1.computer network

8/12/2019 1.Computer Network

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COMPUTER NETWORK

Instructor:

Niranjan Baral


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Computer Network

A computer network is a collection of autonomous computer and other computing

hardware devices that are interconnected by a

single technology through communication

channels to facilitate communication and

resource-sharing among a wide range of users

Communication channels : Copper wire, optical

fiber, microwaves, communication satellite

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Advantages of Networking

Easy Communication and Speed

Share Files, Data and Information

Sharing Hardware and Software(so Cheap) Supports the way we live, the way we learn and

the way we work .

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Disadvantages of Networking

Security Issues

High installation cost

Breakdown of the whole network Bandwidth Issues

Need of skilled human resources



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Uses of Computer Network

1. Business Applications

Resource Sharing(Both Hardware and Software)

Communication medium among employees Videoconferencing

Electronic business(E-Commerce)



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Uses of Computer Network cont..

2. Home Applications

Access to Remote Information

Person to Person Communication Entertainment

Electronic Commerce



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Uses of Computer Network cont..

3. Mobile Users

Portable electronic equipment as notebook to

send and receive telephone calls, mail, forweb surfing, access remote files and log on to

remote machines

Use wireless Network



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Networking Models1. Client Server Model

Network architecture in which each computer or process on the

network is either a client or a server. client host requests, receives service from always-on

server e.g. Web browser/server; email client/server

Servers are powerful computers or processesdedicated to managing disk drives (file servers),printers(print servers), or network traffic (networkservers ).

Clients are PCs or workstations on which users runapplications. Clients rely on servers for resources, suchas files, devices, and even processing power.



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Client Server Model cont


PC running

Explorer

Server

running

Apache Web

server

client: browser that requests,

receives, displays Webobjects

server: Web server sends

objects in response to

requests


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Networking Models cont..2.Peer to peer model:

Distributed network architecture

in which individual nodes in the

network (called "peers") can act

as both suppliers and consumers

of resources, no use of dedicated servers

e.g. Skype, BitTorrent


client/server

peer-peer


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Active Network

It has a set of 'Active Nodes' that perform customized

operations on the data flowing through them.

Traditional data networks provide a transport

mechanism to transfer bits from one end system to

another, with a minimal amount of computation(e.g., header processing and signaling).In contrast to

that active networks not only allows the network nodes

to perform computations on the data but also allowtheir users to inject customized programs into the

nodes of the network, that may modify, store or

redirect the user data flowing through the network.



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Active Network Cont.. This enables such ideas as sending code along with

packets of information allowing the data to change its

form (code) to match the channel characteristics.

Example: there may be a video multicast session where

at every node the video compression scheme is

modified, based on the computation done by that nodeand depending on the network bandwidth available.

Applications such a packet filtering in firewalls (also

routers) where the filters in the firewall decide whichpacket should go through and which should be blocked.



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PROTOCOLS AND STANDARDS



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Whats a protocol?

human protocols: whats the time?

I have a question

introductions

specific msgs sent

specific actions taken

when msgs received, or

other events

network protocols: machines rather than

humans

all communication activity

in Internet governed byprotocols

protocols define format, order ofmsgs sent and received amongnetwork entities, and actionstaken on msg transmission, receiptof a message or other event


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Protocols cont

Networking protocol is a set of rules that governs thedata communication and describe processes such as

The format or structure of the message

The method by which networking devices shareinformation about pathways with other networks

How and when error and system messages are

passed between devices The setup and termination of data transfer sessions



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Key Elements of Protocols1. Syntax: Structure or format of data. It refers the

order in which data are processed.(eg: first 16 bitsgive address of sender, following 8 bits message tobe sent and so on)

2. Semantics: Meaning of each section of bits. How aparticular pattern to be interpreted and what actionto be taken on interpretation.(eg: An addressspecifies route to be taken or final destination)

3. Timing: When and how fast data is to be sent.(eg:When a sender produces a data at 100 Mbps andreceiver receives at 1 mbps, overload and data lostoccurs)



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STANDARDSNeed of Standards:

Create and maintain open and competitive market forequipment manufacturers.

Guarantee Interoperability

Give a fixed quality and product to customers

To aid to design and implementation ideas To Provide guidelines to manufactures, vendors, government

agencies and service providers.

