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    Telecommunications
         Ch.11-A,B,C



           FALL 2000
           Rob Wolfe



                         1
9                                                        Goal

     Explain Shannon’s comm model
     Define bandwidth and effects
     Difference between:
          simplex, half duplex, full duplex, echoplex
     Odd/even parity
     Synchronous/asynchronous comms




                                                           2
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9                                    Goal (continued)

     Packet and circuit switching
     LAN standards/protocols
     Adv/Disadv of Internet over
          POTS, Cell, cable TV, satellite




                                                  3
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9                      Data Communications (A)




                                           4
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9                Model of Communication Systems




                                       Simplex

                                       Half Duplex


                                       Full Duplex


                                                 5
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9                              Communication Signals




            Signal frequency is measured in
                  Hertz (Hz)
                  Megahertz (MHz)
                  Gigahertz (GHz)
            Hertz = one wave (oscillation) per second


                                                         6
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9                      Data Communications (cont)

     Communications Channel
     Communications Medium
          twisted pair, coax, fiber-optic
     Bandwidth
          Digital(bps), Analog (Hz)
     Transmission Speed
          Serial, Parallel transmission
     Signal Direction
          Simplex, Half-duplex, Duplex, Echoplex
     Parity Protocol (even/odd parity)
     Synchronous/Async Protocols                   7
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9                      Communications Links (B)

     Twisted Pair Cable
     Coaxial Cable
     Fiber Optic Cable




                                            8
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9                                Twisted Pair Cable

     Terminates with RJ-45 connector
          Note: Twisted pair cable used for telephones use
           smaller RJ-11 connector
     Shielded (STP) — wires are coated with a
      foil shield that reduces signal noise that
      might interfere with data transmission.
     Unshielded (UTP) — contain no shielding
      and are...
          less expensive
          more susceptible to noise


                                                       9
    DIT 2006 - Wolfe
9                                                  Twisted Pair Cable


                                                       Usually contains four
                        Each wire is coated with       pairs of copper wires
                         plastic so wires don’t
                          have direct contact.
    RJ-45 wall
      outlet

                                                                   Plastic sheath
                                                                   protects wires




                       RJ-45 connector
                                                          To computer



                                                                               10
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9                                Twisted Pair Cable

     Category 1:
          UTP are recommended for analog voice
           communication but not data
          Referred to as voice-grade cable
     Category 2:
          Higher grade of UTP suitable for voice and data
     Categories 3-5: (16, 20, 100Mbps)
          Higher grade of UTP and STP
          Suitable for voice and data
          Referred to as data grade cable


                                                       11
    DIT 2006 - Wolfe
9                                 Coaxial Cable

      Coaxial cable — a high-capacity
      communications cable that consists of:
          Copper wire              Metal BNC connector
           conductor                links cable to a T-
                                    shaped connector on
          Non conducting
                                    back of a computer
           insulator
          Foil shield
          Woven metal outer
           shielding
          Plastic outer
           coating
                               Copper wire
                               core
                                                   12
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9                                      Coaxial Cable

     Called Category 6 cable
     Has a bandwidth greater than twisted pair
      cable(100mbps+)
     Thin coax (3/16 inch)
          Found in local area networks
          Used in home cable TV wiring
     Thick coax (3/8 inch)
          Found in older local area networks
          Used in cable TV trunk lines



                                                 13
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9          Coaxial Cable vs. Twisted Pair Cable

           Twisted Pair            Coaxial
     Category 5               Used to be widely used
     Used more in networks     in LAN
      today                    Excellent bandwidth
     More durable             Less durable
     Cheaper                  More expensive




                                                  14
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9                           Fiber Optic Cable

    Fiber Optic Cable — a bundle of extremely
    thin tubes of glass called optical fibers.

    Optical fibers are:
     Thinner than the diameter of a human hair
     A relatively new development- since 1980s
     Purified glass without traces of water or
      metals



                                             15
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9                                     Fiber Optic Cable

       Plastic coating protects the
          bundle of glass fibers.




       Metal wire strengthens
             the cable.                  Category 7 Cable


                                       Fiber is wrapped in cladding
                                        to reflect light that travels
                                             through the fiber.



