Study Unit 3 - Chapter Three Conducted and Wireless Media Flashcards
The world of computer networks would not exist if there were
no medium by which to transfer data
* The two major categories of media include:
– Conducted media
– Wireless media
Twisted Pair Wire
Twisted Pair Wire
* One or more pairs of single conductor wires that have been
twisted around each other
* Twisted pair wire is classified by category. Twisted pair is
currently Category 1 through Category 7, although
Categories 1, 2 and 4 are nearly obsolete
* Twisting the wires helps to eliminate electromagnetic
interference between the two wires
* Shielding can further help to eliminate interference
Twisted Pair Summary
Twisted Pair Summary
* Most common form of wire
* Relatively inexpensive
* Easy to install
* Carries high data rates (but not the highest)
* Can suffer from electromagnetic noise
* Can be easily wire-tapped
* Comes in shielded and unshielded forms
Coaxial Cable
Coaxial Cable
* A single wire wrapped in a foam insulation surrounded by a
braided metal shield, then covered in a plastic jacket. Cable
comes in various thicknesses
* Baseband coaxial technology uses digital signaling in which
the cable carries only one channel of digital data
* Broadband coaxial technology transmits analog signals and
is capable of supporting multiple channels
Coaxial Cable Summary
Coaxial Cable Summary
* A single wire surrounded by a braided shield
* Because of shielding, can carry a wide bandwidth of
frequencies
* Thus is good with applications such as cable television
* Not as easy to install as twisted pair
* More expensive than twisted pair
Fiber-Optic Cable
- A thin glass cable approximately a little thicker than a human
hair surrounded by a plastic coating and packaged into an
insulated cable - A photo diode or laser generates pulses of light which travel
down the fiber optic cable and are received by a photo
receptor
Fibre optic cable summary
Fiber optic cable can carry the highest data rate for the
longest distances
* Initial cost-wise, more expensive than twisted pair, but less
than coaxial cable
* But when you consider the superiority of fiber, initial costs
outweighed by capacities
* Need to fibers for a round-trip connection
* Not affected by electromagnetic noise and cannot be easily
wiretapped, but still noise
Wireless Media
Wireless Media
* Radio, satellite transmissions, and infrared light are all
different forms of electromagnetic waves that are used to
transmit data
* Technically speaking – in wireless transmissions, space is
the medium
* Note in the following figure how each source occupies a
different set of frequencies
Terrestrial Microwave Transmission
Terrestrial Microwave Transmission
* Land-based, line-of-sight transmission
* Approximately 20-30 miles between towers
* Transmits data at hundreds of millions of bits per second
* Signals will not pass through solid objects
* Popular with telephone companies and business to business
transmissions
Satellite Microwave Transmission
Satellite Microwave Transmission
* Similar to terrestrial microwave except the signal travels from
a ground station on earth to a satellite and back to another
ground station
* Can also transmit signals from one satellite to another
* Satellites can be classified by how far out into orbit each one
is (LEO, MEO, GEO, and HEO)
LEO MEO GEO HEO
LEO (Low-Earth-Orbit) – 100 to 1000 miles out
– Used for wireless e-mail, special mobile telephones, pagers, spying,
videoconferencing
* MEO (Middle-Earth-Orbit) – 1000 to 22,300 miles
– Used for GPS (global positioning systems) and government
* GEO (Geosynchronous-Earth-Orbit) – 22,300 miles
– Always over the same position on earth (and always over the equator)
– Used for weather, television, government operations
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Satellite Microwave Transmission
(continued)
* HEO (Highly Elliptical Earth orbit) – satellite follows an
elliptical orbit
– Used by the military for spying and by scientific organizations for
photographing celestial bodies
Satellite microwave can also be classified by its configuration
(see next figure):
Bulk carrier configuration
– Multiplexed configuration
– Single-user earth station configuration (e.g. VSAT)
Cellular Telephones
Cellular Telephones
* Wireless telephone service, also called mobile telephone,
cell phone, and PCS
* To support multiple users in a metropolitan area (market),
the market is broken into cells
* Each cell has its own transmission tower and set of
assignable channels
Placing a call on a cell phone
You enter a phone number on your cell phone and press Send. Your
cell phone contacts the nearest cell tower and grabs a set-up
channel. Your mobile identification information is exchanged to make
sure you are a current subscriber.
– If you are current, you are dynamically assigned two channels: one
for talking, and one for listening. The telephone call is placed. You
talk.
Receiving a call on a cell phone
Receiving a call on a cell phone
– Whenever a cell phone is on, it “pings” the nearest cell tower every
several seconds, exchanging mobile ID information. This way, the
cell phone system knows where each cell phone is.
– When someone calls your cell phone number, since the cell phone
system knows what cell you are in, the tower “calls” your cell phone.
Cellular Telephones (continued)
* 1st Generation
Cellular Telephones (continued)
* 1st Generation
– AMPS (Advanced Mobile Phone Service) – first popular cell phone
service; used analog signals and dynamically assigned channels
– D-AMPS (Digital AMPS) – applied digital multiplexing techniques on
top of AMPS analog channels
2nd Generation
2nd Generation
– PCS (Personal Communication Systems) – essentially all-digital cell
phone service
– PCS phones came in three technologies:
* TDMA – Time Division Multiple Access
* CDMA – Code Division Multiple Access
* GSM – Global System for Mobile Communications
2.5 Generation
2.5 Generation
– Using GPRS (General Packet Radio Service) in a GSM networks (can
transmit data at 30 kbps to 40 kbps)
– Using CDMA2000 1xRTT (one carrier radio- transmission technology)
(50 kbps to 75 kbps)
3rd Generation
3rd Generation
– UMTS (Universal Mobile Telecommunications System) – also called
Wideband CDMA
* The 3G version of GPRS
* UMTS not backward compatible with GSM (thus requires phones with
multiple decoders)
– 1XEV (1 x Enhanced Version) –3G replacement for 1xRTT
* two forms:
– 1xEV-DO for data only
– 1xEV-DV for data and voice
4th Generation
4th Generation
– LTE (Long Term Evolution) – theoretical speeds of 100 Mbps or
more, actual download speeds 10-15 Mbps
– WiMax – introduced in a couple slides – theoretical speeds of 128
Mbps; actual download speeds 4 Mbps
– HSPA (High Speed Packet Access) – 14 Mbps downlink, 5.8 Mbps
uplink; is this 3.5G or 4G?
