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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 Divides channel into time slots--each
device is allotted a time slot Statistical Multiplexing
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. Measured in bits per second
Bandwidth is the range of frequencies that the media can transmit 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
Installation—cable cost, ease of installation Maintenance—troubleshooting, repairing, replacing
Scalability Node Capacity—max # of node, Attenuation—max length of segment, max number of
segments Noise immunity
electromagnetic interference, radio frequency interference, and eavesdropping
Connectors
Network Media
Copper• Coaxial cable• Twisted-pair cable
Glass• Fiber-optic cable
Wireless (Air)• Radio waves• Microwaves• Infrared
Anything that carries the message through the network
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
Thicknet
Thinnet
Coaxial cable showing various layers
Outer shield
Insulation (PVC, Teflon)
Conducting coreCopper wire mesh oraluminum sleeve
Thicknet cable transceiver with detail of a vampire tap piercing the core
Thicknet
Transceiver
Drop Cable
Vampire tap
BNC cable connector
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; n-
connectors are used for Thicknet
BNC Terminator
BNC T-connector
Coaxial Characteristics
Thinnet (10Base2) Thicknet (10Base5) Cost Relatively inexpensive More than Category 5 Installation Relatively easy More difficult Bandwidth 10 Mbps 10 Mbps Nodes 30 100 Attenuation 185 meters 500 meters EMI Better than UTP Better than UTP Connectors BNC 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
Shielding
UTP
STP
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
Fiber-optic connectors:ST and SC
Optical fiber (core) 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 ComparisonFactor UTP STP Coaxial Fiber-optic Cost Lowest Moderate Moderate Highest Installation Easy Fairly easy Fairly easy Difficult Bandwidth 10-100 Mbps
(typical) 10-100 Mbps (typical)
Typically 10 Mbps 1 Gbps (100 Mbps)
Nodes 2 2 30 (10base2) 100 (10base5)
2
Attenuation High (100 meters)
High (100 meters)
Lower Thinnet--185 m Thicknet--500 m
Lowest (several kilometers)
EMI Yes Yes but less than UTP
Yes but less than UTP and STP
No
Connectors RJ-45 RJ-45 BNC (thinnet) N connectors (thicknet)
ST and SC
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
Light must be able to reach target Bandwidth: 100 Kbps to 16 Mbps
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. Point-to-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
Narrowband Spread-spectrum Frequency range
Single frequency Multiple frequencies simultaneously
Cost Moderate Moderate Installation Simple Moderate Bandwidth Up to 10Mbps Up to 10Mbps Attenuation High High EMI Poor 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