8 chapter 08 computer network

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Chapter-08

Computer Networks

Source: http://www.futurerayz.com/career-in-networking/

Management Information Systems Page 103

Chapter 8 Computer Network

8.1 Introduction to Computer Network

A computer network or data network is a telecommunications network that allows

computers to exchange data. In computer networks, networked computing devices

(network nodes) pass data to each other along data connections. The connections

(network links) between nodes are established using either cable media or wireless

media. The best-known computer network is the Internet.

Network devices that originate, route and terminate the data are called network nodes.

Nodes can include hosts such as servers and personal computers, as well as networking

hardware. Two devices are said to be networked when a device is able to exchange

information with another device.

Computer networks support applications such as access to the World Wide Web, shared

use of application and storage servers, printers, and fax machines, and use of email and

instant messaging applications. This article discusses computer network technologies and

classifies them according to the following characteristics: the physical media used to

transmit signals, the communications protocols used to organize network traffic, along

with the network's size, its topology and its organizational intent.

A network is a group of devices connected to each other. Networks may be classified into

a wide variety of characteristics, such as the medium used to transport the data,

communications protocol used, scale, topology, benefit, and organizational scope.

Information and communication are two of the most important strategic issues for the

success of every enterprise. While today nearly every organization uses a substantial

number of computers and communication tools (like telephone or fax), they are often still

isolated. While managers today are able to use applications like wordprocessors or

spreadsheets, not very many of them use computer-based tools to communicate with

other departments or information retrieval programs.

To overcome these obstacles in an effective usage of information technology, computer

networks are necessary. They are a new kind (one might call it paradigm) of organization

of computer systems produced by the need to merge computers and communications. At

the same time they are the means to converge the two areas; the unnecessary distinction

between tools to process and store information and tools to collect and transport

information can disappear. Computer networks can manage to put down the barriers

between information held on several (not only computer) systems. Only with the help of

computer networks can a borderless communication and information environment be

built.

Computer networks allow the user to access remote programs and remote databases either

of the same organization or from other enterprises or public sources. Computer networks

provide communication possibilities faster than other facilities. Because of these optimal

information and communication possibilities, computer networks may increase the



organizational learning rate, which many authors declare as the only fundamental

advantage in competition.

Besides this major reason why any organization should not fail to have a computer

network, there are other reasons as well:

cost reduction by sharing hard- and software resources

high reliability by having multiple sources of supply

cost reduction by downsizing to microcomputer-based networks instead of using

mainframes

greater flexibility because of possibility to connect devices from various vendors

8.2 What is Computer Network? Write importance of computer network in

modern Information Technology (IT).

A computer network is a group of computers connected to each other electronically. This means that the computers can "talk" to

each other and that every computer in the network can send

information to the others. Usually, this means that the speed of the connection is fast - faster than a normal connection to the Internet.

Some basic types of computer networks include:1

A local area network (often called a LAN) connects two or more computers, and

may be called a corporate network in an office or business setting.

An "internetwork", sometimes called a Wide Area Network (because of the wide

distance between networks) connects two or more smaller networks together. The

largest internetwork is called the Internet. 2

Figure 8.1 Cisco, Networking Academy, Communicating over the Network, Network Fundamentals, p.42



Computers can be part of several different networks. Networks can also be parts of bigger

networks. The local area network in a small business is usually connected to the

corporate network of the larger company. Any connected machine at any level of the

organization may be able to access the Internet, for example to demonstrate computers in

the store, display its catalogue through a web server, or convert received orders into

shipping instructions.

Microsoft Windows, Linux and most other operating systems use TCP/IP for networking.

Apple Macintosh computers used Appletalk in the past, but it uses TCP/IP now.

To set up a network an appropriate media is required. This can be wired or wireless.

Twisted-pair, co-axial or fiber-optic are examples of cable and infra-red, blue-tooth,

radio-wave, micro-wave etc. are wireless media used for networking. When you are

working with a mere LAN, computers, media and peripherals are sufficient. But when

you are working with a wider range you have use some additional devices like bridge,

gateway or router to connect different small or large networks. And obviously a protocol

must be maintained.

To set up a network you have to select an appropriate topology to arrange the hardware

devices using the media. Topologies generally used are bus-topology, ring-topology, star-

topology, tree-topology, object-oriented topology etc. Among these star-topology and

tree-topology are most popular nowadays.[

A computer network, or simply a network, is a collection of computers and other

hardware interconnected by communication channels that allow sharing of resources and

information. Where at least one process in one device is able to send/receive data to/from

at least one process residing in a remote device, then the two devices are said to be in a

network. 3



Figure 8.2 http://rashid007.blogspot.com/2011/03/what-is-computer-network.html

8.3 Define Computer Network. Write different types of Network in business.

A combination of two or more computers connected through a communication system

that allows exchange of information between computers is termed as Computer Network

It is classified into:

a) LAN

b) WAN

d) Internet

LAN is the full form of Local Area Network. It is the connection of computers inside a building or a Lab. Connected computers in a Computer lab, computers in a

Bank or in a Hospital. This will be a private network owned by a company or an

institutions etc.

WAN is Wide Area Network.overall Connection of computers in a city/town. For example, the network of different branches of a company in a city. This is a private

network

MAN is the full form of Metropolitan Area Network. The network of computers in metropolitan city. The network of computers of different branches of a company

inside a metropolitan city. This will be a private network.

