In certain cases, applications may make advantage of services provided by both of these transport-layer protocols (UDP or TCP). Because of this, how can a computer determine whichever tier of the transport stack is responsible for sending a packet?

Two transport-layer protocols offer services that certain applications may make use of (UDP or TCP). So, when a packet arrives at its destination, how can a computer tell which transport layer is involved?

A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. Data sent through the internet, such as a web page or email, is in the form of data packets. A packet is typically forwarded from one router to another router through the networks that constitute an internetwork (e.g. the Internet) until it reaches its destination node.How does a router distribute bandwidth in networks.

Some applications may utilise the capabilities of both UDP and TCP transport-layer protocols. How does the computer know which transport layer to employ when a payload ultimately reaches its destination?