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Internet Technologies Overview

Content

1. How do Computer Networks and Internets

Operate?

2. Explosive growth

3. Internet

4. Economic impact

5. Complexity

6. Abstractions and concepts7. Motivations and services

8. Protocol and layering

9. Internetworking and TCP/IP

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How do Computer Networks and

Internets Operate?

Network: system for connecting computers using a single

transmission technology

Internet: set of networks connected by routers that are

configured to pass traffic among any computers attached to

networks in the set

* Data transmission - transmission media, data encoding

* Packet transmission-

data exchange over a network* Internetworking - universal service over a collection of

networks (with different technologies)

* Network applications -programs that use an internet

(Eg. WWW)

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Explosive growth

New phenomenon - now, networks are an important part of

everyday activities

Business

Home

Government

Education

Global Internet growing exponentially

Initially a research project with a few dozen sites

Today, millions of computers and hundreds of networks

world-wide and ever-increasing

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Internet

Roots in military network called ARPANET (initiated byAdvancedResearch Projects Agency, USA)

Fundamental changes from centralized to distributed

computing

Incorporated features forreliability and robustness

Multiple links

Distributed routing

Ethernet made localnetworking feasible

TCP/IPprotocol made internetworking possible

a network protocolis a set of rules that specify the format and meaning of

messages exchanged between computers across a network

Exponential growth - doubling every 18 months and ever-

increasing

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Economic impact

Large industry has grown around:

Networking hardware

Computers

Software

Companies must integrate planning,

implementation, management and upgrade

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Complexity

Computer networking is complex

Many different hardware technologies

Many different software technologies

All can be interconnected in an internet

No underlying theory

Terminology can be confusing

Industry redefines or changes terminology from academia New terms invented all the time

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Abstractions and concepts

Will concentrate on abstractions and

concepts to unravel complexity

Examples:

Types of LAN and their basic structures and

operations, rather than details of LAN hardware

Definition and concept of routing, rather thanthe hardware routing mechanisms

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Motivation & Tools

1. Motivation of Networking &

Internetworking

2. Services

3. History and Growth

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Motivation

Cost effective

Early computers were expensive, scare and centralized

Couldn't afford to put computers everywhere

interconnect computers so that computing powers can

be shared by many sites

Resource sharing

access peripheral devices through the network

Eg. Many users sharing the same printer

sharing the same files on a disk Higher reliability

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Communication Services

Access to remote information

World-Wide-Web

File Transfer (FTP)

Exchange of information

Email

News Group

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Military Network (ARPANET)

Advanced Research Projects Agency initiated

project to connect researchers with computers

Adopted new technology: Packet switching (accept & deliver individual

parcels of data called packets)

Internetworking

Resulted in system for remote access to

expensive resources

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Packet switching

Data transmitted in small, independent

pieces

Source divides outgoing messages into packets

Destination recovers original data

Each packet travels independently

Includes enough information for delivery

May follow different paths

Can be retransmitted if lost

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Internetworking

Many (mutually incompatible) network

technologies

No one technology appropriate for everysituation

Internetworkingglues together networks of

dissimilar technologies with routers

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History and growth

ARPANET began in late 1960s (not using

TCP/IP)

TCP/IP developed in late 1970s ARPANET switched to TCP/IP in early 80s

Start of Internet

Few hundred computers

Few tens of networks

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Growth since 1981

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Why Network Models ?

Network communication is an extremely complex task

Need co-operative effort

A standard model helps to describe the task of anetworking product or service

Also help in troubleshooting by providing a frame of

reference

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Who Define Network Model ?

ISO -International Standards Organization e.g. OSI,

MPEG-1,2,4, etc.

IEEE-Institute of Electrical & Electronic Engineers e.g.

IEEE 802, IEEE 754, etc.

ITU -International Telecommunication Union e.g. V.34,

H.323, H.324, etc.

