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Electronic - II
Data communications
Lecture- 1
Dr. Eng. Samy Elmokadem
Chapter 1
References :
Data Communications and Networking , 4 edition , Behrouz,Forouzan .
Table of Contents

Data communications

* Components * Data Representation * Data Flow
Networks
* Distribution processing
* Network Criteria
* physical structure
* Network Models
* Category of Networks
* Interconnection of Networks
Table of Contents ( CONTINUE )

The Internet
* Brief History
* The Internet Today
 Protocols and standards
* protocols
* Standards Organizations
* Internet Standards
1- Data communications


Data communication : Is the exchange of data
between devices via some form of transmission
medium such as a wire cable .
For data communication to occur , the
communicating devices must be part of
communication system made up of a combination
of
1- Hardware ( physical equipment )
2- Software (programs)
1- Data communications
The effectiveness of data communications
system depend on four fundamental
characteristics :
1- Delivery
2- Accuracy

3- Timelines
4- Jitter
1- Data communications
1- Delivery : the system must deliver data to the
correct destination
2- Accuracy : the system must deliver data accurately .
3- Timelines : the system must deliver data in a timely
manner . Data delivered late are useless .
4- Jitter : refers to the variation of the packet arrival time
it is the uneven delay in the delivery of data .
Component of Data
communications system
 Data communications system has five components:
1- Message : is the information (data) to be
communicated such as ( text – picture – audio –
video) .
2- Sender : the device that sends the data massage
such as ( computer – workstation – telephone –
video camera )
3-Receiver : is the device that receives the massage
such as ( computer – workstation – telephone –
video camera )
4- Transmission medium : is the physical path
by which a massage travels from sender to
receiver such as ( Twisted pair wire – Coaxial
cable – fiber optic cable - Radio waves)
5- Protocol : is a set of rules that govern data
communications. It represents an agreement
between the communicating devices . Without a
Protocol , Tow devices may be connected but
not communicating . Just as a person speaking
French can not be understood by a person who
speaks only Japanese .

Block diagram of data communication system
Protocol
Protocol
Rule 1
Rule 2
Rule 3
Rule 1
Rule 2
Rule 3
Massage
Receiver
Sender
Medium
Five Components of Data
Communication
1.
2.
Message
Sender
3.
Receiver
4.
Medium
5.
Protocol
Data Representation
Information has a different forms such as :
1- Text
2- Numbers
3- Images
4- audio
5- video

Data Flow
Communication between two devices can be :
1- Simplex : in simplex mode the communication is
unidirectional , as on a one way street .only one of the
two devices on a link can transmit ; the other can only
receive .
• Example of simplex devices . The keyboard can only
introduce input & the Monitor can only accept output .
• * the simplex mode can only the entire capacity of the
channel to send data in one direction .

Data Flow
2- Half - Duplex : Each station can both transmit
and receive , but not at the same time .
 When one device is sending the other can only
receive and vice versa
 In half-Duplex transmission , the entire of
channel is taken over by whichever of the two
devices is transmitting at the time .
 Example on Half Duplex is walkie-talkies.
Data Flow
3- Full-Duplex : In the full-Duplex mode , both station can
transmit and receive simultaneously.
- Signal going in one direction share the capacity of the link
with signals going in the other direction . This share can occur
in two ways :
- Either the link must contain two physically separate
transmission paths one for sending and the other for
receiving
or The capacity of the channel is divided between signals
traveling in both direction
• The full -Duplex mode is used when communication in both
directions is required all the time. The capacity of the channel
must be divided between the tow directions.
• EX: The Telephone Network.
1-Simplex
Data Flow
Direction of data
Monitor
Mainframe
2-Half duplex
Direction of data at time 1
station
Direction of data at time 2
station
3-Full-Duplex
Direction of data all the time
station
station
Networks

