Lecture 01 by wulinqing


									       Lecture 03

Conducted and Wireless Media

• 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                (to p4)

   – Wireless media                 (to p28)

• How to subscribe them for organizations?
   – Selection criteria        (to p65)

                                   (to p3)                       2
       Application examples
       Application examples
• Conducted
  – Example 1   (to p71)

  – Example 2   (to p73)

• Wireless
  – Example 1   (to p74)

  – Example 2   (to p75)

  – Example 3   (to p77)

            Conducted media
• Physical connection between source and
  sink points
• Three common media:
  – i) wire                (to p5)

  – ii) coaxial cable      (to p10)

  – iii) optical fiber     (to p13)

  – Comparison between their transmission
    speeds      (to p27)

                                            (to p2)

                        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) (to p6)
       – Categorizations            (to   p9)

– 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                        (to   p4)

FIGURE 9-6   Twisted pair wires are the most commonly used medium for communications transmission.   (to   p5)

                       -As to oppose different layout as shown in Figure 3.2                                                 (to   p7)
                       -Different ways of twisted pair way adopted in industries                                                    (to   p5)
                                                                                                                 (to   p8)
(to   p6)
(to   p6)
(to   p5)
           ii) coaxial cable
– Cable that made of several layers of material
  around a central core, which often a copper
     – (see Figure 9-8)   (to   p12)

– 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        to p11) (
        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
                                                     (to   p4)
FIGURE 9-8   Parts of a coaxial cable. (to   p10)

           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
                                          (to   p17)
FIGURE 9-9   Parts of optical fiber cable.   (to   p13)

                                                          (to   p15)   14
                                Alternative view
                                   (to   p16)
Thin vs. Thick fiber optic cable

                                                 (to   p13)
  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
                                                     (to   p15)
         iii) optical fiber (cont.)
– Two primary types of fiber:
   • a) single mode
   • b) multi mode          (to p18)

   • How more lights can be traveled together          (to   p19)

– Layout of optical fiber worldwide              (to   p20)

– Fiber optic cable is difficult to splice - requires
  a reflectometer to detect such work
– SONET concept              to p22)

– Adv         to p24)

– Disv          to p25)

                                                         17(to p4)
(to   p17)

          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

                                                             (to   p17)
FIGURE 9-10a   The world’s undersea cable network.

                                                     (to   p21)

FIGURE 9-10b   Continued

                           (to   p17)

• Synchronous Optical Network
  – A technique facilitates easy to connect carriers that
    using different brands/products of their optical
  – It is a standard for the ANSI (American National Standard Institute)
  – Transmission rate at Gpbs
  – Data speed for different networks                 (to p23)

                                                                            (to   p17)
FIGURE 9-11   Comparative data rates for the SONET and ITU-T optical fiber transmission standards.

                                                                                                      (to   p22)
        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

                                                            (to   p17)
• 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
                                                               (to   p26)
                       Concepts of refraction and reflection
                                                                       (to   p17)
Fiber-Optic Cable (continued)

                                 (to   p25)
Conducted Media

                   (to   p4)
             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      ( to p29)

• Different types of applications           to p30)

• Comparisons         ( to p63)

                                                   (to   p2)
Wireless Media (continued)

                              (to   p28)
– i) microwave radio          to p31)

– ii) satellite               to p35)

– iii) cellular phones        to p43)

– Iv) Infrared Transmissions          to p52)

– v) Wireless Application Protocol (WAP)                      (to   p53)

– Broadband Wireless Systems                to p56)

– Bluetooth           to p59)

– Wireless Local Area Networks              to p60)

– Free Space Optics and Ultra-Wideband                        (to   p61)

                                                      (to   p28)
      iv) microwave radio
– Is a medium most common carriers for
  long distance comm (how it looks like )
                                        ( to p32)

– transmit in the range of 4-28 Ghz freq
– 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 to p33)

  signals will not pass through solid objects
– requirement          ( to p34)
  Terrestrial Microwave
Transmission (continued)

                            (to   p31)
  Terrestrial Microwave
Transmission (continued)

                            (to   p31)
    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

– Disadv
  • may interfere by the weather condition (why?)