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Protocols and Layering

1. Communication (network) protocol

2. Protocol family (suite)

3. Layered Protocol - OSI 7 layers

4. Layered Software & stack

5. Protocol Headers

6. Techniques for Reliable communication

Sequencing (Ordered delivery)

Retransmission

Flow control (stop-and-go & sliding window)

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Layering

y LAN/WAN hardware can't solve all computer

communication problems

y Why network software?

y Sending data through raw hardware is awkward and inconvenient-

doesn't match programming paradigms well

y Network softwareprovides high-level interface to applications

y Software for LAN and WAN systems is large and

complicatedy Layeringis a structuring technique to organize networking

software design and implementation

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Why protocols?

Name is derived from the Greekprotokollen, the index to a

scroll

Diplomats use rules, called protocols, as guides to formal

interactions A network protocolorcomputercommunication protocolis

a set of rules that specify the format and meaning of

messages exchanged between computers across a network

Format is sometimes calledsyntax

Meaning is sometimes calledsemantics

Protocols are implemented byprotocol software

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One or many protocols?

y Computer communication across a network

is a very hard problem

y Complexity requires multiple protocols,each of which manages a part of the problem

y May be simple or complex; must all work

together

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Protocol suites

A set of related protocols that are designed forcompatibility is called aprotocol suite (family)

Protocol suite designers:

Analyze communication problem

Divide problems into subproblems

Design a protocol for each subproblem

A well-designed protocol suite

Is efficient and effective-

solves the problem withoutredundancy and makes best use of network capacity

Allows replacement of individual protocols without

changes to other protocols

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Layered protocol design

Layering modelis a solution to the problem of complexity

in network protocols

Model suggests dividing the network protocol into

layers, each of which solves part of the networkcommunication problem

These layers address several constraints, which ease the

design problem

Network protocol designed to have a protocol or protocolsfor each layer

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The OSI 7-layer reference model

International Organization for Standards defined a 7-layer referencemodelas a guide to the design of a network protocol suite

Layers are named and numbered; reference to ` layern'' often means

the nth layer of the OSI 7-layer reference model

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The layers in the OSI model

Note-

many modern protocols do not exactly fit the OSI model, and

the OSI protocol suite is mostly of historic interest

Concepts are still largely useful and terminology persists

Layer 7: Application

Application-specific protocols such as FTP (file transfer) and SMTP

(electronic mail), directly support user applications

Example protocols: FTP, Telnet, HTTP

Layer 6: Presentation Common formats for representation of data, provide data encryption

Example application program: redirector (NT), SSL

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The layers in the OSI model

Layer 5: Session Management of sessions such as login to a remote computer, provide

dialog management

Example protocols: TCP, NamedPipes, NetBIOS

Layer 4: Transport

Reliable delivery of data between computers, translate between packets

and message

Example protocols: TCP, SPX, NWLink

Layer 3:Network

Address assignment and data delivery across a physical network,

determine route from source to destination

Example protocols: IP, IPX

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The layers in the OSI model

Layer 2: Data Link

Format of data in frames and delivery of frames through network interface,

translate data frame and bits

Example protocols: Ethernet, Token Ring

Layer 1: Physical

Basic network hardware - such as RS-232 or Ethernet, define how cable is

attached to Network card

Example protocols: Ethernet, Token Ring (Physical Part)

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Application Layer: e.g. File Transfer

The most traditional network task

Implemented by a simple Application Layer protocol

called FTP

FTP Client FTP Server

Network

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Layering principle

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Layered software and stacks

Software implemented from layered design has layered

organization

Related modules from previous figure are called a

protocol stackor simply a stack

Two constraints:

The software for each layer depends only on the services of the

software provided by lower layers

The software at layern at the destination receives exactly the same

protocol message sent by layern at the sender

These constraints mean that protocols can be tested

independently and can be replaced within a protocol stack

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Messages and protocol stacks

On the sender, each layer:

Accepts an outgoing message from the layer above

Adds a header and other processing

Passes resulting message to next lower layer

On the receiver, each layer:

