting the transverse electromagnetic mod found in copper lines and must use some other mode. Consequently, they cannot be directly connected to cable and a mechanism for launching the waveguide mode must be provided at the interface. Electromagnetic waves are oscillations that propagate free space with velocity of light .when high frequency signal is applied to an antenna system it emits electromagnetic waves; this is called propagation of radio waves.

Data communication consists of primary source, a transmission medium and destination. The primary source is the source of the information and secondary destination is the user of the information. The primary host is a mainframe computer. It is connected to many local terminals. The data is given from host to DTE or vice versa. The data terminal equipment is the interface between user computer and DCE or modem. And the data communication equipment it is modem. It converts digital signals to analog signals. The terminal equipment is interfaced to transmission medium through DEC. To establish the data transmission between the computers / terminals of different manufactures, there was a need to develop some common minimum standards.

International standards organization develops standards for graphics, document exchange and related technologies. Consultative committee for international telephony and telegraphy develops the standards for telephone and telegraph communications. CCITT has developed V series for modems and interface. X series for data communications and I & Q series for ISDN. American national standards institute is the official standards agency for U.S. IEEE is the US professional organization of electrical, electronics, computer and communication engineers. The electronic industries association establishes and recommends industrial standards. It develops recommended standard series of standards for data and telecommunications.

When telephone networks and network switching hierarchies were first engineered, their creators gave little thought about future technological advancements. Early telephone systems were based on transferring analog voice signals using analog equipment over analog transmission media. As a result early telephone systems were not well suited for modern-day digital services, such as data, digitized voice, or digitized video transmission. Therefore, when digital services were first offered in the early 1960s, the telephone networks were ill prepared to handle them, and the need for an intelligent all-digital network rapidly became evident.

The ITU commissioned the committee consultative international telephonique ET telegrapique to study the possibility of developing an intelligent all-digital telecommunications network. In the mid-1960s, the international telecommunications union telecommunications standardization sector developed a digital signaling standard known as signaling system. signaling refers to the exchange of information between call components required to provide and maintain service,SS6 based on a proprietary, high-speed data communication network, evolved into signaling system SS7 ,  which is now the telephone industry standard for most of the civilized world. High speed packet data and out-of-band signaling characterize SS7.out -of –band signaling is signaling that does not take place over the same path as the conversation. Out-of-band signaling establishes a separate d\digital channel for exchanging signaling information. This channel is called a signaling link.

The protocol used with SS7 uses a message structure, similar to X.25 and other message-based protocols, to request services from other networks, the messages propagate from one network to another in small bundies of data called packets that are independent of the subscriber voice or data signals they pertain to. In the early 1960s, the ITU-TS developed a common channel signaling known as common channel interoffice system SS6. The basic concept of the common channel signaling is to use a facility for transferring control and signaling information between telephone offices.

Today, SS7 is being used throughout the bell operating companies’ telephone network and most of the independent telephone companies. This is itself SS7 the world’s largest data communications network, as it links wire line telephone companies, cellular companies, and long distance telephone companies together with a common signaling system. Because SS7 has the ability to transfer all types of digital information, it supports most of the new telephone features and applications and it used with ATM, ISDN and cellular telephone.

Open-wire Transmission Lines:

Open-wire transmission lines consist simply of two parallel wires closely spaced and separated by air. Non conductive spacers are placed at periodic intervals not only for support but also to keep the distance between the conductors constant. The distance between the two conductors is generally between 2 inches and 6 inches. The dielectric is simply the air between and around the two conductors in which the TEM wave propagates. The only real advantage of this type of transmission line is its simple construction. Because there is no shielding, radiation losses are high, and the cable is susceptible to picking up signals through mutual induction, which produces crosstalk. Crosstalk occurs when a signal on one cable interferes with a signal on adjacent cable. The primary use of open-wire transmission lines is in standard voice-graded telephone applications.

Twisted-pair Transmission Lines:

A twisted-pair transmission line is formed by twisting two insulated conductors around each other. Twisted pairs are often stranded in units, and the units are then cabled into cores containing up to 3000 pairs of wire. The cores are then covered with various types of sheaths forming cables. Neighboring pairs are sometimes twisted with different pitches to reduce the effected of electromagnetic interference and radio frequency interference from external sources, such as fluorescent lights, power cables, motors, relays, and transformers. Twisting the wires also reduces crosstalk between cable pairs.

Unshielded Twisted-pair:

Unshielded twisted-pair (UTP) cable consists of two copper wires where each wire is separately encapsulated in (PVC) poly vinyl chloride insulation. Because a wire can act like an antenna, the wires are twisted two or more times at varying lengths to reduce crosstalk and interference. By carefully controlling the number of twists per foot and the manner in which multiple pairs are twisted around each other, manufactures can improve the bandwidth of the cable pair significantly. Most telephone systems use UTP cable, and the majority of new buildings are prewired with UTP cable. Generally, more cable is installed than is initially needed, providing room for orderly growth. This is one of the primary reasons why UTP cable is so popular. UTP is expensive, flexible, and easy to install. It is the least expensive transmission medium, but it is also the most susceptible to external electromagnetic interference.