复旦大学：《计算机网络 Computer Networking》课程电子教案（PPT课件讲稿）05 physical_Transmission

Lecture 5 Transmission Dejian Ye Software School Fudan University 15-441 Networking, Spring 2008

1 Lecture 5 Transmission Dejian Ye Software School Fudan University 15-441 Networking, Spring 2008

Physical and Datalink Layers. 3 Lectures 1. Physical layer. Application 2. Datalink layer Presentation introduction, framing, error coding, switched Session networks Transport roadcast-networks Network home networking Datalink Physical 2

2 Physical and Datalink Layers: 3 Lectures 1. Physical layer. 2. Datalink layer introduction, framing, error coding, switched networks. 3. Broadcast-networks, home networking. Application Presentation Session Transport Network Datalink Physical

From Signals to Packets Analog signal “ Digital” Signal Bit stream 00101110001 Packets 0l000l0l0l0l1001010101010ll01l100000011l01010l1l0101010l01010l1010111001 Header/body Header/body Header/body Packet Transmission Sender Receiver 3

3 From Signals to Packets Analog Signal “Digital” Signal Bit Stream 0 0 1 0 1 1 1 0 0 0 1 Packets 0100010101011100101010101011101110000001111010101110101010101101011010111001 Header/Body Header/Body Header/Body Sender Receiver Packet Transmission

Today's Lecture Modulation Bandwidth limitations Frequency spectrum and its use Multiplexing Media: Copper, Fiber, Optical, Wireless Coding Framing

4 Today’s Lecture Modulation. Bandwidth limitations. Frequency spectrum and its use. Multiplexing. Media: Copper, Fiber, Optical, Wireless. Coding. Framing

Why Do We Care? I am not an electrical engineer? Physical layer places constraints on what the hardware network infrastructure can deliver reality check Need to understand impact of the physical layer on the higher protocol layers 》 Fiber fiber copper? > Why do we need wires at all? > Error characteristic and failure modes 》 Effects of distance 5

5 Why Do We Care? I am not an electrical engineer? Physical layer places constraints on what the hardware network infrastructure can deliver = reality check Need to understand impact of the physical layer on the higher protocol layers »Fiber fiber copper? »Why do we need wires at all? »Error characteristic and failure modes »Effects of distance

Modulation Sender changes the nature of the signal in a way that the receiver can recognize Similar to radio: AM or FM Digital transmission; encodes the values o or in the signal. >)It is also possible to encode multi-valued symbols Amplitude modulation: change the strength of the signal, typically between on and off 》 Sender and receiver agree on a“rate” >)On means 1, Off means 0 Similar frequency or phase modulation Can also combine method modulation types. 6

6 Modulation Sender changes the nature of the signal in a way that the receiver can recognize. » Similar to radio: AM or FM Digital transmission: encodes the values 0 or 1 in the signal. » It is also possible to encode multi-valued symbols Amplitude modulation: change the strength of the signal, typically between on and off. » Sender and receiver agree on a “rate” » On means 1, Off means 0 Similar: frequency or phase modulation. Can also combine method modulation types

Amplitude and Frequency Modulation 00110011000111000110001110

7 Amplitude and Frequency Modulation 0 0 1 1 0 0 1 1 0 0 0 1 1 1 0 0 0 1 1 0 0 0 1 1 1 0 0 1 1 0 1 1 0 0 0 1

The Frequency domain A(periodic) signal can be viewed as a sum of sine waves of different strengths. >)Corresponds to energy at a certain frequency Every signal has an equivalent representation in the frequency domain > What frequencies are present and what is their strength(energy) Again: Similar to radio and Tv signals lme requency 8

8 The Frequency Domain A (periodic) signal can be viewed as a sum of sine waves of different strengths. » Corresponds to energy at a certain frequency Every signal has an equivalent representation in the frequency domain. » What frequencies are present and what is their strength (energy) Again: Similar to radio and TV signals. Time Frequency Amplitude

Signal= Sum of Waves +13X +0.56X A∧ +1.15X 9

9 Signal = Sum of Waves = + 1.3 X + 0.56 X + 1.15 X

Why Do We Care? How much bandwidth can I get out of a specific wire(transmission medium)? What limits the physical size of the network? How can multiple hosts communicate over the same wire at the same time? How can I manage bandwidth on a transmission medium? How do the properties of copper, fiber, and wireless compare? 10

10 Why Do We Care? How much bandwidth can I get out of a specific wire (transmission medium)? What limits the physical size of the network? How can multiple hosts communicate over the same wire at the same time? How can I manage bandwidth on a transmission medium? How do the properties of copper, fiber, and wireless compare?