College of Computer and Information Sciences
Dept. of Computer Engineering
King Saud University
CEN341 – Data Communication
Dr. Ridha Ouni
Associate Professor
Department of Computer Engineering
College of Computer and Information Sciences
King Saud University
rouni@ksu.edu.sa
College of Computer and Information Sciences
Dept. of Computer Engineering
King Saud University
CEN341 – Data Communications
Chapter 1 – Intro. To Communication
Systems
Dr. Ridha Ouni
Associate Professor
Department of Computer Engineering
College of Computer and Information Sciences
King Saud University
Overview
Communication is the transfer of
information from one place to another.
This should be done
Figure 1.1 Transfer of information
 as efficiently as possible
 with as much fidelity/reliability as possible
 as securely as possible
Communication System: Components/subsystems act together to accomplish
information transfer/exchange.
3
Elements of a Communication System
Input
message
Input
Transducer
Transmitter
Channel
Receiver
Output
Transducer
Output
message
(a) General block diagram
(b) Example
Figure 1.2 Simplified Communications Model
4
Elements of a Communication System
Data Communications Model
Figure 1.3 Simplified Data Communications Model
5
Elements of a Communication System
Data Communications Model: analogy
Figure 1.4 Simplified Data Communications Model: analogy
6
Data & Signal
To be transmitted, Information (Data)
must be transformed to:
• Digital signal,
• Analog signal
• Electromagnetic signals.
7
Analog and Digital
Data (Information) can be analog or digital. The term analog data
refers to information that is continuous; digital data refers to
information that has discrete states. Analog data take on
continuous values. Digital data take on discrete values.
Topics discussed in this section:
• Analog and Digital Data
• Analog and Digital Signals
• Periodic and Nonperiodic Signals
8
Types of signals
.
c. Electromagnetic Wave
Figure 1.5 Types of signals
9
Types of signals
Periodic and nonperiodic signal
Analog
signal
Digital
signal
Periodic signal
Nonperiodic signal
Figure 1.6 Periodic & aperiodic signals
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Periodic analog signals - Sine Wave
s(t) = A sin(2f t + )
 peak amplitude (A)
• maximum strength of signal
• volts
 frequency (f)
•
•
•
•
rate of change of signal
Hertz (Hz) or cycles per second
period = time for one repetition (T)
T = 1/f
Figure 1.7 Sine wave
 phase ()
• relative position in time
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Sine Wave – Properties
Figure 1.8 Sine wave - s(t) = A sin(2f t + )
12
Wavelength () and period (T)
Wavelength () is a distance (expressed in meters)
• Is distance occupied by one cycle
• between two points of corresponding phase in two consecutive
cycles
• assuming signal velocity V have  = V * T
• or equivalently  * f = V
• especially when V = C, where C = 3*108 m/s speed of light in free space)
13
Time-domain and Frequency-domain
representations
1s
Figure 1.9 The time-domain and frequency-domain
plots of a sine wave
14
Time-domain and Frequency-domain
representations
Figure 1.10 Time & Frequency Domain Representations
15
Bandwidth of composite signals
𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ = 𝑓𝑚𝑎𝑥 − 𝑓𝑚𝑖𝑛
Figure 1.15 Bandwidth of a composite signal.
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Relationship between Data Rate and
Bandwidth
𝐷𝑎𝑡𝑎 𝑟𝑎𝑡𝑒 =
𝑑𝑎𝑡𝑎
𝑡𝑖𝑚𝑒
8 𝑏𝑖𝑡𝑠
𝐷𝑎𝑡𝑎 𝑟𝑎𝑡𝑒 =
1𝑠
= 8 𝑏𝑝𝑠 (8 𝑏/𝑠 𝑜𝑟 1 𝐵/𝑠)
16 𝑏𝑖𝑡𝑠
1𝑠
= 16 𝑏𝑝𝑠 (8 𝑏/𝑠 𝑜𝑟 2 𝐵/𝑠)
𝐷𝑎𝑡𝑎 𝑟𝑎𝑡𝑒 =
Figure 1.16 Data Rate and Bandwidth.
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Components of communication systems (1)
Transmission Media

Coaxial cable

Twisted pair cable

Fiber optic cable

Microwave

Satellite link

Cellular phones
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Components of communication systems
Transmission Modes

Simplex. One way of
transmission

Half-Duplex. provides both
directions, but only one direction
at a time (not simultaneously).

