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- Transmission Basics and Networking Media
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- Explain data transmission concepts including full-duplexing,
attenuation, and noise
- Describe the physical characteristics of coaxial cable, STP, UTP, and
fiber-optic media
- Explain the benefits and limitations of different networking media
- Identify the best practices for cabling buildings and work areas
- Describe the methods of transmitting data through the atmosphere
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- Transmission has two meanings:
- Refers to process of issuing data signals on a medium
- Refers to progress of data signals over a medium
- On a data network, information can be transmitted via one of two
methods:
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- Both analog and digital signals are generated by electrical current,
pressure of which is measured in volts
- In analog signals, voltage varies continuously
- In digital signals, voltage turns off and on repeatedly
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- Amplitude
- Measure of a signal’s strength
- Frequency
- Number of times a signal’s amplitude changes over a period of time
- Expressed in hertz (Hz)
- Wavelength
- Distances between corresponding points on a wave’s cycle
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- Phase
- Refers to progress of a wave over time in relationship to a fixed point
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- Binary system encodes using 1s and 0s
- Bits can only have a value of either 1 or 0
- Eight bits together form a byte
- Noise or any interference that may degrade signals affects digital
signals less than analog signals
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- Modem
- Name reflects function as modulator/demodulator
- Modulation
- Technique for formatting signals
- Frequency modulation (FM)
- Method of data modulation in which frequency of carrier signal is
modified by application of a data signal
- Amplitude modulation (AM)
- Modulation technique in which amplitude of carrier signal is modified
by application of a data signal
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- Simplex
- Signals travel in only one direction
- Half-duplex
- Signals may travel in both directions over a medium but in only one
direction at a time
- Full-duplex
- Signals are free to travel in both directions over a medium
simultaneously
- Also referred to just as duplex
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- Channel
- Distinct communication path between two or more nodes
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- Multiplexing
- Allows multiple signals to travel simultaneously over one medium
- To accommodate multiple signals, single medium is logically separated
into subchannels
- For each type of multiplexing:
- Multiplexer (mux) is required at sending end of channel
- Demultiplexer (demux) separates the combined signals and regenerates
them in original form
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- Time division multiplexing (TDM)
- Divides channel into multiple intervals of time
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- Statistical multiplexing
- Similar to TDM
- Assigns slots to nodes according to priority and need instead of in
succession
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- Wavelength division multiplexing (WDM)
- Used only with fiber-optic cable
- Data is transmitted as pulses of light
- Fiber-optic modem (FOM) is a demultiplexer used on fiber networks that
employ WDM
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- Point-to-point
- Transmission involving one transmitter and one receiver
- Broadcast
- Transmission involving one transmitter and multiple receivers
- Webcasting
- Broadcast transmission used over the Web
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- Throughput is amount of data the medium can transmit during a given
period of time
- Bandwidth measures difference between highest and lowest frequencies a
media can transmit
- Range of frequencies is directly related to throughput
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- Baseband
- Transmission form in which (typically) digital signals are sent through
direct current (DC) pulses applied to the wire
- Broadband
- Transmission form in which signals are modulated as radiofrequency (RF)
pulses that use different frequency ranges
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- Electromagnetic interference (EMI)
- Interference that may be caused by motors, power lines, television,
copiers, fluorescent lights, or other sources of electrical activity
- Radiofrequency interference (RFI)
- Interference that may be generated by motors, power lines, televisions,
copiers, fluorescent lights, or broadcast signals from radio or TV
towers
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- Attenuation
- Loss of signal strength as transmission travels away from source
- Analog signals pass through an amplifier, which increases not only
voltage of a signal but also noise accumulated
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- Regeneration
- Process of retransmitting a digital signal
- Repeater
- Device used to regenerate a signal
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- Throughput
- Perhaps most significant factor in choosing a transmission medium is
throughput
- Cost
- Cost of installation
- Cost of new infrastructure versus reusing existing infrastructure
- Cost of maintenance and support