A network is a set of devices (nodes ) connected by
communication links , A node can be a computer, printer ,
or any other device capable of sending or receiving data
generated by other nodes on the network
 Distributed processing : Task is divided among multiple
computers instead of single large machine.
 Network Criteria : A network must be able to meet a
certain number of criteria , the most important of this are :
1-performance 2- reliability
3-security .
1- Performance : can be measured in many ways ,
including transit time and response time .
- Transit time : is the amount of time required for a
message to travel from one device to another .
- Response time : is the elapsed time between an inquiry
and a response .
- the performance of a network depends on a number of
factors , including: 1- the number of users 2- the type of
transmission medium 3- the capabilities of the connected
hardware 4- the efficiency of the software
- performance is often evaluated by two network matrices :
throughput and delay.

2- Reliability:

The network reliability is measured by the frequency of failure, (the
time it takes a link to recover from of failure).
In addition to accuracy of delivery, network reliability is measured
by :
 Frequency of failure
 Recovery time of a network after a failure
 Catastrophe.

3- Security : network security include protecting data from
unauthorized access , protecting data from damage
development , and implementing policies procedures for
recovery from preaches and data losses
Physical Structures
We need to define some network attributes :
type of connection : there are two possible type
of connections:
1- Point to Point .
2- point to Multipoint.

Types of connections: point-to-point and multipoint
Point to point communication not usually practical
Devices are too far apart
Large set of devices would need impractical number of connections
Solution is a communications network
Wide Area Network (WAN)
Local Area Network (LAN)
Physical Topology


Physical Topology refers to the way in which
a network is laid out physical .
The topology of a network : is the trigonometric
representation of the relationship of all the links
and linking devices
Why Computer Network?
To share information or receive a service via a network,
group members must be able to communicate with each
other.
“ A computer network is a collection of computers and other
devices (nodes) that use a common network protocol to share
resources (Printer, Scanner, Memory, Information , Data Base,
Network Bandwidth, Internet Services , etc )
with each other over a network medium such as a wire cable .
Categories of Networks

Computer networks can be classified
according to their size to three categories :
1- Local Area Network (LAN)
2- Metropolitan Area Network (MAN)
3- Wide Area Network (WAN)
LAN
MAN
WAN
Network Classification
Upon the scale (size) :1.
2.
3.
4.
5.
PAN (Personal Area Network).
LAN (Local Area Network).
CAN (Campus Area Network).
MAN (Metropolitan Area Network).
WAN (Wide Area Network).
1-PAN (Personal Area Network)



PAN is a short-distance network design to individual user
(person).
PAN may be contain:- printer, mobile, computer, wireless
printers , PDA, etc.
components of PAN connected together via Bluetooth , USB
cable ,IrDA (infrared), etc.
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2-LAN (Local Area Network)


A LAN is a group of node connected together
in a small specific area.
LAN may be contain workstations, computers,
scanner, printers, servers, etc.
3- CAN (Campus Area Network)

A CAN is a group of interconnection LAN within limited
geographical area.

A CAN using in school campus, military base, university campus ,etc.
4- MAN (Metropolitan Area Network)



A MAN is a large computer network uses to connect between
LAN in different location (cities).
Is a network with a size between a LAN and WAN .
A MAN is a group of node connect together over city.
5- Wide Area Network (WAN )




Provides long distance transmission of data.
It has no geographical limit .
A WAN is made up of a number of
interconnected LANs.
Ex : Internet
WAN (Wide Area Network)


A WAN is a computer network that covers large geographical area.
WANs are used to connect types of networks together.
WAN
MAN
CAN
LAN
PAN
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LAN Basics
1- Local Area Network ( LAN)
• A LAN is a network that is used for communicating among
computer devices, usually within an office building or home
• LAN’s enable the sharing of resources such as files or
hardware devices that may be needed by multiple users
• Is limited in size, typically spanning a few hundred meters,
and no more than a mile
• Is fast, with speeds from 10 Mbps to 10 Gbps
• Requires little wiring, typically a single cable connecting to
each device
• Has lower cost compared to MAN’s or WAN’s
LAN Basics



