Transcript OSI - Castle College - The IT Advanced Diploma

Network Concepts
OSI 7 Layer model
Higher National Diploma
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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
Btec National Diploma Level 3
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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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OSI
What 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
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Application
Email and web browsers – many protocols associated
to it.
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Presentation
Organisation of data into a format that can be used by
humans
ASCII - Plain text for web pages
Doc – Word documents
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Session
This allows you to have multiple browsers and
resources open simultaneously without data conflicts
in transmission.
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Transport
Firewalls, layer 4 switches operate at this level;
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Network
Logical address for a server or workstation is
managed here – common protocol is TCP/IP.
Routing takes place at this level
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Data Link
Physical address (Media access control (MAC)) Used
to identify the device.
Frame relay
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Physical
Cables/wireless encoding of bits of data
0001111010101, Hubs
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Application Layer 7
The 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 6
Presents 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 5
Manages connections between machines
Determines whether all data transmitted /
received
It 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 4
The Transport Layer provides transparent
transfer of data between end users,
providing reliable data transfer services to
the upper layers.
Examples?
Firewalls
VOIP
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Network Layer 3
Routing 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 2
Organisation 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 1
Transmits / 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
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