Internet is a public network. It is the collection of inter connected networks. It is a network of networks which is capable of communicating with computers on other

network and sending data, files and other information back and forth. The internet

connects tens of thousands of independent networks into a vast global Internet. It is

probably the Largest Wide Area Network.

Figure 8.3 http://simple.wikipedia.org/wiki/ring_topology



8.4 Define Network Topology. Write different types of Network Network

Topologies.

A network topology is the arrangement of computers, cables, and others components on a

network. Network topology is a map of the physical network. Network topology is the

arrangement of the various elements of a computer network. Essentially, it is the

topological structure of a network, and may be depicted physically or logically. Physical

topology refers to the placement of the network's various components, including device

location and cable installation, while logical topology shows how data flows within a

network, regardless of its physical design. Distances between nodes, physical

interconnections, transmission rates, and/or signal types may differ between two

networks, yet their topologies may be identical.4

Five most common topologies are:

1) Bus 2) Star 3) Ring 4) Mesh 5) Hybrid Topology

Figure 8.4 http://simple.wikipedia.org/wiki/ring_topology

A good example is a local area network (LAN): Any given node in the LAN has one or

more physical links to other devices in the network; graphically mapping these links

results in a geometric shape that can be used to describe the physical topology of the

network. Conversely, mapping the data flow between the components determines the

logical topology of the network.



1. Bus Topology- Computers are connected to a common, shared cable.

Figure 8.5 http://rashid007.blogspot.com/2011/03/what-is-computer-network.html

In a bus topology all of the computers in a network are attached to a continuous cable.

And all the devices on a bus topology are connected by one single cable. When one

computer sends a signal up the wire, all the computers on the network receive the

information, but only one accepts the information. The rest regrets the message. One

computer can send a message at a time. A computer must wait until the bus is free before

it can transmit. When the signal reaches the end of the wire, it bounces back and travels

back up the wire. When a signal echoes back and forth along an unterminated bus, it is

called ringing. To stop the signals from ringing, attach terminators at either end of the

segment. The terminators absorb the electrical energy and stop the reflection.

Advantage of network topology

The bus is simple, reliable in small network, easy to use and understand

Requires the least amount of cable to connect the computers and less expensive

Easy to extend the bus

2. Star Topology:

All the cables run from the computers to a central location, where they are all connected

by a device called a hub or switch. Each computer on a star network communicates with

a central hub/switch that resends the message either to all the computers or only to the

destination computers.



Figure 8.6 http://1.bp.blogspot.com/-f1_JocDm57Y/UA-rnslcCCI/aaa /jVQ9wo3hIgE/s1600/star+topology.jpg

Hub can be active or passive in the star network Active hub regenerates the electrical

signal and sends it to all the computers connected to it. Passive hub does not amplify or

regenerate signal and does not require electrical power to run. We can expand a star

network by placing another star hub.

Advantages:

Easy to modify and add new computers to a star net

Center of a star net is a good place to diagnose network faults

Single computer failure do not necessarily bring down the whole net

Several cable types can be used with the hub

3. Ring Topology:

Figure 8.7 http://1.bp.blogspot.com/-5yh0peyUJig/UA-t77rV09I/AAAAAAAAAIM/ceKhsjWCCPs/s1600/ RingTopology%255B1%255D.jpg

In a ring topology, computers are connected on a single circle of cable. Unlike the bus

topology, there are no terminated ends. Each computer is connected to the next computer

with the last one connected to the first. Every computer is connected to the next computer

in the ring, and each retransmits what it receives from the previous computer. The

message flow around the ring in one direction. Some ring networks do token passing. It



passes around the ring until a computer wishes to send information to another computer.

The computer adds an electronic address and data and sends it around the ring. Each

computer in sequence receives the token and the information and passes them to the next

until either the electronic address matches the address of the computer or the token

returns to the origin. The receiving computer returns a message to the originator

indicating that the message has been received. The sending computer then creates another

token and place it on the network, allowing another station to capture the token and being

transmitted.

Advantages:

In a ring topology, each computer acts as a repeater, regenerating the signal and

sending it on to the next computer.

No computer can monopolize the network

The fair sharing of the network allows the net to degrade gracefully as more user

are added.

4. Mesh Topology:

The mesh topology connects all devices (nodes) to each other for redundancy and fault

tolerance. It is used in WANs to interconnect LANs and for mission critical networks like

those used by banks and financial institutions. Implementing the mesh topology is

expensive and difficult.

Figure 8.8 http://1.bp.blogspot.com/-L0hOL9Cq4yg/UA-vxKhZNqI/AAAAAAAAAIc/kiEk8AW dqJc/s1600/Mesh-Topology.jpg

Advantages mesh topology:

Fault tolerance

Guaranteed communication channel capacity

Easy to troubleshoot.

Communications protocols define the rules and data formats for exchanging information

in a computer network, and provide the basis for network programming. Well-known

communications protocols include two Ethernet, a hardware and link layer standard that

is ubiquitous in local area networks, and the Internet protocol suite, which defines a set of



protocols for internetworking, i.e. for data communication between multiple networks, as

well as host-to-host data transfer, and application-specific data transmission formats.5

Figure 8.8 http://1.bp.blogspot.com/-f1_JocDm57Y/UA-rnslcCCI/aaa /jVQ9wo3hIgE/s1600

Computer networking is sometimes considered a sub-discipline of electrical engineering,

telecommunications, computer science, information technology or computer engineering,

since it relies upon the theoretical and practical application of these disciplines.

