The TCP/IP network stack defines two completely different protocols at the transport layer - TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Being defined above the network layer and corresponding IP protocols (IPv4 and IPv6), both transport layer protocols include additional identification (addressing) of network processes, by introducing a transport layer port. All the other features are TCP or UDP specific - while TCP provides reliable communication, flow and congestion control mechanisms, establishing a virtual connection between source and destination, UDP offers simple (and unreliable) exchange of user datagrams. Theoretically, TCP and UDP have almost nothing in common. But, standard communication between clients and servers may look functionally the same for end-users not familiar with networking theory details. That is why we find it quite important to give a proper, lab example based explanation of protocol differences when teaching networking to STEM students. This paper gives a short introduction to the transport layer protocols and standard client-server architecture. It includes a description of our standard networking lab - using the well-known, but quite simple tool called netcat (nc) both TCP and UDP client-server communication are implemented on the virtual testbed network. Generated and exchanged traffic is analyzed using Wireshark, and a few specific events and protocol behaviors are noted and explained. TCP connection establishment and termination is discused and visualized, too. The goal of the paper is to provide an explanatory example that can help STEM students understand both the usage and differences of standard transport layer protocols. The educational relevance of the paper is summarised as follows. STEM students, especially engineers, should be familiar with basic details of networking: TCP and UDP differences and specifics, with emphasis to TCP as most used transport protocol. The paper shows that it can be identified and analysed using virtual testbed based labs (controlled, but completely realistic environment), which should be considered a benefit for engineering oriented students.