Higher National Diploma1 Network Concepts OSI 7 Layer model.

Higher National Diploma 1

Network Concepts

OSI 7 Layer model

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Aims Discuss what is meant by a Standard

Look into the different aspects of OSI and

discuss what devices relate to the 7 layers

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OSI

What is a standard?

“A principle commonly agreed to by experts in the conduct and use of evaluation for the measure of the value or quality of an evaluation.”

ec.wmich.edu/glossary/prog-glossary.htf

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OSIWhat does OSI stand for?Open Systems Interconnection

What is OSI for?Describe network communication between network devices.

It is a standard that has been agreed by the ISO – international standards organisation.

Any two computers can communicate when connected regardless of underlying architecture

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OSI Cont.The OSI model is represented by seven layers.

The seventh layer being the top which is nearest the user.

One being the bottom for the communication medium (the data leaving the computer).

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Layer OSI Role Related to a Network

7 Application Email and web browsers – many protocols associated to it.

6 Presentation Organisation of data into a format that can be used by humansASCII - Plain text for web pagesDoc – Word documents

5 Session This allows you to have multiple browsers and resources open simultaneously without data conflicts in transmission.

4 Transport Firewalls, layer 4 switches operate at this level;

3 Network Logical address for a server or workstation is managed here – common protocol is TCP/IP.Routing takes place at this level

2 Data Link Physical address (Media access control (MAC)) Used to identify the device.Frame relay

1 Physical Cables/wireless encoding of bits of data 0001111010101, Hubs

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Application Layer 7The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application.

This layer interacts with software applications that implement a communicating component.

Examples?

Web browser, Email

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Presentation Layer 6Presents data to the user in understandable format

Provides conversion functions for application layer data.

Examples?Data representation – graphic formats

Character representation – text / ASCII

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Session Layer 5Manages connections between machines

Determines whether all data transmitted / receivedIt provides for full-duplex, half-duplex, or simplex operation.

Enables the use of multiple browser, chat and email to be opened simultaneously.

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Transport Layer 4The Transport Layer provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers.

Examples?FirewallsVOIP

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Network Layer 3Routing and addressing functions – correct destinations

Receives incoming packets of data

Routing – decides what route to use

Forwarding – sends on packets to other hosts

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Data Link Layer 2Organisation of data bits into frame structure

•The beginning and end of the data frame•The address of the sender•The address of the receiver•Error checking of the data frame

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Physical Layer 1Transmits / receives data bits as electrical pulses

Controls physical link between communicating systems

•Describes network topology•Transmission media – cabling / broadcasting•Transmission devices – NICs / modems•Electrical or optical (fibre optic) signalling

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Conclusion

Discussed what is meant by a Standard

Look into the different aspects of OSI and

discussed what devices relate to the 7 layers