8.5 What are the differences between Physical and Logical topologies?

Explain with figure.

There are two basic categories of network topologies:

1. Physical topologies 2. Logical topologies

Figure 8.9 Physical Topology :Source: http://en.wikipedia.org/wiki/Token_Ring



Network Topology is the particular shape or manner the clients or nodes are arranged. for

example if someone says that the computers are arranged in a star network it doesn't

mean that the computers are arranged physically in star but logically arranged based on

the tasks it can carry out and how it does so.

Figure 8.10 http://en.wikipedia.org/wiki/physical_topology

Physical Topologie

The logical topology, in contrast, is the way that the signals act on the network media, or

the way that the data passes through the network from one device to the next without

regard to the physical interconnection of the devices. A network's logical topology is not

necessarily the same as its physical topology. For example, the original twisted pair

Ethernet using repeater hubs was a logical bus topology with a physical star topology

layout. Token Ring is a logical ring topology, but is wired a physical star from the Media

Access Unit.6

Figure 8.11 http://en.wikipedia.org/wiki/logical_topology

Logical Topology



The logical classification of network topologies generally follows the same classifications

as those in the physical classifications of network topologies but describes the path that

the data takes between nodes being used as opposed to the actual physical connections

between nodes. The logical topologies are generally determined by network protocols as

opposed to being determined by the physical layout of cables, wires, and network devices

or by the flow of the electrical signals, although in many cases the paths that the electrical

signals take between nodes may closely match the logical flow of data, hence the

convention of using the terms logical topology and signal topology interchangeably.

Logical topologies are often closely associated with Media Access Control methods and

protocols. Logical topologies are able to be dynamically reconfigured by special types of

equipment such as routers and switches.

8.6 What is the Point-to-Point Topology? Explain with figure.

Figure 8.12 http://en.wikipedia.org/wiki/Token_Ring

The simplest topology is a permanent link between two endpoints. Switched point-to-

point topologies are the basic model of conventional telephony. The value of a permanent

point-to-point network is unimpeded communications between the two endpoints. The

value of an on-demand point-to-point connection is proportional to the number of

potential pairs of subscribers, and has been expressed as Metcalfe's Law.




Switched:

Using circuit-switching or packet-switching technologies, a point-to-point circuit

can be set up dynamically, and dropped when no longer needed. This is the basic

mode of conventional telephony.


8.7 What are the Network Technologies? Write different types of

network technologies. Explain.

Network technologies refer to the hardware and software used to connect a group of two

or more computers. In scope, it can encompass setting up peer-to-peer connection,

through local area networks (LAN) and even includes an understanding of how the internet and the World Wide Web function.

7

There are different types of the Network technologies in the world like :-

a) Ethernet b) Local Talk c) Token Ring d) FDDI e) ATM



The following is some common-used network symbols to draw different

kinds of network protocols.

In today's business world, reliable and efficient access to information has become an

important asset in the quest to achieve a competitive advantage. File cabinets and

mountains of papers have given way to computers that store and manage information

electronically. Coworkers thousands of miles apart can share information

instantaneously, just as hundreds of workers in a single location can simultaneously

review research data maintained online.

Computer networking technologies are the glue that binds these elements together. The

public Internet allows businesses around the world to share information with each other

and their customers. The global computer network known as the World Wide Web

provides services that let consumers buy books, clothes, and even cars online, or auction

those same items off when no longer wanted.

In this article, we will take a very close look at networking, and in particular the Ethernet

networking standard, so you can understand the actual mechanics of how all of these

computers connect to one another.

Figure 8.15 http://computer.howstuffworks.com/home-network.htm



Ethernet


The Ethernet Technology is by far the most widely used. Ethernet uses an access method

called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system

where each computer listens to the cable before sending anything through the network. If

the network is clear, the computer will transmit. If some other node is already

transmitting on the cable, the computer will wait and try again when the line is clear.

Sometimes, two computers attempt to transmit at the same instant. When this happens a

collision occurs. Each computer then backs off and waits a random amount of time before

attempting to retransmit. With this access method, it is normal to have collisions.

However, the delay caused by collisions and retransmitting is very small and does not

normally effect the speed of transmission on the network.

The Ethernet Technology allows for linear bus, star, or tree topologies. Data can be

transmitted over wireless access points, twisted pair, coaxial, or fiber optic cable at a

speed of 10 Mbps up to 1000 Mbps.

Fast Ethernet

To allow for an increased speed of transmission, the Ethernet Technology has developed

a new standard that supports 100 Mbps. This is commonly called Fast Ethernet. Fast

Ethernet requires the use of different, more expensive network concentrators/hubs and

network interface cards. In addition, category 5 twisted pair or fiber optic cable is

necessary. Fast Ethernet is becoming common in schools that have been recently wired.



Figure 8.17 http://computer.howstuffworks.com/fast_ethernet

To allow for an increased speed of transmission, the Ethernet Technology has developed

a new standard that supports 100 Mbps. This is commonly called Fast Ethernet. Fast

Ethernet requires the use of different, more expensive network concentrators/hubs and

network interface cards. In addition, category 5 twisted pair or fiber optic cable is

necessary. Fast Ethernet is becoming common in schools that have been recently wired.

