Network Definition
A network is a group of two or more computer systems linked together. There are many types
of computer networks, including:
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Local-area networks (LANs) : The computers are geographically close together (that is,
in the same building).
Wide-area networks (WANs) : The computers are farther apart and are connected by
telephone lines or radio waves.
Campus-area networks (CANs): The computers are within a limited geographic area,
such as a campus or military base.
metropolitan-area networks MANs): A data network designed for a town or city.
Home-area networks (HANs): A network contained within a user's home that connects
a person's digital devices.

Topology : The geometric arrangement of a computer system. Common topologies
include a bus, star, and ring. See the Network topology diagrams in the Quick
Reference section of Webopedia.

Protocol : The protocol defines a common set of rules and signals that computers on the
network use to communicate. One of the most popular protocols for LANs is called

Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network.
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Architecture : Networks can be broadly classified as using either a peer-topeer or client/server architecture.
OSI Model

The Open Systems Interconnection model (OSI) is a conceptual model that characterizes
and standardizes the internal functions of a communication system by partitioning it
into abstraction layers.
The seven layers of the OSI Basic Reference Model are (from bottom to top):
 The Physical Layer describes the physical properties of the various communications
media, as well as the electrical properties and interpretation of the exchanged signals. Ex:
this layer defines the size of Ethernet coaxial cable, the type of BNC connector used, and
the termination method.
 The Data Link Layer describes the logical organization of data bits transmitted on a
particular medium. Ex: this layer defines the framing, addressing and check summing of
Ethernet packets.
 The Network Layer describes how a series of exchanges over various data links can
deliver data between any two nodes in a network. Ex: this layer defines the addressing
and routing structure of the Internet.
 The Transport Layer describes the quality and nature of the data delivery. Ex: this layer
defines if and how retransmissions will be used to ensure data delivery.
 The Session Layer describes the organization of data sequences larger than the packets
handled by lower layers. Ex: this layer describes how request and reply packets are paired
in a remote procedure call.
 The Presentation Layer describes the syntax of data being transferred. Ex: this layer
describes how floating point numbers can be exchanged between hosts with different
math formats.
 The Application Layer describes how real work actually gets done. Ex: this layer would
implement file system operations.
Token Ring
Token Ring/IEEE 802.5

Token ring local area network (LAN) technology is a protocol which resides at the data
link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that
travels around the ring. Token-possession grants the possessor permission to transmit on
the medium. Token ring frames travel completely around the loop. Media Access Unit
Fiber Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) provides a 100 Mbit/s optical standard for data
transmission in a local area network that can extend in range up to 200 kilometers (120
mi). Although FDDI logical topology is a ring-based token network, it does not use the
IEEE 802.5 token ring protocol as its basis; instead, its protocol is derived from the IEEE
802.4 token burs timed token protocol.
Wireless Networks
In this networks the networks are connected by means of wireless devices The most prominent
type of wireless networks are
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Blue Tooth
Wi-Fi
Wi-Max
802.11
Bluetooth is a proprietary open wireless technology standard for exchanging data over short
distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz)
from fixed and mobile devices, creating personal area networks (PANs) with high levels of
security.
Wi-Fi is a popular technology that allows an electronic device to exchange data wirelessly (using
radio waves) over a computer network, including high-speed Internet connections.
WiMAX (Worldwide Interoperability for Microwave Access) is a wireless communications
standard designed to provide 30 to 40 megabit-per-second data rates, with the 2011 update
providing up to 1 Gbit/s for fixed stations.
IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN)
computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and
maintained by the IEEELAN/MAN Standards Committee (IEEE 802).
Wireless PAN
Wireless personal area networks (WPANs) interconnect devices within a relatively small area,
that is generally within a person's reach.[3] For example, both Bluetooth radio and invisible
infrared light provides a WPAN for interconnecting a headset to a laptop.
Wireless LAN
A wireless local area network (WLAN) links two or more devices over a short distance using a
wireless distribution method, usually providing a connection through an access point for Internet
access. The use of spectrum. Products using the IEEE 802.11
Wireless mesh network
A wireless mesh network is a wireless network made up of radio nodes organized in a mesh
topology. Each node forwards messages on behalf of the other nodes. Mesh networks can "self
heal", automatically re-routing around a node that has lost power.
Wireless MAN
Wireless metropolitan area networks are a type of wireless network that connects several
wireless LANs. Example WiMAX
Wireless WAN
Wireless wide area networks are wireless networks that typically cover large areas, such as
between neighboring towns and cities, or city and suburb. Point to point microwave links
Cellular network
A cellular network or mobile network is a radio network distributed over land areas called cells,
each served by at least one fixed-location transceiver, known as a cell site or base station.
Repeater
A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher
power, or onto the other side of an obstruction, so that the signal can cover longer distances
Ethernet Hub
An Ethernet hub, active hub, network hub, repeater hub, multiport repeater or hub is a device for
connecting multiple Ethernet devices together and making them act as a single network segment.
Network Switch
A network switch or switching hub is a computer networking device that connects network segments or
network devices.
CSU/DSU
A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to
connect a Data Terminal Equipment device or DTE, such as a router, to a digital circuit, such as
a T1 line.
Functions of CSU/DSU
The CSU/DSU implements two different functions.
The CSU is responsible for

