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Networking
Version2 04/20/23 Slide 1
FormatLayered models of processesThe seven layers OSI ModelNetwork RequirementsNetwork Topology
Networking
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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.
Networking
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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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Networking
Network RequirementsHigh data rate ?
Bank transactionWeb browsing
Low delay ?live video/ audio linksroutine backup
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Networking
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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
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