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Lecture

Chapter 7-1.docx

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Department
Administrative Studies
Course Code
ADMS 2511
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Donna Rex

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Chapter 7: Evaluate the advantages and disadvantages of the main types of transmission media • Define and describe different wireless transmission media that facilitate data transfer through the air or in space o Microwave Transmission systems are widely used for high-volume, long-distance, line-of-sight communication. Line- of-sight means that the transmitter and receiver are in view of each other. The requirement for adjacent microwave towers to be in view of each other creates problems because the earth's surface is curved. For this reason, microwave towers usually cannot be spaced more than about 48 kilometres apart.  This requirement severely limits the usefulness of microwave transmissions as a solution to data communications needs, especially over very long distances. Additionally, microwave transmissions are susceptible to environmental interference during severe weather such as heavy rain or snowstorms. Although long-distance microwave data communications systems are still widely used, they are being replaced by satellite communications systems. o Satellite Transmission systems make use of communication satellites.  Currently, there are three types of satellites around the earth: geostationary-earth- orbit (GEO), medium-earth-orbit (MEO), and low-earth-orbit (LEO). Each type has a different orbit, with the GE O being farthest from the earth and the LEO the closest.  satellites must receive and transmit data via line-of-sight. However, the enormous footprint—the area of the earth's surface reached by a satellite's transmission— overcomes the limitations of microwave data relay stations. The most basic rule governing footprint size is simple: the higher a satellite orbits, the larger its footprint. Thus, middle-earth-orbit satellites have a smaller footprint than geostationary satellites, and low-earth-orbit satellites have the smallest footprint. o Radio Transmission uses radio-wave frequencies to send data directly between transmitters and receivers.  Radio transmission has several advantages. To begin with, radio waves travel easily through normal office walls. In addition, radio devices are fairly inexpensive and easy to install. Finally, radio waves can transmit data at high speeds. For these reasons, radio is increasingly being used to connect computers to both peripheral equipment and local area networks.  As with other technologies, however, radio transmission has its drawbacks as well. First, radio media can create electrical interference problems. Also, radio transmissions are susceptible to snooping by anyone who has similar equipment that operates on the same frequency. o Infrared Transmission light is red light that is not commonly visible to human eyes.  Common applications of infrared light are in remote control units for televisions, VCRs, DVDs, and CD players.  In addition, like radio transmission, infrared transceivers are used for short-distance connections between computers and peripheral equipment and local area networks. A transceiver is a device that can transmit and receive signals. Many portable PCs have infrared ports, which are handy when cable connections with a peripheral (such as a printer or modem) are not practical. Be able to define and describe different wireless networks according to their range and discuss their applications within the context of a case Short Range:  Bluetooth is an industry specification used to create small personal area networks. o A Personal area Network is a computer network used for communication among computer devices (for example, telephones, personal digital assistants, and smart phones) close to one person. o Bluetooth can link up to eight devices within a 10-metre area using low-power, radio-based communication. o It can transmit up to 2.1 Mbps (megabits per second).  Ultra Wideband (UWB) is a high-bandwidth wireless technology with transmission speeds in excess of 100 Mbps. o This very high speed makes UWB a good choice for applications such as streaming multimedia from, say, a personal computer to a television. o Developers of Bluetooth and UWB are now collaborating so the two technologies will work together seamlessly.  Nearfield Communications (NFC) has the smallest range of any short-range wireless networks. o It is designed to be embedded in mobile devices such as cell phones and credit cards. o Using NFC, you can swipe your device or card within a few centimetres of point-of-sale terminals to pay for items. Medium Range:  Wireless Fidelity (WI-FI) is a medium-range Wireless Local Area Network (WLAN), which is like a wired LAN but without the cables. o In a typical configuration, a transmitter with an antenna, called a Wireless Access Point, connects to a wired LAN or to satellite dishes that provide an Internet connection.  A wireless access point provides service to a number of users within a small geographical perimeter (up to about 70 metres), known as a Hotspot.  To support a larger number of users across a larger geographical area, several wireless access points are needed. To communicate wirelessly, mobile devices, such as laptop PCs, typically have a built-in Wireless Network Interface Card (NIC).  Wi-Fi provides fast and easy Internet or intranet broadband access from public hotspots located at airports, hotels, Internet cafés, universities, conference centres, offices, and homes. o most WLANs use the 802.11g standard, which can transmit up to 54 Mbps and has a range of about 90 metres. As of mid-2007, the 802.11n standard was still under development. This standard is designed to have wireless transmission speeds between 250 and 300 Mbps, and a range double that of 802.11g, or some 180 metres.  