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C o n f i d e n t i a l Course : BCA Semester : IV Subject Code : BC 0048 Subject Name : Computer Networks Unit number : 2 Unit Title : Network software & Network Standardization HOME NEXT

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Page 1: Computer Networks  UNIT-2

C o n f i d e n t i a l

Course : BCA

Semester : IV

Subject Code : BC 0048

Subject Name : Computer Networks

Unit number : 2

Unit Title : Network software & Network

Standardization

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Page 2: Computer Networks  UNIT-2

C o n f i d e n t i a l

Unit-2 Network software & Network Standardization

Network software & Network Standardization

Objectives

After going through the presentation, you should be able to learn:

• Meaning of Network software

• What are Reference Models

• Architecture of ISO-OSI and TCP/IP reference model

• Different Network Standardization

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Page 3: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Lecture outline

• Introduction

•Networks Software

•Reference models

•Network standardization

•Summary

Introduction to Computer networks

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Page 4: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Introduction

• To reduce the design complexity, most networks are organized a series

of layers or levels.

• Each layer built one above the other.

•The number of layers, name of each layer, functions of each layer differs

from network to network.

•The purpose of each layer is to offer certain set of services to the higher

layers, shielding those layers from the details of how the offered services

are actually implemented.

• In this unit we will study two models, the different layers and the tasks

performed by these layers of the model. We compare these two standard

reference models and also discuss their critics. Finally we well see the

network standardization.

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Page 5: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Networks Software

What is Protocol ?

A protocol is an agreement between the communicating parties on how

communication is to proceed.

To reduce their design complexity, most networks are organized as a

stack of layers or levels, each one built upon the one below it. The

number of layers, the name of each layer, the contents of each layer, and

the function of each layer differ from network to network.

The purpose of each layer is to offer certain services to the higher layers.

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Page 6: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Networks Software

A five-layer network is illustrated in figure.

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Page 7: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Networks Software

• The entities comprising the corresponding layers on different machines

are called peers.

• This lowest layer is usually referred as physical layer, which interfaces

directly with the physical medium.

• Between each pair of adjacent layers there is an interface.

• The interface defines which primitive operations and services the lower

layer offers to the upper one.

•The set of layers and protocols is called Network architecture. A list of

protocols used by a system is called a protocol stack.

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Page 8: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Networks Software

Merits and de-merits of Layered Architecture :

Advantages of Layered Architecture :

•Any given layer can be modified or upgraded without affecting the other layers.

•Modulazition by means of layering simplifies the overall design.

•Different layers can be assigned to different standards, committees, and design teams.

•Mechanisms like packet-switching, circuit-switching may be used without effecting more than one layer.

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Unit-2 Network software & Network Standardization

Networks Software

Advantages of Layered Architecture (CONTINUED..)

• Different machines may be plugged in at different layers.

• The relation between different control functions can be better

understood.

• Common lower levels may be shared by different higher levels.

• Functions (especially at lower levels) may be removed from software

to hardware and micro-codes.

• Increases the compatibility of different machines.

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Unit-2 Network software & Network Standardization

Networks Software

Disadvantages of Layered Architecture

•Total overhead is higher.

•Two communicating machines may have to use certain functions which

they could do without layers.

•As technology changes, the functions may not be in the most cost-

effective layer.

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Page 11: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Reference models

There are two important network architectures.

They are ISO-OSI reference model and TCP/IP reference model.

1. The OSI Reference Model :

This reference model is proposed by International standard organization

(ISO) as a a first step towards standardization of the protocols used in

various layers in 1983 by Day and Zimmermann.

This model is called Open system Interconnection (OSI) reference model.

It is referred OSI as it deals with connection open systems.

The OSI- ISO reference model consists of seven layers.

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Page 12: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Reference models

1.Physical Layer :This layer is the bottom most layer that is concerned with transmitting raw bits over the communication channel (physical medium).2. Data Link Layer :The Data Link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical layer. 3. Network Layer :The Network layer performs network routing functions, and might also perform fragmentation and reassembly, and report delivery errors. 4. Transport Layer :•The major tasks of Transport layer are listed below:•It locates the other party•It creates a transport pipe between both end-users.•It breaks the message into packets and reassembles them at the destination.•It applies flow control to the packet stream.

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Unit-2 Network software & Network Standardization

Reference models

5. Session Layer :

The major tasks of session layer are listed

• It is responsible for the relation between two end-users.

• It maintains the integrity and controls the data exchanged between

the end-users.

• The end-users are aware of each other when the relation is

established (synchronization).

• It uses naming and addressing to identify a particular user.

• It makes sure that the lower layer guarantees delivering the message

(flow control).

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Page 14: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Reference models

6. Presentation Layer:

The major tasks of presentation layer are :

• It translates the language used by the application layer.

• It makes the users as independent as possible, and then they can

concentrate on conversation.

7. Application Layer (end users) :

The application layer is the seventh level of the seven-layer OSI model.

It interfaces directly to the users and performs common application

services for the application processes.

It also issues requests to the presentation layer.

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Page 15: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Reference models

• The TCP/IP Reference Model :

The TCP/IP reference model is the network model used in the current

Internet architecture.

It was created in the 1970s by DARPA for use in developing the Internet's

protocols, and the structure of the Internet is still closely reflected by

the TCP/IP model.

It has fewer, less rigidly defined layers than the commonly referenced OSI

model, and thus provides an easier fit for real world protocols.

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Unit-2 Network software & Network Standardization

Reference models

The original four-layer version of the model has layers as shown in figure.

It consists of the following four layers

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Unit-2 Network software & Network Standardization

Reference models

Layer 4 – Process Layer or Application Layer:

This is where the "higher level" protocols such as FTP, HTTP, etc. operate.

The original TCP/IP specification described a number of different

applications that fit into the top layer of the protocol stack.

These applications include Telnet, FTP, SMTP and DNS.

Layer 3 – Host-To-Host (Transport) Layer :

This is where flow-control and connection protocols exist, such as TCP.

This layer deals with opening and maintaining connections, ensuring that

packets are in fact received.

The transport layer is the interface between the application layer and the

complex hardware of the network.

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Unit-2 Network software & Network Standardization

Reference models

Layer 2 – Internet or Internetworking Layer :

This layer defines IP addresses, with many routing schemes for navigating

packets from one IP address to another.

The job of the network layer is to inject packets into any network and

have them travel independently to the destination.

Layer 1 – Network Access Layer :

This layer describes the physical equipment necessary for

communications, such as twisted pair cables, the signalling used on that

equipment, and the low-level protocols using that signalling.

The Host-to-Network layer interfaces the TCP/IP protocol stack to the

physical network.

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Page 19: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Network standardization

Network standardization is a definition that has been approved by a

recognized standards organization.

Two categories of standards:

1.De facto (Latin for “from the fact'') standards:

These are those that have just happened without any formal plan. These

are formats that have become standard simply because a large number of

companies have agreed to use them.

PostScript is a good example of a de facto standard.

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Unit-2 Network software & Network Standardization

Network standardization

2. De jure (Latin for “by law'') standards:

These are formal legal standards adopted by some authorized

standardization body.

Two classes of standard organizations

• Organizations established by treaty among national governments.

• Voluntary, nontreaty organizations.

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Page 21: Computer Networks  UNIT-2

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Unit-2 Network software & Network Standardization

Summary

This presentation of unit 2 covered the following topics:

• Importance of Network Software

• Advantages and Disadvantages of Layered Architecture

• Architecture of OSI-ISO reference model

• Architecture of TCP/IP reference Model

• Different Network standards

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