Data Communications
DNT 1013
Prepared By:
Mdm Noor Suhana Bt Sulaiman
FKMT-NT, TATiUC
Introduction to Data
Communications
Chapter 1
What is data communication?

Not to be confused with telecommunication—
– Any process that permits the passage from a
sender to one or more receivers of information of
any nature, delivered in any easy to use form by
any electromagnetic system.

Data communication– Defined as a subset of telecommunication
involving the transmission of data to and from
computers and components of computer systems.
• More specifically data communication is transmitted via
mediums such as wires, coaxial cables, fiber optics, or
radiated electromagnetic waves such as broadcast radio,
infrared light, microwaves, and satellites.
History of Telecommunications
Invention of telegraph Samuel Morse –
1837
 Invention of telephone- Alexander
Graham Bell – 1876
 Development of wireless By ??? – 1896
 Concept of universal access and growth
of AT&T
 Divestiture of AT&T—what year??

History of Telecommunications
Continued….

Telecommunications Act of 1996
 Three main developments that led to the
growth of data communications systems:
– Large-scale integration of circuits reduced the cost
and size of terminals and comm equipment
– Developments of software systems made
establishment of communication networks easy
– Competition among providers of transmission
facilities reduced the cost of data circuits
History of Data Communication
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Transistor developed by Bell Labs (which is
now ???) 1947
Hush-a-Phone Case
Carterphone case
MCI and Long Distance
Creation of networks (LAN’s and WAN’s)
Data Link Protocols
Microcomputers
Framework for Global Electronic Commerce
A Framework for Global Electronic
Commerce was released in 1997
 It’s release underscores the importance
of Internet-based commerce in the
global economy
 It outlines several guiding principles for
e-commerce planners and strategists

Table 1-3
Table 1-4
Features of Communication

Four things required
– Sender, receiver, medium, and message

Types of messages
–
–
–
–
–
–

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File
Request
Response
Status
Control
Correspondence
Understandability
Error Detection
Network Applications

The network applications environment
consists of several important
components:
– Application programs
– Operating systems
– Data communication systems
– Database management systems

The application environment is
illustrated in Figure 1-10
Figure 1-10
Online System Requirements

Response Time
 Throughput
 Consistency
 Flexibility
Online Systems Requirements
Continued

Availability
 Reliability
– Mean time between failure (MTBF)
– Mean time to repair (MTTR)
– Fault Tolerance

Recovery
 Security
Business Data Communication
Applications

Major data communication applications
include:
– E-mail
– Groupware
– Knowledge management systems
– E-commerce and e-business applications
– Wireless applications
Groupware Applications

Group calendar
systems
 Electronic filing
cabinets
 Project
management
software
 Group support
systems

Electronic meeting
and
videoconferencing
systems
 Document
management
systems (image
processing systems)
Other Data Communication
Applications

Batch applications
 Data entry
applications
 Distributed
applications
 Inquiry/response
applications

Interactive
applications
 Sensor-based
applications
 Combined
applications
Application Service Providers

Many businesses have turned to third-party
services for some or all of their business and
data communications applications
 Application service providers (ASPs) are
third-party organizations that manage and
distribute software and services to other
companies over the Web
 Many ASPs specialize in integrated ecommerce and e-business applications
Business Data Communications
Issues

Major data communications issues
include:
– Cost-effectiveness
– The Internet
– Bandwidth
– Evolving technologies
– Convergence
– Standards
– Privacy and security
Important Standard-Setting
Organizations
Table 1-5
Business Data Communication
Careers
There are numerous job opportunities
and career paths for individuals
interested in data communications and
networking
 Table 1-6 includes examples of data
communication job titles
 Table 1-7 summarizes some of the
major professional certifications for
networking and data communications
specialists

Table 1-6
Table 1-7
Introduction to Networks
Can be defined as a single computer ,
called a host, together with
communication circuits, communication
equipment, and terminals.
 There are many different types of
network configurations (see figures1-4
to 1-8)

Key Data Communication Concepts
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Session: communication dialog between network users or
applications
Network: interconnected group of computers and
communication devices
Node: a network-attached computer
Link: connects adjacent nodes (see Figure 1-4)
Path: end-to-end route within a network
Circuit: the conduit over which data travels
Packetizing: dividing messages into fixed-length packets prior
to transmission over a network’s communication media
Routing: determining a message’s path from sending to
receiving nodes.
Store-and-Forward Systems

Messages may be stored at intermediate
nodes along the transmission path between
sender and receiver in store-and-forward
systems
– This helps ensure message delivery without
obligating the sender to wait until a message is
delivered before transmitting other messages
– It also helps ensure message delivery in the case
of link or destination failure while the message is
in transit
– Store-and forward algorithms are valuable in timestaged delivery systems and in networks that
assign priorities to different messages
Network Topology, Architecture,
and Complexity

Network topology refers to the physical layout
of a network, the way that nodes attach to the
communication medium
 Network architecture refers to the way in
which media, hardware, and software are
integrated to form a network
 Network complexity is concerned with extent
to which network architectures are simple or
diverse in their make
– Figures 1-5, 1-6, and 1-7 illustrate various levels of
complexity
Figure 1-5
Figure 1-6
Figure 1-7
Data Communication
Frameworks

Two major data communication
frameworks have been developed to
help ensure that networks meet
business and communication
requirements:
– Open Systems Interconnection (OSI)
reference model developed by the
International Standards Organization (ISO)
– Transmission Control Protocol/Internet
Protocol (TCP/IP) suite
History of the OSI Model

Open Systems Interconnected Model
– was created in the 70’s by the ISO (although the
CCITT came up with their own model)
• 10 different people got together and considered all
functions of communications
– was created because people realized that our
computers needed to talk to each other(and there
was no one dominant computer system)
– ISDN was a big factor
– 7 layers = 4 upper and 3 lower
OSI Reference Model in Practice

The OSI reference model is used in many
ways:
– To provide assistance when troubleshooting
network problems
– To provide a common terminology and framework
for networking technology developers
– To facilitate the development of connectivity
standards needed for flexible open architectures
– To enable the development of protocol stacks that
allow network nodes to communicate with one
another
Network Models
Using a formal model allows us to deal
with various aspects of Networks
abstractly.
 We will look at a popular model (OSI
reference model).
 The OSI reference model is a layered
model.

Layering
Divide a task into pieces and then solve
each piece independently (or nearly so).
 Establishing a well defined interface
between layers makes porting easier.
 Major Advantages:

Code Reuse
Extensibility
Layering Example: Federal Express
Letter in envelope, address on outside
 FedX guy adds addressing information,
barcode.
 Local office drives to airport and
delivers to hub.
 Sent via airplane to nearest city.
 Delivered to right office
 Delivered to right person

FedX Layers
Letter
Addressed
Envelope
Letter
Addressed
Envelope
OSI MODEL

Established in 1947, the International Standards
Organization (ISO) is a multinational body
dedicated to worldwide agreement on
international standards. An ISO standard that
covers all aspects of network communications is
the Open Systems Interconnection (OSI) model.
It was first introduced in the late 1970s.
ISO is the organization.
OSI is the model
Why the structure
of network need
Network Model
-OSI Model?
Cont..
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The OSI model describes how information or
data makes its way from application programmes
(such as spreadsheets) through a network
medium (such as wire) to another application
programme located on another network.
The OSI reference model divides the problem of
moving information between computers over a
network medium into SEVEN smaller and more
manageable problems .
This separation into smaller more manageable
functions is known as layering.
Cont..
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The OSI Reference Model is composed of 7 layers, each
specifying particular network functions.
The process of breaking up the functions or tasks of
networking into layers reduces complexity.
Each layer provides a service to the layer above it in the
protocol specification.
Each layer communicates with the same layer’s software or
hardware on other computers.
The lower 4 layers (transport, network, data link and physical
—Layers 4, 3, 2, and 1) are concerned with the flow of data
from end to end through the network.
The upper four layers of the OSI model (application,
presentation and session—Layers 7, 6 and 5) are orientated
more toward services to the applications.
Data is Encapsulated with the necessary protocol information
as it moves down the layers before network transit.
Figure 1.0: OSI Model
Layer 7: Application
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The application layer is the OSI layer that is closest to
the user.
It provides network services to the user’s applications.
It differs from the other layers in that it does not
provide services to any other OSI layer, but rather,
only to applications outside the OSI model.
Examples of such applications are spreadsheet
programs, word processing programs, and bank
terminal programs.
The application layer establishes the availability of
intended communication partners, synchronizes and
establishes agreement on procedures for error
recovery and control of data integrity.
Layer 6: Presentation

The presentation layer ensures that the
information that the application layer of one
system sends out is readable by the
application layer of another system.
 If necessary, the presentation layer
translates between multiple data formats by
using a common format.
 Provides encryption and compression of data.
 Examples :- JPEG, MPEG, ASCII, EBCDIC,
HTML.
Layer 5: Session
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The session layer defines how to start, control and
end conversations (called sessions) between
applications.
This includes the control and management of
multiple bi-directional messages using dialogue
control.
It also synchronizes dialogue between two hosts'
presentation layers and manages their data
exchange.
The session layer offers provisions for efficient
data transfer.
Examples :- SQL, ASP(AppleTalk Session
Protocol).
Layer 4: Transport
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The transport layer regulates information flow to
ensure end-to-end connectivity between host
applications reliably and accurately.
The transport layer segments data from the sending
host's system and reassembles the data into a data
stream on the receiving host's system.
The boundary between the transport layer and the
session layer can be thought of as the boundary
between application protocols and data-flow
protocols. Whereas the application, presentation, and
session layers are concerned with application issues,
the lower four layers are concerned with data
transport issues.
Layer 4 protocols include TCP (Transmission Control
Protocol) and UDP (User Datagram Protocol).
Layer 3: Network
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Defines end-to-end delivery of packets.
Defines logical addressing so that any
endpoint can be identified.
Defines how routing works and how routes
are learned so that the packets can be
delivered.
The network layer also defines how to
fragment a packet into smaller packets to
accommodate different media.
Routers operate at Layer 3.
Examples :- IP, IPX, AppleTalk.
Layer 2: Data Link
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The data link layer provides access to the networking
media and physical transmission across the media and
this enables the data to locate its intended destination on
a network.
The data link layer provides reliable transit of data across
a physical link by using the Media Access Control (MAC)
addresses.
The data link layer uses the MAC address to define a
hardware or data link address in order for multiple stations
to share the same medium and still uniquely identify each
other.
Concerned with network topology, network access, error
notification, ordered delivery of frames, and flow control.
Examples :- Ethernet, Frame Relay, FDDI.
Layer 1: Physical
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The physical layer deals with the physical
characteristics of the transmission medium.
It defines the electrical, mechanical, procedural,
and functional specifications for activating,
maintaining, and deactivating the physical link
between end systems.
Such characteristics as voltage levels, timing of
voltage changes, physical data rates, maximum
transmission distances, physical connectors, and
other similar attributes are defined by physical
layer specifications.
Examples :RJ45
TCP/IP Protocol Suite

The TCP/IP suite provides insights into the
inner workings of the Internet
 Like the OSI model, the TCP/IP suite is
layered
– Because the protocols found at each layer are
independent of those at the other layers, a given
protocol can be modified without affecting those
found at other layers
– TCP/IP layers and layer-specific protocols are
illustrated in Figure 1-9
TCP/IP

TCP-Transmission Control Protocol
 In OSI reference model terminology -the TCP/IP
protocol suite covers the network and transport layers.
 TCP/IP can be used on many data-link layers (can
support many network hardware implementations).
 The TCP/IP protocol suite is made of five layers:
physical, data link, network, transport, and application.
 The first four layers provide physical standards,
network interface, internetworking, and transport
functions that correspond to the first four layers of the
OSI model.
 The three topmost layers in the OSI model, however,
are represented in TCP/IP by a single layer called the
application layer.
Cont..
Relationship of layers and address in
TCP/IP
Cont..
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TCP/IP is the basic communication language or
protocol of the Internet.
It can also be used as a communications protocol
in a private network (either an intranet or an
extranet).
When user are set up with direct access to the
Internet, your computer is provided with a copy of
the TCP/IP program just as every other computer
that you may send messages to or get
information from also has a copy of TCP/IP.
Cont..
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TCP/IP is a two-layer program. The higher layer,
Transmission Control Protocol, manages the
assembling of a message or file into smaller packets
that are transmitted over the Internet and received by
a TCP layer that reassembles the packets into the
original message.
The lower layer, Internet Protocol, handles the
address part of each packet so that it gets to the right
destination.
Each gateway computer on the network checks this
address to see where to forward the message. Even
though some packets from the same message are
routed differently than others, they'll be reassembled
at the destination.
Cont..

Many Internet users are familiar with the even
higher layer application protocols that use
TCP/IP to get to the Internet.
 These include the World Wide Web's
Hypertext Transfer Protocol (HTTP), the File
Transfer Protocol (FTP), Telnet (Telnet) which
lets you logon to remote computers, and the
Simple Mail Transfer Protocol (SMTP).
 These and other protocols are often
packaged together with TCP/IP as a "suite."
The IP in TCP/IP

IP is the network layer
– packet delivery service (host-to-host).
– translation between different data-link protocols.

IP provides connectionless, unreliable
delivery of IP datagrams.
– Connectionless: each datagram is independent of
all others.
– Unreliable: there is no guarantee that datagrams
are delivered correctly or even delivered at all.
Moving Bits through the Network
Analog Signal
1
0
Digital Signal
1
1
1
0
0
digital
Computer
0
analog
Modem
digital
Modem
telephone lines
Computer
Putting It all Together
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Data Communications Supports Applications
 The Operating System manages the
resources of the computer.
 There must however, be a system that
provides a bridge between applications and
the devices so they can communicate—this is
called a Transaction Control Process (TCP)