lecture 18 Telecommunication and Networks Notes

Introduction to Telecommunication and Networks

  • Instructor: Jiang Lu
  • Department: Computer Engineering, University of Houston Clear Lake

Circuit Switching Network

  • A dedicated communication path between two stations.
  • Types of Circuit Switching:
    • Space Division Switching
    • Allocates physical channels to each call.
    • Time Division Switching
    • Allocates time slots for each call over a shared medium.

WAN Technology and Protocols

  • Key topics of discussion:
    • Switched Communication Networks (9.1)
    • Circuit-Switching (9.2, 9.3)
    • Softswitch Architecture (9.4)
    • Packet-Switching (9.5)

Softswitch Architecture

  • Emerging trend in circuit-switching technology.
  • Definition and functions:
    • Converts devices into smart phone-switches through specialized software.
    • Facilitates traditional circuit-switching functions.
    • Enables conversion of digitized voice streams into packets (VoIP).
  • Components of Softswitch:
    • Media Gateway (MG): Handles physical switching functions.
    • Media Gateway Controller (MGC): Manages call processing.
    • Relevant Protocol: RFC 3015

Packet-Switching Principles

  • Shortcomings of Circuit-Switching:
    • Inefficiency in data connections, as connections may remain idle.
    • Fixed data rate limits versatility across different hosts and workstations.
  • Packet-Switching Definition:
    • Transmits long messages by subdividing them into shorter packets.

Packet Structure

  • Each packet consists of:
    • Data
    • Control Information (Packet Header)

Packet-Switching Architecture Example

  • Illustration of a packet-switching network with various nodes, including personal computers and servers connected through switches.

Advantages of Packet-Switching

  • Line Efficiency: Shares the line among multiple packets over time.
  • Variable Data Rates (Time Division Multiplexing): Allows different data transmission rates.
  • No Block Connection: Can experience delays, but no strict connections required.
  • Priority Handling: Allows higher-priority packets to transmit first.

Switching Techniques in Packet-Switching

  • Datagram:
    • Each packet is routed independently and can follow different paths.
  • Virtual Circuit:
    • Establishes a logical connection beforehand; packets follow a predetermined route.

Datagram vs. Virtual Circuit Comparison

  • Datagram:
    • Offers flexibility and faster transmission with no pre-setup phase.
    • Packets may arrive out of sequence but avoid congested routes.
  • Virtual Circuit:
    • Guarantees delivery in the original order with better error control.
    • Transit packets more rapidly through pre-established paths.

Issues in Packet-Switching Networks

  • Packet Size Issues: Each packet includes overhead which affects performance.
  • Delay Factors:
    • Node Delay: Time for processing at nodes.
    • Transmission Time: Time taken to send data blocks.
    • Propagation Delay: Time signal takes to travel across nodes.

Timing and Delays in Circuit vs. Packet Switching

  • Circuit Switching Delay:

    • Includes call setup time, message transmission time, and propagation delay.
    • Total Delay Formula:
      Total ext{ }Delay = 3ML + \frac{B}{W} + (M-1)P
    • Where M = number of hops, P = per-hop processing delay, L = link propagation delay, W = transmission speed (bits/s), and B = message size (bits).

  • Packet Switching Delay:

    • Virtual circuit requires connection setup.
    • Total Delay for Datagram networks:
      Total ext{ }Delay = ML + NT + (M-1)T + (M-1)P
    • Where N = number of packets.

Example Problem: Alice and Bob Transmission

  • Situation: Alice and Bob are 4 hops apart on a datagram packet-switched network.
  • Given data:
    • Link length: 100 miles,
    • Per-hop processing delay: 5µs,
    • Packet size: 1500 bytes,
    • Transmission speed: 56 kbit/s,
    • Speed of light: 125,000 miles/s.
  • Task: Calculate total time for Alice to receive a 10-packet message sent from Bob.