Circuit Switching vs. Packet Switching: A Comprehensive Guide to Network Technologies

Posted on Apr 30, 2024 in Computers

Circuit Switching vs. Packet Switching: Understanding Network Technologies

Introduction

Wide area switched networks utilize two primary technologies: circuit switching and packet switching. These technologies differ in how nodes transfer information between links, ultimately reaching the destination from the source.

Circuit Switching Technology

Circuit switching, ideal for voice traffic applications, prioritizes minimal transmission delay and consistent delay. It excels in analog voice signal transmission but falls short in digital transmission efficiency. Once a circuit is established, it functions as a direct, transparent connection without requiring specialized logic.

Key Characteristics:

  • Dedicated path between stations
  • Potential inefficiency due to dedicated channel capacity
  • Connection setup time
  • Transparent transfer after connection
  • Three phases: Establish, Transfer, Disconnect

Circuit Switching Concepts

  • Digital Switch: Provides a transparent signal path for full-duplex transmission.
  • Network Interface: Connects digital devices with necessary functions and hardware.
  • Control Unit: Establishes, maintains, and terminates connections.

Network Types:

  • Blocking Network: Connection may fail if all paths are occupied. Suitable for voice systems with short call durations and low simultaneous usage.
  • Non-Blocking Network: Allows simultaneous connections for all stations, ideal for data connections with prolonged terminal usage.

Switching Techniques in Circuit Switching

  • Space Division Switching: Physically separate signal paths dedicated to signal transfer. Building block: metallic crosspoint or semiconductor gate.
  • Time Division Switching: Intelligent control of space and time division elements using TSI, TMS, and SoftSwitch technologies.

Packet Switching Technology

Designed for data transmission, packet switching divides data into small packets (around 1000 bytes) containing user data and control information for routing. Packets are received, buffered, and forwarded to the next node.

Advantages:

  • Efficient line utilization
  • Data rate conversion
  • Accepts packets even during network congestion
  • Prioritization capabilities

Packet Switching Techniques

  • Datagram: Each packet is treated independently without reference to previous packets.
  • Virtual Circuit: A pre-established route before packet transmission.

Virtual Circuit vs. Datagram

  • Virtual Circuits: Offer sequencing and error control, faster packet forwarding, but less reliability.
  • Datagram: No call setup phase, more flexible and reliable.

Comparison: Circuit Switching vs. Packet Switching

Three types of delay are considered:

  • Propagation Delay: Time for signal to travel between nodes (negligible).
  • Transmission Time: Time to transmit data block.
  • Node Delay: Processing time at nodes for switching data.

Circuit switching involves call setup, while packet switching (datagram) does not. Virtual circuit packet switching requires call setup but experiences node delays. For short messages, datagram is faster, while virtual circuit excels for longer messages.

Ethernet and CSMA/CD

Traditional Ethernet evolved from ALOHA protocols, leading to CSMA/CD (Carrier Sense Multiple Access with Collision Detection). CSMA/CD allows stations to transmit if the medium is idle, but collisions can occur. Various persistence algorithms, such as 1-persistent and p-persistent, address collision handling.

Binary Exponential Backoff

IEEE 802.3 and Ethernet employ binary exponential backoff to manage retransmission attempts after collisions. The backoff time doubles with each attempt, up to a limit, before reporting an error.

IEEE 802.3 MAC Frames

IEEE 802.3 defines three MAC frame types: basic, Q-tagged (for VLANs), and envelope (for higher-layer encapsulation). Each frame includes fields like preamble, SFD, source address, length/type, data, pad, and FCS.

Full Duplex and Mixed Configurations

Full-duplex Ethernet allows simultaneous transmission and reception, doubling theoretical transfer rates. Mixed configurations support both 10 Mbps and 100 Mbps LANs, integrating older and newer technologies.

Routing in Packet Switching Networks

Routing protocols enable routers to make informed decisions based on network topology and traffic conditions. Routing algorithms determine the path for each datagram based on available information.

Routing Strategies

  • Fixed Routing: Uses a single, permanent route for each source-destination pair, offering simplicity but lacking flexibility.
  • Flooding: Sends packets to all neighbors, ensuring robustness but generating high traffic.
  • Random Routing: Selects outgoing paths randomly or based on probability, reducing traffic compared to flooding.
  • Adaptive Routing: Adjusts routes based on changing network conditions, improving performance and congestion control.

Adaptive Routing Classifications

  • Local (Isolated): Routes to the outgoing link with the shortest queue.
  • Adjacent Nodes: Utilizes delay and outage information from neighboring nodes.
  • All Nodes: Similar to adjacent nodes but gathers information from all nodes on potential routes.

ARPANET Routing Strategies

ARPANET’s routing strategies evolved through generations, from distance vector routing to link-state routing and finally, link cost calculations based on average utilization.

Firewalls and Network Security

Firewalls act as barriers between untrusted networks (e.g., the Internet) and trusted networks (e.g., internal networks), preventing unauthorized access and data breaches.

Firewall Processing Modes

  • Packet Filtering: Examines packet header information to make filtering decisions.
  • Application Gateways (Proxy Servers): Operate at the application layer, providing additional security.
  • Circuit Gateways: Control circuit-level connections.
  • MAC Layer Firewalls: Filter based on MAC addresses.
  • Hybrid Firewalls: Combine elements of different firewall types.

Firewall Architectures

  • Packet-Filtering Routers: Basic filtering at the network perimeter.
  • Bastion Hosts: Dedicated systems exposed to external networks, acting as sacrificial hosts.
  • Screened Host Firewalls: Combine packet-filtering routers with proxy servers for enhanced security.
  • Screened Subnet Firewalls (with DMZ): Dominant architecture with multiple layers of protection and a DMZ for semi-trusted systems.

Configuring and Managing Firewalls

Best practices include allowing outbound traffic from trusted networks, restricting direct access to the firewall device, and implementing firewall rules based on packet header information.

Virtual Private Networks (VPNs)

VPNs create secure connections over public networks, extending internal networks to remote locations.

VPN Technologies

  • Trusted VPN: Relies on trust relationships between participating networks.
  • Secure VPN: Employs encryption and authentication for secure communication.
  • Hybrid VPN: Combines trusted and secure VPN elements.

VPN Modes

  • Transport Mode: Encrypts only the data portion of IP packets.
  • Tunnel Mode: Encrypts the entire IP packet, including the header.

VPNs provide secure remote access and data transmission over the Internet, enhancing privacy and security for organizations and individuals.