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Recap of Layers Application, Data Link and Physical

Recap of Layers Application, Data Link and Physical. S305 – Network Infrastructure. Network Layers. Computer 1. Computer 2. 2. Application Layer. Applications (e.g., email, web, word processing). Application Layer. Transport Layer. Network Layer.

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Recap of Layers Application, Data Link and Physical

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  1. Recap of LayersApplication, Data Link and Physical S305 – Network Infrastructure

  2. Network Layers Computer 1 Computer 2 2

  3. Application Layer Applications (e.g., email, web, word processing) Application Layer Transport Layer Network Layer • The software that enables the user to perform useful work • Application architecture • The way in which the functions of the application layer software are spread among the clients and servers on the network • Functions of Application Layer 3

  4. Application Layer Characteristics * From Business Data Communications (Manish Agrawal) 4

  5. Application Architecture • Splitting the work across the client and the server • Basic Software Components: • Presentation Logic • Application Logic • Data Access Logic • Data • Types of Architectures: • Host (or Server) Based • Client Based • Client/Server Based 5

  6. How the web and email work: • Web: • HTTP Request sent from a client to a server • What is included in the request? • Server responds back with an HTTP Response • What is included in the response? • Email: • SMTP Packet sent from client to server • POP • IMAP 6

  7. Network Layers Computer 1 Computer 2 7

  8. Physical Layer - Overview Network Layer Data Link Layer Physical Layer • Includes network hardware and circuits • Types of Circuits • Physical circuits connect devices & include actual wires • Logical circuits refer to the transmission characteristics of the circuit • Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits.

  9. Circuit Configurations & Data Flow • Configuration: • Basic physical layout of the circuit • Configuration types: • Point-to-Point Configuration • Multipoint Configuration • Data Flow (Transmission): • Simplex • Half-Duplex • Full-Duplex • Multiplexing 9

  10. Media • Physical matter that carries the transmission • Signal transmitting properties of chosen media are important • Types: • Guided Media • Radiated (Unguided) Media 10

  11. Data Transmission • Data - Representation of facts in a formalized manner suitable for communication, interpretation, or processing by humans or by automatic means • Signal - Detectable transmitted energy that can be used to carry information • Bits in a message can be sent on: • a single wire one after another (Serial transmission) • multiple wires simultaneously (Parallel transmission) • Modes of transmission: • Serial Mode • Parallel Mode

  12. Transmission Types • Digital Transmission (Digital Data) – Voltage Encoding • Unipolar • Bipolar NRZ • Bipolar RZ • Analog Transmission (Digital Data) – Modulation • Amplitude Modulation (AM) • Frequency Modulation (FM) • Phase Modulation (PM) • Digital Transmission (Analog Data) • Requires a pair of special devices called Codec - Coder/decoder • A device that converts an analog voice signal into digital form • Converts it back to analog data at the receiving end • Used by the phone system 12

  13. Network Layers Computer 1 Computer 2 13

  14. Data Link Layer - Introduction Network Layer Data Link Layer Physical Layer • Responsible for moving messages from • one device to another • Controls the way messages are sent on media • Organizes physical layer bit streams into • coherent messages for the network layer • Major functions of a data link layer protocol • Media Access Control • Error Control • Message Delineation 14

  15. 4.1 Media Access Control (MAC) • Controlling when and what computer transmit • Important when more than one computer wants to send data at the same time over the same, shared circuit • Point-to-point half duplex links • Multipoint configurations • Two possible approaches • Controlled access • Contention based access 15

  16. Source of Error What causes it How to prevent it Line Outages Faulty equipment, Storms, Accidents (circuit fails) White Noise Movement of electrons (thermal energy) Increase signal strength (increase SNR) Impulse Noise Sudden increases in electricity (e.g., lightning, power surges) Shield or move the wires Cross-talk Multiplexer guard bands are too small or wires too close together Increase the guard bands, or move or shield the wires Echo Poor connections (causing signal to be reflected back to the source) Fix the connections, or tune equipment Attenuation Gradual decrease in signal over distance (weakening of a signal) Use repeaters or amplifiers Intermodulation Noise Signals from several circuits combine Move or shield the wires Jitter Analog signals change (small changes in amp., freq., and phase) Tune equipment Harmonic Distortion Amplifier changes phase (does not correctly amplify its input signal) Tune equipment Error Control - Sources of Errors and Prevention More important mostly on analog 16

  17. Major Functions of Error Control • Error prevention • Error detection • Parity checks • Check Sum • Cyclic Redundancy Check (CRC) • Error correction • Retransmission • Stop and Wait ARQ (A half duplex technique) • Continuous ARQ (A full duplex technique) • Forward Error Correction 17

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