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Network Media Chapter 4 Signal Transmission Network Media Signal Transmission Signaling—the way data is transmitted across the media Digital signaling Two discrete states • 0 or 1, on or off Analog signaling Constantly changing electromagnetic waves Digital Signaling Two different voltages are used. One voltage to represent on and another voltage to represent off Data 0 0 1 1 0 1 0 0 Voltage Time 0 1 2 3 4 5 6 7 Analog Signaling Constantly changing electromagnetic wave Characteristics: Amplitude • Strength of signal (height of wave) Frequency • Amount of time needed to complete one cycle of the wave Phase • Relative state of one wave in reference to another wave Attenuation/Noise Loss of signal strength as signal travels across media Signal must be amplified or regenerated to ensure that data is transmitted correctly Noise on media can disrupt data signal Static, cross-talk, etc. Electromagnetic interference (EMI) Radio frequency interference (RFI) Amplifiers and regenerators are used to increase the distance that signals can travel Converting Analog to Digital Modems At sending computer, convert computer digital signal to analog signal for transmission via media At receiving computer, convert analog signal to digital signal Modulator/Demodulator Transmission Direction Simplex—transmission of data in one direction only (television) Half-duplex—transmission of data in both directions but only one direction at a time (CB radio) Full-duplex—simultaneous sending and receiving of data (telephone) Multiplexers Enables multiple signals to travel simultaneously by combining two or more separate signals and transmitting them together. Multiplexer (mux) at sending end combines signals and demultiplexer (demux) at receiving end separates signals Example: Cable TV--numerous signals travel through coaxial cable; circuitry in the TV, VCR, or cable box separate the signals into different channels Multiplexing Methods Time Division Multiplexing Statistical Multiplexing Divides channel into time slots--each device is allotted a time slot Number of time slots allotted for each device varies depending on priority and need Wavelength Division Multiplexing Used for fiber-optic (light); different wavelength used for each channel Throughput/Bandwidth Throughput is the amount of data that can be sent across the network media in a given time. Bandwidth is the range of frequencies that the media can transmit Measured in bits per second Frequently throughput and bandwidth are used interchangable Two methods for allocating bandwidth: Baseband Broadband Baseband Transmission signals use the entire media bandwidth. Commonly used for digital signaling. Most LANs use baseband signaling Broadband Media bandwidth is divided into multiple channels. Each channel can carry different analog signals Broadband networks support multiple simultaneous signals over a single transmission medium Network Adapters (NICs or NACs) Provide the physical connection between your computer and the network media Transmit and receive data Prepare data for the network cable Send the data to another computer or device Control the flow of data between the computer and the network media Media Characteristics Throughput/bandwidth Cost Scalability Node Capacity—max # of node, Attenuation—max length of segment, max number of segments Noise immunity Installation—cable cost, ease of installation Maintenance—troubleshooting, repairing, replacing electromagnetic interference, radio frequency interference, and eavesdropping Connectors Network Media Anything that carries the message through the network Copper • Coaxial cable • Twisted-pair cable Glass Wireless (Air) • Radio waves • Microwaves • Infrared • Fiber-optic cable Transmission media—Physical path through which computers send and receive signals Coaxial Cable (Coax) Copper core surrounded by insulation and a sheath Shielding makes it more resistant to interference Two types of coax cable used in networks Thinnet (10Base2)—RG 58 A/U Thicknet (10Base5)—RG 62 Thinnet Thicknet Coaxial cable showing various layers Outer shield Insulation (PVC, Teflon) Copper wire mesh or aluminum sleeve Conducting core Thicknet cable transceiver with detail of a vampire tap piercing the core Thicknet Vampire tap Transceiver Drop Cable Coaxial Cable Terminators used at both ends of network to prevent signal bounce back Used with bus topology BNC cable connector used for Thinnet cable; nconnectors are used for Thicknet BNC T-connector BNC cable connector BNC Terminator Coaxial Characteristics