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Open System Interconnection

Open System Interconnection. ISO Model. ISO. Developed in 1984 by the standards organisation ISO, the OSI model is used by all network engineers to construct ICT hardware and software that needs to communicate with other equipment.

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Open System Interconnection

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  1. Open System Interconnection ISO Model

  2. ISO • Developed in 1984 by the standards organisation ISO, the OSI model is used by all network engineers to construct ICT hardware and software that needs to communicate with other equipment. • The OSI Reference Model describes a set of seven layers that define the different stages that data must go through to travel from one device to another over a network. • For VCE Software Development, the main emphasis is on level 1 physical, and how it relates to the TCP/IP protocol, Level 4, network layer • The OSI layers • 8 April 2010 The 7 layers of the OSI model are divided into 2 sets: the application set and the transport set. • To get from point A to point B on a network, data passes through each layer like a car being built on a factory production line.

  3. Analogy Beginning • The Manager (User, Level 1) – Calls PA • Personal Assistant (Level 2,3) • Write the letter, Gives to Mail Manager • Mail Manager and Work Experience Kid (Level 4,5,6) • Handles the Transport, Routing of Information, Prepare and Checks Letter for transport. • Delivery Boy and Receptionist (level 7) • Physical Transportation and Physical Receiving

  4. A Crude Analogy • Layer 7: Application - Mr A of A Corporation wants to send a message to Mr B of B corporation. He picks up the phone and calls for his personal assistant (his PA). • Layer 6: Presentation - The PA writes down the message in German (which Mr A speaks) into his notebook. • Layer 5: Session - The PA rips off the page with the message and sends it to the mail room with its destination address attached. • Layer 4: Transport - The mail room takes the page (along with many other messages from employees), checks that the address is present and sorts messages into departments. • Layer 3: Network - The mail room manager decides how best to send the message - does it needs to go airmail, by container ship, express post, bicycle courier? • Layer 2: Data - The mail room manager puts the message into a standard waterproof envelope with its destination and delivery rules written on it (e.g. does the message need to be signed for? Does it need to be delivered to the recipient in person? How urgent is it?). Tim, the bicycle courier is summoned, and told to deliver the envelope. • Layer 1: Physical - Tim jumps on his bike and pedals madly across town to Corporation B, steering and changing gear, jumping gutters and swerving to miss oncoming traffic. He arrives at the front door of Corporation B and hands over the envelope to the receptionist.

  5. A Crude Analogy - Backwards • Layer 1: Physical - The receptionist at Corporation B gives the envelope to corporation B's mail manager, who opens the envelope to see where it needs to go in their building. • Layer 2: Data - The mail manager sees that it needs to go to Mr B. He puts the message into a standard Corporation B inter-office memo envelope. • Layer 3: Network - Mr B's office number is written on the envelope, which is then given to the work experience kid. The kid is told where the office is, that he is to keep left in the corridors, and not interrupt Mr B if he is in a meeting. • Layer 4: Transport - The Mail Kid trots down the corridors, checking office numbers and making sure the envelope is not being damaged by his sweaty hands. • Layer 5: Session - The kid arrives at Mr B's office, checks the authenticity of the ID badge of Mr B's PA, gets the secretary to sign a receipt for the message, and hands the envelope over. • Layer 6: Presentation - The PA opens the envelope, takes out the page, translates it into French (which Mr B speaks) out and puts it in Mr B's in-tray. • Layer 7: Application - Mr B removes the translated message from his in-tray, reads it and thinks about its contents.  

  6. Things We Need to Know • Rough Overview of each of the layers • Note how each step of the process is logically separated from the others. • Each layer does not need to know how the other layers work: they just do their own jobs within their own limited walls. • TASK – Summarise in one or 2 lines for each layer your understanding of what it does in your own words.

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