ch1-Basics Of DCN.new.ppt

Prepared & Complied by Mrs. Twinkle v
Doshi,E & C dept.BIT 1
Introduction To Data
communication & networking
181001

Prepared & Complied by Mrs. Twinkle v Doshi,E & C dept.BIT
2
Name of the Books
Computer Networks, by A.S
.Tanenbaum, PHI
Data and Communication Networking,
by Behrouz Forouzan, TMH

3
Data : Data is the information presented in whatever form is
agreed upon by the parties creating and using the data.
Data communication : is the exchange of data between two
devices via some of transmission medium such as a wire cable.
Data communication system depend on 3 fundamental
characteristics:
•Delivery: The system must deliver data to the correct
destination.
•Accuracy:The system must deliver the data accurately.
•Timeliness:The system must deliver data in timely manner.
Data delivered late are useless.

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For data communication require 5 components: Message,
Sender, Receiver, Medium and Protocol.
Message:-The message is the information(data) to be communicated.
It can consist of text, numbers, pictures, sound or video or any
combination of these.
Protocol:- The protocol is set of rules that governs data
communication. It represent agreement between the communicating
devices.Without a protocol two devices may be connected but not
communicating, just as a person speaking French can’t be understood
by a person who only speak Japanese.
Networks :- A network is set of devices or nodes connected by
communication links. Devices can be computer, printer or any other
device capable of sending and/ or receiving data generated by other
node on network.

Elements of Protocols
Syntax: The structure or format of data.
The order in which the data is presented.
Symantics: Semantics means the meaning
of each section of bits, or how to interpret a
particular pattern. Also tells What action to
be taken based on this interpretation.
Timing: The instant of sending the data
and the speed at which it is to be sent.
Two standards : De Fecto and De Jure
5

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Network Hardware
Broadcast Link : single communication
channel shared by all machines on n/w.
‘Multicasting’ is transmission to a subset
of machines.
Point to Point link : Consists of many
connections between individual pair of
machines. Point to point transmission
with 1 sender & 1 receiver is called
‘unicasting’.

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Broadcast
In this network, one link is shared by all
Any machine can talk directly to any other
But only one machine can send at
any one time
A
B
C
D

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Broadcast (how channel is
allocated?)
Static
Dividetimeslots
Westofchannelcapacitywhendevicehasnothingtosay
Centralized
Centralsystem tofindwhogoesnext
Acceptrequest&makedecision
Decentralized
Eachmachinedecideitselfwhethertotransmit
collisionavoidedusingalgorithams
Dynamic
Broadcast

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Point to Point
Implication is that each machine on network will
typically have more than one network
connection
In this network, each link is separate.
A can only talk to C by relaying
messages through B (or D)
But A can talk to B at the
same time that C is talking
to D
A
B
C
D

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Simplex Half-duplex Full-duplex
Transmission mode

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Simplex

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Half-Duplex

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Full-Duplex

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Uses of Computer Networks
• Business Applications
• Home Applications
• Mobile Users
• Social Issues

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Business Application
Resource sharing
printers, scanners,CD burners,data, etc.
Communication
especially email,video conferencing
eCommerce
e.g. Amazon, eBay
“eTainment”
e.g. potential for on-line video, etc. Cable TV

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Business Applications of Networks
A network with two clients and one
server.

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Business Applications of
Networks (2)
The client-server model involves
requests and replies.

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Home Network Applications
Access to remote information
Person-to-person
communication
Interactive entertainment
Electronic commerce

Comparison between Peer to Peer Network and Client-Server
Network
No. Peer to Peer Client - Server
1 Decentralized Management Centralized Management
2 Each Machine has same Power Strong computer act as server,
Client has less power
3 Use less expensive Computer
Hardware
Expensive hardware and Software
required
4 Easy to setup and administer Complex and require proffessional
administer
5 Less secure Very secure
6 Decentralized Back-up Centralized Back-up
7 Network Operating system is not
required
Network Operating system is
required
8 Built in redundancy No built-in redundancy
9 Support small network Support large network
10 Might hurt user’s performance Better performance
19

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In peer-to-peer system there are no
fixed clients and servers.

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(3)
Some forms of e-commerce.

