With diagrams compare Essay Example for Free

With diagrams compare Essay This type of communication is between the sender and the receiver is known as connectionless (rather than dedicated) Contrasted with packet-switched is circuit-switched, a type of network such as the regular voice telephone network in which the communication circuit (path) for the call is set up and dedicated to the participants in that call. For the duration of the connection, all the resources on that circuit are unavailable for other users. Voice calls using the Internets packet-switched system are possible. Each end of the conversation is broken down into packets that are reassembled at the other end. The principles of packet switching are as follow. Messages are divided into data packets, which are then directed through the network to their destination under computer control. Besides a message portion, each packet contains data concerning. The principles of packet switching are as follow. Messages are divided into data packets, which are then directed through the network to their destination under computer control. Besides a message portion, each packet contains data concerning: Â  The destination of the address; Â  The source identification; The sequence of the packet in the complete message; Â  The detection and control of transmission errors. Â  Pre-determined routing. With this method, the routing details are included in the packet itself, each switching exchange forwarding the packet according to the embedded instructions; Â  Directory routing. Each switching exchange has a copy of a routing table to which it refers before forwarding each packet. The appropriate output queue is determined from the table and the packet destination Diagram shown below: Identify three types of cabling used in data communication. State which one you would recommend in an implement requiring high security consideration and why? The three types of cables used in data communication are: Optical Fiber Coaxial Coaxial cable is a copper that is used by TV companies between the community antenna, and also the user homes and businesses. At times these cable are also used by telephone companies from their central office to the telephones near users. This is also widely installed for use in business and corporation Ethernet and other types of local area network. Coaxial cable is called coaxial this is because this includes one physical channel that carries the signal surrounded (after a layer of insulation) by another concentric physical channel, both running along the same axis. The outer channel serves as a ground. Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, they can carry information for a great distance. This is a diagram shown below: UPT UPT stands for Unshielded twisted pair. This cable is the most common kind of copper telephone wiring. Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company. To reduce crosstalk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted around each other. Each signal on twisted pair requires both wires. Since some telephone sets or desktop locations require multiple connections, twisted pair is sometimes installed in two or more pairs, all within a single cable. For some business locations, twisted pair is enclosed into a shield that functions as a ground. This is known as shielded twisted pair (STP). The twisted pair is now frequently installed with the two pairs to the home, with the extra pair making it possible for you to add another line (perhaps for use of a modem) when you will need it. These twisted pair comes with each pair uniquely colour coded when it is packaged in multiple pairs. Different uses such as analogue, digital, and Ethernet require different pair multiples. Although twisted pair is often associated with home use, with a higher grade of twisted pair is often used for horizontal wiring in LAN installations because it is less expensive than coaxial cable. The wire that you buy at a local hardware store for extensions from your phone or computer modem to a wall jack is not twisted pair. It is a side-by-side wire known as silver satin. The wall jack can have as many five kinds of hole arrangements or pin outs, depending on what kinds of wire the installation you expects that will be plugged in (for example, digital, analogue, or LAN) . (Thats why you may sometimes find when you carry your notebook computer to another location that the wall jack connections wont match your plug. ) This is a diagram shown below: Optical Fiber. Optical fiber (or fiber optic) refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than the conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber. Transmission on optical fiber wire requires repeaters at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any of the new wiring is labour-intensive, few communities yet have optical fiber wires or cables from the phone companys branch office to local customers (known as local loops). A type of fiber known as single mode fiber is used for longer distances; multimode fiber is used for shorter distances. This is the diagram shown below: By analyzing and researching the three above cable I would recommend the Fiber Optic cable this is because I believe it has a high security and also has the following. Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data. Â  Fiber optic cables are less susceptible than metal cables to interference. Fiber optic cables are much thinner and lighter than metal wires. Data can be transmitted digitally (the natural form for computer data) rather than analogically. Identify the alternative forms of communication media and provide examples of their use in different forms of network. Microwave Microwave frequencies require a direct line of sight between sending and receiving station to operate. Microwave systems were the preferred method of communications transmission before the introduction of fiber optic. Radio The lowest-frequency domain that needed to name. This extends from wavelengths of a kilometre or so, the longest that will propagate through the interstellar medium, down to about a millimetre. The detection of radio radiation is often done using wave techniques rather than photon-counting, this is because of the low photon energies, and this offers distinct advantages for such applications as interferometer which astronomers working in the infrared and optical regimes view with some envy. From active nuclei, we often detect the synchrotron radiation in this range radiation produced energetic charged particles (mostly electrons) produce when they are deflected by the magnetic fields. a) Define the basic signal theory with the aid of diagrams? 1) In electronics, a signal is an electric current or electromagnetic field that is used to convey data from one place to another. The simplest form of signal is a direct current (DC) that is switched on and off; this is the principle by which the early telegraph worked. More complex signals consist of an alternating-current (AC) or electromagnetic carrier that contains one or more data streams. Data is superimposed on a carrier current or a wave this is by means of a process called a modulation. Signal modulation can be done by two main ways: analogue and digital. In recent years, digital modulation has been getting more common, while analogue modulation methods have been used less and less. There are still plenty of analogue signals around, however, and they will probably never become totally extinct. Except for DC signals such as telegraph and base band, all signal carriers have a definable frequency or frequencies. Signals also have a property called wavelength, which is inversely proportional to the frequency. 2) In some information technology contexts, a signal are simply that which is sent or received, thus including both the carrier and the data together. 