mt jaringan-komputer 1 stikom

7/29/2019 MT Jaringan-Komputer 1 STIKOM

1/72

0

Komunikasi Data danJaringan Komputer


2/72

1

Referensi

W. Stallings, Data and ComputerCommunications, 4ed, Macmillan, 1994.

F. Halsall, Data Communications,Computer Networks and OpenSystems, Addison Wesley, 1996.


3/72

2

A Communications Model

Source

generates data to be transmitted

Transmitter

Converts data into transmittable signalsTransmission System

Carries data

Receiver

Converts received signal into data

Destination

Takes incoming data


4/72

3

Simplified Communications

Model - Diagram


5/72

4

Simplified Data

Communications Model


6/72

5

Key Communications Tasks

Transmission System Utilization

Interfacing

Signal Generation

SynchronizationExchange Management

Error detection and correction

Addressing and routing

Recovery

Message formatting

Security

Network Management


7/72

6

Communications Standard

Many types of connection media :

telephone lines, optical fibers,

cables, radios, etc.

Many different types of machines and

operating systems

Many different network applications


8/72

7

What Standard means?

How many volts pulse is a 0 and 1 ?

How to determine the end of a message ?

How to handle lost messages ?

How many bits for different data types ?

Integers/Strings, etc.; are ASCII chars ?

How machines are identified ?

How to find the way to reach a machine ?

How applications speaks together through the

network ?


9/72

8

Standard Bodies

International Telecommunications Union

Telecommunications Sector (ITU-T)

Institute of Electrical and Electronics

Engineers (IEEE)

International Standards Organization (ISO)

Electronic Industries Alliance (EIA)dll


10/72

9

The ISO/OSI Model

ISO (the International Standards Organization) has

developed a reference model for communications,

called the

OSI(Open Systems Interconnection)

OPEN SYSTEM means that it can communicate with

any other system that follows the specified standards,formats and semantics.


11/72

10

OSI Networking Model

Application ApplicationDataAH

Presentation PresentationDataunitPH

Session SessionData unitSH

Transport TransportData unitTH

Network NetworkData unitNH

Data link Data linkData unitLH LT

Physical PhysicalBits

Physical transmission medium

DataProgram X Program Y


12/72

11

OSI Layers (1)

Physical

Physical interface between devices

Mechanical

ElectricalFunctional

Procedural

Data Link

Means of activating, maintaining and deactivating areliable link

Error detection and control

Higher layers may assume error free transmission


13/72

12

OSI Layers (2)

Network

Transport of information

Higher layers do not need to know about underlying technology

Not needed on direct links

Transport

Exchange of data between end systems

Error free

In sequence

No losses No duplicates

Quality of service


14/72

13

OSI Layers (3)

Session

Control of dialogues between applications

Dialogue discipline

Grouping Recovery

Presentation

Data formats and coding

Data compression

Encryption

Application

Means for applications to access OSI environment


15/72

14

Transmission Medium

Guided - wire

Unguided - wireless

Characteristics and quality determined bymedium and signal

For guided, the medium is more important

For unguided, the bandwidth produced bythe antenna is more important

Key concerns are data rate and distance


16/72

15

Guided Transmission Media

Twisted Pair

Coaxial cable

Optical fiber


17/72

16

Twisted pair - INEXPENSIVE

Two wires twisted together.

Makes them less susceptible to acting likean antenna and picking up radio frequency

information or appliance noise.

Telephone company uses twisted-pair

copper wires to link telephones.

Twisted Pair


18/72

17

Twisted Pair


19/72

18

Twisted Pair - Applications

Most common medium

Telephone network

Between house and local exchange

(subscriber loop)

Within buildings

To private branch exchange (PBX)

For local area networks (LAN)

10Mbps or 100Mbps


20/72

19

Twisted Pair - Pros and Cons

Cheap

Easy to work with

Low data rateShort range


21/72

20

Twisted Pair - Transmission

CharacteristicsAnalog

Amplifiers every 5km to 6km

Digital

Use either analog or digital signals repeater every 2km or 3km

Limited distance

Limited bandwidth (1MHz)

Limited data rate (100MHz)

Susceptible to interference and noise


22/72

21

Unshielded and Shielded TP

Unshielded Twisted Pair (UTP)

Ordinary telephone wire

Cheapest

Easiest to install Suffers from external EM interference

Shielded Twisted Pair (STP)

Metal braid or sheathing that reduces interference

More expensive

Harder to handle (thick, heavy)


23/72

22

UTP Categories

Cat 3

up to 16MHz

Voice grade found in most offices

Twist length of 7.5 cm to 10 cmCat 4

up to 20 MHz

Cat 5 or Cat 6

up to 100MHz

Commonly pre-installed in new office buildings

Twist length 0.6 cm to 0.85 cm


24/72

23

Coaxial Cable (1)

Coaxial cable

Also two wires:

One of the wires is woven of fine strands ofcopper forming a tube.