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Mobile Network Users
Combinations of wireless networks and
mobile computing.

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Network Hardware
Local Area Networks
Metropolitan Area Networks
Wide Area Networks
Wireless Networks
Home Networks
Internetworks

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Local Area
Network (LAN)
Metropolitan Area
Network (MAN)
Wide Area
Network (WAN)
Networks

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Interprocessor
distance
Processors
located in same
Example
1 m Square meter Personal Area
Network
10 m Room Local Area
Network
100 m Building
1 km Campus
10 km City Metropolitan
Area Network
100 km Country Wide Area
Network
1000 km Continent
10,000 km Planet The Internet

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Local Area Network

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• A LAN is privately owned links the devices in a
single office, building or campus.
• They are widely used to connect personal
computers and workstations in company offices and
factories to share resources and exchange
information.
•LAN size is limited to few kilometers.So worst case
transmission time is known in advance.
•LANs are distinguished from other kind of network
by three characteristics : (1) their size, (2) their
transmission topology, and (3) their topology

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Local Area Network

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Local Area Networks
Two broadcast networks
(a) Bus(IEEE 802.3 Ethernet)
(b) Ring(IEEE 802.5 IBM token Ring)

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Metropolitan Area Network(IEEE802.16)

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Metropolitan Area
Networks(IEEE802.16)
A metropolitan area network based on
cable TV.

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Wide Area Network

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Wide Area Networks
Relation between hosts on LANs and
the subnet.
subnet

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Wide Area Networks (2)
A stream of packets from sender to
receiver.

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Internetworks
Networks in the world have different
hard-wares & soft-wares. They are
connected by machines called
‘gateways’ which provide necessary
translation.
‘Internetworks’ or ‘Internet’ is a
collection of internetworked networks

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Internetwork
(Internet)

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Wireless networks
Three major Categories
1.System interconnection : Interconnecting
components of a computer using short range radio
(Bluetooth)
2. Wireless LAN : Each computer has a radio
modem & antenna to communicate with
others.(IEEE 802.11-Most commonly used
standard)
3. Wireless WAN : .
Eg. Low BW wireless N/W ,
High BW wireless internet access.(IEEE 802.16)

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Wireless Networks (2)
(a) Bluetooth configuration (b) Wireless LAN

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Home Network Categories
Computers (desktop PC, PDA, shared
peripherals
Entertainment (TV, DVD, VCR, camera,
stereo, MP3)
Telecomm (telephone, cell phone, intercom,
fax)
Appliances (microwave, fridge, clock,
furnace)
Telemetry (utility meter, burglar alarm,
babycam).

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Passive Topology vs. Active
Topology
In an active topology network,
computers and other devices
regenerate signals and are responsible
for moving data through the network
In a passive topology network,
computers only listen for data being
sent; they are not responsible for
moving data from one computer to the
next.
41

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Topology : Topology of the network is the
geometric representation of the relationship
of all the links and linking devices to one
another.
There are basic four topologies :
1. Mesh
2. Star
3. Bus
4. Ring

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Mesh Topology

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• Every device has dedicated point –to – point link to every
other device.
• It has n(n-1)/2 physical channel to link n devices.
Advantages
1. Eliminating the traffic problems.
2. A mesh topology is robust.
3. Privacy and security.
4. Fault identification and fault isolation is easy.
Disadvantages:-
1. Large amount of cabling and no of I/O ports required.
2. Installation and reconnection are difficult.
3. The hardware required to connect each link can be expensive.

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Star topology

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• Each device has a dedicated point-to-point link only to a
central controller, called hub.
• The controller act as an exchange.
Advantages:-
1. It is a less expensive than mesh topology.
2. Each device need only one link and one I/O port to connect
any no of others.so easy to install and reconfigure.
3. Less cabling
4. Robustness
5. Fault identification and fault isolation is easy.

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Tree Topology

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Bus Topology

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• It is a multipoint connection.one long cable act as a backbone
to link all the devices in a network.
• Nodes are connected to the bus cable by drop lines and taps.
• When one computer sends the signal on the cable; all the
computers on the network receive the information, but the one
with the address that matches the one encoded in the message
accepts the information while all the other reject the message.
Advantages:-
1. It include ease of installation.
2. Less cabling
Disadvantages:-
1. Difficult reconnection and fault isolation.
2. As a signal travels along the backbone, some of its energy is
transformed into heat. So,it become weaker and weaker as it
has to travel further and further.

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For this reason there is a limit on the number of taps and bus.
3. A fault or break in the bus cable stops all transmission.

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Ring Topology

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• Each device has a dedicated point-to –point connection only
with the two devices on either side of it.
Advantages:-
1. Easy to install and reconfigure.
2. To add and delete a device requires changing only two
connections.
3. Fault isolation is simplified.
Disadvantages :-
1. Unidirectional traffic
2. A break in the ring can disable the entire network.

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Hybrid Topology

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Network Software
Protocol Hierarchies
Design Issues for the Layers
Connection-Oriented and Connectionless
Services
Service Primitives
The Relationship of Services to Protocols

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Network Software
Networks organized as a stack of layers
or levels.
Each layer offers certain services to
higher layers.
Layers communicate with each other
using certain rules & convention known
as Protocol.
Protocol - an agreement between
parties on how communication is to
proceed.

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Network Software
Protocol Hierarchies
Layers, protocols, and interfaces.

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Protocol Hierarchies (3)
Example information flow supporting
virtual communication in layer 5.

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Design Issues for the Layers
Addressing
Error Control
Flow Control
Multiplexing
Routing

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Connection-Oriented and
Connectionless Services
Six different types of service.

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Service Primitives
Five service primitives for
implementing a simple
connection-oriented service.

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Service Primitives (2)
Packets sent in a simple client-server
interaction on a connection-oriented network.

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Services to Protocols
Relationship

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Reference Models
The OSI Reference Model
The TCP/IP Reference Model
A Comparison of OSI and TCP/IP
A Critique of the OSI Model and
Protocols
A Critique of the TCP/IP Reference
Model

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Reference Models
The OSI
reference
model.

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The Physical Layer
Concerned with transmitting raw bits over a
communication channel
Largly deals with mechanical, electrical, physical
transmission medium & timing interfaces.
Converts digital bits in Electrical signals
Decide whether the transmission: Simplex, Half duplex,
Duplex
 How many volts represent ‘1’ & ‘0’?
 What is bit rate?
 How connection is established & released?
 How many pins network connector has?
 Does not detect & correct errors
 Does not decide the medium or modulation
 Example: RS-232 and RS-449 standards

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The Data Link Layer
Transforms raw transmission facility into a
line that appears free of errors to N/W
layer.
Breaks up the input data in data frame &
transmit them sequentially.
Receiver confirms correct receipt by
sending back an acknowledge frame.
Error Control, flow Control, Framing and
Synchronization are main functions of DLL

67
The Network Layer
Controls operation of the subnet.
Key issue is how packets are routed.
Routes - static or dynamic.
Congestion control.
Quality of Service(delay,transit time,jitter)

68
The Transport Layer
As name suggests provide Transport
Services
Accepts data from above
splits it into smaller units
pass them to N/W layer
Ensures that all pieces arrive correctly
at the other end.
Decide the data Tx should take place on
single or parallel path

69
The Session layer
Allows user on different machines to
establish sessions.
It manage synchronization between
two different applications
Controls logging on and off, user
Identification, billing and session
management.
Offers services - Dialog control, token
management & Synchronization.

70
The Presentation Layer
It makes it sure that the information is
delivered in such a form that the
receiving system will understand and
use it.
Concerned with syntax & semantics
of the information transmitted.
Manages abstract data structures &
allows higher level data structures to
be defined & exchanged.

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The Application Layer
Services: Manipulation of information in
various ways, retransferring the file of
information in various ways etc.
Contains variety of protocols
HTTP(HyperText Transfer Protocol)
HTTP is basis of world wide web.
Other protocols are for file transfer,
electronic mail & network news.

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The TCP/IP Reference Model
The name is TCP/IP after its two
primary protocols.
Major design goal is to connect multiple
networks in a seamless way.
Requirement is that connections to
remain intact even if some of the
machines or transmission lines are out
of order.

