OSI Reference Model

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OSI Reference Model Layered Communication

• S. Sukaridhoto, ST

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OSI Layer

• Open Systems Interconnection for Communications
• There are 7 Layers
• Layers 7,6,5 are oriented more toward services to
  the applications
• Layer 4,3,2,1 are oriented more toward the flows
  data from end-to-end through network

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7 Layer OSI
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How to Remember (CISCO)

• Please ? Physical
• Do ? Data Link
• Not ? Network
• Throw ? Transport
• Sousces ? Session
• Pizza ? Presentation
• Away ? Application

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Application

• Layer 7

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Function Description

• An application that communicates with other
  computers is implementing OSI application layer
  concepts. Application layer refer to
  communications service to application.

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Example

• Telnet
• HTTP
• FTP
• WWW Browser
• NFS
• SMTP Gateway
• SNMP

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Presentation

• Layer 6

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Function Description

• This layer main purpose is defining data format
  such as ASCII text, EBCDIC text, binary, BCD,
  JPEG.
• Encryption is also defined by OSI as presentation
  layer service.

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Example

• JPEG
• ASCII
• TIFF
• GIF
• PICT
• MPEG
• MIDI
• Encryption

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Session

• Layer 5

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Function Description

• This session layer defines how to start, control,
  and end conversation (called session).
• This includes the control and management of multi
  bidirectional messages so that application can be
  notified if only some of a series of messages are
  completed.

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Example

• RPC
• SQL
• NFS
• Netbios Names
• AppleTalk
• ASP
• SCP
• DECnet

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Transport

• Layer 4

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Function Description

• Layer 4 includes the choice of protocols that
  either do or do not provide error recovery.
  Multiplexing of incoming data for different flows
  to applications on the same host.

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Example

• TCP
• UDP
• SPX

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Network

• Layer 3

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Function Description

• This layer defines end-to-end delivery packets.
  To accomplish this, the network layer defines
  logical addressing so that any endpoint can be
  identified. It also defines how routing works and
  how routes are learned so that the packets can be
  delivered
• Network layer also defines how to fragment a
  packet into smaller packets to accommodate media
  with smaller maximum transmission unit size

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Example

• IP
• IPX
• AppleTalk DDP

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Data Link

• Layer 2

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Function Description

• The data link specifications are concerned with
  getting data across one particular link or
  medium. The data link protocols define delivery
  across an individual link. These protocols are
  necessary concerned with the type of media in
  question.

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Example

• IEEE 802.3/802.2
• HDLC
• Frame Relay
• PPP
• FDDI
• ATM

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Physical

• Layer 1

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Function Description

• Deal with the physical characteristics of the
  transmission medium, Connection pins, use of
  pins, electrical currents, encoding and light
  modulation.

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Example

• Ethernet
• RJ-45
• V.35
• FDDI
• EIA/TIA-232

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• Some protocol define details of multiple layers.
• Example NFS

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Summary

• Application (Layer 7) ? User Interface ? Telnet,
  HTTP
• Application (Layer 6) ? How data is presented ?
  JPEG, ASCII
• Session (Layer 5) ? Keeping data separate from
  different application ? OS, application access
  scheduling
• Transport (Layer 4) ? Reliable or unreliable
  delivery, Multiplexing ? TCP, UDP, SPX
• Network (Layer 3) ? Logical addressing, Routing ?
  IP, IPX
• Data Link (Layer 2) ? MAC, error detection ?
  802.3/802.2, HDLC
• Physical (Layer 1) ? Devices ? Ethernet, V.35