Open Socket Communications testing

• Raw connections might be used for developers to connect a TCP/IP socket for testing (e.g., when developing a network application that listens on a TCP/IP port). 

https://www.ssh.com/ssh/putty/windows/

• Testing Open Socket Communications Using PuTTY

What are open sockets and why use them?

Within the context of Ethernet/LAN connections, sockets are like mailboxes. If you want to deliver information to a specific place, you need to be sure that your information is delivered to the correct address.
In the context of test instrumentation, an open socket is a fixed address (or port number) on the Ethernet/LAN bus that is dedicated to process remote commands.
Open sockets allow remote computers to simply use existing raw Ethernet connections for communications without having to add additional libraries (VISA or similar) that require additional storage space and processing overhead.
Programs that utilize sockets for LAN communication tend to take up less memory and operate more quickly.
https://siglentna.com/application-note/testing-open-socket-communications-using-putty/