Packet switching is a method of data transmission where data is broken down into small units called packets. Each packet contains a header with addressing information (source and destination) and the data itself. These packets are then routed independently through the network, potentially taking different paths to reach the destination.

The key steps involved are:

• Segmentation: The sending device divides the data into packets.
• Packet Formation: Each packet is encapsulated with a header containing source and destination addresses, sequence numbers, and error detection codes.
• Routing: Packets are routed independently through the network based on their destination addresses. Routers examine the destination address in the packet header and forward the packet to the next hop.
• Reassembly: At the destination, the packets are reassembled in the correct order based on the sequence numbers in the headers.

Advantages of Packet Switching:

• Efficient Use of Bandwidth: Bandwidth is only used when packets are being transmitted.
• Robustness: If one path is congested or unavailable, packets can be rerouted.
• Flexibility: Supports various data types and variable data sizes.

Disadvantages of Packet Switching:

• Variable Delay: Packets may experience different delays due to varying network conditions.
• Overhead: The packet headers add overhead to the data transmission.
• Complexity: Requires more complex network infrastructure than circuit switching.

Comparison with Circuit Switching: Circuit switching establishes a dedicated, end-to-end connection before data transmission begins. Packet switching does not require a dedicated connection; packets are routed independently. Circuit switching guarantees bandwidth, while packet switching does not. Circuit switching has a fixed delay, while packet switching has variable delay. Packet switching is generally more efficient for bursty data traffic.

Call routing is the process by which a switching centre determines the optimal path for a call to reach its destination within a network of interconnected switching centres. The switching centre uses information contained in the dialed number (the destination number) to make this decision.

The routing process typically involves consulting a routing table. This table contains information about the network topology – the connections between switching centres and the associated costs (e.g., delay, congestion). The switching centre examines the destination number and uses the routing table to identify the sequence of switching centres that will lead to the destination.

Factors that might influence the routing decision include:

• Network Congestion: The switching centre may choose a path that avoids congested links.
• Link Capacity: The capacity of the links between switching centres will be considered.
• Delay: The switching centre may choose a path that minimizes the overall delay.
• Cost: In some networks, the cost of using certain links may be factored into the routing decision.
• Network Availability: The switching centre will avoid paths that are currently unavailable due to maintenance or failures.

Sophisticated routing algorithms are used to dynamically adapt to changes in the network topology and to ensure that calls are routed efficiently and reliably.

Circuit switching establishes a dedicated physical path between the sender and receiver for the duration of the communication. This dedicated path ensures a consistent bandwidth and predictable delay. However, resources are reserved even when no data is being transmitted, leading to potential inefficiency. Reliability is generally high as the dedicated path is maintained. A real-world example is traditional telephone networks.

Packet switching, on the other hand, breaks data into small packets, each containing addressing information. These packets are routed independently through the network, potentially taking different paths. This allows for more efficient use of network resources, as bandwidth is only used when packets are being transmitted. However, delay can be variable due to queuing and routing decisions. Reliability is achieved through retransmission mechanisms. The internet is a prime example of a packet-switched network.

Here's a table summarizing the key differences: