Networking

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FormatLayered models of processesThe seven layers OSI ModelNetwork RequirementsNetwork Topology

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ISO OSI Reference ModelInternational Standards Organisation

the standards bodyOpen Systems Interconnection seven layer

reference modeltasks of a communications system broken

down into manageable partsorganised into a hierarchical architecture.

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OSI model – Why bother?Real-world network protocols don’t implement

the OSI seven layer protocol stack modelBut nearly all network protocols are based on

a simplified layered modelThe layered model helps us think about the

many processes involved in communicating over networks

A good model provides support for thinking

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Communication Between Two Systems

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ISO OSI Reference Model

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ISO OSI Reference ModelEach layer takes data (a Protocol Data

Unit(PDU)) from the layer aboveEach layer processes and encapsulates the

data into a new PDUEach layer passes the new PDU to the lower

layer

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Data Transformation

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Encapsulation

Physical Layer

MAC Layer

Network Layer

(IP)

Transport Layer

(TCP)

----DATA----

----DATA----TCP - HEAD

----DATA----TCP - HEADIP - HEAD

----DATA----TCP - HEADIP - HEADMAC - HEAD

Data field

Data field

Data field

TCP PDU

IP Packet

MAC frame

CRC

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The Seven Layer Model

Please do not throw sausage pizza away!

All People Seem To Need Data Processing

At the top, the Application layer provides OS services for application software

At the bottom, the Physical layer deals with wiring issues

Application

Presentation

Session

Transport

Network

Data link

Physical

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TCP / IP Reference modelExisted before OSI modelUses

TCP - Transmission Control ProtocolIP Internet Protocol

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OSI Model TCP/IP

Transmission Control Protocol/Internet Protocol (TCP/IP)

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Network RequirementsHigh data rate ?

Bank transactionWeb browsing

Low delay ?live video/ audio linksroutine backup

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Network RequirementsLow (zero) error rate ?

video signalbank account details

Guaranteed Connectionsafety critical controlinternet phone

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Mesh Topology

Fully connected

3 lines : 2 ports per machine

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Mesh Topology

Fully connected

6 lines : 3 ports per machine

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Mesh Topology

Fully connected

10 lines : 4 ports per machine

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Mesh Topology

Fully connected systems use too much wiring.

Each computer may need an interface for each connection.

Not a practical system.

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Star Topology

STAR

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Ring Topology

RING

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Bus Topology

BUSBUS

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ConclusionWe have discussed:-Standard “root concepts” of networkingLayered models of processes and layers in our

conceptual model of networkingWhy protocols are required for interoperabilityBrief of the seven layers of the OSI model and

encapsulationBasics of Network RequirementsTypes of network topologies