Final answer:
The protocol header information used at the transport layer to identify a target application is the port number. TCP and UDP use port numbers to determine which application or service the data should be delivered to.
Step-by-step explanation:
The protocol header information used at the transport layer to identify a target application is the port number. Port numbers are used to determine which application or service the data should be delivered to.
For example, the Transmission Control Protocol (TCP) uses a 16-bit integer value as the port number, allowing for a range of 0 to 65535. Common port numbers include 80 for HTTP, 443 for HTTPS, and 22 for SSH.
Similarly, the User Datagram Protocol (UDP) also uses port numbers to identify applications or services. UDP port numbers range from 0 to 65535 as well.