Data communications and Networking

Data Communications
‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬
Department of Computer Science,
Abdul Wali Khan University
Mardan Pakistan.
Module-1

Chapter 1: Introduction
1.1 Data Communications
1.2 Networks
1.3 The Internet
1.4 Protocols and Standards

Introduction
 Data communications and networking
 Change the way we do business and the way we live
 Business decisions have to be made more quickly
 Decision depends on immediate access to accurate
information
 Business today rely on computer networks and
internetworks
 Before get hooked up, we need to know:
 How networks operate
 What types of technologies are available
 Which design best fills which set of needs

Introduction
 Development of the PC changes a lot in business,
industry, science and education.
 Similar revolution is occurring in data communication
and networking
Technologies advances are making it possible for
communications links to carry more and faster signals
Services are evolving to allow the use of this expanded
capacity
For example telephone services extended to have:
• Conference calling
• Call waiting
• Voice mail
• Caller ID

1.1 Data Communications
Communication:
 Means sharing information
• Local (face to face) or remote (over distance)
 Telecommunication
• Telephone, telegraph and television
• Means communication at a distance
• Tele is Greek for far

Data Communications
Data:
 Refers to information
• Presented in any form
• Agreed upon by the parties ( creating & using)
Data communication : is the exchange of data
between two devices via some form of
transmission medium (wire cable).

Data Communications
 Communication system made up of a combination of
hardware and software
 Effectiveness of data communication system depends
on:
1. Delivery : The system must deliver data to correct
destination. Data received by the indented user only
2. Accuracy: The system must deliver data accurately (no
change).
• Data changed & uncorrected is unusable

Data Communications
3. Timeliness: The system must deliver data in timely
manner
• Data arrived late are useless
• In the same order (video and audio) & without delay (Real time
transmission)
4. Jitter: Variation in the packet arrival time (uneven
quality in the video is the result)

Components
 A data communication system is made up
of five components

Components
1. Message: the information (data) to be communicated
– Consist of text, numbers, pictures, audio, or video
2. Sender: the device that sends the data message
– Computer, workstation, telephone handset, video
camera, …
3. Receiver: the device that receives the message
– Computer, workstation, telephone handset, television,
….

Components
4. Medium: The physical path by which a message
travels from sender to receiver
– twisted pair, coaxial cable, fiber-optic, radio waves

Components
5. Protocol: a set of rules that govern data
communications
– An agreement between the communicating devices
– Devices may be connected but not communicating (no
protocol)
– Arabic speaker with Japanese speaker

Data Representation
Text
Audio
Video
Numbers
Images

Data Representation
Text:
Sequence of bits (0s or 1s)
Different sets of patterns to represent text
symbols (each set is called: code)
ASCII: 7 bits (128 symbols)
common coding system today is:
Unicode uses: 32 bits to represent a symbol or
character in any language
Unicode
(4,294,967,296)

Data Representation
Numbers:
Represented by bit patterns
The number is directly converted to a binary
number

Data Representation
Images:
Represented by bit patterns
A matrix of
Resolution: size of the pixels
High resolution: more memory is needed
Each pixel is assigned a bit pattern
1-bit pattern (black and white dots image)
2-bit pattern (4 levels of gray)
RGB (color images)
pixels

Data Representation
Audio:
Continuous not discrete
Video:
Recording or broadcasting of a picture or movie

Data Flow
 Communication between two devices can be:
 Simplex
 Half-Duplex
 Full-Duplex

Data Flow
Simplex (one way street)
 The communication is unidirectional
 Only one device on a link can transmit; the other
can only receive
 Use the entire capacity of the channel to send data
 Example: Keyboards, Monitors
Data

Data Flow
Half-Duplex (one-lane with two-directional traffic)
 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
 The entire capacity of a channel is taken over by
the transmitting device
 Example: Walkie-talkies
Data
Data

Data Flow
Full-Duplex (Duplex) (two-way street)
 Both stations can transmit and receive at same time
 Signals going in either direction sharing the capacity
of the link
 Sharing can occur in two ways:
 Link has two physically separate transmission paths
• One for sending and the other for receiving
 The capacity of the channel is divided between signals
travelling in both directions
 Example: Telephone network
Data
Data

Exercise
 What mode of data flow the following exhibits shows?
 Answer: Full-Duplex
Data
Data

Networks
 Network : A set of devices (nodes)
connected by communication links
Node : computer, printer, …
- Distributed Processing :
- Most networks used it
- Task is divided among multiple computers instead of
one single large computer

Networks
Network Criteria
– Network must meet a certain number of criteria
– The most important of the network criterions are:
– Performance
– Reliability
– Security

Networks
 Performance
 Transit time: A mount of time required for a message
to travel from one device to another
 Response time: Elapsed time between an inquiry and
a response

Networks
 Performance
 Performance depends on :
1- Number of users: large number slow response
time.
2- Type of transmission medium: fiber-optic cabling
faster than others cables.
3- Capabilities of the connected hardware: affect
both the speed and capacity of transmission.
4- Efficiency of the software: process data at the
sender and receiver and intermediate affects
network performance.