73
Reference Models (2)
The TCP/IP reference model.

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The Internet Layer
It is a packet switching network based on a
connectionless internetwork layer.
It permits hosts to inject packets into
network & have them travel independently
to destination.
Analogy with mail system.
It defines an official packet format &
protocol called IP (Internet Protocol).

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The Transport Layer
Allows peer entities on source &
destination hosts to carry out conversation.
Two protocols
TCP – Transmission Control Protocol
reliable, connection oriented protocol.
UDP – User Datagram Protocol
Unreliable, connectionless protocol.

76
The Application Layer
It contains all higher level protocols.
TELNET - Virtual Terminal
FTP - File Transfer Protocol
SMTP – Electronic Mail
DNS – Domain Name System

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The Host To Network Layer
The Host has to connect to the network
using some protocol so IP packets can
be sent to it.
This protocol is not defined & varies
from host to host & network to network.

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Reference Models (3)
Protocols and networks in the TCP/IP
model initially.

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Comparing OSI and TCP/IP
Models
Concepts central to the
OSI model
Services
Interfaces
Protocols

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A Critique of the OSI Model and
Protocols
Why OSI did not take over
the world
Bad timing
Bad technology
Bad implementations
Bad politics

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Bad Timing
The apocalypse of the two elephants.

82
A Critique of the TCP/IP
Reference Model
Problems:
Service, interface, and protocol not distinguished
Not a general model
Host-to-network “layer” not really a layer
No mention of physical and data link layers
Minor protocols deeply entrenched, hard to
replace

83
Hybrid Model
The hybrid reference model to be used
in this book.

Example Networks
• The Internet
• Connection-Oriented Networks:
X.25, Frame Relay, and ATM
• Ethernet
• Wireless LANs: 802:11
84

The ARPANET(Advanced Researvh
Project Agency)
(a) Structure of the telephone system.
(b) Baran’s proposed distributed
switching system.
85

The ARPANET (2)
The original ARPANET design.
IMPS(Interface Message processor) are
minicomputers connected by 56-Kbps
Tx line
86

NSFNET(National Science
Foundation)
The NSFNET backbone in 1988.
87

Internet Usage
A machine is on the internet if it runs the
TCP/IP protocol stack, has an IP address
and can sent the IP packets to all other
machines on the Internet.
Traditional applications (1970 – 1990)
• E-mail(uses ARPANET)
• News(Specialized Forum)
• Remote login(log on the other machine, In
which they have account)
• File transfer(copy file from one machine to
other on the same network)
88

Architecture of the Internet
Overview of the Internet.
89

Connection-Oriented Network
X.25
Frame Relay
ATM
90

X.25 and Frame Relay
X.25 is first connection oriented network and first public
data network.
Developed in 1970-In the Era of Telephone companies
Establish connection ->connection was given a
number to be used in data transfer->Data packets(3 byte
of header and 128 bytes of data) have 12-bit connection
number, a packet sequence no., an acknowledgement
number.
1980 it is replaced by new kind of Network Frame Relay.
Frame relay is connection oriented network with no error
control and no flow control.
Most important application is interconnecting LAN at
multiple company office
91

ATM(Asynchronous Transfer
Mode) Virtual Circuits
A virtual circuit. (In telephone system most
transmission is synchronous-closely tied to
a clock, and ATM is not.
92

ATM Virtual Circuits (2)
An ATM cell.
93

The ATM Reference Model
The ATM reference model.
94

The ATM Reference Model (2)
The ATM layers and sublayers and their
functions.
95

Ethernet
Architecture of the original Ethernet.
96

Wireless LANs
(a) Wireless networking with a base
station.
(b) Ad hoc networking.
97

Wireless LANs (2)
The range of a single radio may not
cover the entire system.
98

Wireless LANs (3)
A multicell 802.11 network.
99

ITU
• Main sectors
• Radiocommunications
• Telecommunications Standardization
• Development
• Classes of Members
• National governments
• Sector members
• Associate members
• Regulatory agencies
100

IEEE 802 Standards
The 802 working groups. The important ones are
marked with *. The ones marked with  are
hibernating. The one marked with † gave up.
101

102
Summary
Layered models help us deal with
complexity
Different models exist; we will use 5 layers
We will need to understand what the
layers do...
…and who decides what the practical
standards are

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