Transcript Chapter 3

CEG 2400 FALL 2012
Chapter 3
Transmission Basics and Networking Media
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Transmission Basics
• Transmit
– Issue signals along network medium
• Transmission
– Process of transmitting
– Signal progress after transmitting
• Transceiver
– Transmits and receives signals
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Analog and Digital Signaling
• Important data transmission characteristic
– Signaling type: analog or digital
• Volt
– Measure of electrical current pressure
• Voltage = Electrical signal strength
• Signal Types
– Current, light pulses, electromagnetic waves
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Analog and Digital Signaling (cont’d.)
• Analog data signals
– Voltage varies continuously
• Fundamental properties of analog signals
– Amplitude
• Measure of strength at given point in time
– Frequency
• Number of times amplitude cycles over fixed time
– Wavelength
• Distance between one peak and the next
– Phase
• Progress of wave over time compared to a fixed point
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Wavelength
Frequency
An example of an analog signal
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Phase
Waves with a 90 degree phase difference
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Analog and Digital Signaling (cont’d.)
• Analog signal benefit over digital
– Conveys greater subtleties with less energy
• Drawback of analog signals
– Susceptible to transmission flaws
• Digital signals
– Pulses of voltages
• Positive voltage represents a 1
• Zero voltage represents a 0
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An example of a digital signal
Components of a byte
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Analog and Digital Signaling (cont’d.)
• Convert byte to decimal number
– Determine value represented by each bit
– Add values = Decimal number
• Convert decimal number to a byte
– Reverse the process
• Convert between binary and decimal
– Can be done by hand or calculator
– For class learn by hand
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Analog and Digital Signaling (cont’d.)
• Digital signal benefits over analog signal
– More reliable
– Less severe noise interference
• Digital signal drawback
– Many pulses required to transmit same amount of
information
– More overhead than analog
• Nondata information
• Required for proper signal routing and interpretation
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Data Modulation
• Data modulation
– Technology modifying analog signals
– Make data suitable for carrying over communication
path
• Used if data relies on digital transmission and
network connection may handle only analog signals
• Device - Modem
– Accomplishes translation
– Modulator/demodulator
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Data Modulation (cont’d.)
• Carrier wave
– Combined with another analog signal to produce a
unique signal
• Transmitted from one node to another
• Information wave (data wave)
– Added to carrier wave
– Modifies one carrier wave property
• Result – Blended wave
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Data Modulation (cont’d.)
• Frequency modulation (FM)
– Carrier frequency modified by application of data
signal
• Amplitude modulation (AM)
– Carrier signal amplitude modified by application of
data signal
• EX. Digital subscriber line (DSL)
– Makes use of modulation
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A carrier wave modified through frequency modulation
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Kinds of Transmission
Simplex, Half-Duplex, and Duplex
• Simplex
– Signals travel in one direction
• Half-duplex transmission
– Signals travel in both directions one way at a time
– Shared communication channel
• Full-duplex
– Signals travel in both directions simultaneously
– Used on data networks
– Increases speed of data travel
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Simplex, half-duplex, and full-duplex transmission
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Multiplexing
• Multiplexing
– Multiple signals travel simultaneously over one
medium
– Subchannels - Logical multiple smaller channels
• Multiplexer (mux)
– Combines many channel signals
• Demultiplexer (demux)
– Separates combined signals and regenerates them
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Types of Multiplexing
• Time division multiplexing (TDM)
– Divides channel into multiple time intervals – not
efficient
Time division multiplexing
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Types of Multiplexing (cont’d.)
• Statistical multiplexing
– Transmitter assigns slots to nodes
• According to priority, need
– More efficient than Time division multiplexing
Statistical multiplexing
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Types of Multiplexing (cont’d.)
• Frequency division multiplexing (FDM)
– Unique frequency band for each communications
subchannel
– Cellular telephone transmission
– DSL Internet access
Frequency division multiplexing
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Types of Multiplexing (cont’d.)
• Wavelength division multiplexing (WDM)
– One fiber-optic connection
– Carries multiple light signals simultaneously
Wavelength division multiplexing
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Types of Multiplexing (cont’d.)
• Dense wavelength division multiplexing (DWDM)
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Similar to Wavelength division multiplexing (WDM)
Used on most modern fiber-optic networks
Extraordinary capacity
WDM – up to 40 channels
DWDM – up to160 channels
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Relationships Between Nodes
• Point-to-Point transmission
– One transmitter and one receiver
• Point-to-Multipoint transmission
– One transmitter and multiple receivers
– Two Types
• Broadcast transmission
– One transmitter and multiple, undefined receivers
• Nonbroadcast
– One transmitter and multiple, defined recipients
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Point-to-point versus broadcast transmission
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Throughput and Bandwidth
• Throughput
– Amount of data transmitted during given time period
– Also called capacity or bandwidth
– Expressed as bits transmitted per second
• Bandwidth (strict definition)
– Difference between highest and lowest frequencies
medium can transmit measured in hertz (Hz)
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Throughput measures
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Baseband and Broadband
• Baseband transmission
– Digital signals sent through direct current (DC) pulses
applied to wire
– Requires exclusive use of wire’s capacity
– Transmit one signal (channel) at a time
– Example: Ethernet
• Broadband transmission
– Signals modulated as radio frequency (RF) analog
waves
– Uses different frequency ranges
– Does not encode information as digital pulses
– Example: Cable TV
– Broadband can have different meanings!
