Chapter 8 Switching
Chapter 8 of Data Communications and Networking by Behrouz A. Forouzan is titled "Switching" and explores the methods of switching used in networks. Here are detailed notes on the chapter:
1. Introduction to Switching
Definition: Switching refers to the process of directing data to its intended destination in a network by passing it through various network devices known as switches.
Types of Networks:
Circuit-switched networks: Used for dedicated connections between two devices.
Packet-switched networks: Data is divided into packets and each packet is sent independently.
Message-switched networks: Entire messages are sent without being broken into packets (phased out in most applications).
2. Types of Switching
Circuit Switching:
A circuit-switched network establishes a dedicated path between source and destination before communication begins.
Phases of Communication:
Setup Phase: The path is reserved.
Data Transfer Phase: Data is transferred.
Teardown Phase: The path is released.
Examples: Used in traditional telephone networks.
Efficiency: Dedicated but inefficient as the reserved path is unused for long periods if the data flow is intermittent.
Packet Switching:
Data is broken into packets and each packet is routed independently to the destination.
Two Methods:
Datagram Approach: Each packet is treated independently, and packets may take different routes.
Virtual-Circuit Approach: A path is established for the first packet, and subsequent packets follow the same path.
Advantages: More efficient use of network resources as no path is reserved for long periods.
Examples: Used in the Internet.
Message Switching (Phased Out):
An older method where entire messages are routed, stored at each switch, and then forwarded.
Still used in some applications like email.
3. Switching Techniques
Space-Division Switching:
Uses a matrix of crosspoints to connect input and output lines.
Found in crossbar switches, which allow multiple simultaneous connections.
Time-Division Switching:
Uses time-slot interchange (TSI) to allocate time slots for each connection.
Efficient for handling multiple users over a shared line.
Combination Switches: Combine time-division and space-division techniques for enhanced efficiency.
4. Datagram Networks
Each packet contains a destination address and is forwarded independently.
Routers do not establish a dedicated path, which means packets may take different routes, possibly arriving out of order.
Advantages: Flexibility, no setup or teardown phase, efficient for the Internet.
Disadvantages: Packets may experience delays or loss, requiring reassembly.
5. Virtual-Circuit Networks
Characteristics: Combines features of both circuit switching and datagram switching.
A connection-oriented service is established for the first packet, with subsequent packets following the same path.
Advantages: Ensures that packets arrive in order.
6. Switch Components
Input and Output Ports: Responsible for receiving and forwarding data packets.
Routing Processor: Determines the best path for data packets based on routing tables.
Switching Fabric: The internal system that connects input ports to output ports.
7. Applications of Switching
Circuit Switching: Still used in traditional telephony.
Packet Switching: The backbone of Internet communication.
Virtual-Circuit Networks: Applied in some modern networks for specific tasks where order and reliability are essential.
8. Summary
Switching is essential for managing communication in large networks, ensuring that data reaches its intended destination efficiently. Circuit switching is less efficient but still relevant for traditional voice networks, while packet switching dominates data communication on the Internet due to its flexibility and efficiency .
These notes cover the essentials of switching techniques, their implementations, and their relevance to modern networks.
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