Chabot College
ELEC 99.05
Ch 2 - OSI Model
CISCO NETWORKING ACADEMY
What is Networking?
Networking - the interconnection of
workstations, peripherals, terminals
and other devices.
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Network Protocols
In today’s networks, it is possible for
different types of computers to
communicate.
Macs, PCs, and mainframes can all
share devices, data, and information,
as long as they all speak the same
language, or protocol.
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Network Protocols
Protocol - a set of rules, or an agreement,
that determines the format and
transmission of data.
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The Internet Protocol
All devices on the Internet “speak” the
same protocol: the Internet Protocol, or
IP.
The Internet actually uses a group, or
suite, of protocols called TCP/IP which
includes HTTP.
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The Internet Protocol
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Networking Growing Pains
Emerging network technologies were
built using different kinds of hardware
and software.
Many of the new network technologies
were incompatible.
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Toward Standardization
To address the problem, the International
Organization for Standardization (ISO)
researched leading networks schemes:
• Digital’s DECnet
• IBM’s SNA
• DoD’s TCP/IP (non-proprietary)
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The ISO’s Standard
The ISO recognized there was a need
to create a network model that would
help vendors create networks that
would work compatibly and
interoperably with other networks.
In 1984, the ISO released their
networking model.
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ISO’s OSI Reference Model
A Layered Model:
A mnemonic:
All People Seem To Need Data Processing
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ISO’s OSI Reference Model
A Layered Model:
Another mnemonic:
A Present Session Transports Network Data Physically
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ISO’s OSI Reference Model
Open System Interconnection (OSI)
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Layer Functions
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7 - Application Layer
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6 - Presentation Layer
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5 - Session Layer
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4 - Transport Layer
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3 - Network Layer
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2 - Data Link
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Data Link Sublayers
LLC (Logical Link Control)
MAC (Media Access Control)
IEEE 802 Extension to the OSI Model
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1 - Physical Layer
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Media Layers
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Host Layers
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Devices at Layers
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Moving Data
End
System
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End
System
Peer-to-Peer Communication
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Data Encapsulation
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Data Encapsulation Example
End
System
Intermediate
Systems
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TCP/IP’s Model
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TCP/IP
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TCP/IP v OSI Model
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What you will study…
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