Full-Duplex. allows transmission
in both directions,
simultaneously.
Figure 1.17 Transmission modes
19
Components of communication systems
 Hardware/Software
 Network card, router, modem, hub,
programs, soft tools, utilities …
 Media
 The way to connect computers on a
network
 Server
 A computer that provides services to
other networked computers
 Client
Figure 1.18 key elements of the Internet
 A computer in a client/server relationship, e.g., a Web browser
 Data
 Files to be shared by network computers
 Resources
 Peripherals, e.g., printers, to be used by network computers
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Layered Network Architecture
Why protocol and network architectures?
Computer S
Send file
Computer D
MAN, WAN
Receive file
Write email
Read email
encryption
decryption
Routing
Routing
Error control
Error control
Convert to signal
Transmission
medium
Computer D
Computer S
Communication
network
Convert to Data
Figure 1.19 Layered network architecture.
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Layered Network Architecture
Why protocol and network architectures?
Layer 3 (process 3)
Interface 2
Layer 2 (process 2)
Interface 1
Layer 1 (process 1)
 The higher layer includes the application level,
 Below layer 1 (physical layer) is the physical
transmission medium through which actual
communication occurs,
Protocol
stack
 Interface: Defines which primitive operations and
services the lower layer offers to the upper layer,
 Network architecture: A set of layers and protocols.
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Different Layering Architectures
 ISO OSI 7-Layers Architecture
 TCP/IP 5-Layers Architecture
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R. Ouni
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ISO OSI Layering Architecture
 1977 : ISO initiated a layered network architecture,
 1983 : Definition of the OSI model
(Open Systems Interconnection)
• Open : open systems to communicate with other
systems
• Systems : all the resources (hardware and software)
contributing to the processing and transfer of
information
• Interconnection
24
ISO OSI Layering Architecture
Host A
Application
Host B
Application Protocol
Application
Layer
Presentation Protocol
Presentation
Layer
Session Protocol
Session
Layer
Transport Protocol
Transport
Layer
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
Layer
Physical
Layer
Physical
Layer
IMP
IMP
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Layer 1: Physical Layer
 Functions:
• Transmission of a raw bit stream
• Forms the physical interface between devices
 Issues:
•
•
•
•
•
•
Which modulation technique (bits to pulse)?
How long will a bit last?
Bit-serial or parallel transmission?
Half- or Full-duplex transmission?
How many pins does the network connector have?
How is a connection set up or torn down?
The design issues deal with mechanical, electrical, and
procedural interfaces.
26
Layer 2: Data Link Layer
 Functions:
• Provides reliable transfer of information between two
adjacent nodes,
• Creates frames, or packets, from bits and vice versa,
• Provides frame-level error control,
• Provides flow control,
• Establishes, maintains & releases a point-to-point
connection.
 In summary, the data link layer provides the network
layer with what appears to be an error-free link for
packets.
 Broadcast networks have an additional issue in the data
link layer: how to control access to the shared channel. A
special sublayer of the data link layer (MAC: Medium
Access Control) deals with the problem.
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Layer 3: Network Layer
The main task of the network layer is to determine how
data can be delivered from source to destination.
S
 Functions:
• Responsible for routing decisions,
 Dynamic routing
 Fixed routing
D
• Performs congestion control,
• Allows interconnection of heterogeneous networks.
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Layer 4: Transport Layer

Functions:
 Accepts data from the session layer, split it up into
smaller units, pass them to the network layer.
 Provides reliable end-to-end communication.
 Performs end-to-end flow control (acknowledgments).
 Makes sure all information is accounted for:
• Missing information
• Duplicated information
 Performs packet retransmission when packets are lost by
the network.
 Ensures that packets are delivered error free, in sequence
with no losses or duplications.
29
Layer 4: Transport Layer
Host A
first
end-to-end
layer
Application
Layer
Host B
Application Protocol
Presentation
Layer
Presentation Protocol
Session
Layer
Session Protocol
Transport
Layer
Transport Protocol
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
IMP
IMP
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Layer 5: Session Layer
The session layer allows users on different machines to
establish sessions (conversations) between them
 May perform synchronization between several
communicating applications (by inserting checkpoints into the
data stream. if session fails, only data after the most recent checkpoint
need to be retransmitted),
 Groups several user-level connections into a single
“session”,
 Establishes connection between applications,
 Reestablishes connection,
 Manages who can transmit data at a time and for how long
(Token management).
31
Layer 6: Presentation Layer
Performs specific functions that are requested regularly by
applications
 Masks the differences of data formats between dissimilar
systems
 Examples:
•
•
•
•
•
Encodes and decodes data (ex. MPEG2,3…)
ASCII to Unicode, Unicode to ASCII
Encryption (decryption)
Compression (decompression)
LSB-first representations to MSB-first representations
32
Layer 7: Application Layer
 Application layer protocols are application-dependent
 Implements communication between two applications of
the same type
 Examples:
• FTP
• SMTP (email)
33
TCP/IP Layering Architecture
Comparison OSI, TCP/IP  devices (H/S)
OSI
Application
Devices
TCP/IP
File transfer
Application
Presentation
Not present in
the model
Session
Transport
Transport
Network
Network
Data link
Data link
Physical
Physical
TCP/UDP
IP
Protocols
Net Card
Media
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R. Ouni
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General Protocol Functions
Header encapsulation and decapsulation
Sender
APDU
Application
PPDU
Presentation
SPDU
Session
TPDU
Transport
Packet
Network
Frame
Data link
Bit
Physical
Receiver
Data
Application
AH Data
PH
SH
TH
NH
DH
Presentation
Data
Session
Data
Transport
Data
Network
Data
Data
DT
Bits
Data link
Physical
Data transmission channel
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General Protocol Functions
Source
message
segment Ht
datagram Hn Ht
Hl Hn Ht
frame
M
M
M
M
application
transport
network
link
physical
Hl Hn H t
M
link
physical
Hl Hn Ht
M
Switch
Destination
M
Ht
M
Hn Ht
Hl H n Ht
M
M
application
transport
network
link
physical
H n Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
M
Hl Hn Ht
M
Router
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Layer 1 & Layer 2: Functions
Layer 1: Physical Layer
•
•
•
Analog/digital conversion
Encoding (Chapter 4)
Modulation (Chapter 5)
Layer 2: Data Link Layer
•
•
•
•
Digital processing
Framing
Error control
(Chapter 7)
Flow control
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