                                        Core of each fiber is a
                                      perfectly formed glass tube.

                                                                16
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9                            Fiber Optic Cable

    How fiber optic cables work:
     Miniature lasers (LEDs) send pulses of light
      through the fibers
     Electronics at the receiving end convert
      light pulses into electrical signals
     Each fiber is a one-way communications
      channel




                                               17
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9              Low Earth Orbit Satellite Networks

     A low earth orbit
      communications
      system requires a
      web of satellites to
      provide continual
      coverage over an
      area such as North
      America.




                                              18
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9                      Communications Systems(C)

     POTS
     Integrated Services Digital Network (ISDN)
     T1, T3
     Cellular Phones
     CATV
     Internet/Intranet
     LANS (Ethernet, Token Ring)




                                             19
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9                      Communication via Telephone

    Plain Old Telephone Service (POTS)
     Creates dial-up connection when you dial
     Stops connection when you hang up
     Uses analog audio signals
     Must use a modem to send data signals
     Modulation
          Changing the characteristics of a digital pulse
           into an analog signal
     Demodulation
          Changing the signal back to its original state

                                                            20
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9      Internet Access via Telephone System




                                        21
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9                        Internet Access Speed

       Cable Modems (30 Mbps)
       DSL (1.5-8 Mbps)
       T1/T3 (1.5/45 Mbps)
       ISDN (.64-1.54 Mbps)
       Modems
          56 Kbps
          28.8 Kbps
          14.4 Kbps
                          8-20 sec             10 min            46 min

                               10-52 sec                24 min            90 min
                                      52 sec




                                                                               22
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9                      Local Area Networks (LANs)

     Topology
     Three Types
          Star
          Ring
          Bus
     Network Standard
          Ethernet
          Token Ring
     Network Communications Protocol
          TCP/IP, IPX, LAT, AFP

                                              23
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9                      What’s Happening in Telecom?

     How long it took to reach 50 million people
          Radio … 38 years
          TV … 13 years
          PC … 16 years
          Internet … 4 years




                                                24
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9                      What’s Happening in Telecom?

     Cause of Information Overload
     Average US office worker …
          Communicates with 24 different people per day
          Six to 20 incoming messages per hour
     Average UK office worker …
          Receives 48 phone calls, 23 e-mails, 11 voice
           mails, 20 letters, 15 memos, 11 faxes, 13 post-it-
           notes, 8 beeps
     Snail mail growth … less than 2% a year
     The culprit is …

                                                         25
    DIT 2006 - Wolfe
9                      What’s Happening in Telecom?

     Cost of Long-Distance Communication
          1974 … NY to LA, 3 minutes, $1.45
          Today … same call, about a quarter
     Volume of Long-Distance Communication
          1984 … AT&T, 90% market share, 25 million calls
           per day
          Today … AT&T, 50% market share, 250 million
           calls per day




                                                     26
    DIT 2006 - Wolfe
9                      What’s Happening in Telecom?

     How about Faxes …
          In 1997, 3.2 billion pages were faxed.
          US Postal Service estimates that fax drove USPS
           market share (for correspondence industry)
           from 77% in 1988 to less than 59% in 1998.
     Wireless Communications
          More than 21 million sign-ups for wireless
           account every month in the US
          Wireless penetration in US is 21%. In Finland,
           over 50%.


                                                        27
    DIT 2006 - Wolfe
9                      What’s Happening in Telecom?

     Digital Convergence
          “Honey, would you please answer the TV?
            I’m watching the phone.”
          JAVA
          C&C Convergence (Japanese)




                             ?
                                                     28
    DIT 2006 - Wolfe
9                                                        Goal

     Explain Shannon’s comm model
     Define bandwidth and effects
     Difference between:
          simplex, half duplex, full duplex, echoplex
     Odd/even parity
     Synchronous/asynchronous comms




                                                          29
    DIT 2006 - Wolfe
9                                    Goal (continued)

     Packet and circuit switching
     LAN standards/protocols
     Adv/Disadv of Internet over
          POTS, Cell, cable TV, satellite




                                                  30
    DIT 2006 - Wolfe

				
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