3.1.3+-+How+communication+over+networks+is+broken+down+into+layers

__** OSI Model **__
 * OSI : Open System Interconnection
 * What is it?
 * network protocol stack
 * set of rules for communication of data
 * protocols implemented
 * also defines network devices
 * conceptual framework to understand complex interactions
 * control passed from one layer to the next
 * networking framework
 * not a physical existing system
 * only a concept used to guide system programmers, so that the different operating systems can communicate per network
 * seven layers with specific operational functions
 * sending data: moving from the application layer to the physical level
 * receiving data: moving from the physical layer to the application level
 * The 7 layers:
 * 7) Application Layer
 * consists of network applications
 * 1) e.g. email, browser, web pages, file sharing services
 * applications need connectivity of network
 * identifies: communication partner, quality of service, constraints of syntax
 * considers: user authentication, privacy
 * 6) Presentation Layer
 * configures data
 * 1) encryption, compression, translation
 * 2) translates from application to network format (encrypted)
 * translates so application layer accepts format
 * no compatibility problems
 * 5) Session Layer
 * controls communications
 * 1) login rights, permissions, rights
 * 2) establishes, manages, ends connections between applications
 * e.g. Video streamed: combines audio & video
 * 4) Transport Layer
 * guarantees delivery of data
 * 1) end-to-end error recovery → complete transfer
 * transfer of data
 * 1) received from session layer → divided into “messages” (smaller data units)
 * passed to network layer
 * 3) Network Layer
 * finds shortest path to destination (shortest time)
 * 1) different routing protocols
 * switching/routing technology
 * logical paths → virtual circuits for transmitting from node to node
 * data received turned into packets and routes them
 * 2) Data Link Layer
 * bus arbitration → decides whose turn to communicate
 * locates physical devices on network
 * packets encoded → turned into bits
 * transmission protocol
 * handles errors of physical layer
 * 2 sub layers
 * 1) MAC → Media Access Control
 * controls how network gains access to data and transfer permission
 * 1) LLC → Logical Link Control
 * controls error checking
 * error free data transmission
 * 1) packets turned into frames and back → physical layer transmits
 * 1) Physical Layer
 * physical parts → cables, voltages, connectors, bits, transfer rate, etc.
 * 1) electrical/mechanical level
 * 2) hardware for sending/recieving data
 * conveys bit stream → transmission of raw bits
 * 1) encoding methods for bits so it can be transferred over hardware
 * 2) in frame form

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**__Flowchart Example:__**


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__**Link to the game:**__ @http://scratch.mit.edu/projects/42817016/

**__ For more information see our handout! __** =Summary:=
 * OSI model was established as a conceptual framework for constructing networks. It describes the connection between networks/devices.
 * **What is it?**
 * Concept — does not exist physically
 * A set of rules for communicating data.
 * Protocols are implemented.
 * Also describes devices.
 * 7 layers (read from bottom to top)
 * 7) Application Layer
 * 6) Presentation
 * 5) Session
 * 4) Transport
 * 3) Network
 * 2) Data Link
 * 1) Physical
 * each layer controls a specific aspect of the process — control is given from one layer to the next
 * ** The Layers in Detail: **
 * 7) Application
 * network applications (receive input)
 * 6) Presentation
 * configures data — encryption/decryption
 * 5) Session
 * controls communication — login rights, session timeout, permissions
 * 4) Transport
 * transfer of data — divides data into smaller packets “messages"
 * guarantees delivery
 * 3) Network
 * routing protocols — find shortest path in terms of time
 * switching/routing
 * creates packets
 * 2) Data Link
 * locates physical device (MAC - Media Access Control & LLC - Logical Link Control)
 * bus arbitration — who’s turn to talk?
 * encoding — turned into bits
 * transmission protocol — error free transmission
 * 1) Physical
 * physical components (hardware) — cables, routers, etc.
 * conveys bit stream — encodes bits so can be send over hardware

Created By: Lucie Magister Last update: 13/01/2015

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