Receives an incoming message from the layer below

Removes the header for that layer and performs other

processing

Passes the resulting message to the next higher layer

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Protocol headers

The software at each layer communicates with the correspond

inglayer through information stored in headers

Each layer adds its header to the front of the message from the next

higher layer

Headers are nested at the front of the message as the message traverses

the network

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Techniques for reliable network

communication

Model - reliable delivery of a block of data

from one computer to another

Data values unchanged

Data in order

No missing data

No duplicated data

Example -parity bit, checksum and CRC

used to ensure data is unchanged

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Interim Summary

Layering is a technique for guiding

protocol design and implementation

Protocols are grouped together into related

protocol suites

A collection of layered protocols is called a

protocol stack

Protocols use a variety oftechniques for

reliable delivery of data

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Internetworking

1. Internetworking concepts

2. Router

3. protocol for internetworking

4. TCP/ IP layering Model

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Motivation

There are many different LAN and WAN

technologies

In real world, computers are connected by

many different technologies

Any system that spans a large organization

must accommodate multiple technologies

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Universal service

y Telephones are useful because any

telephone can reach any other telephone

y Universal service among computers greatly

increases the usefulness of each computer

y Providing universal service requires

interconnecting networks employing

different technologies

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Internetworking

y Internetworkingis a scheme for

interconnecting multiple networks of

dissimilar technologies

y Uses both hardware and software

y Extra hardware positioned between networks

y Software on each attached computer provides

universal service

y System of interconnected networks is called

an internetworkor an internet

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Routers

y A routeris a hardware component used to interconnect networksy A router has separate interface for each network

Router forwards packets between networks of different technologies

(Eg, between a WAN and a LAN, between Token Ring and Ethernet)

Transforms packets as necessary to meet standards for each network

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Internet architecture

An internetwork is composed of arbitrarily many networks

interconnected by routers

Routers can have more than two interfaces

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Routers in an organization

Would be possible to interconnect all networks in an

organization with a single router

Most organizations use multiple routers

y

Each router has finite capacity; single router would have to handlealltraffic across entire organization

y Because internetworking technology can automatically route

around failed components, using multiple routers increases

reliability

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A protocol suite for internetworking

y The TCP/IP Internet Protocols or, simply, TCP/IPis the

mostly widely used internetworking protocol suite

y

First internetworking protocol suitey Initially funded through ARPA

y Becoming more popular after 1980

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Significance of

Internetworking protocols

TCP/IP is by far the most widely used

Vendor and platform independent

Used in theInternet- 36 million computers

in 107 countries

Others internetworking protocols includeVINES and, AppleTalk

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TCP/IP layering

OSI 7-layer model was developed before TCP/IP model. It

does not include Internet layer

TCP/IP layering model includes five layers

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TCP/IP layering

Layer 5: Application

Corresponds to OSI model layers 6 and 7; used for communication

among applications

Layer 4: Transport

Corresponds to layer 4 in the OSI model; provides reliable delivery

of data

Layer 3: Internet

Defines uniform format of packets forwarded across networks of

different technologies and rules for forwarding packets in routers

Layer 2:Network Access

Corresponds to layer 2 in the OSI model; defines formats forcarrying packets in hardware frames

Layer 1: Hardware

Corresponds to layer 1 in the OSI model; defines basic networking

hardware

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Hosts, routers and protocol layers

y A host computerorhostis any system attached to an

internet that runs applications

y Hosts may be supercomputers or personal computers

y TCP/IP allows any pairof hosts on an internetcommunicate directly

y Both hosts and routers have TCP/IP stacks

y Hosts typically have one interface and don't forward

packets

y Routers don't need layers 4 and 5 for packet forwarding

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Hosts, routers and protocol layers

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Summary

An internetis a collection of physical networks

interconnected into a single virtual network

Routersprovide the physical interconnection and forward

packets between networks Hosts communicate across multiple network through

packets forwarded by routers

TCP/IP is the most widely used internetworking protocol

suite

Reference:Data & Computer Communicationsby William Stallings, Prentice Hall