OSI Open Systems Integration Module

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CISCO Presents
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OSI (Open Systems Integration)Reference Module

• By
• Joe Reed
• 11/1998

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Todays Objectives
Understand the OSI Model
Know the names of the 7 layers of the OSI model
Know about encapsulation
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How do you describe networking?

• You use the OSI
  Reference Model
• Whats OSI?

Open System Interconnection
OSI presents an abstract reference model to
describe the computer communications.
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More OSI Info

• Who made up the OSI?
• It was created by the International Organization
  for Standardization (ISO)

ISO
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What is the OSI Reference Model?

• It is a conceptual framework specifying the
  network functions that occur at each layer
• It is a way of picturing how information travels
  through networks.

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OSI Reference Model (standard)

• Any application process should be able to
  communicate freely with any any application
  process in any other computer that supports the
  same standards
• The OSI Reference Model shows how this takes
  place.

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OSI Reference Model

• The OSI reference model describes how data makes
  its way from application programs through a
  network medium to another application located on
  another computer on a network

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Computer A
Computer B

• To accomplish this task data must travel from the
  application layer to the physical layer on one
  computer across the network media and from the
  physical layer to the application layer of
  another computer

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OSI Reference Model Layers

• The Application Layer provides services to
  application processes (such as electronic mail,
  file transfer, and terminal emulation) that are
  outside of the OSI model.

The application layer identifies and
establishes the availability of intended
communication partners (and the resources
required to connect with them),
synchronizes cooperating applications, and
establishes agreement on procedures for error
recovery and control of data integrity.
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OSI Reference Model

• The Presentation Layer ensures that information
  sent by the application layer will be readable by
  the application layer of the receiving system.
• The presentation layer is also concerned with the
  data structures used by programs and therefore
  negotiates data transfer syntax for the
  application layer.

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OSI Reference Model

• The Session Layer establishes, manages, and
  terminates sessions between applications and
  manages data exchange between presentation layer
  entities
• (Ensures Interhost communication)

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OSI Reference Model

• The Transport Layer is responsible for reliable
  network communication between end nodes.
• The transport layer provides mechanisms for the
  establishment, maintenance, and termination of
  virtual circuits, transport fault detection and
  recover, and information flow control.

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OSI Reference Model

• The Network Layer provides connectivity and path
  selection between two end systems.
• The network layer is the layer at which routing
  occurs.

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OSI Reference Model

• The Data Link Layer provides reliable transit of
  data across a physical link.
• The data link layer is concerned with
• physical addressing,
• network topology,
• line discipline,
• error notification,
• ordered delivery of frames,
• flow control.

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OSI Reference Model

• The physical layer defines the electrical,
  mechanical, procedural, and functional
  specifications for activating, maintaining, and
  deactivating the physical link between end
  systems

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OSI Reference Model
Provide accurate data delivery between computers
Control physical delivery of messages over a
network
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• As data moves down through the layers of the OSI
  model, headers are added.

Computer A
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• As data moves up through the layers of the OSI
  model, headers are removed.

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OSI Reference Model

• There are other models by different vendors
• Most vendors use the OSI Model
• OSI is conceptual other than tangible
• Used to educate how networks function at each
  layer

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What does the OSI Model do?

• It reduces complexity (from one big problem to 7
  small ones)
• It standardizes interfaces
• It facilitates modular engineering
• It assures interoperable technology
• Accelerates evolution
• Simplifies teaching learning

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Review Time!

• Divide into two groups
• Play Jeopardy
• Bonus answer is the layer number

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Jeopardy Review
15 pts

• This layer of the OSI model provides services to
  application processes and identifies and
  establishes the availability of intended
  communication partners, synchronizes cooperating
  applications and establishes agreement on
  procedures for error recovery and control of data
  integrity.

What is the APPLICATION LAYER of the OSI?
Layer 1 (add 3 pts)
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Jeopardy Review
10 pts

• This layer of the OSI model is responsible for
  reliable network communications between end
  nodes. It also provides mechanisms for the
  establishment, maintenance, and termination of
  virtual circuits and information flow control.

What is the TRANSPORT LAYER of the OSI?
Layer 4 (add 5 pts)
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Jeopardy Review
15 pts

• This layer of the OSI model establishes, manages,
  and terminates sessions between applications and
  manages data exchange between layer entities.

What is the SESSION LAYER of the OSI?
Layer 5 (add 3 pts)
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Jeopardy Review
10 pts

• This layer of the OSI model defines the
  electrical, mechanical, procedural, and
  functional specifications for activating,
  maintaining, and deactivating the physical link
  between systems.

What is the PHYSICAL LAYER of the OSI?
Layer 1 (add 5 pts)
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Jeopardy Review
15 pts

• This layer of the OSI model provides connectivity
  and path selection between two end systems. It is
  also the layer at which routing occurs.

What is the NETWORK LAYER of the OSI?
Layer 3 (add 3 pts)
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Jeopardy Review
10 pts

• This layer of the OSI model is concerned with
  physical addressing, network topology, line
  discipline, error notification, ordered delivery
  of frames, and flow control.

What is the DATA LINK layer of the OSI?
Layer 2 (add 5 pts)
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Jeopardy Review
15 pts

• This layer of the OSI model ensures that
  information sent by the application layer will be
  readable by the application layer of another
  system.

What is the PRESENTATION LAYER of the OSI?
Layer 6 (add 3 points)
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Jeopardy Review
15 pts

• Headers and trailers are added to data as it
  moves from a source to a destination.

What is ENCAPSULATION?
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THE END