Komunikasi Data dan Jaringan
Komputer
(Bagian 1)
Dr. Tb. Maulana Kusuma
mkusuma@staff.gunadarma.ac.id
http://staffsite.gunadarma.ac.id/mkusuma
Magister Teknik Elektro
0
Referensi
W. Stallings, Data and Computer
Communications, 4ed, Macmillan, 1994.
F. Halsall, Data Communications,
Computer Networks and Open
Systems, Addison Wesley, 1996.
Magister Teknik Elektro
1
A Communications Model
Source
 generates data to be transmitted
Transmitter
 Converts data into transmittable signals
Transmission System
 Carries data
Receiver
 Converts received signal into data
Destination
 Takes incoming data
Magister Teknik Elektro
2
Simplified Communications
Model - Diagram
Magister Teknik Elektro
3
Simplified Data
Communications Model
Magister Teknik Elektro
4
Key Communications Tasks
Transmission System Utilization
Interfacing
Signal Generation
Synchronization
Exchange Management
Error detection and correction
Addressing and routing
Recovery
Message formatting
Security
Network Management
Magister Teknik Elektro
5
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
Magister Teknik Elektro
6
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 ?
Magister Teknik Elektro
7
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
Magister Teknik Elektro
8
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.
Magister Teknik Elektro
9
OSI Networking Model
Program X
Data
AH Data
Application
Presentation
Presentation
SH Data unit
Transport
TH
Network
Physical
Application
PH Data unit
Session
Data link
Program Y
NH
LH
Session
Data unit
Transport
Data unit
Network
Data unit
Bits
LT
Data link
Physical
Physical transmission medium
Magister Teknik Elektro
10
OSI Layers (1)
Physical
 Physical interface between devices
Mechanical
Electrical
Functional
Procedural
Data Link
 Means of activating, maintaining and deactivating a
reliable link
 Error detection and control
 Higher layers may assume error free transmission
Magister Teknik Elektro
11
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
Magister Teknik Elektro
12
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
Magister Teknik Elektro
13
Transmission Medium
Guided - wire
Unguided - wireless
Characteristics and quality determined by
medium and signal
For guided, the medium is more important
For unguided, the bandwidth produced by
the antenna is more important
Key concerns are data rate and distance
Magister Teknik Elektro
14
Guided Transmission Media
Twisted Pair
Coaxial cable
Optical fiber
Magister Teknik Elektro
15
Twisted Pair
Twisted pair - INEXPENSIVE
 Two wires twisted together.
Makes them less susceptible to acting like
an antenna and picking up radio frequency
information or appliance noise.

Telephone company uses twisted-pair
copper wires to link telephones.
Magister Teknik Elektro
16
Twisted Pair
Magister Teknik Elektro
17
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
Magister Teknik Elektro
18
Twisted Pair - Pros and Cons
Cheap
Easy to work with
Low data rate
Short range
Magister Teknik Elektro
19
Twisted Pair - Transmission
Characteristics
Analog
 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
Magister Teknik Elektro
20
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)
Magister Teknik Elektro
21
UTP Categories
Cat 3
 up to 16MHz
 Voice grade found in most offices
 Twist length of 7.5 cm to 10 cm
Cat 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
Magister Teknik Elektro
22
Coaxial Cable (1)
Coaxial cable
 Also two wires:
Use this when
1. Long distances
2. Lots of interference
One of the wires is woven of fine strands of
copper forming a tube.
The wire mesh surrounds a solid copper
wire that runs down the center.
Space between has a non-conducting
material.
Makes them more impervious to outside
noise.
Magister Teknik Elektro
23
Coaxial Cable (2)
Magister Teknik Elektro
24
Coaxial Cable (3)
Magister Teknik Elektro
25
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
Magister Teknik Elektro
26
Coaxial Cable - Transmission
Characteristics
Analog



