PPT-1--Introduction and Ref model

Page 1

  • DATA: Information presented in whatever form is agreed upon by the communicating parties.
  • DATA COMMUNICATION: Exchange of data between two devices via some form of transmission medium.
  • EFFECTIVENESS OF DATA COMMUNICATION:
    • Delivery: Data must be delivered to the correct destination.
    • Accuracy: Data should not be altered in transmission and left uncorrected.
    • Timeliness: Data delivered late are useless.
    • Jitter: Variation in packet arrival time; uneven delay in the delivery of audio or video packets.

Page 2

  • COMPONENTS OF DATA COMMUNICATION SYSTEM:
    • MESSAGE: Information/data to be communicated.
    • SENDER: Device that sends the data message.
    • RECEIVER: Device that receives the message.
    • TRANSMISSION MEDIUM: Physical path by which message travels from sender to receiver.
    • PROTOCOL: Set of rules that governs data communication.
  • SENDER RECEIVER TRANSMISSION MEDIUM MESSAGE P R O T O C O L P R O T O C O L

Page 3

  • Data Representation:
    • TEXT: Text is represented as a bit pattern.
    • NUMBERS: Numbers are represented in bit pattern.
    • IMAGES: Images are represented in bit pattern.
    • AUDIO: Audio is continuous (not discrete).
    • VIDEO: May be a continuous or discrete entity.

Page 4

  • DATA FLOW:
    • Mainframe → Transmission Mode → Direction of data.
    • Half-duplex: Direction of data alternates.
    • Simplex: Direction of data all the time (e.g., Monitor → Workstation).
    • Full-duplex: Direction of data at time 1 and at time 2 (e.g., Workstation ↔ Workstation, e.g., Telephone Network).

Page 5

  • DATA FLOW DEFINITIONS:
    • SIMPLEX: Communication is unidirectional (e.g., keyboard and monitor).
    • HALF-DUPLEX: Each station can transmit and receive, but not at the same time (e.g., Walkie-Talkie).
    • FULL-DUPLEX: Each station can transmit and receive simultaneously (e.g., Telephone Network).

Page 6

  • NETWORKS and DISTRIBUTED PROCESSING:
    • A Network is a set of devices connected by links.
    • A node on the network may be any device capable of sending and/or receiving data.
    • Networks are usually distributed processing, where a task is divided among multiple computers.

Page 7

  • NETWORK CRITERIA (Most important criteria a network must meet):
    • PERFORMANCE: Measured in several ways:
    • Transit time: time for a message to travel from one device to another.
    • Response time: elapsed time between an inquiry and a response.
    • Throughput: quantity of data being sent/received per unit time.
    • Delay: time required to transfer data across the network.

Page 8

  • NETWORK CRITERIA (continued):
    • RELIABILITY:
    • Measured by the frequency of failure.
    • Time taken by a link to recover from failure.
    • Robustness of the network.
    • SECURITY:
    • Protection of data from unauthorized access.
    • Protecting data from damage and loss.
    • Procedures for recovery from breaches and data losses.

Page 9

  • PHYSICAL STRUCTURES: TYPES OF CONNECTION:
    • Point-to-Point: Provides a dedicated link between two devices.
    • Multipoint: More than two devices share a single link.

Page 10

  • Type of Connections Topology:
    • Physical or logical arrangement of links in a network.
    • Topology describes how computers or nodes are connected.
    • The topology is a geometric representation of the relationship of all links and linking devices.
    • 4 basic types: mesh, star, bus, ring.
    • Hybrid topologies are common.

Page 11

  • MESH TOPOLOGY:
    • Dedicated point-to-point links to every other device.
    • Dedicated means the link carries traffic between only the two devices it connects.
    • Number of duplex links:
    • n(n-1)/2
    • Each device has n-1 I/O ports.

Page 12

  • Mesh Topology Advantages:
    • Dedicated links – no traffic problems.
    • Robust.
    • Privacy/Security.
    • Easy fault identification and isolation.
  • Mesh Topology Disadvantages:
    • More cabling and I/O port requirements.
    • Installation and reconnection is difficult.
    • Expensive.
    • Every device must be connected to every other device; hardware for each link (I/O ports and cables) can be costly.

Page 13

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Page 14

  • STAR TOPOLOGY:
    • Dedicated point-to-point links to a central controller (hub).
    • Controller acts as exchange.
    • Hub in the center.

Page 15

  • Star Topology
    • Advantages: Less expensive; Robustness.
    • Disadvantages: More cab