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Transmission Flaws
• Transmission Flaws – transmission degrades
between sender and receiver
• 1. Noise
– Any undesirable influence degrading or distorting
signal
– Types of noise
• EMI (electromagnetic interference)
– Example: Motors, power lines, magnets
• Cross talk
– Signal on one wire infringes on adjacent wire signal
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Cross talk between wires in a cable
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Transmission Flaws (cont’d.)
• 2. Attenuation
– Loss of signal’s strength as it travels away from
source
– Signal boosting technology
• Analog signals pass through amplifier
– Noise also amplified
• Regeneration
– Digital signals retransmitted in original form
– Repeater: device regenerating digital signals
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An analog signal distorted by noise and then amplified
A digital signal distorted by noise and then repeated
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Transmission Flaws (cont’d.)
• 3. Latency
– Delay between signal transmission and receipt
– May cause network transmission errors
– Latency causes
• Cable length
• Intervening connectivity device
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Common Media Characteristics
• Physical media characteristics
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Throughput
Cost
Noise immunity
Size and scalability
Connectors and media converters
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Throughput
• Causes of throughput limitations
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Laws of physics
Signaling and multiplexing techniques used
Noise
Devices connected to transmission medium
• Most significant factor in choosing transmission
method
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Cost
• Precise costs difficult to pinpoint
• Media cost dependencies
– Existing hardware, network size, labor costs
• Some variables influencing final cost
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Installation cost
New infrastructure cost versus reuse
Maintenance and support costs
Cost of lower transmission rate affecting productivity
Cost of downtime
Cost of obsolescence
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Noise Immunity
• Noise distorts data signals
– Distortion rate dependent upon transmission media
• Limit noise impact on network
– Cable installation
• Far away from powerful electromagnetic forces
– Select media protecting signal from noise
• Fiber-optic: least susceptible to noise
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Size and Scalability
• Three specifications
1. Maximum nodes per segment
2. Maximum segment length
3. Maximum network length
• Maximum nodes per segment
– Each device adds attenuation and latency
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Size and Scalability (cont’d.)
• Maximum segment length
– Attenuation and latency plus segment type
• Segment types
– Populated: contains end nodes
– Unpopulated: no end nodes
• Segment length limitation
– After certain distance, signal loses strength
• Maximum network length
– Same as segment length except it is the sum of the
network’s segments lengths
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Connectors and Media Converters
• Connectors
– Hardware connecting wire to network device
• Piece on end of wire
• Media converter
– Hardware enabling networks or segments running on
different media to interconnect and exchange signals
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Copper wire-to-fiber media converter
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Types of Cables
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Coaxial
STP (Shielded Twisted Pairs)
UTP (Unshielded Twisted Pairs)
Fiber-Optic
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Coaxial Cable
• Central metal core (often copper) surrounded by:
– Insulator
– Braided metal shielding (braiding or shield)
– Outer cover (sheath or jacket)
Coaxial cable
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Coaxial Cable (cont’d.)
• High noise resistance
• Advantage over twisted pair
– Carry signals farther before amplifier required
• Disadvantage over twisted pair cabling
– More expensive
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Coaxial Cable (cont’d.)
• Hundreds of specifications
– RG specification number
• Data networks
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RG-6 (Cable TV)
RG-8 (Thicknet)
RG-58 (Thinnet)
RG-59 (used for short distant)
• Differences: shielding and conducting cores
– Conducting core
• American Wire Gauge (AWG) size
– Larger AWG size, smaller wire diameter
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Twisted Pair Cable
• Color-coded insulated copper wire pairs
– 0.4 to 0.8 mm diameter
– Encased in a plastic sheath
Twisted pair cable
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Twisted Pair Cable (cont’d.)
• More wire pair twists per foot
– More resistance to cross talk
– Higher-quality
– More expensive
• Twist ratio
– Twists per meter or foot
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Twisted Pair Cable (cont’d.)
• Hundreds of different designs
– Twist ratio, number of wire pairs, copper grade,
shielding type, shielding materials
– 1 to 4200 wire pairs possible
• Most common twisted pair types
– Category (cat) 3, 5, 5e, 6, 6a, 7
– CAT 5 or higher used in modern LANs
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Twisted Pair Cable (cont’d.)
