Network Media

Chapter 4Signal TransmissionNetwork 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