Circuit Switching vs. Packet Switching: Understanding Network Concepts

Posted on Sep 5, 2024 in Computers

Circuit Switching

Circuit switching establishes a dedicated communication channel between two stations. Resources like bandwidth and switching network capacity are reserved exclusively for this connection. Once established, the transmission is transparent, as if the devices were directly connected. Circuit switching involves three phases:

  1. Circuit Establishment
  2. Data Transfer
  3. Circuit Disconnection

Key Points about Circuit Switching

  • Operates at the physical layer.
  • Requires prior resource reservation before communication.
  • Data transfer occurs as a continuous signal at the physical layer.
  • No need for data transfer addresses; end-to-end addresses are used during the establishment phase.

Packet Switching

Packet switching uses a “mesh” network infrastructure. Data is divided into packets, each independently routed from source to destination. No dedicated resources are allocated; packets utilize available bandwidth and processing power on a first-come, first-served basis.

Datagram Networks

Datagram networks utilize datagrams, self-contained data packets with complete addressing information. Each datagram has a header and data section. They are independent, potentially arriving out of order and with varying delays. Datagram switching occurs at the network layer. These networks are connectionless, lacking establishment and release phases. Data is sent without recipient confirmation.

Datagram Network Features

  • Routing Tables: Store destination addresses and corresponding output ports for packet forwarding. These tables are dynamic and regularly updated.
  • Destination Address: Switches use the packet’s destination address to consult routing tables and determine the appropriate output port.
  • Delay: While lacking establishment and release phases, packets may experience delays at switches. Delays can vary between packets within a message due to different routing paths.

Characteristics of Virtual Circuit Networks

Virtual circuit networks combine aspects of circuit-switched and datagram networks. Key features include:

  • Establishment, data transfer, and release phases like circuit-switched networks.
  • Resource allocation can be during establishment (like circuit switching) or on-demand (like datagram networks).
  • Data is divided into packets with headers, similar to datagram networks. However, headers have local significance, guiding the packet to the next switch.
  • All packets follow the same predetermined path, like circuit-switched networks.
  • Typically implemented at the data link layer, compared to the physical layer for circuit switching and the network layer for datagram networks.

Types of Routing in Virtual Circuit Networks

  • Global Addressing: Sources and destinations have globally unique addresses used to establish the virtual circuit.
  • Virtual Circuit Identifier (VCI): A local identifier assigned within each switch-to-switch link. Frames entering a switch with one VCI exit with a different VCI, ensuring localized routing.

Three Stages of Virtual Circuit Networks

Virtual circuit networks, like their circuit-switched counterparts, have three phases:

  1. Establishment: Source and destination use global addresses to establish the virtual circuit. Switches create routing table entries for the connection.
  2. Data Transfer: Data packets, each with a VCI, traverse the established path.
  3. Release: Source and destination inform switches to remove the corresponding routing table entries, tearing down the virtual circuit.