Physical Layer Chapter 7,8,9 (Study from lecture notes) - PowerPoint PPT Presentation

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Physical Layer Chapter 7,8,9 (Study from lecture notes)

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Chapter 7: Transmission Media – PowerPoint PPT presentation

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Title: Physical Layer Chapter 7,8,9 (Study from lecture notes)


1
Physical Layer Chapter 7,8,9 (Study from
lecture notes)
2
Classes of Transmission Media
  • Conducted or guided media
  • use a conductor such as a wire or a fiber optic
    cable to move the signal from sender to receiver
  • Wireless or unguided media
  • use radio waves of different frequencies and do
    not need a wire or cable conductor to transmit
    signals

3
Guided Transmission Media
  • Transmission capacity depends on the distance and
    on whether the medium is point-to-point or
    multipoint
  • Examples
  • twisted pair wires
  • coaxial cables
  • optical fiber

4
Twisted Pair Wires
  • Consists of two insulated copper wires arranged
    in a regular spiral pattern to minimize the
    electromagnetic interference between adjacent
    pairs
  • Often used at customer facilities and also over
    distances to carry voice as well as data
    communications
  • R-J45 connector

5
Types of Twisted Pair
  • STP (shielded twisted pair)
  • the pair is wrapped with metallic foil or braid
    to insulate the pair from electromagnetic
    interference
  • UTP (unshielded twisted pair)
  • each wire is insulated with plastic wrap, but the
    pair is encased in an outer covering

6
Ratings of Twisted Pair
  • Category 3 UTP
  • data rates of up to 16mbps are achievable
  • Category 5 UTP
  • data rates of up to 100mbps are achievable
  • more expensive, but better performance
  • STP
  • More expensive, harder to work with

7
Twisted Pair Advantages
  • Inexpensive and readily available
  • Flexible and light weight
  • Easy to work with and install

8
Twisted Pair Disadvantages
  • Susceptibility to interference and noise
  • Attenuation problem
  • Relatively low bandwidth (3000Hz)

9
Coaxial Cable (or Coax)
  • Used for cable television, LANs, telephony

BNC Connector
10
Coax Advantages
  • Higher bandwidth
  • 400 to 600Mhz
  • up to 10,800 voice conversations
  • Can be tapped easily (pros and cons)
  • Much less susceptible to interference than
    twisted pair

11
Coax Disadvantages
  • High attenuation rate makes it expensive over
    long distance
  • Bulky

12
Fiber Optic Cable
  • Relatively new transmission medium used by
    telephone companies in place of long-distance
    trunk lines
  • Also used by private companies in implementing
    local data communications networks
  • Require a light source with injection laser diode
    (ILD) or light-emitting diodes (LED)

13
Fiber Optic Layers
  • consists of three concentric sections

14
Fiber Optic Advantages
  • greater capacity (bandwidth of up to 2 Gbps)
  • smaller size and lighter weight
  • lower attenuation
  • immunity to environmental interference
  • highly secure due to tap difficulty and lack of
    signal radiation

15
Fiber Optic Disadvantages
  • expensive over short distance
  • requires highly skilled installers
  • adding additional nodes is difficult

16
Wireless (Unguided Media) Transmission
  • transmission and reception are achieved by means
    of an antenna
  • directional
  • transmitting antenna puts out focused beam
  • transmitter and receiver must be aligned
  • omnidirectional
  • signal spreads out in all directions
  • can be received by many antennas

17
Wireless Examples
  • terrestrial microwave
  • satellite microwave
  • broadcast radio
  • infrared

18
Terrestrial Microwave
  • used for long-distance telephone service
  • uses radio frequency spectrum, from 2 to 40 Ghz
  • parabolic dish transmitter, mounted high
  • used by common carriers as well as private
    networks
  • requires unobstructed line of sight between
    source and receiver
  • curvature of the earth requires stations
    (repeaters) 30 miles apart

19
Microwave Transmission Disadvantages
  • line of sight requirement
  • expensive towers and repeaters
  • subject to interference such as passing airplanes
    and rain

20
Satellite Microwave Transmission
  • a microwave relay station in space
  • can relay signals over long distances
  • geostationary satellites
  • remain above the equator at a height of 22,300
    miles (geosynchronous orbit)
  • travel around the earth in exactly the time the
    earth takes to rotate

21
Satellite Transmission Links
  • earth stations communicate by sending signals to
    the satellite on an uplink
  • the satellite then repeats those signals on a
    downlink
  • the broadcast nature of the downlink makes it
    attractive for services such as the distribution
    of television programming

22
Satellite Transmission Process
satellite transponder
dish
dish
22,300 miles
uplink station
downlink station
23
Radio
  • radio is omnidirectional and microwave is
    directional
  • Radio is a general term often used to encompass
    frequencies in the range 3 kHz to 300 GHz.
  • Mobile telephony occupies several frequency bands
    just under 1 GHz.