Local Talk

Local Talk is a network Technology that was developed by Apple Computer, Inc. for

Macintosh computers. The method used by Local Talk is called CSMA/CA (Carrier

Sense Multiple Access with Collision Avoidance). It is similar to CSMA/CD except that

a computer signals its intent to transmit before it actually does so. Local Talk adapters

and special twisted pair cable can be used to connect a series of computers through the

serial port. The Macintosh operating system allows the establishment of a peer-to-peer

network without the need for additional software. With the addition of the server version

of AppleShare software, a client/server network can be established.

The Local Talk Technology allows for linear bus, star, or tree topologies using twisted

pair cable. A primary disadvantage of Local Talk is speed. Its speed of transmission is

only 230 Kbps.

Token Ring

The Token Ring Technology was developed by IBM in the mid-1980s. The access

method used involves token-passing. In Token Ring, the computers are connected so that

the signal travels around the network from one computer to another in a logical ring. A

single electronic token moves around the ring from one computer to the next. If a

computer does not have information to transmit, it simply passes the token on to the next

workstation. If a computer wishes to transmit and receives an empty token, it attaches

data to the token. The token then proceeds around the ring until it comes to the computer

for which the data is meant. At this point, the data is captured by the receiving computer.

The Token Ring Technology requires a star-wired ring using twisted pair or fiber optic

cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to the increasing

popularity of Ethernet, the use of Token Ring in school environments has decreased.



FDDI Fiber Distributed Data Interface (FDDI) is a network Technology that is used primarily to

interconnect two or more local area networks, often over large distances. The access

method used by FDDI involves token-passing. FDDI uses a dual ring physical topology.

Transmission normally occurs on one of the rings; however, if a break occurs, the system

keeps information moving by automatically using portions of the second ring to create a

new complete ring. A major advantage of FDDI is speed. It operates over fiber optic

cable at 100 Mbps.

Figure 8.18 http://techsoftcomputing.com/internetworking/FDDI.html

ATM

Asynchronous Transfer Mode (ATM) is a network Technology that transmits data at a

speed of 155 Mbps and higher. ATM works by transmitting all data in small packets of a

fixed size; whereas, other Technologies transfer variable length packets. ATM supports a

variety of media such as video, CD-quality audio, and imaging. ATM employs a star

topology, which can work with fiber optic as well as twisted pair cable.

ATM is most often used to interconnect two or more local area networks. It is also

frequently used by Internet Service Providers to utilize high-speed access to the Internet

for their clients. As ATM technology becomes more cost-effective, it will provide

another solution for constructing faster local area networks.

Gigabit Ethernet

The most recent development in the Ethernet standard is a Technology that has a

transmission speed of 1 GBPS. Gigabit Ethernet is primarily used for backbones on a

network at this time. In the future, it will probably be used for workstation and server

connections also. It can be used with both fiber optic cabling and copper. The

1000BaseTX, the copper cable used for Gigabit Ethernet, is expected to become the

formal standard in 1999.



Compare the Network Technologies

Technologies Cable Speed Topology

Ethernet Twisted Pair, Coaxial,

Fiber 10 Mbps Linear Bus, Star, Tree

Fast Ethernet Twisted Pair, Fiber 100 Mbps Star

Local Talk Twisted Pair .23 Mbps Linear Bus or Star

Token Ring Twisted Pair 4 Mbps - 16

Mbps Star-Wired Ring

FDDI Fiber 100 Mbps Dual ring

ATM Twisted Pair, Fiber 155-2488 Mbps Linear Bus, Star, Tree

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 Technology as its basis; instead, its protocol is derived from

the IEEE 802.4 token bus timed token Technology. In addition to covering large

geographical areas, FDDI local area networks can support thousands of users. As a

standard underlying medium it uses optical fiber, although it can use copper cable, in

which case it may be referred to as CDDI (Copper Distributed Data Interface). FDDI

offers both a Dual-Attached Station (DAS), counter-rotating token ring topology and a

Single-Attached Station (SAS), token bus passing ring topology.

Figure 8.19 http://computer.howstuffworks.com/fddi



FDDI was considered an attractive campus backbone technology in the early to mid

1990s since existing Ethernet networks only offered 10 Mbit/s transfer speeds and Token

Ring networks only offered 4 Mbit/s or 16 Mbit/s speeds. Thus it was the preferred

choice of that era for a high-speed backbone, but FDDI has since been effectively

obsolesced by fast Ethernet which offered the same 100 Mbit/s speeds, but at a much

lower cost and, since 1998, by Gigabit Ethernet due to its speed, and even lower cost, and

ubiquity.

Figure 8.20 http://computer.howstuffworks.com/fddi.htm

FDDI, as a product of American National Standards Institute X3T9.5 (now X3T12),

conforms to the Open Systems Interconnection (OSI) model of functional layering of

LANs using other Technologys. FDDI-II, a version of FDDI, adds the capability to add

circuit-switched service to the network so that it can also handle voice and video signals.

Work has started to connect FDDI networks to the developing Synchronous Optical

Network (SONET).


A FDDI network contains two rings, one as a secondary backup in case the primary ring

fails. The primary ring offers up to 100 Mbit/s capacity. When a network has no

requirement for the secondary ring to do backup, it can also carry data, extending

capacity to 200 Mbit/s. The single ring can extend the maximum distance; a dual ring can

extend 100 km (62 mi). FDDI has a larger maximum-frame size (4,352 bytes) than

standard 100 Mbit/s Ethernet which only supports a maximum-frame size of 1,500 bytes,

allowing better throughput.