3) In telephony, a signal has a special data that is used to set up or control communication. Almost everything in the world can be described or represented in one of two forms: analogue or digital. The principal feature of analogue representations is that they are continuous. In contrast, digital representations consist of values measured at discrete intervals. Digital watches are called digital because they go from one value to the next without displaying all intermediate values. Consequently, they can display only a finite number of times of the day. In contrast, watches with hands are analogue, this is mainly because the hands move continuously around the clock face. As the minute hand goes around, it not only touches the numbers 1 through 12, but also the infinite number of points in between. Early attempts at building computers used analogue techniques, but the accuracy and reliability were not good enough. Today, almost all computers are digital. Analogue and Digital Technology Analogue and Digital are the words we hear when people talk about Communication and Information Technology. What do the words Analogue and Digital mean? Analogy means a likeness between two things that are really quite different. For example the analogy between the brain and the computer or the heart and a pump. Digit means either a finger or toe, or one of the numbers 1 to 9. Some examples might help to explain what analogue and digital mean in technology. A simple example of analogue and digital technology Clocks are examples of analogue and digital technology. An analogue clock face can display the time without numbers. The hands keep moving all the time and they continue to rotate, just like the earth around the sun. This is the analogy between the movement of the sun and earth, and the hands of the clock. The digital clock displays the time in numbers, and the time displayed only changes at each minute. In the analogue clock the hands keep moving all the time, while the digital clock is more like an on and off movement. Each minutes the time moves and then stops for another 60 seconds, when it changes again. Some other examples of displaying information using analogue and digital forms. b) How the signal theory affects the choice of transmission methods and media? Analogue and Digital Signals Sound can be converted into analogue and digital electrical signals. Analogue Signal A microphone or handset of a telephone will convert sound into an analogue signal. The shape of the wave seen on an oscilloscope represents the volume and pitch. The diagram is shown below: This is called an analogue signal because, when the volume and pitch change, so does the shape of the wave. The signal is an analogue of the sound. Digital signal Today we see many sound systems described as digital. This means the sound is converted into digital signals so it can be transmitted or recorded. In the microphone example shown on the diagram above, the analogue signal is converted into a digital signal by electronic circuits. In a digital signal the electricity, this can be either on or off, is combined with a binary code. The voltage of the analogue signal is measured electronically, many thousands of times per second, by an analogue-digital converter. The analogue signal is converted into a 16 bit binary number, which gives 65,536 levels of voltage. In electronics 1 = ON and 0 = OFF. This means the binary number can be converted into an electrical signal. A diagram below shows the process of converting analogue signals into a binary numbers and digital signals. To keep the explanation simple the analogue signal has been converted into a 3 bit binary number, which means there are seven voltage levels. A digital-analogue converter reverses the conversion this is because the speakers (output device) need an analogue signal. Light and sound can be converted into binary numbers and digital signals that are used to record and transmit information. This diagram is shown below: Why are digital systems better than the analogue ones? An analogue signal is affected by changes in the voltage as it travels along a wire. If the voltage changes, so does the signal at the output. The digital signal is not affected by changes in the voltage this is because all that matters is whether it is ON or OFF. How signal affects transmission methods? Noise is any sound on the CD or record that wasnt there at the performance during the recording session. More generally, it is any unwanted signal that adds on to the information that is being transmitted. When a vinyl record is being made, noise is introduced at every step of the recording process, although of course the company makes an every effort to reduce such noise to as low a level as possible. The sound that reaches the microphones is converted into an electrical signal that is then recorded on a wide magnetic tape moving at high speed. This tape is then used to control the cutting of a master disc, from which moulds are then made. These in turn are used to mass-produce the records that are eventually sold in shops. Noise is produced at every step, not forgetting that introduced by your own stereo equipment. It can never be entirely eliminated. The same problems of noise are shared by any method of transmitting information, and are certainly by telecommunications, including telephone calls. In the production of vinyl records, the companies have used purely analogue this means to transfer the information representing the sound of the music from one point to another. That means they use an electrical signal that changes smoothly in strength, exactly modelling the smooth but complex changes in the sound. When a noise is created in the recording process because of tape hiss, dust on the master disc, electrical interference or any other cause this is added on as a random signal on top of the complex electrical signal representing the sound. There is no way that electronic equipment can tell such random noise from the original electrical signal, so there is no way it can be removed again without removing some of the original signal. We can see more clearly if we draw a graph of the level of the analogue audio signal over a period of time (diagram 1a). The shape of this graph represents both the changes in the electrical sound and the changes in the electrical signal that model it. Now if we add to this audio signal some random noise, this affects the shape of the signal, and this degrades the sound that your stereo reproduces (diagram 1b). The trouble with an analogue audio signal is that its exact shape has to be preserved if you are to hear the music exactly as it was when it was played. If there were a means of transmitting the signal so that only the overall shape of the signal mattered, then noise would not be so important. The port authorities used to find the shape of the bottom of the harbour, so that ships could navigate more safely. It certainly wasnt possible to drain the harbour and take a photograph of it, so what they did instead was send out a boat which travelled slowly across the harbour. Every few meters a person at the back of the boat dropped down a plumb-line (a weight at the end of a rope), until it reached the bottom of the harbour. The line had knots tied in it at regular spaces and the person called out the number of knots under water, so indicating the depth of the harbour at that point. A clerk wrote these down, and eventually it was possible for him to draw a graph of the shape of the harbour by using these numbers. The person in the boat had been taking samples of the depth of the harbour at frequent intervals, so that the graph would accurately describe the ups and downs of the harbour bottom.