Categories:

De-facto( from the fact and not been approved by an organizedbody. Adopted as standards through widespread use)

De jure( legislated by a officially recognized body)



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Some Standards Organization

ITU( International Telecommunications

Organization)

IEEE( Institute of Electrical and Electronics

Engineer)

ISO: International Organization For

Standardization

IETF: Internet Engineering Task Force



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Reference Models

1. OSI Reference Model

2. TCP/IP Reference Model



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Layered ArchitectureOrganization of air travel

a series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing


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ticket (purchase)

baggage (check)

gates (load)

runway (takeoff)

airplane routing

departure

airportarrival

airport

intermediate air-traffic

control centers

airplane routing airplane routing

ticket (complain)

baggage (claim

gates (unload)

runway (land)

airplane routing

ticket

baggage

gate

takeoff/landing

airplane routing

Layering of airline functionality

Layers: each layer implements a service

via its own internal-layer actions

relying on services provided by layer below


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Layered Architecture contAdvantages:

Reduced Complexity(complex system broken downinto smaller and understandable pieces)

Modular Engineering(Dividing a large work into

smaller modules) Interoperable Technology(Provide common language

to describe networking functions and capabilities)

Accelerated Evolution Prevent s technology or capability changes in one

layer from affecting other layers above and below.



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Basic Principles of layered Approach A layer should be created where a different level of

abstraction is needed. Each layer should perform a well defined functions.

The function of each layer should be chosen with aeye towards defining internationally standardized

protocols. The layer boundaries should be chosen to minimize

the information flow across the interfaces.

The number of layers should be large enough that

distinct functions need not be thrown together in thesame layer out of necessity and small enough that thearchitecture does not become unwieldy.



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Interface and Services Between each pair of adjacent layers is an interface.

Interface defines which primitive operations and

service the lowest makes available to the upper one

Service is a set of functions offered by a layer to the

upper layer in the protocol hierarchy.



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Open Systems Interconnection (OSI)

Reference Model Developed by ISO(International Organization for

standardization.

Called ISO-OSI Reference Model because it deals

with connecting open systems-that is, systems thatare open for communication with other systems.

The OSI model is not a network architecture - it

does not specify the exact services and protocols. Itjust tells what each layer should do.


OSI Reference Model


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OSI Reference Model


Ph i l L


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Physical Layer

The Physical layer controls how data is placed on

the communication media. The role of the OSI Physical layer is to encode the

binary digits that represent Data Link layer frames

into signals and to transmit and receive these

signals across the physical media - copper wires,

optical fiber, and wireless - that connect network

devices.



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Physical Layer cont.Major Responsibilities:

Define physical characteristics of Interfaces between

the devices and transmission media and defines thetype of transmission medium.

Data Rate

Bit Signal Representation: Representing the bits bysignal( electrical, optical or electromagnetic)

Bit synchronization( By providing the clockingmechanism between sender and receiver)

Multiplexing

Devices: Hubs, Repeater

Protocols: RS-232, T1, E1


D t Li k L


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Data Link Layer Responsible for reliable and error-free transmission of

packets across a single link. It controls how data is placed onto the media and is received from the media

Framing: Determine the start and end of the packets Error detection :Determine which packets contain

transmission errors

Error correction: Retransmission schemes (Automatic Repeat

Request (ARQ) Flow control and Access Control

Physical Addressing

Packet Data Unit( PDU): Frame

Protocols: HDLC, PPP, Frame Relay

Devices: Bridges, Switches



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Data Link Layer ..SUBLAYERS:

Logical Link Control

Logical Link Control (LLC) places information in the frame thatidentifies which Network layer protocol is being used for theframe. LLC header tells what to do with a packet once a frameis received.This information allows multiple Layer 3 protocols,

such as IP to utilize the same network interface and media.

Media Access Control

Media Access Control (MAC) provides Data Link layeraddressing and delimiting of data according to the physicalsignaling requirements of the medium. It defines how dataare placed on media



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Network Layer The Network layer manages devices addressing, tracks

the location of device on the network and provides

services to exchange the individual piece of data overthe network. It provides internetworking i.e logicalglueing of heterogeneous physical networks together tolook like a single network to upper layers.

To accomplish end to end transport, Network layer usesfour basic process:

1. Addressing: Identification of each node or end deviceson a network with unique logical address i.e IP

address.2. Encapsulation: The Upper layer segment is

encapsulated with source and destination addrss toform a packet.


Network Layer


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Network Layer..3. Routing: Finding the best path between source and

destination using different routing algorithm.

4. Decapsulation: In the receiver side, packets are

stripped off the logical address to reveal data

segments and passed to upper level.

PDU: packet

Devices: Router

Protocols: IP, ICMP, Apple talk, RIP


T t l


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Transport layerThe basic function of transport layer is to accept the data

from the session layer, split it up to the smaller units if

need arises, pass these pieces to the network layer toensure that all pieces arrive correctly at the end.

Major Responsibilities:

Port addressing: Transport layer header includes a portaddress to allow multiples process on computers run atsame time and deliver the message from a specificprocess on one computer to specific process on other.

It tracks individual conversation Segmentation and Reassembly: Segments the data,

give sequence number so that it can be reassembled atreceiver side without error.


T t l


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Transport layer Connection Control: Connection oriented or

Connectionless transfer of data.

Error Control: The transport layer makes sure that

the entire message arrives at the receiving tx layer

without error.

