COTN1220_04_Guided_And_Wireless_Media (PDF)

CELLULAR TELEPHONES Wireless telephone service, also called mobile telephone, cell phone, and PCS To support multiple users in a metropolitan area (market), the market is broken into cells Each cell has its own transmission tower and set of assignable channels CELLULAR TELEPHONES CELLU...

CELLULAR TELEPHONES Wireless telephone service, also called mobile telephone, cell phone, and PCS To support multiple users in a metropolitan area (market), the market is broken into cells Each cell has its own transmission tower and set of assignable channels CELLULAR TELEPHONES CELLULAR TELEPHONES CELLULAR TELEPHONES CELLULAR TELEPHONES Placing a call on a cell phone You enter a phone number on your cell phone and press Send. Your cell phone contacts the nearest cell tower and grabs a set-up channel. Your mobile identification information is exchanged to make sure you are a current subscriber. If you are current, you are dynamically assigned two channels: one for talking, and one for listening. The telephone call is placed. You talk. CELLULAR TELEPHONES Receiving a call on a cell phone Whenever a cell phone is on, it “pings” the nearest cell tower every several seconds, exchanging mobile ID information. This way, the cell phone system knows where each cell phone is. When someone calls your cell phone number, since the cell phone system knows what cell you are in, the tower “calls” your cell phone. BLUETOOTH Bluetooth is a specification for short-range, point-to-point or point- to-multipoint voice and data transfer Bluetooth can transmit through solid, non-metal objects Its typical link range is from 10 cm to 10 m, but can be extended to 100 m by increasing the power Bluetooth enable users to connect to a wide range of computing and telecommunication devices without the need of connecting cables Typical uses include phones, modems, LAN access devices, headsets, notebooks, and desktop computers WIRELESS LOCAL AREA NETWORKS (IEEE 802.11) This technology transmits data between workstations and local area networks using high-speed radio frequencies Current technologies allow up to 100 Mbps (theoretical) data transfer at distances up to hundreds of feet Four popular standards: IEEE 802.11b, a, g, n, ac, ax More on this later in the course INFRARED TRANSMISSIONS Transmissions that use a focused ray of light in the infrared frequency range Very common with remote control devices, but can also be used for device-to-device transfers, such as PDA to computer MEDIA SELECTION CRITERIA Cost Speed Distance and expandability Environment Security COST Different types of costs Initial cost – what does a particular type of medium cost to purchase? To install? Maintenance / support cost ROI (return on investment) – if one medium is cheaper to purchase and install but is not cost effective, where are the savings? SPEED Two different forms of speed: Propagation speed – the time to send the first bit across the medium This speed depends upon the medium Airwaves and fiber are speed of light Copper wire is two thirds the speed of light Data transfer speed – the time to transmit the rest of the bits in the message This speed is measured in bits per second EXPANDABILITY AND DISTANCE Certain media lend themselves more easily to expansion Don’t forget right-of-way issue for conducted media and line-of-sight for certain wireless media ENVIRONMENT Many types of environments are hazardous to certain media Electromagnetic noise Scintillation and movement Extreme environmental conditions SECURITY If data must be secure during transmission, it is important that the medium not be easy to tap Make the wire impervious to electromagnetic wiretapping Encrypt the signal going over the medium SUMMARY All data communication media can be divided into two basic categories: (1) physical or conducted media, and (2) radiated or wireless media, such as satellite systems The three types of conducted media are twisted pair, coaxial cable, and fiber-optic cable Twisted pair and coaxial cable are both metal wires and are subject to electromagnetic interference SUMMARY Fiber-optic cable is a glass wire and is impervious to electromagnetic interference Experiences a lower noise level Has best transmission speeds and long-distance performance of all conducted media Several basic groups of wireless media exist: terrestrial microwave transmissions, satellite transmissions, cellular telephone systems, infrared transmissions, WiMAX, and Bluetooth SUMMARY Each of the wireless technologies is designed for specific applications When trying to select particular medium for an application, it helps to compare the different media using these six criteria: cost, speed, expandability and distance, right-of-way, environment, and security