Data Communications, Data Networks, and Internet Notes

Data Communications, Data Networks, and Internet

Introduction to Communication

  • Communication involves the exchange of data between two or more entities.

Simplified Communication Model

  • Consists of a source system and a destination system.
  • Source: Generates the data to be transmitted.
  • Transmitter: Converts the data into transmittable signals.
  • Transmission System: Carries the data.
  • Receiver: Converts the received signal back into data.
  • Destination: Takes the incoming data.

Block Diagram

  • Source -> Transmitter -> Transmission System -> Receiver -> Destination.

Example

  • Workstation -> Modem -> Public Telephone Network -> Modem -> Server.

Communications Model Components

  • Source: Generates data.
  • Transmitter: Converts data into signals.
  • Transmission System: Carries signals.
  • Receiver: Converts signals back into data.
  • Destination: Takes incoming data.

Key Communication Tasks

  • Transmission System Utilization: Efficient use of transmission facilities.
    • Multiplexing, congestion control.
  • Interfacing: Devices must interface with the transmission system for signals to propagate.
  • Signal Generation:
    • Form: Signals must be capable of propagation.
    • Intensity: Signals must be interpretable as data.
  • Synchronization: Receiver must determine when a signal begins, ends, and its duration.
  • Exchange Management:
    • Establishment of a connection.
    • Management of bidirectional data exchange.
    • Deciding on simultaneous or alternating transmission.
    • Defining data amount and format.

More Key Communication Tasks

  • Error Detection and Correction: Handling errors due to signal distortion.
  • Flow Control: Preventing the source from overwhelming the destination.
  • Addressing and Routing:
    • Identifying the intended destination when multiple devices share a transmission facility.
    • Ensuring data is delivered only to the intended destination.
  • Recovery: Resuming activity after interruptions.
  • Message Formatting: Agreement on the form of data to be exchanged.
  • Security: Ensuring only intended receivers access data.
  • Network Management: System management, monitoring, failure response, troubleshooting, and future planning.
    • Configuration, monitoring system status, planning, alarm reporting, and troubleshooting.

Simplified Data Communications Model

  • Input Information -> Source -> Transmitter -> Transmission System -> Receiver -> Destination -> Output Information.
  • Digital bit stream converted to analog signal for transmission, then back to digital bit stream.

Networking Needs

  • Point to Point Communication: Basic data exchange between source and destination.
  • Handling Distance: Devices being too far apart.
  • Routing: Transmitting signal over multiple devices and mediums.
  • Increased User Devices: Managing more connections.
  • Efficient Transmission: Ensuring signal recovery without data loss or delays.
  • Communication Network: Interconnected nodes covering a specific area.

Wide Area Networks (WANs)

  • Span a large geographical area.
  • Consist of interconnected switching nodes (routers).
  • Intermediate nodes route data without concerning themselves with the content.
  • Data is routed from node to node to reach the destination using the best or shortest route.
  • Implementation Technologies:
    • Circuit Switching
    • Packet Switching

Circuit Switching Vs. Packet Switching

  • Circuit Switching:
    • Uses a dedicated communication path.
    • Connected sequence of physical links.
    • Logical channel dedicated on each link.
    • Data transmitted rapidly along the dedicated path.
    • Example: Telephone Network.
  • Packet Switching:
    • Does not require dedicated transmission capacity.
    • Data sent in small chunks called packets.
    • Packets passed from node to node.
    • Commonly used for terminal-to-terminal and computer-to-computer communications.

Frame Relay

  • Packet switching systems have large overheads to compensate for errors.
  • Modern systems are more reliable, and errors can be caught in end systems.
  • Most overhead for error control is stripped out.

Local Area Networks (LANs)

  • Cover a smaller area (building, small campus).
  • Connect a small network of interconnected devices for data exchange.
  • Usually owned by the same organization that owns the attached devices.
  • Internal data rates are typically much higher than WANs.
  • Implementation:
    • Switched LAN (Switched Ethernet LAN).
    • Wireless LAN (WLAN).

WAN vs LAN

  • Connecting two or more LANs in different locations requires a Wide Area Network (WAN).

The Internet

  • Key elements include routers, LANs, WANs, Ethernet switches, information servers, and workstations.

Internet Structure Example

  • Corporate LANs, residential subscribers, backbone ISPs, regional ISPs, and servers are interconnected.

Networking Configuration Example

  • Enterprise networks connect via ATM WANs and Ethernet LANs.
  • Residential Wi-Fi networks and public cellular networks connect through routers and switches.

Networking Icons

  • Router
  • Firewall
  • Ethernet Switch
  • ATM Switch
  • Wi-Fi Access Point