Networks
 Performance
 Performance is evaluated by two contradictory
networking metrics:
 Throughput (high): a measure of how fast we can
actually send data through a network
 Delay (low)

Networks
 Reliability
 Reliability is measured by:
1. Frequency of failure
2. Recovery time of a network after a failure
3. Network’s robustness in a catastrophe: protect by
good back up network system

Networks
 Security
 Protecting data from unauthorized access
 Protecting data from damage and
development
 Implementing policies and procedures for
recovery from breaches and data losses
(Recovery plan)

Networks
Physical Structures:
Type of connection
Network: Two or more devices connected through
links
Link: Communication pathway that transfers data
from one device two another
Two devices must be connected in some way to the
same link at the same time. Two possible types:
• Point-to-Point
• Multipoint

Networks
Point-to-Point
 Dedicated link between two devices
Entire capacity of the link is reserved for
transmission between those two devices
Use an actual length of wire or cable

Networks
Point-to-Point
 Other options, such as microwave or satellite
is possible
Example: Television remote control

Networks
Multipoint (multidrop)
 More than two devices share a single link
Capacity is shared
Channel is shared either spatially or temporally
 Spatially shared: if devices use link at same time
 Timeshare: if users must take turns

Networks
Physical Topology
 The way a network is laid out physically
Two or more links form a topology
The topology of a network is the geometric
representation of the relationship of all the
links and linking devices (nodes) to one
another.
Four topologies : Mesh, Star, Bus, and Ring

Physical Topology
Mesh
Every link is dedicated point-to-point link
The term dedicated means that the link carries
traffic only between the two devices it connects

Physical Topology
Mesh
To link n devices fully connected mesh has:
n ( n - 1) / 2 physical channels (Full-Duplex)
Every Device on the network must have
n - 1 ports

Physical Topology
Mesh
Example:
8 devices in mesh has links: n(n-1) / 2
number of links = 8 (8-1)/2 = 28
number of ports per device = n – 1 = 8 –1 = 7

Physical Topology
Mesh
Advantages
Each connection carry its own data load (no traffic
problems)
A mesh topology is robust
Privacy or security
Fault identification and fault isolation

Physical Topology
Mesh:
Disadvantages
Big amount of cabling
Big number of I/O ports
Installation and reconnection are difficult
Sheer bulk of the wiring can be greater than the
available space
Hardware connect to each I/O could be expensive
 Mesh topology is implemented in a limited
fashion; e.g., as backbone of hybrid network

Physical Topology
Star:
Dedicated point-to-point to a central controller
(Hub)
No direct traffic between devices
The control acts as an exchange

Physical Topology
Star
Advantages
Less expensive than mesh
(1 Link + 1 port per device)
Easy to install and reconfigure
Less cabling
Additions, moves, and deletions required one
connection
Robustness : one fail does not affect others
Easy fault identification and fault isolation

Physical Topology
Star
Disadvantages
Dependency of the whole topology on one single
point (hub)
More cabling than other topologies ( ring or bus)
 Used in LAN

Physical Topology
Bus
It is multipoint
One long cable acts as a backbone
Used in the design of early LANS, and Ethernet
LANs

Physical Topology
Bus
Nodes connect to cable by drop lines and taps
Signal travels along the backbone and some of
its energy is transformed to heat
Limit of number of taps and the distance
between taps

Physical Topology
Bus
Advantages
Ease of installation
Less cables than mesh, star topologies
Disadvantages
Difficult reconnection and fault isolation ( limit of taps)
Adding new device requires modification of backbone
Fault or break stops all transmission
The damaged area reflects signals back in the
direction of the origin, creating noise in both
directions

Physical Topology
Ring
Each device has dedicated point-to-point connection
with only the two devices on either side of it
A signal is passed along the ring in one direction from
device to device until it reaches its destination
Each devices incorporates a Repeater

Physical Topology
Ring
Advantages
Easy of install and reconfigure
Connect to immediate neighbors
Move two connections for any moving (Add/Delete)
Easy of fault isolation
Disadvantage
Unidirectional
One broken device can disable the entire network. This
weakness can be solved by using a dual ring or a switch
capable of closing off the break