- Cost of a lower transmission rate affecting productivity
- Cost of obsolescence
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- Size and scalability
- Specifications determining size and scalability:
- Maximum nodes per segment
- Maximum segment length
- Maximum network length
- Latency is the delay between the transmission of a signal and its
receipt
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- Connectors
- Connects wire to network device
- Noise immunity
- Thicker cables are generally less susceptible to noise
- Possible to use antinoise algorithms to protect data from being
corrupted by noise
- Conduits can protect cabling from noise
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- Consists of central copper core surrounded by an insulator, braiding,
and outer cover called a sheath
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- Also called thickwire Ethernet
- Rigid coaxial cable used on original Ethernet networks
- IEEE designates Thicknet as 10Base5 Ethernet
- Almost never used on new networks but you may find it on older networks
- Used to connect one data closet to another as part of network backbone
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- Throughput
- According to IEEE 802.3, Thicknet transmits data at maximum rate of 10
Mbps
- Cost
- Less expensive than fiber-optic but more expensive than some other
types of coaxial cable
- Connector
- Can include a few different types of connectors, which are very
different from those used on modern networks
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- In Thicknet networking, the transceiver is a separate device and may
also be called a media access unit (MAU)
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- Attachment Unit Interface (AUI)
- Ethernet standard establishing physical specifications for connecting
coaxial cables with transceivers and networked nodes
- An AUI connector may also be called a DIX or DB-15 connector
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- N-series connector (or n connector)
- Screw-and-barrel arrangement securely connects coaxial cable segments
and devices
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- Noise immunity
- Because of its wide diameter and excellent shielding, has the highest
resistance to noise of any commonly used types of network wiring
- Size and scalability
- Because of its high noise resistance, it allows data to travel longer
than other types of cabling
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- Also known as thin Ethernet
- Characteristics:
- Throughput
- Can transmit at maximum rate of 10 Mbps
- Cost
- Less expensive than Thicknet and fiber-optic cable
- More expensive than twisted-pair wiring
- Connectors
- Connects wire to network devices with BNC T-connectors
- A seen in Figure 4-19, BNC barrel connectors are used to join two
Thinnet cable segments together
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- Characteristics (cont.):
- Size and scalability
- Allows a maximum of 185 m per network segment (see Figure 4-20)
- Noise immunity
- More resistant than twisted-pair wiring
- Less resistant than twisted-pair wiring
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- Signal bounce
- Caused by improper termination on a bus network
- Travels endlessly between two ends of network
- Prevents new signals from getting through
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- Color-coded pairs of insulated copper wires twisted around each other
and encased in plastic coating
- Twists in wire help reduce effects of crosstalk
- Number of twists per meter or foot known as twist ratio
- Alien Crosstalk
- When signals from adjacent cables interfere with another cable’s
transmission
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- STP cable consists of twisted wire pairs that are individually insulated
and surrounded by shielding made of metallic substance
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- Consists of one or more insulated wire pairs encased in a plastic sheath
- Does not contain additional shielding
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- To manage network cabling, it is necessary to be familiar with standards
used on modern networks, particularly Category 3 (CAT3) and Category 5
(CAT5)
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- Popular Ethernet networking standard that replaced 10Base2 and 10Base5
technologies
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- Enterprise-wide network
- Spans entire organization
- Often services needs of many diverse users
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- Enables LANs to run at 100-Mbps data transfer rate
- Also known as Fast Ethernet
- Two 100BaseT specifications have competed for popularity as
organizations move to 100-Mbps technology:
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- Cousin of Ethernet 100 Mbps technologies
- VG stands for voice grade
- Also called 100VG-AnyLAN
- Originally developed by Hewlett-Packard and AT&T
- Now governed by IEEE standard 802.12
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- Throughput
- Both can transmit up to 100 Mbps
- Cost
- Typically, STP is more expensive
- Connector
- Both use RJ-45 connectors (see Figure 4-27) and data jacks
- Noise immunity
- STP is more noise-resistant
- Size and scalability
- Maximum segment length for both is 100 meters
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- Contains one or several glass fibers at its core
- Surrounding the fibers is a layer of glass called cladding