The connection to the telecom network
The DSU is responsible

For handling the interface with the DTE.
DSL
A digital subscriber line (DSL) modem is a device used to connect a computer or router to a
telephone line which has the digital subscriber line service configured, to allow the computer to
connect to the Internet.
OR
A DSL modem or DSL router is what you need in order to connect to DSL broadband.
IP addressing
Types of IP address
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Static address
Dynamic address
Static IP address
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manually input by network administrator
manageable for small networks
requires careful checks to avoid duplication
Dynamic IP address
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examples - BOOTP, DHCP
assigned by server when host boots
derived automatically from a range of addresses
duration of ‘lease’ negotiated, then address released back to server
Classes of IP address
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Class A - large organizations , governments
Class B - medium sized organizations
Class C - small organizations
An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g.,
computer, printer) participating in a computer network that uses the Internet Protocol for
communication.
Total # Of
IP
Bits For
Address Network
Class
ID / Host
ID
First
Octet of
IP
Address
# Of
Network
ID Bits
Used To
Identify
Class
Class A
8 / 24
0xxx xxxx
1
8-1 = 7
27-2 = 126
224-2 =
16,277,214
Class B
16 / 16
10xx xxxx
2
16-2 = 14
214 =
16,384
216-2 =
65,534
Usable # Number of
# Of Host
Of
Possible
IDs Per
Network
Network
Network ID
ID Bits
IDs
Class C
24 / 8
110x xxxx
3
24-3 = 21
221 =
2,097,152
28-2 = 254
TCP/IP networking
IP : Internet Protocol
UDP : User Datagram Protocol
RTP, traceroute
–
TCP : Transmission Control Protocol
HTTP, FTP, ssh
TCP
•
Reliable, full-duplex, connection-oriented, stream delivery
– Interface presented to the application doesn’t require data in individual packets
– Data is guaranteed to arrive, and in the correct order without duplications
•
Or the connection will be dropped
– Imposes significant overheads
Applications of TCP
•
Most things!
– HTTP, FTP, …
•
Saves the application a lot of work, so used unless there’s a good reason not to
TCP implementation
•
Connections are established using a three-way handshake
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Data is divided up into packets by the operating system
•
Packets are numbered, and received packets are acknowledged
•
Connections are explicitly closed (or may abnormally terminate)
TCP Segment
Three Way Handshake
Numerical Problems on the Network
Store-and-forward (SF) switching
This technique is alternatively called packet switching.
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Each packet hasheader.
Buffersfor packet.
Move from source to the destination.
One step of SF is called hop.
Routing decisions are done by intermediate router
Next – Hop Forwarding
The routing table consists of at least three information fields:
1. the network id: i.e. the destination network id
2. cost: i.e. the cost or metric of the path through which the packet is to be sent
3. next hop: The next hop, or gateway, is the address of the next station to which the packet is to be
sent on the way to its final destination
Router based Architecture
Address Resolution Protocol
The Address Resolution Protocol (ARP) feature performs a required function in IP routing. ARP
finds the hardware address, also known as Media Access Control (MAC) address, of a host from
its known IP address. ARP maintains a cache (table) in which MAC addresses are mapped to IP
addresses.
The ARP request message has the following fields:
•
HLN--Hardware address length. Specifies how long the hardware addresses are in the
message. For IEEE 802 MAC addresses (Ethernet) the value is 6.
•
PLN--Protocol address length. Specifies how long the protocol (Layer 3) addresses are in
the message. For IPv4, the value is 4.
•
OP--Opcode. Specifies the nature of the message by code:
–
1--ARP request.
–
2--ARP reply.
–
3 through 9--RARP and Inverse ARP requests and replies.
•
SHA--Sender hardware address. Specifies the Layer 2 hardware address of the device
sending the message.
•
SPA--Sender protocol address. Specifies the IP address of the sending device.
•
THA--Target hardware address. Specifies the Layer 2 hardware address of the receiving
device.
•
TPA--Target protocol address. Specifies the IP address of the receiving device.
Datagram Encapsulation
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A datagram is encapsulated in a frame
•
The destination address in the frame is the address of the next hop
•
The destination of the next hop is obtained by translating the IP address of the next hop to
an equivalent hardware address.
Architecture of encapsulation
Fragmentation
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A smaller MTU, it is possible to further fragment a fragment.
•
No distinguish between original fragments and sub fragments.
•
Reassembly without first reassembling sub fragments.
Link state Algorithm:
Each router must do the following:
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Discover neighbors, know their network address.
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Find delay or cost to each of its neighbors.
•
Construct a packet.
•
Send this packet to all other routers.
•
Compute the shortest path to every other router.
Applications of Link state Algorithm:
•
Calculating the routing tables.
•
Distributing the maps
•
Finding the shortest paths.