Figure 8.22 http://computer.howstuffworks.com/fddi_ring

Designers normally construct FDDI rings in the form of a "dual ring of trees" (see

network topology). A small number of devices (typically infrastructure devices such as

routers and concentrators rather than host computers) connect to both rings - hence the

term "dual-attached". Host computers then connect as single-attached devices to the

routers or concentrators. The dual ring in its most degenerate form simply collapses into a

single device. Typically, a computer-room contains the whole dual ring, although some

implementations have deployed FDDI as a Metropolitan area network.

Token Ring

Token ring local area network (LAN) technology is a Technology 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.

Figure 8.23 http://computer.howstuffworks.com/token_ring.htm



8.8 What is Protocols? Write different types of Network Protocols.

Explain with figure.

A protocol is a set of rules that governs the communications between computers on a

network. These rules include guidelines that regulate the following characteristics of a

network: access method, allowed physical topologies, types of cabling, and speed of data

transfer.

Telnet Telephone Network

WWW

HTTP Hyper Text Transfer Protocol

HTTPS Secure Hyper Text Transfer Protocol

SFTP Secure File Transfer Protocol

SSL Secure Socket Layer

TLS Transport Layer Security

POP post office protocol

SSH Secure Shell

FTP File Transfer Protocol

SMTP Simple Mail Transfer Protocol

Bluetooth protocols

Fiber Channel network protocols

Internet Protocol Suite or TCP/IP model or TCP/IP stack

OSI protocols family of information exchange standards developed jointly by the

ISO and the ITU-T

Routing protocols

List of IP protocol numbers, protocol numbers used in the Protocol field of the

IPv4 header and the Next Header field of IPv6 header

Yahoo! Messenger Protocol, underlying protocol used by the Yahoo messenger

RTPS protocol, an interoperability protocol

Telnet

Telnet is a network protocol used on the Internet or local area networks to provide a

bidirectional interactive text-oriented communication facility using a virtual terminal

connection. User data is interspersed in-band with Telnet control information in an 8-bit

byte oriented data connection over the Transmission Control Protocol (TCP).8

Telnet was developed in 1969 beginning with RFC 15, extended in RFC 854, and

standardized as Internet Engineering Task Force (IETF) Internet Standard STD 8, one of

the first Internet standards.

Historically, Telnet provided access to a command-line interface (usually, of an operating

system) on a remote host. Most network equipment and operating systems with a TCP/IP

stack support a Telnet service for remote configuration (including systems based on



Windows NT). Because of security issues with Telnet, its use for this purpose has waned

in favor of SSH.

The term telnet may also refer to the software that implements the client part of the

protocol. Telnet client applications are available for virtually all computer platforms.

Telnet is also used as a verb. To telnet means to establish a connection with the Telnet

protocol, either with command line client or with a programmatic interface. For example,

a common directive might be: "To change your password, telnet to the server, log in and

run the passed command." Most often, a user will be telnetting to a Unix-like server

system or a network device (such as a router) and obtain a login prompt to a command

line text interface or a character-based full-screen manager.

Hypertext Transfer Protocol

Hypertext is a multi-linear set of objects, building a network by using logical links (the

so-called hyperlinks) between the nodes (e.g. text or words). HTTP is the protocol to

exchange or transfer hypertext.

The standards development of HTTP was coordinated by the Internet Engineering Task

Force (IETF) and the World Wide Web Consortium (W3C), culminating in the

publication of a series of Requests for Comments (RFCs), most notably RFC 2616 (June

1999), which defines HTTP/1.1, the version of HTTP in common use.

HTTP Secure

For secure communication over a computer network, with especially wide deployment on

the Internet. Technically, it is not a protocol in itself; rather, it is the result of simply

layering the Hypertext Transfer Protocol (HTTP) on top of the SSL/TLS protocol, thus

adding the security capabilities of SSL/TLS to standard HTTP communications.

In its popular deployment on the internet. HTTPS provides authentication of the web site

and associated web server that one is communicating with, which protects against Man-

in-the-middle attacks. Additionally, it provides bidirectional encryption of

communications between a client and server, which protects against eavesdropping and

tampering with and/or forging the contents of the communication.9 In practice, this

provides a reasonable guarantee that one is communicating with precisely the web site

that one intended to communicate with (as opposed to an impostor), as well as ensuring

that the contents of communications between the user and site cannot be read or forged

by any third party.

A site must be completely hosted over HTTPS, without having some of its contents

loaded over HTTP, or the user will be vulnerable to some attacks and surveillance. E.g.

Having scripts etc. loaded insecurely on a HTTPS page makes the user vulnerable to

attacks. Also having only a certain page that contains sensitive information (such as a

log-in page) of a website loaded over HTTPS, while having the rest of the website loaded

over plain HTTP will expose the user to attacks. E.g. if the user first accesses the front



page of the website with HTTP where he only after that clicks an HTTPS link to the log-

in page, the session has already been compromised. On a site that has sensitive

information somewhere on it, every time that site is accessed with HTTP instead of

HTTPS, the user and the session will get exposed. Similarly, cookies on a site served

through HTTPS have to have the secure attribute enabled.10

SSH File Transfer Protocol

In computing, the SSH File Transfer Protocol (also Secure File Transfer Protocol, Secure

FTP, or SFTP) is a network protocol that provides file access, file transfer, and file

management functionalities over any reliable data stream. It was designed by the Internet

Engineering Task Force (IETF) as an extension of the Secure Shell protocol (SSH)

version 2.0 to provide secure file transfer capability, but is also intended to be usable with

other protocols. The IETF of the Internet Draft states that even though this protocol is

described in the context of the SSH-2 protocol, it could be used in a number of different

applications, such as secure file transfer over Transport Layer Security (TLS) and transfer

of management information in VPN applications.11

This protocol assumes that it is run over a secure channel, such as SSH, that the server

has already authenticated the client, and that the identity of the client user is available to

the protocol.