– HSPA+ – theoretical downlink of 84 Mbps, 22 Mbps uplink 3.5G or
4G?
WiMax - Broadband Wireless Systems
WiMax - Broadband Wireless Systems
* Delivers Internet services into homes, businesses and
mobile devices
* Designed to bypass the local loop telephone line
* Transmits voice, data, and video over high frequency radio
signals
* Maximum range of 20-30 miles and transmission speeds in
Mbps
* IEEE 802.16 set of standards
Bluetooth
Bluetooth
* Bluetooth is a specification for short-range, point-to-point or
point-to-multipoint voice and data transfer
* Bluetooth can transmit through solid, non-metal objects
* Its typical link range is from 10 cm to 10 m, but can be
extended to 100 m by increasing the power
Wireless Local Area Networks
(IEEE 802.11)
Wireless Local Area Networks
(IEEE 802.11)
* This technology transmits data between workstations and
local area networks using high-speed radio frequencies
* Current technologies allow up to 100 Mbps (theoretical) data
transfer at distances up to hundreds of feet
* Three popular standards: IEEE 802.11b, a, g, n
* More on this in Chapter Seven (LANs)
Free Space Optics and
Ultra-Wideband
Free Space Optics and
Ultra-Wideband
* Free space optics
– Uses lasers, or more economically, infrared transmitting devices
– Line of sight between buildings
– Typically short distances, such as across the street
– Newer auto-tracking systems keep lasers aligned when buildings
shake from wind and traffic
Ultra-wideband (continued)
Ultra-wideband (continued)
– Proponents for UWB say it gets something for nothing, since it shares
frequencies with other sources. Opponents disagree
– Cell phone industry against UWB because CDMA most susceptible to
interference of UWB
– GPS may also be affected
– One solution may be to have two types of systems – one for indoors
(stronger) and one for outdoors (1/10 the power)
Ultra-wideband
– UWB not limited to a fixed bandwidth but broadcasts over a wide
range of frequencies simultaneously
– Many of these frequencies are used by other sources, but UWB uses
such low power that it “should not” interfere with these other sources
– Can achieve speeds up to 100 Mbps but for small distances such as
wireless LANs
Infrared Transmissions
Infrared Transmissions
* Transmissions that use a focused ray of light in the infrared
frequency range
* Very common with remote control devices, but can also be
used for device-to-device transfers, such as PDA to
computer
ZigBee
ZigBee
* Based upon IEEE 802.15.4 standard
* Used for low data transfer rates (20-250 Kbps)
* Also uses low power consumption
* Ideal for heating, cooling, security, lighting, and smoke and
CO detector systems
* ZigBee can use a mesh design – a ZigBee-enabled device
can both accept and then pass on ZigBee signals
Media Selection Criteria
Media Selection Criteria
* Cost
* Speed
* Distance and expandability
* Environment
* Security
Cost
* Different types of costs
Cost
* Different types of costs
– Initial cost – what does a particular type of medium cost to purchase?
To install?
– Maintenance / support cost
* ROI (return on investment) – if one medium is cheaper to
purchase and install but is not cost effective, where are the
savings?
Speed
* Two different forms of speed:
Speed
* Two different forms of speed:
– Propagation speed – the time to send the first bit across the medium
* This speed depends upon the medium
* Airwaves and fiber are speed of light
* Copper wire is two thirds the speed of light
– Data transfer speed – the time to transmit the rest of the bits in the
message
* This speed is measured in bits per second
Expandability and Distance
Certain media lend themselves more easily to expansion
* Don’t forget right-of-way issue for conducted media and lineof-sight for certain wireless media
Environment
* Many types of environments are hazardous to certain media
Environment
* Many types of environments are hazardous to certain media
– Electromagnetic noise
– Scintillation and movement
– Extreme environmental conditions
Security
Security
* If data must be secure during transmission, it is important
that the medium not be easy to tap
– Make the wire impervious to electromagnetic wiretapping
– Encrypt the signal going over the medium
Conducted Media in Action:
Two Examples
Conducted Media in Action:
Two Examples
* First example – simple local area network
– Hub typically used
– To select proper medium, consider:
* Cable distance
* Data rate
Second example – company wishes to transmit data
between buildings that are one mile apart
– Is property between buildings owned by company?
* If not consider using wireless
* When making decision, need to consider:
– Cost
– Speed
– Expandability and distance
– Environment
– Security
Wireless Media In Action:
Three Examples
Wireless Media In Action:
Three Examples
* First example – you wish to connect two computers in your
home to Internet, and want both computers to share a printer
– Can purchase wireless network interface cards
– May consider using Bluetooth devices
* Second example – company wants to transmit data between
two locations, Chicago and Los Angeles
– Company considering two-way data communications service offered
through VSAT satellite system
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Wireless Media In Action:
Three Examples (continued)
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Wireless Media In Action:
Three Examples (continued)
* Third example – second company wishes to transmit data
between offices two miles apart
– Considering terrestrial microwave system