LAN’s can be either wired or wireless.
Twisted pair, coaxial or fiber optic cable can be
used in wired LAN’s
Nodes in a LAN are linked together with a certain
topology. These topologies include:
 Bus
 Ring
 Star
 Mesh
 Branching tree
Network topologies
1- Bus
2- Ring
3- Star
4- Mesh
5- Branching tree
Mostly used network topologies
bus
star
Ring
mesh
Network Topologies
1- Bus Topology
Each node is connected one after the
other (like Christmas lights)

Nodes communicate with each other along
the same path called the backbone
PC
A bus topology connecting three stations
Advantages of Bus Topology
1- Use of cable is economical
2- media is inexpensive and easy to work with it.
3- Easy to be extended
4- if any computer on the Bus stopped to
work, that does not effect on the entire network
Disadvantages of bus topology
1- Network can slow in heavy traffic.
2- Cable (backbone) break effect on the entire network.
3- Number of computers is limited.
2- Ring topology
-The ring network is like a bus network, but the “end”
of the network is connected to the first node.
-Nodes in the network use tokens to communicate
with each other.
PC (NODE)
Backbone
A ring topology connecting six stations
Ring Topology
*Advantages
- High performance ,despite many users.
*Disadvantages
- Failure of one computer can impact the rest of
the network.
- failure of one cable impact the entire network
3- Star Topology
- Each node is connected to a device in the center
of the network called a Hub
- The hub simply passes the signal arriving from
any node to the other nodes in the network
- The hub does not route the data
Hub
A star topology connecting four stations
Star Topology
Advantages
Adding new computers is easy.
- centralized monitoring and management are
possible .
- failure of one computer does not affect the rest of
the network.
Disadvantages
1- If the centralized point fails the entire network
will be got down also.
2- Many cables are used for connection.
4- Mesh topology
PC
FULLY CONNECTED
Advantages
System increased redundancy and reliability.
Disadvantages
system is expensive to install because it uses a lot of
cabling.
A fully connected mesh topology (five devices)
5-Branching tree Topology
A hybrid topology:
a star backbone with three bus networks
3- Wide Area Network (WAN )




Provides long distance transmission of data.
It has no geographical limit .
A WAN is made up of a number of
interconnected LANs.
Ex : Internet
WANs : a switched WAN and a point-to-point WAN
A heterogeneous network made of four WANs and two LANs
THE INTERNET
The Internet is the network of internetworking .
The Internet is a communication system that
has brought a wealth of information to our
fingertips and organized it for our use.
It has revolutionized many aspects of our daily lives.
It has affected the way we do business as well as the
way we spend our leisure time.
Hierarchical organization of the Internet
PROTOCOLS AND STANDARDS
protocols and standards. First, we define protocol,
which is synonymous with rule. Then we discuss
standards, which are agreed-upon rules.
Protocols and Standards
Protocol

Protocol : is a set of rules that govern data
communications. It represents an agreement
between the communicating devices .
Without a Protocol , Tow devices may be connected
but not communicating.

The key element of a Protocol are:
1- Syntax
2- Semantics
3-Timing
Protocol ( CONTINUE )
Syntax : is the structure or format of data .
- For example : a simple protocol might expect
the first 8 bit of data to be the address of the
sender , the second 8 bits to be the address of
the receiver , and the rest of the stream to be the
massage itself.


Semantics : refers to the meaning of each section
of bits
Protocol ( CONTINUE )
Timing : refers to two characteristics
1- when data should be sent
2- how fast they can be sent
Ex : if a sender produces data at 100 Mbps but the
receiver can process data at 1 Mbps , the
transmission will overload the receiver and some
data will be lost

Standards



Standards : are necessary to ensure that products
from different manufacturers can work together
as expected .
Examples on some organizations involved in
standards creation are :
1- The International Standards Organization (ISO))
2-Institute of Electrical and Electronic Engineers (IEEE)
References
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