CISCO Slides OSI Model

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International Organization for Standards (ISO)

• recognized the need to create a network model
  that would help network builders implement
  networks that could communicate and work
  together--OSI Model
• The OSI model is a layered communication process
  with each layer performing a specific task.

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The OSI Reference Model
The OSI model describes how information or data
moves from one computer through a network to
another computer.
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The OSI Reference Model
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Networking concepts . . .

• Networking is the interconnection of
  workstations, peripherals, and other devices.
• In networking, it is possible for different types
  of computer systems to communicate.
• In networking, what is important is that all
  devices speak the same language or use the same
  protocol (use same set of rules).

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Source, Destination, and Data Packets . . .

• Data is sent in bits, 1s and 0s.
• Data is not the information itself but an encoded
  form of information which is a series of
  electrical impulses into which information is
  transmitted for sending.
• Small, easily transmitted units into which
  computer data is broken for transmission across a
  network are called packets.

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Source, Destination, and Data Packets . . .

• Using the OSI model, data can be called packets,
  or frames or segments.
• Source address specifies the identity of the
  computer sending the packet.
• Destination address specifies the identity of the
  computer designated to receive the packet.

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Why Data Packets?

• Computers can take turns sending packets.
• If packet is lost, only small amount of data must
  be retransmitted.
• Data can take different paths.

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Different Media Types
AIR carries light, radio, microwave
Mediamaterial through which data packets travel
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The OSI Reference Model . . .

• uses a layered model because
• it breaks network communication into smaller,
  simpler parts that are easier to develop.
• it facilitates standardization of network
  components to allow multiple-vendor development
  and support.

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The OSI Reference Model

• allows different types of network hardware and
  software to communicate with each other.
• prevents changes in one layer from affecting the
  other layers so that they can develop more
  quickly.
• breaks network communication into smaller parts
  to make learning it easier to understand.

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KNOW THE CORRECT ORDER OF THE LAYERS!
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The OSI Reference Model
Each layer has a unique function.
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The OSI Reference Model
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The OSI Reference Model
The top 3 layers are known as the appli-cation
layers because they deal with the user interface,
data formatting, and the application access.
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The OSI Reference Model
Layers 1-4 are known as the data flow layers
because they control the physical delivery of
messages over the network.
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Keyword browsers
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The OSI Reference Model

• LAYER 7 THE APPLICATION LAYER
• closest to the user
• provides network services to user applications
• does not provide services to any other OSI layer
  but rather to application processes outside the
  scope of the OSI model

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The OSI Reference Model

• LAYER 7 THE APPLICATION LAYER
• identifies and establishes the availability of
  intended communication partners
• synchronizes cooperating applications
• establishes agreement on procedures for error
  recovery and control of data integrity

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Keywords common data format
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The OSI Reference Model

• LAYER 6 THE PRESENTATION LAYER
• ensures that information sent by the application
  layer of one system is readable by the
  application layer of another system
• translates between multiple data representation
  formats by using a common data representation
  format
• concerned with data structures and negotiation of
  data transfer syntax
• responsible for compression and encryption

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Keywords dialogues and conversations
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The OSI Reference Model

• LAYER 5 THE SESSION LAYER
• establishes, manages, and terminates sessions
  between communicating hosts
• synchronizes dialog between presentation layer
  entities and manages their data exchange
• offers provisions for efficient data transfer,
  class of service, and exception reporting of
  session, presentation, and application layer
  problems
• manages data exchange between presentation layer
  entities

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Keywords reliability flow control error
correction
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The OSI Reference Model

• LAYER 4 THE TRANSPORT LAYER
• segments and reassembles data into a data stream
• concerned with how reliable transport over an
  internetwork is accomplished
• responsible for reliable network communication
  between end nodes and provides mechanisms for the
  establishment, maintenance, and termination of
  virtual circuits, transport fault detection and
  recovery, and information flow control

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Keywords path selection routing addressing
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The OSI Reference Model

• LAYER 3 THE NETWORK LAYER
• provides connectivity and path selection between
  two end systems where routing occursthese may be
  located on geographically separated networks

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Keywords frames media access control
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The OSI Reference Model

• LAYER 2 THE DATA LINK LAYER
• provides reliable transit of data across a
  physical link
• is concerned with physical (as opposed to
  logical) addressing, network topology, network
  access, error notification, ordered delivery of
  frames, and flow control

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Keywords signals and media
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The OSI Reference Model

• LAYER 1 THE PHYSICAL LAYER
• defines the electrical and functional
  specifications for the link between end systems
  (including media)
• defines voltage levels, timing of voltage
  changes, physical data rates, maximum
  transmission distances, physical connectors, and
  other, similar, attributes

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How Data is Encapsulated

• Build the data.
• Package the data for end-to-end transport.
• Append (add) the network address to the header
  (includes control information).
• Append (add) the local address to the data link
  header.
• Convert to bits for transmission.

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The End