Example on Link state algorithm
Distance Vector routing algorithm:
Dijkstra's algorithm:
It is a graph search algorithm that solves the single-source shortest path problem for a graph with
nonnegative edge path costs, producing a shortest path tree
Algorithm working
•
It starts with the initial root node
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Compare all the distance
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Select the Minimum cost node
Application
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Traffic Information system
•
Travelling Sales person problem
Client /Server concepts:
Client
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is one who sends the requests.
•
is the consumer because he consumes the data from the producer.
•
is connected to the server
•
Server:
•
is one who produces the data to the client whenever he request
•
is producer.
•
is connected to many clients.
Applications: it will be used in the distributed computing.
The client and server are connected through the computer networks.
It will be sued in the cloud computing.
Disadvantages:
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Limited Band width.
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Congestion
•
Low configuration servers to respond clients.
Port De-multiplexing:
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Port Multiplexing is responsible for running multiple network applications.
•
These network applications are responsible for sending and receiving data.
•
Transport layer protocols will implement these network applications by using port
Numbers.
Port Number:
It used to to address particular applications to which we need to send the data. Port Numbers are
classified into 3 categories. They are
•
Well known ports: range is 0-1023 registered by IANA
•
Registered ports: 1024-49151
•
Private ports: 49152- 65535
Examples Port: port 1 –TCP 25 –SMTP
Socket
•
Socket is used as end – end point connections between sender and receiver hosts.
•
Socket is used for inter Process communications.
•
Socket will be addressed by both IP and Port numbers.
•
IP used to address to the host or system and port used to address the applications
program.
•
Sockets are developed between the transport layer and internet layer.
Types of sockets:
There are 3 types of sockets.
•
Stream socket (connection Oriented) example: TCP Sockets.
•
Data Gram Sockets (Connection Less) Example: UDP sockets.
•
Raw Sockets.
Implementation:
•
Sockets can be implemented using Application Programming Interface API called Socket
API by using C and other Programming’s languages like java.
Server concurrency:
Concurrent server means One Server can able to communicate many clients at a time But where
as Iterative server means one server can respond to one one client at a time. There are 2 types of
concurrency servers they are TCP and UDP concurrent servers.
DNS (Domain name System):
•
DNS means mapping IP address to Host name and host name to IP address.
•
IP address is 32 bit
•
Information is indexed by Domain Name
•
The tree of domain names together is called the Domain Name Space
Types of DNS
•
Iterative DNS Server
•
Recursive DNS Server
TELNET (Telemetry Network)
•
It is network protocol used in internet or LAN to provide bidirectional text data transfer.
•
It used to connect client with their servers and can implement the client part.
•
It is used in both windows and Linux operating systems.
Web Technologies:
The following are the types of web technologies used they are :
•
HTML
•
HTTP
•
CGI
•
JAVA
•
RPC
•
Middle ware
Java
Java has evolved to be the most predominant and popular general purpose programming
language of the current age.
Java is a
•
Developed by Sun Microsystems
•
Simple,
•
Portable,
•
Distributed,
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Robust,
•
Secure,
•
Dynamic,
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Architecture neutral,
RPC: Remote Procedure Calls.
•
It defines Procedures
•
It defines methods
•
Communication can be had between computer which are distributed geographically
Middle Ware Technologies:
Middleware is computer software that connects software components or people and their
applications.
Types of Middle ware technologies:
•
RMI - Remote Method Invocations
•
CORBA – Common Object Recourse Broker Architecture
•
.Net Technologies: C#, ASP.Net, VB.Net
Network management system
A network management system (NMS) is a combination of hardware and software used to
monitor and administer a computer network or networks. Individual network elements (NEs) in a
network are managed by an element management system.
Network Security:
•
Network security starts with authenticating the user, commonly with a username and a
password
•
Communication between two hosts using a network may be encrypted to maintain
privacy.
Cryptography:
•
It is the process of encryption and decryption of data using key.
Encryption:
It is the process of transforming the plain text to cipher text
Example. Hello – Plain text Shift each character by 3 character positions.
Khoor – Cipher text
Decryption:
It is the process of transforming the cipher text to plain text
Encryption and decryption can be performed by using encryption algorithm and decryption
algorithm by using the public and private key.
Example
•
Khoor – Cipher text
•
Hello – Plain text
Types of Cryptography
•
Traditional Cryptography
•
Symmetric Cryptography.
Types of Cryptography Algorithms
•
RSA ( Ron Rivest, Adi Shamir and Leonard Adleman,)
•
AES (Advance Encryption Standards)
•
Triple DES (Data Encryption Standard