Chapter 2 The Physical Layer - PowerPoint PPT Presentation

Loading...

PPT – Chapter 2 The Physical Layer PowerPoint presentation | free to download - id: 65b36d-OTFhZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Chapter 2 The Physical Layer

Description:

Chapter 2 The Physical Layer The lowest layer of reference model. It defines the mechanical, electrical, and timing interfaces to the network. Bandwidth-Limited ... – PowerPoint PPT presentation

Number of Views:16
Avg rating:3.0/5.0
Date added: 15 October 2019
Slides: 27
Provided by: Steve1580
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Chapter 2 The Physical Layer


1
  • Chapter 2 The Physical Layer

The lowest layer of reference model. It defines
the mechanical, electrical, and timing interfaces
to the network.
2
Bandwidth-Limited Signals
  • A binary signal and its root-mean-square Fourier
    amplitudes.
  • (b) (c) Successive approximations to the
    original signal.

3
Bandwidth-Limited Signals (2)
  • (d) (e) Successive approximations to the
    original signal.

4
BANDWIDTH AND INFORMATION CAPACITY
Bandwidth is the span of frequencies within the
spectrum occupied by a signal and used by the
signal for conveying information. Carrying
information requires bandwidth.
5
Noiseless Channel Nyquist Bit Rate
L is the number of signal levels used to
represent data.
Increasing the levels of a signal may reduce the
reliability of the system.
6
Noisy Channel Shannon Capacity
The theoretical highest data rate for a noisy
channel
where capacity is in bits/second, bandwidth is in
hertz, and signal and noise powers are measured
in the same physical units, such as watts. Bits
are fundamental units of information.
7
Using both limits
  • The Shannon capacity gives us the upper limit
  • the Nyquist formula tells us how many signal
    levels we need.

8
Guided Transmission Data
  • Magnetic Media
  • Twisted Pair
  • Coaxial Cable
  • Fiber Optics

WirelessTransmission
  • The Electromagnetic Spectrum
  • Radio Transmission
  • Microwave Transmission
  • Infrared and Millimeter Waves
  • Lightwave Transmission

9
The Electromagnetic Spectrum
  • The electromagnetic spectrum and its uses for
    communication.

10
Structure of the Telephone System
Public Switched Telephone System
  • (a) Fully-interconnected network.
  • (b) Centralized switch.
  • (c) Two-level hierarchy.

11
Signal Encoding Techniques
  1. Digital data, digital signal
  2. Analog data, digital signal
  3. Digital data, analog signal
  4. Analog data, analog signal

12
Encoding Schemes
13
NRZ
14
Biphase
  • Manchester
  • Transition in middle of each bit period
  • Transition serves as clock and data
  • Low to high represents one
  • High to low represents zero
  • Used by IEEE 802.3
  • Differential Manchester
  • Mid-bit transition is clocking only
  • Transition at start of a bit period represents
    zero
  • No transition at start of a bit period represents
    one
  • Note this is a differential encoding scheme
  • Used by IEEE 802.5

15
Manchester Encoding
16
  • TQ 6. The waveform of following figure belongs to
    a Manchester encoded binary data stream.
    Determine the beginning and end of bit periods
    (i.e., extract clock information) and give the
    data sequence.

17
Modulation Rate
18
Digital Data, Analog Signal
  • Public telephone system
  • 300Hz to 3400Hz
  • Use modem (modulator-demodulator)
  • Amplitude shift keying (ASK)
  • Frequency shift keying (FSK)
  • Phase shift keying (PK)

19
Modulation Techniques
20
Modems (2)
Constellation Diagrams
  • (a) QPSK.
  • (b) QAM-16.
  • (c) QAM-64.

21
Modems (3)
(b)
(a)
  • (a) V.32 for 9600 bps.
  • (b) V32 bis for 14,400 bps.

22
Multiplexing
Frequency Division Multiplexing Wavelength
Division Multiplexing Time Division Multiplexing
23
Simple Circuit Switched Network
24
Packet Switching
25
Basic Operation
  • Data transmitted in small packets
  • Typically 1000 octets (bytes)
  • Longer messages split into series of packets
  • Each packet contains a portion of user data plus
    some control information
  • Control information
  • Routing (addressing) information
  • Packets are received, stored briefly (buffered)
    and past on to the next node
  • Store and forward

26
Advantages
  • Line efficiency
  • Single node to node link can be shared by many
    packets over time
  • Packets queued and transmitted as fast as
    possible
  • Data rate conversion
  • Each station connects to the local node at its
    own speed
  • Nodes buffer data if required to equalize rates
  • Packets are accepted even when network is busy
  • Delivery may slow down
  • Priorities can be used
About PowerShow.com