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Network Model

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Divide and Conquer

A method of managing large system

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Network Model

A method of managing, describing and analyzing data communications networks, by breaking the entire set of communications functions into a series of layers, each of which can be defined separately.

This allows vendors to develop software and hardware to provide the functions separately.

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Networking Model

Open System Interconnection (OSI) Model, developed in 1984, by International Standards Organization (ISO).

Other models like TCP/IP, developed in 1982 have become more prominent in the design of networks and network technology.

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Simplified Network Model

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Simplified Network Model

Application layer (Layer 4)The application software used by the network

user, allows the user to define what message are sent over the network.

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Simplified Network Model

Network layer (Layer 3)Takes the message generated by the application

layer and performs three functions before passing them to the data link layer.

1. Translates the destination of the message into an address understood by the network.

2. If multiple routes possible, it decides which routes to take.

3. Collects message accounting information that can be used to identify how many messages each user has sent and to track errors.

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Simplified Network Model

Data link layer (Layer 2)Takes the message generated by the network layer

and performs three functions before passing the message on the physical layer.

1. It controls the physical layer by deciding when to transmit messages over the media.

2. It formats the message by indicating where messages start and end, and which part is the address. (It may break it into smaller packets).

3. It detects and corrects any errors that have occurred in the transmission of the message.

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Simplified Network Model

Physical layer (Layer 1)The physical connection between the sender

and receiver.

It transfers a series of electrical, radio, or light signals through the circuit from sender to receiver.

It specifies the type of connection, and the signals that pass through it.

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Network Models

For Communications to be successful, each layer in one computer must be able to communicate with its matching layer in the other computer.

This is accomplished by standards.

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OSI Network Model

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OSI Network Model

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OSI versus TCP/IP

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Research, Standard & Investment

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Network Standards

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The Importance of Standards

Standards are necessary in almost every business and public service entity.

The primary reason for standards is to ensure that hardware and software produced by different vendors can work together.

The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time.

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The Standards Making Process

Two types of standards:

• Formal standards are developed by an official industry or government body.

• Defacto standards emerge in the marketplace and supported by several vendors, but have no official standing.

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The Standards Making Process

Formal standardization process has three stages

1. Specification stage: developing a nomenclature and identifying the problems to be addressed.

2. Identification of choices stage: those working on the standard identify the various solutions and choose the optimum solution from among the alternatives.

3. Acceptance, the most difficult stage: defining the solution and getting recognized industry leaders to agree on a single, uniform solution

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Telecommunications Standards Organizations

International Organization for Standards (ISO)Member of the ITU, makes technical

recommendations about data communications interfaces.

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Telecommunications Standards Organizations

International Telecommunications Union - Telecommunication Standardization Sector (ITU-TSS)Technical standard setting organization of the UN

ITU. Formerly called the Consultative Committee on International Telegraph and Telephone (CCITT)

Comprised of representatives of over 150 Postal Telephone and Telegraphs (PTTs), like AT&T, RBOCs, or common carriers.

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Telecom Standards Organizations

• American National Standards Institute (ANSI)• Institute of Electrical and Electronics Engineers (IEEE)• Electronic Industries Association (EIA)• National Institute of Standards and Technology (NIST)• National Exchange Carriers Association (NECA)• Corporation for Open Systems (COS)• Electronic Data Interchange -(EDI) of Electronic Data

Interchange for Administration Commerce and Transport (EDIFACT).

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The Integration of Voice, Video and Data

The integration of voice and data is largely complete in wide area networks.

The integration of video into computer networks has been much slower, partly due to past legal restrictions, and partly due to the immense communications needs of video.

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A Comparison of the TCP/IP and OSI Protocol Architectures

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Message Routing

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Configuration for TCP/IP Example

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Protocol Data Units in the TCP/IP Architecture