• Advantages
– Relatively inexpensive
– Flexible
– Easy installation
• Two categories
– Shielded twisted pair (STP)
– Unshielded twisted pair (UTP)
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STP (Shielded Twisted Pair)
• Individually insulated
• Surrounded by metallic substance shielding (foil)
– Barrier to external electromagnetic forces
– Contains electrical energy of signals inside
STP cable
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UTP (Unshielded Twisted Pair)
• One or more insulated wire pairs
– Encased in plastic sheath
– No additional shielding
• Less expensive, less noise resistance
UTP cable
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Terminating Twisted Pair Cable
• Patch cable
– Relatively short cable
– Connectors at both ends
• TIA/EIA standards
– TIA/EIA 568A
– TIA/EIA 568B
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TIA/EIA 568A standard terminations
TIA/EIA 568B standard terminations
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Terminating Twisted Pair Cable
(cont’d.)
• Straight-through cable (ex. Patch cable)
– Terminate RJ-45 plugs at both ends identically
• Crossover cable
– Transmit and receive wires on one end reversed
RJ-45 terminations on a
crossover cable
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Fiber-Optic Cable
• Fiber-optic cable (fiber)
– One or more glass or plastic fibers at its center (core)
• Data transmission
– Pulsing light sent from laser or light-emitting diode
(LED) through central fibers
• Cladding (surrounds fiber)
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Layer of glass or plastic surrounding fibers
Different density from glass or plastic in strands
Reflects light back to core
Allows fiber to bend
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Fiber-Optic Cable (cont’d.)
• Plastic buffer outside cladding
– Protects cladding and core
– Opaque to absorb escaping light
– Surrounded by Kevlar (polymeric fiber) strands
• Plastic sheath covers Kevlar strands
A fiber-optic cable
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Fiber-Optic Cable (cont’d.)
• Benefits over copper cabling
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Extremely high throughput
Very high noise resistance
Excellent security
Able to carry signals for longer distances
• Drawbacks
– More expensive than twisted pair cable
– Requires special equipment to splice
• Two Types
– Single-mode and Multimode
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SMF (Single-Mode Fiber)
• Consists of narrow core (8-10 microns in diameter)
– Laser-generated light travels over one path
• Little reflection
– Light does not disperse as signal travels
• Can carry signals many miles before repeating
required
• Rarely used for shorter connections due to cost
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MMF (Multimode Fiber)
• Larger diameter core than single-mode fiber
– Common sizes: 50 or 62.5 microns
• Laser or LED generated light pulses travel at
different angles
• Common uses
– Cables connecting router to a switch
– Cables connecting server on network backbone
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Serial Cables
• Used to connect to a device such as router or switch
• Data transmission style
– Pulses issued sequentially, not simultaneously
• Serial transmission method
– RS-232 standard
• Uses DB-9, DB-25, and RJ-45 connectors
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Structured Cabling
• Cable plant
– Hardware that makes up the entire enterprise cabling
system
• Cabling standard
– TIA/EIA’s joint 568 Commercial Building Wiring
Standard
• Also known as structured cabling
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Structured Cabling (cont’d.)
• Components
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Entrance facilities
MDF (main distribution frame)
Cross-connect facilities (Punch-down, Patch panel)
IDF (intermediate distribution frame)
Backbone wiring
Telecommunications closet
Horizontal wiring
Work area
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Horizontal wiring
TIA/EIA structured cabling in an enterprise
Summary
• Information transmission methods
– Analog
– Digital
• Multiplexing allows multiple signals to travel
simultaneously over one medium
• Full and half-duplex specifies whether signals can
travel in both directions or one direction at a time
• Noise distorts both analog and digital signals
• Attenuation
– Loss of signal as it travels
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Summary (cont’d.)
• Coaxial cable composed of core, insulator,
shielding, sheath
• Types of twisted pair cable
– Shielded and unshielded
• Fiber-optic cable transmits data through light
passing through the central fibers
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Summary (cont’d.)
• Fiber-optic cable categories
– Single and multimode fiber
• Serial communication often used for short
connections between devices
• Structured cabling standard provides wiring
guidelines
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Testing Internet Bandwidth
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http://www.speedtest.net
http://www.speakeasy.net/speedtest/
http://www.att.com/speedtest/
http://www.bandwidthplace.com/
• Wideband is the next generation of Internet and is
considered to be faster than broadband.
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WideBand
• Most people have become familiar with the term
broadband internet but not as many are familiar with
the term wideband internet. Wideband was a term
that has previously been used in conjunction with
radio and television frequencies, not the internet.
That has changed in the last couple of years and
you will begin hearing it more and more in the future.
• Just as broadband has come to mean faster,
smoother internet connections that took the
consumer to the next level beyond dial-up,
wideband is a term that refers to the next step
beyond broadband. It provides more than just a
higher speed connection, but a whole new level of
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interaction.
End of Chapter 3
Questions
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