Physical Topology
Hybrid Topology
Example: having a main star topology with each
branch connecting several stations in a bus
topology

Categories of Networks
Network Category depends on its size
Two primary categories
LAN: Covers area < 2miles
WAN: Can be worldwide
MAN: Between LAN & WAN, span 10s of miles

Local Area Network (LAN)
 Privately owned
 Links devices in the same office, building, or
campus
 Simple LAN: 2 PCs & 1 printer in home or office
 Size is limited to a few kilometers
 Allow resources to be shared (hardware,
software, or data)

An isolated LAN connecting 12 computers to a hub in a closet

 LAN is distinguished by:
Size (# users of OS, or licensing restrictions)
Transmission medium (only one type)
Topology (bus, ring, star)
 Data Rates (speed):
Early: 4 to 16 Mbps
Today: 100 to 1000 Mbps

Wide Area Networks (WAN)
 Provides long-distance transmission of data over
large geographic areas (country, continent,
world)

Wide Area Networks (WAN)
 Switched WAN
Backbone of the Internet
 Dialup line point-to-point WAN
Leased line from a telephone company

Metropolitan Area Networks (MAN)
 Size between LAN and WAN
 Inside a town or a city
 Example: the part of the telephone company
network that can provide a high-speed DSL to
the customer

Interconnection of Networks:
Internetworks
 Two or more networks connected together

The Internet
 Internet 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.
 Internet is a communication system that has brought a
wealth of information to our fingertips and organized it for
our use
 An internet is 2 or more networks that can communicate
with each other
 The Internet is a collaboration of more than hundreds of
thousands of interconnected networks

The Internet
 An internet (small i) is two or more networks
 Notable internet is called the Internet (hundreds of thousands interconnected
networks)
 Private individuals + government agencies + school + research facilities +
Corporations + libraries in more than 100 countries
 This communication system came in 1969
 Mid-1960 (ARPA) Advanced Research Projects Agency in (DOD) was interested to
connect mainframes in research organizations
 1967, ARPA presented its ideas for ARPANET
 Host computer connecting to (IMP) interface message processor.
 Each IMP communicate with other IMP
 1969, four nodes (universities) connected via IMPs to form a network
 Software (NCP) Network Control Protocol provided communication between the
hosts.
 1972, Vint Cerf and Bob Kahn invented (TCP) Transmission Control Protocol
 Later TCP was split to (TCP) Transmission Control Protocol and (IP) Internetworking
Protocol

The Internet
Internet Today
Made of many LANs and WANs
Every day new networks area added and
removed
Internet services Providers (ISPs) offer services
to the end users
International service providers
National service providers
Regional service providers
Local service providers
Data
rate

The Internet
Hierarchical organization of the Internet

Protocols and Standards
 Protocol synonymous with rule
 Standards: agreed-upon rules
 Protocols
A protocol is a set of rules that govern data
communications
Defines What, How, and When it is communicated

Protocols and Standards
 Elements of a protocol:
Syntax: structure or format of data
Example: 8-bits address of sender, 8-bits address of
receiver
Semantics: meaning of each section of bits
Example: Does the address is a route to be taken or the
final destination of the message
Timing: when data should be sent and how fast they
can be sent
Example: sender produces data at 100 Mbps but the
receiver can process data at only 1 Mbps  overload and
data loose

Standards
 Essential in creating and maintaining an open
and competitive market for equipment
manufactures
 Guaranteeing national and international
interoperability of data and telecommunication
technology and processes
 Providing guidelines to manufacturers, vendors,
government agencies, and other service
providers to ensure the kind of interconnectivity
necessary in today’s marketplace and in
international communications

Standards
Two categories
De facto: not approved by an organized body
but adopted as standards through widespread
use
De jure: Legislated by an officially recognized
body

Standards
 Standards are developed through the
cooperation of:
Standards Creation Committees
ISO, ITU-T, CCITT, ANSI, IEEE, EIA
Forums
 Created by special-interest groups
 Present their conclusions to the standards bodies
Regulatory Agencies
 Ministry of Telecommunication and Information Technology
(KSA)
 Purpose: Protecting the public by regulating radio, television,
and communication

Standards
 Internet standards
Tested thoroughly tested specification that is useful
to be adhered to by those who work with the
Internet
Formalized regulation that must be followed
Specification become Internet standard
Begins as Internet draft for 6 months
Upon recommendation from the Internet authorities
draft published as Request for Comment (RFC)
RFC is edited, assigned a number, and made available to
all interested parties

Data communications and Networking

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