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- Single-mode fiber
- Carries light pulses along single path
- Multimode fiber
- Many pulses of light generated by LED travel at different angles
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- Throughput
- Reliable in transmitting up to 1 gigabit per second
- Cost
- Most expensive type of cable
- Connector
- You can use any of 10 different types of connectors (see Figure 4-30)
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- Noise immunity
- Unaffected by either EMI or RFI
- Size and scalability
- Network segments made from fiber can span 100 meters
- Signals transmitted over fiber can experience optical loss
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- Two popular connectors used with fiber-optic cable:
- ST connectors
- SC connectors
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- 10BaseF
- Physical layer standard for networks specifying baseband transmission,
multimode fiber cabling, and 10-Mbps throughput
- 100BaseFX
- Physical layer standard for networks specifying baseband transmission,
multimode fiber cabling, and 100-Mbps throughput
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- Cable plant
- Hardware comprising enterprise-wide cabling system
- Structured cabling
- Method for uniform, enterprise-wide, multivendor cabling systems
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- Entrance facilities
- Backbone wiring
- Backbone cabling that provides vertical connections between floors of a
building are called risers
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- Equipment room
- Telecommunications closet
- Punch-down block is a panel of data receptors
- Patch panel is a wall-mounted panel of data receptors
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- Work area
- Patch cable is a relatively short section of twisted-pair cabling with
connectors on both ends that connect network devices to data outlets
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- Straight-through cable
- Terminations at both ends are identical
- Crossover cable
- Terminations locations of transmit and receiver wires on one end of
cable are reversed
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- Do not untwist twisted-pair cables more than one-half inch before
inserting them
- Do not strip off more than one inch of insulation from copper wire in
twisted-pair cables
- Watch bend radius limitations for cable being installed
- Test each segment of cabling with cable tester
- Use only cable ties to cinch groups of cable together
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- Avoid laying cable across floor where it may sustain damage
- Install cable at least three feet away from fluorescent lights or other
sources of EMI
- Always leave slack in cable runs
- If running cable in plenum, area above ceiling tile or below
subflooring, make sure cable sheath is plenum-rated
- Pay attention to grounding requirements
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- Infrared transmission
- Infrared networks use infrared light signals to transmit data through
space
- Direct infrared transmission depends on transmitter and receiver
remaining within line of sight
- In indirect infrared transmission, signals can bounce off of walls,
ceilings, and any other objects in their path
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- RF transmission
- Radio frequency (RF) transmission relies on signals broadcast over
specific frequencies
- Two most common RF technologies:
- Narrowband
- Spread spectrum
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- Areas of high EMI or RFI
- Corners and small spaces
- Distance
- Security
- Existing infrastructure
- Growth
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- Information can be transmitted via analog or digital methodology
- Throughput is the amount of data a medium can transmit during a given
period of time
- Noise is interference that distorts an analog or digital signal
- Costs depend on many factors
- There are three specifications that dictate size and scalability of
networking media
- Connectors connect wire to the network device
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- Coaxial cable consists of central copper core surrounded by an insulator
and a sheath
- Thicknet cabling is a rigid coaxial cable used for original Ethernet
networks
- Both Thicknet and Thinnet coaxial cable rely on bus topology and must be
terminated at both ends with a resistor
- Twisted-pair cable consists of color-coded pairs of insulated copper
wires, twisted around each other and encased in plastic coating
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- STP cable consists of twisted pair wires individually insulated and
surrounded by a shielding made of metallic substance
- UTP cabling consists of one or more insulated wire pairs encased in a
plastic sheath
- Fiber-optic cable contains one or several glass fibers in its core
- On today’s networks, fiber is used primarily as backbone cable
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- Best practice for installing cable is to follow the TIA/EIA 568
specifications and manufacturer’s recommendations
- Wireless LANs can use radio frequency (RF) or infrared transmission
- RF transmission can be narrowband or spread spectrum
- Infrared transmission can be indirect or direct
- To make correct media transmission choices, consider throughput,
cabling, noise resistance, security/flexibility, and plans for growth
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