Solution

In a packet-switched network, data is transmitted using a connectionless service. The correct method for this is datagrams.

 

• Datagram: In a packet-switched network, especially in a connectionless service like the Internet, data is divided into smaller packets called datagrams. Each datagram is sent independently and can take different paths to reach the destination. The network does not establish a dedicated connection before transmitting the data, which is why it's called connectionless.

Why Other Options are Incorrect:

• (b) Segments: These are typically used in connection-oriented protocols like TCP, where data is segmented and reassembled at the destination.
• (c) Switches: These are devices used to route data within a network but do not themselves transmit data on a connectionless service.
• (d) Message: This is a general term for data but does not specify the method used for transmission in a connectionless service.