Thinnet (10Base2) Cost Relatively inexpensive Installation Relatively easy Bandwidth 10 Mbps Nodes 30 Attenuation 185 meters EMI Better than UTP Connectors BNC Thicknet (10Base5) More than Category 5 More difficult 10 Mbps 100 500 meters Better than UTP n connectors Twisted-Pair Cable Similar to telephone wiring Color-coded pairs of wire; twisted and encased in plastic coating Unshielded twisted-pair and shielded twisted-pair cables UTP STP Shielding RJ-45 connector and jack Twisted Pair Cable Categories Category 1-2: Voice communications and low speed data communications. Category 3: Suitable for computer networks. Data transmission rates up to 10 Mbps. Currently used for phone installations (home) Category 4: Data transmission rates up to 20 Mbps Category 5: Data transmission rates up to 100 Mbps. Very popular for LANs. Category 5E: Higher speeds are possible (200 Mbps); more twists Category 6: Speeds up to six times faster than Cat 5 Category 7: Speeds up to 1 Ghz (Gigabit) UTP Characteristics Cost: Relatively inexpensive; depends on grade of copper and any enhancements Installation: Easy to install Bandwidth: 10-100 Mbps (Cat 5) Higher speeds are possible (up to 1000Mbps— Cat5E, Cat 6 and Cat 7) Node Capacity: Two (computer to hub) Attenuation: 100 meters EMI: Very susceptible to EMI and eavesdropping Connector: RJ-45 STP Characteristics Cost: Relatively inexpensive (more UTP, less than Thicknet or fiber-optic. Installation: Slightly more difficult than UTP Bandwidth: same as UTP Node Capacity: Two Attenuation: 100 meters EMI: Susceptible to EMI (but less susceptible than UTP) and eavesdropping Connector: RJ-45 Plenum Cable A plenum is the space between the false ceiling and the floor above. Plenum-grade cable is fire resistant and produces a minimum of smoke More expensive than PVC cable and less flexible May be required by fire code Fiber-optic cable Contains one or more glass fibers (core) Data transmitted via pulsing light Two categories: Single-mode and multi-mode Optical fiber (core) Fiber-optic connectors: ST and SC Glass cladding Protective outer sheath (jacket) Fiber-optic Characteristics Cost: More expensive than copper cable Installation: More difficult than copper cable Bandwidth: 100 Mbps to 1 Gbps Node: 2 Attenuation: Several kilometers EMI: Not subject to EMI; immune to eavesdropping Connectors: ST and SC are popular Cable Media Comparison Factor UTP STP Coaxial Cost Installation Bandwidth Lowest Easy 10-100 Mbps (typical) 2 Moderate Fairly easy 10-100 Mbps (typical) 2 Attenuation High (100 meters) High (100 meters) EMI Yes Connectors RJ-45 Yes but less than UTP RJ-45 Moderate Highest Fairly easy Difficult Typically 10 Mbps 1 Gbps (100 Mbps) 30 (10base2) 2 100 (10base5) Lower Lowest Thinnet--185 m (several Thicknet--500 m kilometers) Yes but less than No UTP and STP BNC (thinnet) ST and SC N connectors (thicknet) Nodes Fiber-optic Wireless Media (Atmospheric) Infrared Radio Frequency (RF) Narrow-band Spread-spectrum Microwaves Wireless portable computer using an infrared light beam to print Infrared Infrared Transmission Systems Use infrared light to transmit signals Point-to-Point (Direct) or Broadcast (Indirect) Point-to-Point (Direct)—highly focused and directed at a specific target • Line of Site Broadcast—spread the signal to cover a wider area and allow reception of signal by several receivers • Signal can be bounced off walls and ceilings Infrared Characteristics Line of site Bandwidth: 100 Kbps to 16 Mbps Light must be able to reach target Tested at up to 100Mbps but slower speeds are currently standard Attenuation: Depends upon the quality of light and atmospheric conditions EMI: Can be affected by intense light. Pointto-Point transmissions are fairly immune to eavesdropping. However, broadcast transmission are more easily intercepted. Wireless portable computer connecting to a cabled network access point Network Radio Frequencies Characteristics Frequency range Cost Installation Bandwidth Attenuation EMI Narrowband Single frequency Moderate Simple Up to 10Mbps High Poor Spread-spectrum Multiple frequencies simultaneously Moderate Moderate Up to 10Mbps High Fair Wireless bridge connecting two LANs Microwave Transmission Terrestrial Microwave Line of site (max distance ~ 23 miles) Transmission can be affected by atmospheric conditions (rain/fog). Vulnerable to EMI, jamming and eavesdropping Bandwidth 1-10 Mbps Satellite Microwave Can transmit data over vast distances Extremely expensive if you put up your own satellite Example of Network Wiring patch cable Example Wiring Closet