The wire mesh surrounds a solid copper

wire that runs down the center.

Space between has a non-conductingmaterial.

Makes them more impervious to outside

noise.

Use this when1. Long distances2. Lots of interference


25/72

24

Coaxial Cable (2)


26/72

25

Coaxial Cable (3)


27/72

26

Coaxial Cable Applications

Most versatile medium

Television distribution

Aerial to TV

Cable TV

Long distance telephone transmission

Can carry 10,000 voice calls simultaneously

Being replaced by fiber optic

Short distance computer systems links

Local area networks


28/72

27

Coaxial Cable - Transmission

CharacteristicsAnalog

Amplifiers every few km

Closer if higher frequency

Up to 500MHz

Digital

Repeater every 1km

Closer for higher data rates


29/72

28

Optical Fiber (1)


30/72

29

Optical Fiber (2)


31/72

30

Optical Fiber (3)

Fiber-optic cable

(BIG JOBS + EXPENSIVE)

Light is electromagnetic. Can transmit more information down a single

strand.

It can send a wider set of frequencies.

Each cable can send several thousand phone

conversations or computer communications.


32/72

31

Optical Fiber - Spectrum


33/72

32

Optical Fiber - Benefits

Greater capacity

Data rates of hundreds of Gbps

Smaller size & weight

Lower attenuation

Electromagnetic isolation

Greater repeater spacing 10s of km at least


34/72

33

Optical Fiber - Applications

Long-haul trunks

Metropolitan trunks

Rural exchange trunksSubscriber loops

LANs


35/72

34

Optical Fiber - Transmission

CharacteristicsAct as wave guide for 1014 to 1015 Hz

Portions of infrared and visible spectrum

Light Emitting Diode (LED)

Cheaper Wider operating temp range

Last longer

Injection Laser Diode (ILD)

More efficient Greater data rate

Wavelength Division Multiplexing (WDM)


36/72

35

Optical Fiber Transmission

Modes


37/72

36

Wireless Transmission

Unguided media

Transmission and reception via antenna

Directional Focused beam

Careful alignment required

Omni-directional Signal spreads in all directions

Can be received by many antenna


38/72

37

Frequencies

2GHz to 40GHz

Microwave

Highly

directional

Point to point Satellite

30MHz to 1GHz

Omni-

directional

Broadcast radio

3 x 1011 to 2 x 1014

Infrared

Local


39/72

38

Terrestrial Microwave

Parabolic dish

Focused beam

Line of sightLong haul telecommunications

Higher frequencies give higher data rates


40/72

39

Satellite Microwave

Satellite is relay station

Satellite receives on one frequency,

amplifies or repeats signal and transmitson another frequency

Requires geo-stationary orbit

Height of35,784kmTelevision

Long distance telephone

Private business networks


41/72

40

Broadcast Radio

Omni-directional

FM radio

UHF and VHF televisionLine of sight

Suffers from multi-path interference


42/72

41

Infrared

Modulate non-coherent infrared light

Line of sight (or reflection)

Blocked by wallse.g. TV remote control, IRD port


43/72

42

Terminology (1)

Transmitter

Receiver

Medium Guided medium

e.g. twisted pair, optical fiber

Unguided medium

e.g. air, water, vacuum


44/72

43

Terminology (2)

Direct link

No intermediate devices

Point-to-point

Direct link

Only 2 devices share link

Multi-point

More than two devices share the link


45/72

44

Terminology (3)

Simplex

One direction

e.g. Television

Half duplex

Either direction, but only one way at a time

e.g. police radio

Full duplex Both directions at the same time

e.g. telephone


46/72

45

Terminology (4)

Bits per second (bps).

The number of bits (0s and 1s) that travel

down the channel per second.

Baud rate

The number of bits that travel down the

channel in a given interval.

