How does the client knows which transport protocol to use?

Let's assume that I start a server at one of the computers in my private network (192.168.10.10:9900).

Now when making a request from some other computer in the same network, how does the client computer (OS?) knows which protocol to use / which protocol the server follows ? [TCP or UDP]

EDIT: As mentioned in the answers, I was basically looking for a default protocol which will be used by the client in the absence of any transport protocol information.

Solution

TCP / UDP protocols work at the transport layer level (TCP / IP MODEL) and its main difference is that TCP has a method to ensure the arrival of messages while UDP is lighter because of its virtue is to be faster in Information delivery. The use of one protocol or another is always defined by the application that will use it.

So the reference you put on the private server with ip: port 192.168.10.10:9900 is very vague to be more precise we could say that we have an Apache web server running on the ip: port 192.168.10.10:9900 (the port for default is 80 when installing the server, but it can be changed in the configuration).

Now the web servers (apache, IIS, etc.) work using the TCP protocol because when a client (computer, cell phone, etc.) consults a page through a browser (Chrome, Firefox, etc.), the ideal thing is that all the website and not just some pieces. This is why this type of servers chose and use this protocol in the first instance since they seek that in the end the result is that the user obtains the complete page regardless of whether a few more milliseconds are sacrificed in the validations involved in using TPC.

Now going to the client side. The user when visiting a web page from any browser (Chrome, Firefox, etc.) will use TCP since this protocol is already configured in the browser to send the query messages and subsequently receive the messages with the same form Website information.

Now this behavior is going to be repeated for any client / server application. For example, to change the type of application on the UDP side, we can observe the operation of DHCP services which are used to receive an IP when connecting any device to a Wi-Fi network. In this case, this service seeks to be as fast as possible (instead of the most reliable) since you want the device to connect as quickly as possible to the network, so use the UDP protocol and in this case any equipment when connecting To a WIFI network you will send your messages using this protocol.

Finally, if you want to know promptly about the type of TCP / UDP protocol used by a specific application, you can search on the Wireshark application which allows you to scan the messages that leave the device or show the protocol used in the different layers of the application.