Transcript Telecommunications

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Telecommunications
Ch.11-A,B,C
FALL 2000
Rob Wolfe
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Goal
 Explain Shannon’s comm model
 Define bandwidth and effects
 Difference between:
 simplex, half duplex, full duplex, echoplex
 Odd/even parity
 Synchronous/asynchronous comms
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Goal (continued)
 Packet and circuit switching
 LAN standards/protocols
 Adv/Disadv of Internet over
 POTS, Cell, cable TV, satellite
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Data Communications (A)
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Model of Communication Systems
Simplex
Half Duplex
Full Duplex
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Communication Signals
 Signal frequency is measured in
 Hertz (Hz)
 Megahertz (MHz)
 Gigahertz (GHz)
 Hertz = one wave (oscillation) per second
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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
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Communications Links (B)
 Twisted Pair Cable
 Coaxial Cable
 Fiber Optic Cable
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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
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Twisted Pair Cable
RJ-45 wall
outlet
Each wire is coated with
plastic so wires don’t
have direct contact.
Usually contains four
pairs of copper wires
Plastic sheath
protects wires
RJ-45 connector
To computer
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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
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Coaxial Cable
Coaxial cable — a high-capacity
communications cable that consists of:
 Copper wire
conductor
 Non conducting
insulator
 Foil shield
 Woven metal outer
shielding
 Plastic outer
coating
Metal BNC connector
links cable to a Tshaped connector on
back of a computer
Copper wire
core
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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
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Coaxial Cable vs. Twisted Pair Cable
Twisted Pair
 Category 5
 Used more in networks
today
 More durable
 Cheaper
Coaxial
 Used to be widely used
in LAN
 Excellent bandwidth
 Less durable
 More expensive
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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
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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.
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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
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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.
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Communications Systems(C)
 POTS
 Integrated Services Digital Network (ISDN)
 T1, T3
 Cellular Phones
 CATV
 Internet/Intranet
 LANS (Ethernet, Token Ring)
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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
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Internet Access via Telephone System
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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
10-52 sec
46 min
24 min
90 min
52 sec
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Local Area Networks (LANs)
 Topology
 Three Types
 Star
 Ring
 Bus
 Network Standard
 Ethernet
 Token Ring
 Network Communications Protocol
 TCP/IP, IPX, LAT, AFP
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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
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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-itnotes, 8 beeps
 Snail mail growth … less than 2% a year
 The culprit is …
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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
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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%.
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What’s Happening in Telecom?
 Digital Convergence
 “Honey, would you please answer the TV?
I’m watching the phone.”
 JAVA
 C&C Convergence (Japanese)
?
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Goal
 Explain Shannon’s comm model
 Define bandwidth and effects
 Difference between:
 simplex, half duplex, full duplex, echoplex
 Odd/even parity
 Synchronous/asynchronous comms
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Goal (continued)
 Packet and circuit switching
 LAN standards/protocols
 Adv/Disadv of Internet over
 POTS, Cell, cable TV, satellite
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