A free utility called WireShark can be downloaded at https://www.wireshark.org/ . It's a network protocol analyzer. Go to the Interface list and select a network connection, and then click Start. Transmission Control Protocol (TCP) traffic is in green; and User Datagram Protocol (UDP) traffic is in light blue.
TCP network protocols will request lost files when a connection is lost. UDP will not do this if there is an interruption. TCP messages are always sent in order, whereas UDP messages can arrive out of order. If TCP messages do arrive out of order, resend requests are sent, and the sequence needs to be put back in order. Black rows in WireShark signify when a TCP connection has a problem like this. In UDP individual packets are sent one by one. TCP has packets but they are sent in a stream with nothing to show where one begins and another ends. The World Wide Web; SMTP email; FTP are examples of TCP. Voice over IP (VoIP) and Domain Name System (DNS) are UDP.