Conducted and Wireless Media

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Lecture 03

• Conducted and Wireless Media

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Introduction

• Communications are conducted through a medium,
• For example, we talked, our voice transmitted
  through air
• Thus, 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
• How to subscribe them for organizations?
• Selection criteria

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Application examples
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Application examples

• Conducted
• Example 1
• Example 2
• Wireless
• Example 1
• Example 2
• Example 3

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Conducted media

• Physical connection between source and sink
  points
• Three common media
• i) wire
• ii) coaxial cable
• iii) optical fiber
• Comparison between their transmission speeds

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i) wire

• usually made of copper with a pair of wire
• Or called twisted pair of wire
• the pairs of wires are almost insulated with
  plastic coating and twisted together -- known as
  twisted pair wires
• (see Figure 9-6)
• Categorizations
• the twisting has the effect of electrically
  canceling the signals radiating form each wire
  ---- prevents the signals on one pair of wires
  from interfering the adjacent pair
• the effect is known as crosswalk

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FIGURE 9-6 Twisted pair wires are the most
commonly used medium for communications
transmission.
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• As to oppose different layout as shown in Figure
  3.2
• Different ways of twisted pair way adopted in
  industries

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ii) coaxial cable

• Cable that made of several layers of material
  around a central core, which often a copper wire
• (see Figure 9-8)
• has a very wide bandwidth (400 Mhz to 600 Hhz),
  thus carries a very high data capacity
• one coaxial cable carries up to 10,800 voice
  conversations or over 50 television channles
• Its max capacity is dependent on the thickness of
  the copper wire
• Two main applications

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ii) coaxial cable (cont.)

• It has two main applications
• 1) Baseband coaxial technology uses digital
  signaling in which the cable carries only one
  channel of digital data
• 2) Broadband coaxial technology transmits analog
  signals and is capable of supporting multiple
  channels
• Disadv it is easy to tape and thus lack of a
  high security measure

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FIGURE 9-8 Parts of a coaxial cable.
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iii) optical fiber

• Is a new media for comm
• is a very thin glass fiber which core provides
  the transmission capability
• the core is surrounded by another type of glass
  called cladding, which protected by a plastic
  coating
• (see Figure 9-9) (to p14)
• data is placed on with a light source or a laser.
  Light source stays in the core as the cladding
  has a low refractive index

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FIGURE 9-9 Parts of optical fiber cable.
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Alternative view
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Thin vs. Thick fiber optic cable
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Fiber-Optic Cable (continued)

• Fiber-optic cable is capable of supporting
  millions of bits per second for 1000s of meters
• Thick cable (62.5/125 microns) causes more ray
  collisions, so you have to transmit slower. This
  is step index multimode fiber. Typically use LED
  for light source, shorter distance transmissions
• Thin cable (8.3/125 microns) very little
  reflection, fast transmission, typically uses a
  laser, longer transmission distances known as
  single mode fiber

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iii) optical fiber (cont.)

• Two primary types of fiber
• a) single mode
• b) multi mode
• How more lights can be traveled together
• Layout of optical fiber worldwide
• Fiber optic cable is difficult to splice -
  requires a reflectometer to detect such work
• SONET concept
• Adv
• Disv

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Wavelength division

• Wavelength division multiplexing
• A technique which allows many light beams of
  different wavelengths can travel along a single
  fiber simultaneously without interfering with one
  another

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FIGURE 9-10a The worlds undersea cable
network.
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FIGURE 9-10b Continued
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SONET

• Synchronous Optical Network
• A technique facilitates easy to connect carriers
  that using different brands/products of their
  optical networks
• It is a standard for the ANSI (American National
  Standard Institute)
• Transmission rate at Gpbs
• Data speed for different networks

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FIGURE 9-11 Comparative data rates for the
SONET and ITU-T optical fiber transmission
standards.
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iii) optical fiber (cont.)

• Advantages
• 1) do not radiate signal as all electrical
  devices do
• 2) fiber is of light weight
• 3) cost of fibers is getting cheaper
• 4) high bandwidth - high data capability
• 5) little lost of signal strength
• 6) excellent isolation between parallel fiber -
  crossed-talk between fiber does not exist
• 7) very secure, difficult to tape

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Disv

• Because fiber-optic cable is susceptible to
  reflection (where the light source bounces around
  inside the cable) and refraction (where the light
  source passes out of the core and into the
  surrounding cladding), thus Fiber-optic cable is
  not perfect either. Noise is still a potential
  problem

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Concepts of refraction and reflection
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Fiber-Optic Cable (continued)
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Conducted Media
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Wireless media

• Technically speaking in wireless transmissions,
  space is the medium
• Radio, satellite transmissions, and infrared
  light are all different forms of electromagnetic
  waves that are used to transmit data
• Their frequencies of transmission
• Different types of applications
• Comparisons

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Wireless Media (continued)
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Applications

• i) microwave radio
• ii) satellite
• iii) cellular phones
• Iv) Infrared Transmissions
• v) Wireless Application Protocol (WAP)
• Broadband Wireless Systems
• Bluetooth
• Wireless Local Area Networks
• Free Space Optics and Ultra-Wideband

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iv) microwave radio

• Is a medium most common carriers for long
  distance comm (how it looks like )
• transmit in the range of 4-28 Ghz freq range
• up to 6000 voice circuits are carried in a 30 Mhz
  wide radio channel
• travel in a straight line - ie must transmit and
  receive in a direct line of sight , and signals
  will not pass through solid objects
• requirement

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Terrestrial Microwave Transmission (continued)
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Terrestrial Microwave Transmission (continued)
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iv) microwave radio (cont.)

• requires to set up an antenna in the range of 20
  to 30 miles
• Capable to carry either analog and digital form
• Disadv
• may interfere by the weather condition (why?)