24
Infrared
  • Uses transmitters/receivers (transceivers) that
    modulate noncoherent infrared light.
  • Transceivers must be within line of sight of each
    other (directly or via reflection ).
  • Unlike microwaves, infrared does not penetrate
    walls.

25
Electromagnetic Spectrum for Transmission Media
26
Switching Techniques
  • a collection of nodes and connections is a
    communications network
  • have two different switching technologies
  • circuit switching
  • packet switching

27
Circuit Switching
  • uses a dedicated path between two stations
  • has three phases
  • establish
  • transfer
  • disconnect
  • inefficient
  • channel capacity dedicated for duration of
    connection
  • if no data, capacity wasted
  • set up (connection) takes time
  • once connected, transfer is transparent

28
Public Circuit Switched Network
29
Packet Switching
  • circuit switching was designed for voice
  • packet switching was designed for data
  • transmitted in small packets
  • packets contains user data and control info
  • user data may be part of a larger message
  • control info includes routing (addressing) info
  • packets are received, stored briefly (buffered)
    and past on to the next node

30
Switching Techniques
  • station breaks long message into packets
  • packets sent one at a time to the network
  • packets can be handled in two ways
  • datagram
  • virtual circuit

31
Datagram Diagram
32
Virtual Circuit Diagram
33
Network Taxonomy
34
Remote Connectivity
  • How to (technology to) connect a computer (a
    network) to another computer (another network) at
    a remote location
  • Some Examples of technologies for remote
    connectivity (List is not complete)
  • PSTN (POTS)
  • ISDN
  • DSL
  • T1 and T3
  • SONET/SDH and OC

35
Analog versus Digital Telecommunication Technology
  • Analog technology Digital technology
  • PSTN (POTS) ISDN
  • DSL
  • T1 and T3
  • SONET/SDH

36
A telephone system ( POTS)
37
PSTN (POTS)
  • Advantages
  • The cheapest
  • The most widely available
  • Disadvantages
  • The slowest
  • The least reliable
  • Data can get corrupted easily during transmission

38
ISDN (Integrated Services Digital Network)
  • Uses digital technology over the PSTN
  • ISDN
  • Fully digital
  • Dial up connection
  • To connect a computer to an ISDN line, you would
    use a terminal adapter (ISDN modem)

39
ISDN (Integrated Services Digital Network)
  • Two types of ISDN services
  • BRI (Basic Rate Interface)
  • 2 (64 Kbps) B channels 1 (16 Kbps) D channel
  • B channel carries the actual user data
  • D channel carries control data
  • PRI (Primary Rate Interface)
  • 23 (64 Kbps) B channels 1 (64 Kbps) D channel

40
DSL (Digital Subscriber Line)
  • Uses digital technology over the PSTN
  • Dedicated connection
  • No need to dial a number to establish connection
  • The connection is always ON
  • Using
  • PSTN
  • DSL modem
  • DSLAM (Digital Subscriber Line Access Multiplexer)
  • Two versions of DSL
  • Symmetric DSL
  • Asymmetric DSL

41
DSL (Digital Subscriber Line)
42
DSL (Digital Subscriber Line)
43
DSL (Digital Subscriber Line)
  • DSL versus (ISDN and PSTN)
  • Faster
  • DSL weakness
  • The farther the node (computer) from DSLAM, the
    slower the actual throughput

44
T1 and T3
  • T1 and T3 are leased line
  • A dedicated line that is built to connect two
    remote locations
  • PSTN, ISDN, DSL, Cable Modems are NOT leased
    lines because they are shared by multiple users
  • At each end (location), CSU/DSU (Channel Service
    Unit/Digital Service Unit) must be installed
  • Common applications
  • To connect medium/large organizations network to
    the Internet
  • To connect local ISP network to backbone ISP
    network

45
T1 and T3
46
T1 and T3
  • Advantages
  • The actual throughput is more consistent
    (guaranteed speed)
  • Fast
  • T1 1.54 Mbps
  • T3 44.74 Mbps
  • Disadvantages
  • Expensive
  • Inefficient if the subscriber does not use the
    line around the clock

47
SONET/ Synchronous Digital Hierarchy (SDH)
  • Fiber optic line
  • Leased line
  • USA SONET
  • Europe SDH
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