Computer Networks asdssdadas- part 3.pdf

COMPUTER NETWORKS
– PART 2
University Of Kurdistan
Dept. Of Engineering (Computer Group)
By: Khatereh Ahmadi
Khahmadi.uok@gmail.com

SOFTWARE OF COMPUTER NETWORKS
Reference model
TCP/IP
30

TCP/IP
➢ Older than OSI (Introduced in 1960)
➢ Simple and more practical design
➢ Reference model used by Internet
31

TCP/IP
Network Access (Network Interface):
Physical and datalink tasks
transmission channels (physical media)
➢ Telephone lines
➢ Twisted Pair cables
➢ Coaxial Cables
➢ Optical Fiber
➢ Satellite channels
32

Reference model – Network Interface
TCP/IP
Twisted Pair cable
A type of cable made using pairs of
copper wires.
These cables are used in communication
networks and data transmission.
Two main categories:
STP, UTP
33

TCP/IP
Coaxial cable
A shielded type of cable that has an inner conductor surrounded by
concentric insulating layers that are surrounded by a conductive
shielding.
34

TCP/IP
Optical Fibers
The technology that transmits information as light pulses along a
glass or plastic fiber.
Fiber optic cables are commonly used because of their advantages
over copper cables including higher bandwidth and transmit speeds.
35

TCP/IP
Optical Fibers: Total internal reflection phenomenon.
36

TCP/IP
Common parameters
Bitrate:
The number of bits that are conveyed or processed per unit of time.
Bandwidth:
A measurement indicating the maximum capacity of a wired or
wireless communications link to transmit data over a network
connection in a given amount of time.
37

TCP/IP
Common parameters
Multiplexing: A technique that allows a number of lower bandwidth
communication channels to be combined and transmitted
simultaneously over one higher bandwidth channel
Two types of multiplexing:
➢ FDM (Frequency Division Multiplexing)
➢ TDM (Time Division Multiplexing)
38

TCP/IP
Common parameters
Error Control
Checksum – error detection method based on data integrity
CRC – Cyclic Redundancy Check
39

PHYSICAL LAYER
DATA COMMUNICATION BASICS
41

PHYSICAL LAYER
𝒙 𝒕 = 𝒙 𝒕 + 𝑻
𝒇 =
𝟏
𝑻
𝝎 = 𝟐𝝅𝒇
42

PHYSICAL LAYER
Fourier analysis
𝒙 𝒕 =
𝟏
𝟐
𝒄 + σ𝒏=𝟏
∞
𝒂𝒏𝒔𝒊𝒏(𝟐𝝅𝒏𝒇𝒕) + σ𝒏=𝟏
∞
𝒃𝒏𝒄𝒐𝒔(𝟐𝝅𝒏𝒇𝒕)
𝒂𝒏 , 𝒃𝒏 : amplitudes of 𝑛𝑡ℎ harmony of signals
43

PHYSICAL LAYER
44

PHYSICAL LAYER
45

PHYSICAL LAYER
Bitrate, Frequency and Bandwidth
Consider a telephone line with the following features:
Bitrate=300 b/s
T (for 1 byte) = 8/300 = 0.02667 (sec)
f = 1/T = 1/0.02667 = 37.5 (Hz)
Bandwidth= f (high) – f (low) = ? > 300b/s
46

PHYSICAL LAYER
Bitrate Vs Baud rate
Bitrate: number of bits transmitted per second
Baud rate: number of signal changes per second
47

PHYSICAL LAYER
Channel capacity - Nyquist’s Theorem: (Noiseless channels)
C = 𝟐 × 𝑩𝒂𝒏𝒅𝒘𝒊𝒅𝒕𝒉 × log𝟐 𝑳
Example #1: Consider a noiseless channel with a bandwidth of 3000 Hz
transmitting a signal with two signal levels. What can be the maximum bit
rate?
C = 2 * 3000 * log2(2) = 6000bps
Example #2: We need to send 265 kbps over a noiseless channel with a
bandwidth of 20 kHz. How many signal levels do we need?
265000 = 2 * 20000 * log2(L) → log2(L) = 6.625
L = 26.625 = 98.7 levels 48

PHYSICAL LAYER
Channel capacity - Shannon's Theorem (Noisy channel)
𝑪 = 𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ × log𝟐(1 +
𝑺
𝑵
) , SNR (db) = 10 × log𝟏𝟎(
𝑺
𝑵
)
Example #1: A telephone line normally has a bandwidth of 3000 Hz (300
to 3300 Hz) assigned for data communication. The Signal to noise ratio is
usually 3162. What will be the capacity for this channel?
C = 3000 * log2(1 +
𝑺
𝑵
) = 3000 * 11.62 = 34860 bps
Example #2: Assume that SNR(dB) is 36 and the channel bandwidth is 2
MHz Calculate the theoretical channel capacity.
SNR(dB) = 10 * log10(S/N) → 36 = 10 * log10(S/N)
log10(S/N) = 3.6 → S/N = 103.6= 3981 → 𝐶 = 2 × 106 × 𝑙𝑜𝑔2( 3982)
49

PHYSICAL LAYER
Modulation
➢ Frequency Modulation (FM)
➢ Phase Modulation (PM)
➢ Amplitude Modulation (AM)
➢ Quadrature amplitude modulation (QAM) – AM + PM
50

PHYSICAL LAYER
Modulation
51

PHYSICAL LAYER
Phase Modulation
52

PHYSICAL LAYER
QAM Modulation
53

PHYSICAL LAYER
QAM Modulation
54

PHYSICAL LAYER
Multiplexing
➢Multiplexing: to combine information streams from multiple
sources for the purpose of transmitting them over a shared medium.
➢Multiplexer: a device that performs multiplexing
➢Demultiplexing: to separate information that has been multiplexed
back into its constituent information streams.
➢Demultiplexer: a device that performs demultiplexing
55

PHYSICAL LAYER
Multiplexing
56

PHYSICAL LAYER
Basic types of Multiplexing
➢Frequency Division Multiplexing (FDM, widely used)
➢Wavelength Division Multiplexing (form of FDM used with fiber)
➢Time Division Multiplexing (TDM, widely used)
➢Code Division Multiplexing (cell phone mechanisms)
57

PHYSICAL LAYER
FDM: the idea of using multiple carriers of different frequencies
simultaneously on a medium like a copper wire or optical fiber
58

PHYSICAL LAYER
59

PHYSICAL LAYER
Carrier frequencies that are too close are difficult for a demultiplexer
to separate, and they can interfere with each other.
FDM schemes separate carriers with gaps called guard bands.
60

PHYSICAL LAYER
An example assignment of frequencies to channels with a guard band
between adjacent channels.
61

PHYSICAL LAYER
WDM: Wavelength Division in the case of optical fibers
(multiplexors and demultiplexers use prisms)
62

PHYSICAL LAYER
TDM: Time Division Multiplexing
63

PHYSICAL LAYER
64

PHYSICAL LAYER
CDMA (Code Division Multiple Access)
65

Computer Networks asdssdadas- part 3.pdf

More Related Content

Similar to Computer Networks asdssdadas- part 3.pdf (20)

Recently uploaded (20)

Computer Networks asdssdadas- part 3.pdf