Final answer:
Port Address Translation (PAT) is the technique used by routers to track port numbers and direct incoming data packets to the correct computer on a home network.
Step-by-step explanation:
The technique a router uses to track a port number for when a data packet is returned to a home network to identify which computer to deliver the packet to is known as Port Address Translation (PAT).
PAT is a type of network address translation (NAT) that allows multiple devices on a local network to be mapped to a single public IP address but with a different port number for each session. This is how a router can manage the incoming traffic and direct it to the correct internal IP address. For example, if one computer is browsing a web page while another is streaming video, the router uses PAT to ensure that the responses from the internet are directed to the appropriate device on the network based on the source port number tracked in the PAT table.
Without PAT, every device on the network would need a unique public IP address to communicate with the internet, which is not feasible due to the limited number of available IPv4 addresses.