PDU: Segments

Protocols: TCP, UDP



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Session Layer:Allow users on separate machine to define how data

conversations are established, controlled and terminated.

Major responsibilities:Dialog Control: Keeping track of whose turn is to transmit. It

coordinates between system and servers to organize theircommunication by offering 3 different modes: simplex, Half

duplex or Full duplexToken Management: to prevent two parties from attempting

the same critical operation at same time.

Synchronization: Checkpointing how long transmissions to allow

them to continue from where they were before they crash.Protocols: RPC(Remote Procedure Call), Net Bios

PDU: DATA


P t ti L


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Presentation LayerPresentation layer deals with the presentation of data and is

concerned with syntax and semantics of information

transmitted.Major tasks:

Translation: Networks can connect very different types ofsystems together which may have many distinctcharacteristics and represent data in different ways. Thepresentation layer handles the job of hiding these differencesbetween systems.

Encryption and Decryption

Compression

PDU: DataProtocols: JPEG, ASCII, MP4


A li ti L


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Application LayerOSI model explains application layer as being the user

interface. The OSI application layer is responsible for

displaying data and images to the user in a human-

recognizable format and to interface with the

presentation layer below it.

Application layer provides interface between theapplications we use to communicate and the underlying

network over which our message are transmitted.

PDU: Data

Protocols: HTTP, DNS, FTP


TCP/IP d l


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TCP/IP modelARPANET(Advanced Research Project Agency Network) was a

research network sponsored by DOD(Department of Defense,

US). It connected hundreds of universities and governmentsnetworks. When satellite and radio networks were addedlater, the existing protocols had trouble internetworking withthem, so a new architecture was needed.

So, to connect multiple networks in a seamless way was one

of the major designs goals of TCP/IP from the very beginning.Another goal was to survive the loss of subnet hardware of anetwork i.e DoD wanted connections remain intact as long assource and destination machines were functioning even ifsome of the intermediate devices or transmission lines were

kept out of operation. And a more real time architecture wasfelt necessary to transfer files and speech. TCP/IP wasdeveloped as an open standard. This speed up thedevelopment of TCP/IP as a standard .TCP/IP is named aftertwo of the popular protocolsTCP and IP.


TCP/IP model


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TCP/IP model..


TCP/IP M d l


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TCP/IP Model.. TCP/IP model describes the functionality of the protocols that makes the

TCP/IP protocol suite. Those protocols which are implemented in bothsending and receiving ends to provide end to end delivery.

Acomplete communication process includes these steps:1. Creation of data at the application layer of the originating source end device

2. Segmentation and encapsulation of data as it passes down the protocolstack in the source end device

3. Generation of the data onto the media at the network access layer of the

stack4. Transportation of the data through the internetwork, which consists ofmedia and any intermediary devices

5. Reception of the data at the network access layer of the destination enddevice

6. Decapsulation and reassembly of the data as it passes up the stack in thedestination device

7. Passing this data to the destination application at the Application layer ofthe destination end device


TCP/IP Protocol Family


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TCP/IP Protocol Family


Network Access


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Network AccessThe physical and Data link layer of OSI model is grouped to

form network access(interface) layer which involves

primitive bits that are transmitted on communicationchannels. It provides mechanical, electrical and functional

means and processes required for data transmission. It

provides a correct channel for transmitting data by

implementing error detection, error correction andsynchronization. It is also responsible for flow control. This

describes hardware requirements as pin configurations,

voltage levels and cable requirements.

Protocols: Ethernet, Frame Relay, RS-232, RJ-45


Internet Layer


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Internet Layer Similar to Network layer of OSI model

The internet layer encapsulate the data into IPdatagram to include source and destination

address. The network layer checks network

topology to determine the optimal route for

message transmission, and transfers data. The key

factor is to determine the best route for

transmitting data packets from the source end to

the destination end.

Protocols: IP, ICMP


Transport layer


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Transport layer

The basic function of the transport layer is toimplement end-to-end communication for the

application program between two hosts.

The transport layer receives data from theapplication layer, and then divides it into smaller

units if necessary. Before sending it to the networklayer, the system ensures that the data is sent tocorrect segments of the peer.

Protocols : TCP and UDP (User Datagram Protocol).

TCP reliable and connection oriented

UDP: does not perform end to end reliability check


Application layer


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Application layer Include application, presentation and session layer of OSI

model.

The application layer is responsible for processing details ofa specified application program. The application layer

displays received information, transmits user data to the

lower layer and provides network interfaces for application

software. It includes a number of protocols that provide specific

functionality to a variety of end user applications and

defines how host programs interface with transport layer

services to use network.

Protocols: HTTP, TELNET, FTP, DNS


Comparision of OSI vs TCP/IP model


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Comparision of OSI vs TCP/IP modelSimilarities:

Both are based on concept of stack of

independent protocols.

Both are layered approach. Functionality of the layers is roughly similar.

Both have comparable Network and Transport

layer.



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