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v) satellite

• Use of microwave radio, the signal travels from a
  ground station on earth to a satellite and back
  to another ground station
• Satellites can be classified by how far out into
  orbit each one is (LEO, MEO, GEO, and HEO)
• radio signal is beamed to the satellite on a
  specific frequency called uplink where
  rebroadcast on a different frequency called
  downlink

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Satellite Microwave Transmission (continued)

• 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
• HEO (Highly Elliptical Earth orbit) satellite
  follows an elliptical orbit
• Used by the military for spying and by scientific
  organizations for photographing celestial bodies

Their positions on the orbit
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Satellite Microwave Transmission (continued)
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Satellite Transmission (continued)
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v) satellite (cont.)

• Due to the security reason, information that
  being sent is first encrypted so that tapping and
  interpret its content is difficult
• there exists a delay of receiving information ---
  called propagation delay, is called as
• distance apart of comm device
• ------------------------------------
  -----
• speed in which data is transmitted
• example

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v) satellite (cont.)

• If satellite is 22,300 mile from the ground and
  speed sending data is 186,000 miles per second,
  then
• 2 x 22,300
• Propagation delay ----------------
• 18,6000
• 0.2398 sec
• Classifications by their configuration

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Satellite (continued)

• Satellite microwave can also be classified by its
  configuration
• Bulk carrier configuration
• Multiplexed configuration
• Single-user earth station configuration (e.g.
  VSAT)

Their semantic view
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Satellite Microwave Transmission (continued)
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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
• Different generations of MP

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Cellular Telephones (continued)
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Cellular Telephones (continued)
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Cellular Phones

• 1st generation
• 2nd generation
• 2.5 generation
• 3rd generation

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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

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Cellular Telephones (continued)

• 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

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Cellular Telephones (continued)

• 2.5 Generation
• ATT Wireless, Cingular Wireless, and T-Mobile
  now using GPRS (General Packet Radio Service) in
  their GSM networks (can transmit data at 30 kbps
  to 40 kbps)
• Verizon Wireless, Alltel, U.S.Cellular, and
  Sprint PCS are using CDMA2000 1xRTT (one carrier
  radio- transmission technology) (50 kbps to 75
  kbps)
• Nextel uses IDEN technology

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Cellular Telephones (continued)

• 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
• Will come in two forms
• 1xEV-DO for data only
• 1xEV-DV for data and voice

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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

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Wireless Application Protocol (WAP)

• WAP is a set of protocols that allows wireless
  devices such as cell phones, PDAs, and two-way
  radios to access the Internet
• WAP is designed to work with small screens and
  with limited interactive controls
• WAP incorporates Wireless Markup Language (WML)
  which is used to specify the format and
  presentation of text on the screen
• Their applications

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Wireless Application Protocol (WAP) (continued)
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Wireless Application Protocol (WAP) (continued)

• WAP may be used for applications such as
• Travel directions
• Sports scores
• E-mail
• Online address books
• Traffic alerts
• Banking and news
• Possible short-comings include low speeds,
  security, and very small user interface

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Broadband Wireless Systems

• Delivers Internet services into homes and
  businesses
• Designed to bypass the local loop telephone line,
  in a metropolitan area
• Transmits voice, data, and video over high
  frequency radio signals
• Past and future trends

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Broadband Wireless Systems (continued)
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Broadband Wireless Systems (continued)

• Multichannel multipoint distribution service
  (MMDS) and local multipoint distribution service
  (LMDS) looked promising a few years ago but died
  off
• Now companies are eyeing Wi-Max, an IEEE 802.16
  standard initially 300 kbps to 2 Mbps over a
  range of as much as 30 miles forthcoming
  standard (802.16e) will allow for moving devices

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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
• Bluetooth will enable users to connect to a wide
  range of computing and telecommunication devices
  without the need of connecting cables
• Typical uses include phones, pagers, modems, LAN
  access devices, headsets, notebooks, desktop
  computers, and PDAs

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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 54 Mbps
  (theoretical) data transfer at distances up to
  hundreds of feet
• Three popular standards IEEE 802.11b, a, g
• More on this in Chapter Seven (LANs)

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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
• Current speeds go from T-3 (45 Mbps) to OC-48
  (2.5 Gbps) with faster systems in development
• Major weakness is transmission thru fog
• A typical FSO has a link margin of about 20 dB
• Under perfect conditions, air reduces a systems
  power by approximately 1 dB/km
• Scintillation is also a problem (especially in
  hot weather)

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Free Space Optics and Ultra-Wideband (continued)

• 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
• 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)

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Wireless Media (continued)
more
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Wireless Media (continued)
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Media Selection Criteria

• Cost
• Speed
• Distance and expandability
• Environment
• Security

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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?

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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

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Expandability and Distance

• Certain media lend themselves more easily to
  expansion
• Dont forget right-of-way issue

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Environment

• Many types of environments are hazardous to
  certain media

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Security

• If data must be secure during transmission, it is
  important that the medium not be easy to tap

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Conducted Media in Action Example 1

• First example simple local area network
• Hub typically used
• To select proper medium, consider
• Cable distance
• Data rate
• Layout

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Conducted Media in Action Example 1
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Conducted Media in Action Example 2

• 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

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Wireless Media In Action Example 1

• 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

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Example 2

• Second example company wants to transmit data
  between two locations, such as Beijing and
  Shanghai
• Company considering two-way data communications
  service offered through VSAT satellite system
• Layout

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Wireless Media In Action Three Examples
(continued)
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Wireless Media In Action Example 3

• Third example second company wishes to transmit
  data between offices two miles apart
• Considering terrestrial microwave system
• Layout

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Wireless Media In Action Three Examples
(continued)
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