Transport Layer Security (TLS)

Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are

cryptographic protocols that provide communication security over the Internet.[1] TLS

and SSL encrypt the segments of network connections at the Application Layer for the

Transport Layer, using asymmetric cryptography for key exchange, symmetric

encryption for confidentiality, and message authentication codes for message integrity.

Several versions of the protocols are in widespread use in applications such as web

browsing, electronic mail, Internet faxing, instant messaging and voice-over-IP (VoIP).

TLS is an IETF standards track protocol, last updated in RFC 5246, and is based on the

earlier SSL specifications developed by Netscape Communications.12

File Transfer Protocol (FTP)

File Transfer Protocol (FTP) is a standard network protocol used to transfer files from

one host or to another host over a TCP-based network, such as the Internet.

FTP is built on a client-server architecture and uses separate control and data connections

between the client and the server.[1] FTP users may authenticate themselves using a

clear-text sign-in protocol, normally in the form of a username and password, but can

connect anonymously if the server is configured to allow it. For secure transmission that

hides (encrypts) the username and password, and encrypts the content, FTP is often



secured with SSL/TLS ("FTPS"). SSH File Transfer Protocol ("SFTP") is sometimes also

used instead.

Bluetooth protocols

Wireless data exchange standard Bluetooth uses a variety of protocols. Core protocols are

defined by the trade organization Bluetooth SIG. Additional protocols have been adopted

from other standards bodies. This article gives an overview of the core protocols and

those adopted protocols that are widely used.

The Bluetooth protocol stack is split in two parts: a "controller stack" containing the

timing critical radio interface, and a "host stack" dealing with high level data. The

controller stack is generally implemented in a low cost silicon device containing the

bluetooth radio and a microprocessor. The host stack is generally implemented as part of

an operating system, or as an installable package on top of an operating system. For

integrated devices such as bluetooth headsets, the host stack and controller stack can be

run on the same microprocessor to reduce mass production costs; this is known as a

hostless system.

Internet protocol suite: TCP/IP

The Internet protocol suite is the set of communications protocols used for the Internet

and similar networks, and generally the most popular protocol stack for wide area

networks. It is commonly known as TCP/IP, because of its most important protocols:

Transmission Control Protocol (TCP) and Internet Protocol (IP), which were the first

networking protocols defined in this standard. It is occasionally known as the DoD model

due to the foundational influence of the ARPANET in the 1970s (operated by DARPA,

an agency of the United States Department of Defense).

TCP/IP provides end-to-end connectivity specifying how data should be formatted,

addressed, transmitted, routed and received at the destination. It has four abstraction

layers, each with its own protocols. From lowest to highest, the layers are:

1. The link layer (commonly Ethernet) contains communication technologies for a local network.

2. The internet layer (IP) connects local networks, thus establishing internetworking. 3. The transport layer (TCP) handles host-to-host communication. 4. The application layer (for example HTTP) contains all protocols for specific data

communications services on a process-to-process level (for example how a web

browser communicates with a web server).

The TCP/IP model and related protocols are maintained by the Internet Engineering Task

Force (IETF).



8.8 What is OSI model? Write about OSI protocols

The Open Systems Interconnection (OSI) protocols are a family of information exchange

standards developed jointly by the ISO and the ITU-T starting in 1977.

While the seven-layer OSI model is still often referenced, of the protocols themselves

only X.400, X.500, and IS-IS have had much lasting impact. The goal of a series of open,

non-proprietary network protocols is now met by the competing TCP/IP stack.

OSI protocols stacks are split into seven layers. The layers form a hierarchy of

functionality starting with the physical hardware components to the user interfaces at the

software application level. Each layer receives information from the layer above,

processes it and passes it down to the next layer. Each layer adds its own encapsulation

information (header) to the incoming information before it is passed to the lower layer.

Headers generally include address of destination and source, check sums (for error

control), type of protocol used in the current layer, and other options such as flow control

options and sequence numbers (used to ensure data is sent in order).

Layer 1: Physical layer

This layer deals with the physical plugs and sockets and electrical specification of

signals. This is the medium over which the digital signals are transmitted. It can be

twisted pair, coaxial cable, optical fiber, wireless, or other transmission media.

Layer 2: Data link layer

The data link layer packages raw bits from the physical layer into frames (logical,

structured packets for data). It is specified in ITU-T Rec. X.212 [ISO/IEC 8886], ITU-T

Rec. X.222 and others. This layer is responsible for transferring frames from one host to

another. It might perform error checking.

Layer 3: Network layer

Connectionless Network Service (CLNS) ITU-T Rec. X.213 [ISO/IEC 8348]. SCCP is based on X.213.

Connectionless Network Protocol (CLNP) ITU-T Rec. X.233 [ISO/IEC 8473-1].

Connection-Oriented Network Service (CONS) ITU-T Rec. X.213 [ISO/IEC 8348].

This level is in charge of transferring data between systems in a network, using network-

layer addresses of machines to keep track of destinations and sources. This layer uses

routers and switches to manage its traffic (control flow control, error check, routing etc.)

So here it takes all routing decisions, it deals with end to end data transmission.