Amplifiers every few km
Closer if higher frequency
Up to 500MHz
Digital


Repeater every 1km
Closer for higher data rates
Magister Teknik Elektro
27
Optical Fiber (1)
Magister Teknik Elektro
28
Optical Fiber (2)
Magister Teknik Elektro
29
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.
Magister Teknik Elektro
30
Optical Fiber - Spectrum
Magister Teknik Elektro
31
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
Magister Teknik Elektro
32
Optical Fiber - Applications
Long-haul trunks
Metropolitan trunks
Rural exchange trunks
Subscriber loops
LANs
Magister Teknik Elektro
33
Optical Fiber - Transmission
Characteristics
Act 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)
Magister Teknik Elektro
34
Optical Fiber Transmission
Modes
Magister Teknik Elektro
35
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
Magister Teknik Elektro
36
Frequencies
2GHz to 40GHz

Microwave

Highly
directional

Point to point

Satellite
30MHz to 1GHz

Omnidirectional

Broadcast radio
3 x 1011 to 2 x 1014

Infrared

Local
Magister Teknik Elektro
37
Terrestrial Microwave
Parabolic dish
Focused beam
Line of sight
Long haul telecommunications
Higher frequencies give higher data rates
Magister Teknik Elektro
38
Satellite Microwave
Satellite is relay station
Satellite receives on one frequency,
amplifies or repeats signal and transmits
on another frequency
Requires geo-stationary orbit

Height of ±35,784km
Television
Long distance telephone
Private business networks
Magister Teknik Elektro
39
Broadcast Radio
Omni-directional
FM radio
UHF and VHF television
Line of sight
Suffers from multi-path interference
Magister Teknik Elektro
40
Infrared
Modulate non-coherent infrared light
Line of sight (or reflection)
Blocked by walls
e.g. TV remote control, IRD port
Magister Teknik Elektro
41
Terminology (1)
Transmitter
Receiver
Medium

Guided medium
e.g. twisted pair, optical fiber

Unguided medium
e.g. air, water, vacuum
Magister Teknik Elektro
42
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
Magister Teknik Elektro
43
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
Magister Teknik Elektro
44
Terminology (4)
Bits per second (bps).

The number of bits (0’s and 1’s) 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 per
second, not necessarily bits per second.
Magister Teknik Elektro
45
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, concerning
error detection and block size.
These modems are expensive but very fast.
Magister Teknik Elektro
46
Analog and Digital Data
Transmission
Data

Entities that convey meaning
Signals

Electric or electromagnetic representations of
data
Transmission

Communication of data by propagation and
processing of signals
Magister Teknik Elektro
47
Data
Analog


Continuous values within some interval
e.g. sound, video
Digital


Discrete values
e.g. text, integers
Magister Teknik Elektro
48
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
Magister Teknik Elektro
49
Signals
Type of signal communicated (analog or digital).
 Analog: Those signals that vary with smooth continuous
changes.
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).
Magister Teknik Elektro
50
Analog Signals Carrying Analog
and Digital Data
Magister Teknik Elektro
51
Digital Signals Carrying Analog
and Digital Data
Magister Teknik Elektro
52
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
Magister Teknik Elektro
53
Digital Transmission
Concerned with content
Integrity endangered by noise, attenuation etc.
Repeaters used
Repeater receives signal
Extracts bit pattern
Retransmits
Attenuation is overcome
Noise is not amplified
Magister Teknik Elektro
54
Advantages of Digital
Transmission
Digital 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
Magister Teknik Elektro
55
Transmission Impairments
Signal received may differ from signal
transmitted
Analog - degradation of signal quality
Digital - bit errors
Caused by




Attenuation and attenuation distortion
Propagation delay
Noise
Interference
Magister Teknik Elektro
56
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
Magister Teknik Elektro
57
Propagation Delay
The time required for a signal to travel
from one point to another.
Propagation velocity varies with frequency.
Magister Teknik Elektro
58
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
Magister Teknik Elektro
59
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
Magister Teknik Elektro
60
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
Magister Teknik Elektro
61
Modulation Techniques
Magister Teknik Elektro
62
Adaptive Modulation
Magister Teknik Elektro
63
Data Rate and Bandwidth
Any transmission system has a limited
band of frequencies
This limits the data rate that can be carried
Magister Teknik Elektro
64
Multiplexing
Magister Teknik Elektro
65
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
Magister Teknik Elektro
66
Time Division Multiplexing
Magister Teknik Elektro
67
TDM System
Magister Teknik Elektro
68
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
Magister Teknik Elektro
69
Frequency Division Multiplexing
Diagram
Magister Teknik Elektro
70
FDM System
Magister Teknik Elektro
71