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Communication considerations

Communication considerations. AHHH!! What do those electrical signals mean? How can I send a bit, what signal do I use for 0 and which for 1? How do devices make use of the wire? How do I derive meaningful information from all of these bits

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Communication considerations

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  1. Communication considerations • AHHH!! What do those electrical signals mean? • How can I send a bit, what signal do I use for 0 and which for 1? • How do devices make use of the wire? • How do I derive meaningful information from all of these bits • How are transmission errors discovered and dealt with? • How do packets get from one system to another?

  2. Communication Considerations • How do I send large amounts of data and how do I ensure that I receive all of my data? • How do machines keep track of who there are talking to? • What language is this, how can I the computer understand different formats? • How does a user gain access to the network? • How do programmers write programs to use the network?

  3. Our solution the OSI model • Application • Presentation • Session • Transport • Network • Data link • Physical

  4. What is a Protocol? • Allows entities (i.e. application programs) from different systems to communicate • Shared conventions for communicating information are called protocols • Includes syntax, semantics, and timing

  5. Why Use Protocol Architecture? • Data communications requires complex procedures • Sender identifies data path/receiver • Systems negotiate preparedness • Applications negotiate preparedness • Translation of file formats • For all tasks to occur, high level of cooperation is required

  6. Modular Approach • Breaks complex tasks into subtasks • Each module handles specific subset of tasks • Communication occurs • between different modules on the same system • between similar modules on different systems

  7. OSI Lower Layers • Physical • Data Link • Network

  8. OSI Physical Layer • Concerned with transmission of unstructured bit stream over physical medium • Deals with accessing the physical medium • Mechanical characteristics • Electrical characteristics • Functional characteristics • Procedural characteristics

  9. OSI Data Link Layer • Responsible for error-free, reliable transmission of data • Flow control, error correction

  10. OSI Network Layer • Responsible for routing of messages through network • Concerned with type of switching used (circuit v. packet) • Handles routing between networks, as well as through packet-switching networks

  11. OSI Upper Layers • Transport • Session • Presentation • Application

  12. OSI Transport Layer • Isolates messages from lower and upper layers • Breaks down message size • Monitors quality of communications channel • Selects most efficient communication service necessary for a given transmission

  13. OSI Session Layer • Establishes logical connections between systems • Manages log-ons, password exchange, log-offs • Terminates connection at end of session

  14. OSI Presentation Layer • Provides format and code conversion services • Examples • File conversion from ASCII to EBDIC • Invoking character sequences to generate bold, italics, etc on a printer

  15. OSI Application Layer • Provides access to network for end-user • User’s capabilities are determined by what items are available on this layer

  16. Program issues command to Application Layer Application passes it to Presentation, which may reformat, passes to Session Session requests a connection, passes to Transport Transport breaks file into chunks, passes to Network Network selects the data’s route, passes to Data Link Data Link adds error-checking info, passes to Physical Physical transmits data, which includes information added by each layer OSI in Action: Outgoing File Transfer

  17. Physical receives bits, passes to Data Link Data Link checks for errors, passes to Network Network verifies routing, passes to Transport Transport reassembles data, passes to Session Session determines if transfer is complete, may end session, passes to Presentation Presentation may reformat, perform conversions, pass to Application layer Application presents results to user (e.g. updates FTP program display) OSI in Action: Incoming File Transfer

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