Layer 4: Transport layer

The connection-mode and connectionless-mode transport services are specified by ITU-T

Rec. X.214 [ISO/IEC 8072]; the protocol that provides the connection-mode service is



specified by ITU-T Rec. X.224 [ISO/IEC 8073], and the protocol that provides the

connectionless-mode service is specified by ITU-T Rec. X.234 [ISO/IEC 8602].

Transport Protocol Class 0 (TP0)





Transport Fast Byte Protocol ISO 14699

The transport layer transfers data between source and destination processes. Generally,

two connection modes are recognized, connection-oriented or connectionless.

Connection-oriented service establishes a dedicated virtual circuit and offers various

grades of guaranteed delivery, ensuring that data received is identical to data transmitted.

Connectionless mode provides only best-effort service without the built-in ability to

correct errors, which includes complete loss of data without notifying the data source of

the failure. No logical connection, and no persistent state of the transaction exists

between the endpoints, lending the connectionless mode low overhead and potentially

better real-time performance for timing-critical applications such as voice and video

transmissions.

Layer 5: Session layer

Session service ITU-T Rec. X.215 [ISO/IEC 8326]

Connection-oriented Session protocol ITU-T Rec. X.225 [ISO/IEC 8327-1]

Connectionless Session protocol ITU-T Rec. X.235 [ISO/IEC 9548-1]

The session layer controls the dialogues (connections) between computers. It establishes,

manages and terminates the connections between the local and remote application. It

provides for full-duplex, half-duplex, or simplex operation, and establishes

checkpointing, adjournment, termination, and restart procedures. The OSI model made

this layer responsible for graceful close of sessions, which is a property of the

Transmission Control Protocol, and also for session checkpointing and recovery, which is

not usually used in the Internet Protocol Suite. The session layer is commonly

implemented explicitly in application environments that use remote procedure calls.

Layer 6: Presentation layer

Prsentation service ITU-T Rec. X.216 [ISO/IEC 8822]

Connection-oriented Presentation protocol ITU-T Rec. X.226 [ISO/IEC 8823-1]

Connectionless Presentation protocol ITU-T Rec. X.236 [ISO/IEC 9576-1]

This layer defines and encrypts/decrypts data types from the application layer. Protocols

such as MIDI, MPEG, and GIF are presentation layer formats shared by different

applications.



Layer 7: Application layer

Internet Protocol address (IP address)

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. An IP address serves two principal functions: host or

network interface identification and location addressing. Its role has been characterized as

follows: "A name indicates what we seek. An address indicates where it is. A route

indicates how to get there."13

The designers of the Internet Protocol defined an IP address as a 32-bit number and this

system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due

to the enormous growth of the Internet and the predicted depletion of available addresses,

a new version of IP (IPv6), using 128 bits for the address, was developed in 1995. IPv6

was standardized as RFC 2460 in 1998, and its deployment has been ongoing since the

mid-2000s.

IP addresses are binary numbers, but they are usually stored in text files and displayed in

human-readable notations, such as 172.16.254.1 (for IPv4), and

2001:db8:0:1234:0:567:8:1 (for IPv6).

The Internet Assigned Numbers Authority (IANA) manages the IP address space

allocations globally and delegates five regional Internet registries (RIRs) to allocate IP

address blocks to local Internet registries (Internet service providers) and other entities.

8.9 What is IP Addresses? Write different classes of IP-Address.

IP addresses 32 bit addresses (divided into 4 octets) used by the Internet Protocol (OSI

Layer 3) for delivering packet to a device located in same or remote network. MAC

address (Hardware address) is a globally unique address which represents the network

card and cannot be changed. IP address refers to a logical address, which is a

configurable address used to identify which network this host belongs to and also a

network specific host number. In other words, an IP V4 address consists of two parts, a

network part and a host part.

This can be compared to your home address. A letter addressed to your home address will

be delivered to your house because of this logical address. If you move to another house,

your address will change, and letters addressed to you will be sent to your new address.

But the person who the letter is being delivered to, that is you, is still the same.

IP addresses are stored internally as binary numbers but they are represented in decimal

numbers because of simplicity.

An example of IP address is 192.168.10.100, which is actually

11000000.10101000.00001010.01100100.



For Each network, one address is used to represent the network and one address is used

for broadcast. Network address is an IP address with all host bits are "0". Broadcast

address is an IP address with all host bits are "1".

That means, for a network, the first IP address is the network address and the last IP

address is the broadcast address.You cannot configure these addresses for your devices.

All the usable IP addresses in any IP network are between network address and broadcast

address.

We can use the following equation for find the number of usable IP addresses in a

network (We have to use two IP addresses in each network to represent the network id

and the broadcat id.)

Number of usable IP addresses = (2n)-2. Where "n" is the number of bits in host part.

Many IP addresses are reserved and we cannot use those IP address. There are five IP

address Classes and certain special addresses.

Default Network

The IP address of 0.0.0.0 is used for the default network. When a program sends a packet

to an address that is not added in the on the computer's routing table, the packet is

forwarded to the gateway for 0.0.0.0, which may able to route it to the correct address.

Class A -IP addresses

"Class A" IP addresses are for very large networks. The left most bit of the left most octet

of a "Class A" network is reserved as "0". The first octet of a "Class A" IP address is used

to identify the Network and the three remaining octets are used to identify the host in that

particular network (Network.Host.Host.Host).

The 32 bits of a "Class A" IP address can be represented as

0xxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.