                                                     (to   p30)
             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)        (to p36)

– radio signal is beamed to the satellite on a
  specific frequency called uplink; where
  rebroadcast on a different frequency called
  downlink            (  to p39)

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
   – 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        (to   p37)                                (to   p35)
   Satellite Microwave
Transmission (continued)

                  (to   p38)

                                (to   p36)
Satellite Transmission

                          (to   p37)
            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         (to   p40)

               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 =     ----------------

                 =      0.2398 sec

– Classifications by their configuration             (to   p41)

         Satellite (continued)
• Satellite microwave can also be classified
  by its configuration:
  – Bulk carrier configuration
  – Multiplexed configuration
  – Single-user earth station configuration (e.g.
         Their semantic view   (to   p42)

                                                     (to   p30)
   Satellite Microwave
Transmission (continued)

                            (to   p41)
          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     to p44)

• Each cell has its own transmission tower and set
  of assignable channels       to p45)

• Different generations of MP        to p46)

Cellular Telephones (continued)

                                  (to   p43)
Cellular Telephones (continued)

                                  (to   p43)
             Cellular Phones
•   1st generation   (to   p47)

•   2nd generation   (to   p48)

•   2.5 generation   (to   p49)

•   3rd generation   (to   p50)

                                   (to   p30)
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

                                                     (to   p46)
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

                                                      (to   p46)
Cellular Telephones (continued)
• 2.5 Generation
  – AT&T 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
                                                  (to   p46)
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
                                                     (to   p46)
      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

                                              (to   p30)
  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 to p54)

  (WML) which is used to specify the format and
  presentation of text on the screen
• Their applications      (to   p55)

Wireless Application Protocol
     (WAP) (continued)

                                 (to   p53)
    Wireless Application Protocol (WAP)
• 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
                                                (to   p30)
  Broadband Wireless Systems
• Delivers Internet services into homes and
• Designed to bypass the local loop
  telephone line, in a metropolitan area to p57)

• Transmits voice, data, and video over high
  frequency radio signals
• Past and future trends      to p58)

Broadband Wireless Systems

                              (to   p56)
  Broadband Wireless Systems
• 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
                                                 (to   p30)
• 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

                                                                 (to   p30)
 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,
• More on this in Chapter Seven (LANs)        to p30)
  Free Space Optics and Ultra-
• 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 system’s power by
       approximately 1 dB/km
   –   Scintillation is also a problem (especially in hot weather)
                                                 (to   p62)
      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)

                                                                       (to   p30)
Wireless Media (continued)

                              (to   p64)

Wireless Media (continued)

                              (to   p28)
       Media Selection Criteria
1.   Cost        to p66)

2.   Speed       to p67)

3.   Distance and expandability        (to   p68)

4.   Environment            (to p69)

5.   Security           (to p70)

                                                     (to   p2)
• 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
                                                     (to   p65)
• 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
                                                       (to   p65)
   Expandability and Distance
• Certain media lend themselves more
  easily to expansion
• Don’t forget right-of-way issue

                                        (to   p65)
• Many types of environments are
  hazardous to certain media

                                    (to   p65)
• If data must be secure during transmission,
  it is important that the medium not be easy
  to tap

                                            (to   p65)
   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          (to   p72)

Conducted Media in Action:
       Example 1

                              (to   p3)
   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
     • If not consider using wireless
     • When making decision, need to consider:
        –   Cost
        –   Speed
        –   Expandability and distance
        –   Environment                           (to   p3)
        –   Security
    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
  – May consider using Bluetooth devices

                                               (to   p3)
               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      (to p76)

                                              (to   p3)
 Wireless Media In Action:
Three Examples (continued)

                              (to   p3)
    Wireless Media In Action:
           Example 3
• Third example – second company wishes
  to transmit data between offices two miles
  – Considering terrestrial microwave system
  – Layout       (to p78)

 Wireless Media In Action:
Three Examples (continued)

                              (to   p3)

To top