The number is given in signal changes persecond, not necessarily bits per second.


47/72

46

Terminology (5)

Asynchronous transmission Information is sent byte by byte.

Cheaper and more commonly used.

Synchronous transmission Data is sent in large blocks rather than in

small pieces.

Preceded by special information, concerningerror detection and block size.

These modems are expensive but very fast.

A l d Di it l D t


48/72

47

Analog and Digital Data

TransmissionData

Entities that convey meaning

Signals

Electric or electromagnetic representations of

data

Transmission

Communication of data by propagation and

processing of signals


49/72

48

Data

Analog

Continuous values within some interval

e.g. sound, video

Digital

Discrete values

e.g. text, integers


50/72

49

Data and Signals

Usually use digital signals for digital data

and analog signals for analog data

Can use analog signal to carry digital data

Modem

Can use digital signal to carry analog data

Compact Disc audio


51/72

50

Signals

Type of signal communicated (analog or digital).

Analog: Those signals that vary with smooth continuouschanges.

A continuously changing signal similar to that found on

the speaker wires of a high-fidelity stereo system. Digital: Those signals that vary in steps or jumps from

value to value. They are usually in the form of pulses of

electrical energy (represent 0s or 1s).

Analog Signals Carr ing Analog


52/72

51

Analog Signals Carrying Analog

and Digital Data

Digital Signals Carrying Analog


53/72

52

Digital Signals Carrying Analog

and Digital Data


54/72

53

Analog Transmission

Analog signal transmitted without regard to

content

May be analog or digital data

Attenuated over distance

Use amplifiers to boost signal

Also amplifies noise


55/72

54

Digital Transmission

Concerned with content

Integrity endangered by noise, attenuation etc.

Repeaters used

Repeater receives signal

Extracts bit pattern

Retransmits

Attenuation is overcomeNoise is not amplified

Advantages of Digital


56/72

55

Advantages of Digital

TransmissionDigital technology

Low cost LSI/VLSI technology

Data integrity

Longer distances over lower quality lines

Capacity utilization

High bandwidth links economical

High degree of multiplexing easier with digital techniques

Security & Privacy

Encryption

Integration

Can treat analog and digital data similarly


57/72

56

Transmission Impairments

Signal received may differ from signaltransmitted

Analog - degradation of signal quality

Digital - bit errorsCaused by

Attenuation and attenuation distortion

Propagation delay Noise

Interference


58/72

57

Attenuation

Signal strength falls off with distance

Depends on medium

Received signal strength:

must be enough to be detected

must be sufficiently higher than noise to be

received without error

Attenuation is an increasing function of

frequency


59/72

58

Propagation Delay

The time required for a signal to travel

from one point to another.

Propagation velocity varies with frequency.


60/72

59

Noise (1)

Additional signals inserted between

transmitter and receiver

Thermal

Due to thermal agitation of electrons

White noise

Inter-modulation

Signals that are the sum and difference of

original frequencies sharing a medium


61/72

60

Noise (2)

Crosstalk

A signal from one line is picked up by another

Impulse

Irregular pulses or spikes

e.g. External electromagnetic interference

Short duration

High amplitude


62/72

61

Channel Capacity

Data rate

In bits per second

Rate at which data can be communicated

Bandwidth

In cycles per second of Hertz

Constrained by transmitter and medium


63/72

62

Modulation Techniques


64/72

63

Adaptive Modulation


65/72

64

Data Rate and Bandwidth

Any transmission system has a limited

band of frequencies

This limits the data rate that can be carried


66/72

65

Multiplexing


67/72

66

Time Division Multiplexing

Data rate of medium exceeds data rate of

digital signal to be transmitted

Multiple digital signals interleaved in time

May be at bit level of blocks

Time slots preassigned to sources and

fixed

Time slots allocated even if no data

Time slots do not have to be evenly

distributed amongst sources


68/72

67

Time Division Multiplexing


69/72

68

TDM System


70/72

69

Frequency Division Multiplexing

FDM

Useful bandwidth of medium exceeds

required bandwidth of channel

Each signal is modulated to a different

carrier frequency

Carrier frequencies separated so signals

do not overlap (guard bands)

e.g. broadcast radio

Channel allocated even if no data



71/72

70


Diagram


72/72

FDM System

mt jaringan-komputer 1 stikom

Documents