The minimum possible value for the leftmost octet in binaries is 00000000 (decimal

equivalent is 0) and the maximum possible value for the leftmost octet is 01111111

(decimal equivalent is 127). Therefore for a "Class A" IP address, leftmost octet must

have a value between 0-127 (0.X.X.X to 127.X.X.X).

The network 127.0.0.0 is known as loopback network. The IP address 127.0.0.1 is used

by the host computer to send a message back to itself. It is commonly used for

troubleshooting and network testing.

Computers not connected directly to the Internet need not have globally-unique IP

addresses. They need an IP addresses unique to that network only. 10.0.0.0 network

belongs to "Class A" is reserved for private use and can be used inside any organization.



Class B- IP addresses

"Class B" IP addresses are used for medium-sized networks. Two left most bits of the left

most octet of a "Class B" network is reserved as "10". The first two octets of a "Class B"

IP address is used to identify the Network and the remaining two octets are used to

identify the host in that particular network (Network.Network.Host.Host).

The 32 bits of a "Class B" IP address can be represented as

10xxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.



(decimal equivalent is 191). Therefore for a "Class B" IP address, leftmost octet must


Network 169.254.0.0 is known as APIPA (Automatic Private IP Addresses). APIPA

range of IP addresses are used when a client is configured to automatically obtain an IP

address from the DHCP server was unable to contact the DHCP server for dynamic IP

address.

Networks starting from 172.16.0.0 to 172.31.0.0 are reserved for private use.

Class C- IP addresses

"Class C" IP addresses are commonly used for small to mid-size businesses. Three left

most bits of the left most octet of a "Class C" network is reserved as "110". The first three

octets of a "Class C" IP address is used to identify the Network and the remaining one

octet is used to identify the host in that particular network

(Network.Network.Networkt.Host).

The 32 bits of a "Class C" IP address can be represented as

110xxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx.



(decimal equivalent is 223). Therefore for a "Class C" IP address, leftmost octet must


Networks starting from 192.168.0.0 to 192.168.255.0 are reserved for private use.

Class D- IP addresses

Class D IP addresses are known as multicast IP addresses. Multicasting is a technique

developed to send packets from one device to many other devices, without any

unnecessary packet duplication. In multicasting, one packet is sent from a source and is



replicated as needed in the network to reach as many end-users as necessary. You cannot

assign these IP addresses to your devices.

Four left most bits of the left most octet of a "Class D" network is reserved as "1110".

The other 28 bits are used to identify the group of computers the multicast message is

intended for.

Class E IP addresses

Class E is used for experimental purposes only and you cannot assign these IP addresses

to your devices.

Four left most bits of the left most octet of a "Class E" network is reserved as "1111".

The minimum possible value for the left most octet in binaries is 11110000 (decimal


(decimal equivalent is 255). Therefore for a "Class E" IP address, leftmost octet must


Limited Broadcast

255.255.255.255 is used to send messages to all devices in the LAN and this IP addrress

is known as limited broadcast IP address.

You have learned IP addresses, different classes of IP addresses, Class A IP address,

Class B IP address, Class C IP address, Class D IP address, Class E IP Address, public IP

address, private IP address, multicast IP address, Limited broadcast IP address and

Automatic Private IP Addresses (APIPA).

IP address classes

Class

1st Octet

Decimal

Range

1st Octet

High

Order

Bits

Network/Host ID

(N=Network,

H=Host)

Default

Subnet Mask

Number of

Networks

Hosts per

Network

(Usable

Addresses)

A 1 126* 0 N.H.H.H 255.0.0.0 126 (27 2) 16,777,214 (2

24

2)

B 128 191 10 N.N.H.H 255.255.0.0 16,382 (2

14

2) 65,534 (2

16 2)

C 192 223 110 N.N.N.H 255.255.255.0 2,097,150

(221

2) 254 (2

8 2)

D 224 239 1110 Reserved for Multicasting

E 240 254 1111 Experimental; used for research



Note: Class A addresses 127.0.0.0 to 127.255.255.255 cannot be used and is reserved for

loopback and diagnostic functions.

Private IP Addresses

Class Private Networks Subnet Mask Address Range

A 10.0.0.0 255.0.0.0 10.0.0.0 - 10.255.255.255

B 172.16.0.0 - 172.31.0.0 255.240.0.0 172.16.0.0 - 172.31.255.255

C 192.168.0.0 255.255.0.0 192.168.0.0 - 192.168.255.25



Reference 1 Source http://simple.wikipedia.org/wiki/Computer_network

2 Source : http://simple.wikipedia.org/wiki/Internet 3 Source: http://en.wikipedia.org/wiki/Computer_network 4 http://en.wikipedia.org/wiki/Network_topology#cite_note-atis-2 5 http://en.wikipedia.org/wiki/Twisted_pair_Ethernet 6 http://en.wikipedia.org/wiki/Media_Access_Unit 7 http://computer.howstuffworks.com/home-network.htm 8 http://en.wikipedia.org/wiki/Internet 9 http://en.wikipedia.org/wiki/HTTPS#cite_note-httpse-1 10 http://en.wikipedia.org/wiki/HTTPS#cite_note-deployhttpscorrectly-3 11 http://en.wikipedia.org/wiki/Secure_channel 12 http://en.wikipedia.org/wiki/Secure_Sockets_Layer#cite_note-2 13 http://en.wikipedia.org/wiki/IP_address#cite_note-rfc791-2

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