Wireless Networking Technologies
3. What are the characteristics of the Bluetooth technology?
Wireless replacement for cables (e.g. headphones or mouse) Uses 2.4 GHz frequency band Short distance (up to 5 meters, with variations that extends the range to 10 or 50 meters) Device is master or slave Master grants permission to slave Data rate is up to 721 Kbps
2. Name the three major types of wireless PAN technologies and give a brief description of each
Bluetooth - Communication over a short distance between a small peripheral device such as a headset or mouse and a system such as a cell phone or a computer. Infrared - Line-of-sight communication between a small device, often a hand-held controller and a nearby system such as a computer or an entertainment center ZigBee - Communication over distances about as large as a residence which allows electrical appliances to connect to the Smart Grid.
8. What are the two types of wireless LANs?
The two types of wireless LAN are: Ad hoc and infrastructure.
6. Describe the spread spectrum technique used in Wi-Fi communications.
o With spread spectrum technique, the sender of a message uses multiple frequencies to send the different part of a message (frequency multiplexing). o The major multiplexing techniques used with WiFi are: DSSS (Direct Sequence Spread Spectrum) FHSS (Frequency Hopping Spread Spectrum), OFDM (Orthogonal Frequency Division Multiplexing).
22. Give a brief description of each of the four generations of cellular technologies.
• 1G (1970 - 1980) used analog signal to carry voice. • 2G and 2.5G (1990 - ) uses digital signal to carry voice. 2.5G includes some 3G features 3G and 3.5G (2000 - ) focuses on the addition of higher speed data services. • A 3G system offers download rates of 400 Kbps to 2 Mbps and is intended to support applications such as web browsing and photo sharing o 3G allows a phone to roam across North America, Japan, and Europe. • 4G (2008 - ) o Focuses on support for real-time multimedia such as television programs or high-speed video download o 4G phones include multiple connection technologies such as Wi-Fi and satellite communications. o 4G systems use packet switching, and voice transmission is one specific application. But in practice, many cellular phone providers still send voice over 3G systems and only use 4G protocols for data.
32. How many satellite are used in GPS and how accurate is a GPS system?
• 24 satellites are used, and the accuracy is between 20 and 2 meters.
21. What is a cell cluster, and how does a designer use clusters?
• A cell cluster is a group of 3, 4, 7, or 12 adjacent cells in which each cell is assigned a unique frequency.
16. Give a brief description of a cellular architecture.
• A cellular architecture is designed as follows: o Each cell contains a tower, and o A group of (usually adjacent) cells is connected to a Mobile Switching Center. . o The center tracks a mobile user and manages handoff as the user passes from one cell to another
23. What is a communication satellite?
• A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder
24. What is a transponder?
• A transponder is a device that creates a communication channel between a source transmitter and a receiver at different locations on Earth.
29. What is a VSAT?
• A very small aperture terminal (VSAT) is a two-way satellite ground station with a dish antenna that is smaller than 3.8 meters.
9. Give a description of each of the types of wireless LANs.
• Ad hoc: Wireless hosts communicate among themselves without a base station, and • Infrastructure: a wireless host only communicates with an access point and the access point relays all packets.
20. How do cellular communications minimize interference?
• Cellular communications minimize interference by making sure that pairs of adjacent cells do not communicate at the same frequency.
19. Why are cellular coverages not perfect?
• Cellular coverages are imperfect because most cell towers use omnidirectional antennas that transmit in a circular pattern and obstructions and electrical interference can attenuate a signal or cause an irregular pattern. As a result, cells overlap or gaps exist with no coverage.
26. What types of signals are used in a communication satellite?
• Communication satellite uses electromagnetic waves to carry signals.
25. What are the different usages of communications satellites?
• Communications satellites are used for television, telephone, radio, internet, and military applications.
11. How did the IEEE 802.11 recommend handling overlaps?
• IEEE 802.11 networks require a wireless host to associate with a single access point in order to handle overlaps a wireless host sends frames to a particular access point, which then forwards it across the network.
13. An 802.11 header contains two destination addresses. Explain the purpose of each.
• One destination address is the access point's MAC address and the other is the router's MAC address.
18. When do you have a perfect cellular coverage in a cellular system?
• Perfect cellular coverage occurs when each cell forms a hexagon because cell can be arranged in a honeycomb.
1. What are the four categories wireless technologies in use today?
• Personal Area Networks (PANs) • Local Area Networks (LANS) • Metropolitan Area Networks (MANs), • Wide Area Networks (WANs)
5. What is RFID and where is it used?
• Radio Frequency Identification (RFID) technology consists of a small tag that contains some identification information that a receiver can pull (extract) from the tag. Passive RFIDs draw power from the signal sent by the reader, and • Active RFIDs contain a battery which may last up to 10 years • Limited distance (active RFIDs extend farther than passive RDFIs) Can use frequencies from less than 100 MHz to 868-954 MHz • It is used for inventory control, sensors, passports, and other applications.
31. What are the different uses of VSAT technology?
• Some of the uses of VSAT technology follows: o point-of-sale transactions using credit cards, o Internet access o polling or RFID data, o VoIP or video o Many businesses also use VSAT technology to link all their stores.
7. What are the three building blocks of a wireless LAN?
• The building blocks of a wireless LAN are: o Access points informally called base stations o An interconnection mechanism such as a switch or a router used to connect access points. o A set of wireless hosts also called wireless nodes or wireless stations
15. What are the primary usages of cellular systems today?
• The primary usages of cellular systems today are to provide voice services, data services, and internet connectivity to mobile customers.
30. What is the purpose of a VSAT?
• The purpose of VSATs is to access satellites to relay data from small remote Earth stations (terminals) to other terminals in mesh topology, or master Earth station "hubs" (in star topology).
27. What is the purpose of communications satellites?
• The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated points.
12. What are the two approaches used for coordinating among access points?
• The two approaches used for coordinating among access points are: o The access points communicate among themselves to ensure a smooth handoff as a wireless computer moved from the region of one access point to the region of another. o Access points operate independently and rely on wireless computers to change their association from one access point to another.
14. What are the two major categories of wireless WAN?
• The two major categories of Wireless WAN technologies are cellular communication systems, and satellite communication systems.
10. What are the two major issues with a wireless LAN architecture?
• The two major issues with a wireless LAN architecture are signals overlaps and dead zones.
28. How are the signal interferences avoided in communications satellites?
• To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" are set for certain organizations to use.
17. In a cellular system, what happens when a user moves between two cells?
• When a user moves between two cells that connect to the Mobile Switching Center, the switching center handles the change and when he passes from one geographic region to another, two Mobile Switching Centers are involved in the handoff.
4. What is ZigBee, and where is it used?
• ZigBee is a personal Area Network (PAN) technology . It is used for communication over distances about as large as a residence which allows electrical appliances to connect to the Smart Grid.