Wireless Mesh Networks use multiple Wi-Fi access points to create a wide-area network that can be as large as, for instance, the 350-square-kilometre network being developed in Philadelphia, U.S.A. o Mesh networks could be included in the chapter section on long-range wireless but they are here cuz they are essentially a series of interconnected local area networks. Wide Area Wireless Networks:  Cellular Radio o Cell Phones use radio waves to provide two-way communication.  The cell phone communicates with radio antennas (towers) placed within adjacent geographic areas called cells. A telephone message is transmitted to the local cell (antenna) by the cell phone and then is passed from cell to cell until it reaches the cell of its destination. At this final cell, the message is either transmitted to the receiving cell phone or is transferred to the public switched telephone system to be transmitted to a wireline telephone.  WiMax, is the name for IEEE Standard 802.16. o WiMax has a wireless access range of up to 50 km, compared with 90 metres for Wi-Fi and nine metres for Bluetooth. o WiMax also has a data-transfer rate of up to 75 Mbps. It is a secure system, and offers features such as voice and video. o WiMax is not yet mobile. Rather, it is currently a point-to-point technology.  WiMax antennas can transmit broadband Internet connections to antennas on homes and businesses miles away. The technology can therefore provide long-distance broadband wireless access to rural areas and other locations that are not currently being served. Be able to evaluate different wireless transmission media, their applications and discuss the advantages and disadvantages of each type o (Table 7.1) Define and describe Radio-Frequency Identification (RFID) technology, including its two underlying components  Radio Frequency Identification Technology (RFID) allows manufacturers to attach tags with antennas and computer chips on goods and then track their movement through radio signals. o RFID was developed to replace bar codes. A typical bar code, known as the Universal Product Code (UPC), is made up of 12 digits, in various groups.  The first digit identifies the item type, next five digits identify the manufacturer, the last five identify the product.  The last digit is a check digit for error detection. o Bar codes have worked well, but they have limitations.  First, they require line-of-sight to the scanning device. This is fine in a store, but it can pose substantial problems in a manufacturing plant or a warehouse or on a shipping/receiving dock.  Second, because bar codes are printed on paper, they can be ripped, soiled, or lost.  Third, the bar code identifies the manufacturer and product, but not the actual item. o RFID systems use tags with embedded microchips, which contain data, and antennas to transmit radio signals over a short distance to RFID readers.  The readers pass the data over a network to a computer for processing.  The chip in the RFID tag is programmed with information that uniquely identifies an item. It also contains information about the item such as its location and where and when it was made o RuBee, a wireless networking protocol that relies on magnetic, rather than electrical energy, gives retailers and manufacturers an alternative to RFID for some applications. RuBee works in harsh environments, near metal and water, and in the presence of electromagnetic noise. RuBee is an alternative to, and not a replacement for, RFID. RuBee technology is being used in smart shelf environments. The shelves alert store employees when inventory of a product is running low. Describe wireless sensor networks (WSN), their uses and applications  Wireless Sensor Networks are networks of interconnected, battery-powered, wireless sensors called motes (analogous to nodes) that are placed into the physical environment. o The motes collect data from many points over an extended space.  Each mote contains processing, storage, and radio-frequency sensors and antennas.  Each mote “wakes up” or activates for a fraction of a second when it has data to transmit and then relays that data to its nearest neighbour. So, instead of every mote transmitting its information to a remote computer at a base station, the data is moved mote by mote until they reach a central computer where it can be stored and analyzed. o An advantage of a wireless sensor network is that, if one mote fails, another one can pick up the data. This process makes WSNs very efficient and reliable. Also, if more bandwidth is needed, it is easy to boost performance by placing new motes when and where they are required. o The motes provide information that enables a central computer to integrate reports of the same activity from different angles within the network. Therefore, the network can determine with much greater accuracy information such as the direction in which a person is moving, the weight of a vehicle, or the amount of rainfall over a field of crops. o ZigBee (a kind of wireless sensor) is a set of wireless communications protocols that target applications requiring low data-transmission rates and low power consumption. ZigBee can handle hundreds of devices at once. Its current focus is to wirelessly link sensors that are embedded into industrial controls, medical devices, smoke and intruder alarms, and building and home automation. Be able to discuss the advantages and disadvantages of RFID technology  Advantages  Disadvantages o One problem with RFID has been the expense. Tags remain expensive, which makes them unusable for low-priced items. To alleviate this problem, a California company called Alien Technology Corporation has invented a way to mass-produce RFID tags for less than 10 cents apiece for large production runs. o Another problem with RFID has been the size of the tags. o They do not work in harsh environments Define pervasive computing and how it is impacted by wireless computing and mobile commerce:  A world in which virtually every object has processing power with wireless or wired connections to a global network is the world of pervasive computing, also called ubiquitous computing.  Pervasive computing is invisible “everywhere computing” that is embedded in the objects around us—the floor, th
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