It's a UDP service
UDP port 636 uses the Datagram Protocol, a communications protocol for the Internet network layer, transport layer, and session layer. This protocol when used over PORT 636 makes possible the transmission of a datagram message from one computer to an application running in another computer. Like TCP (Transmission Control Protocol), UDP is used with IP (the Internet Protocol) but unlike TCP on Port 636, UDP Port 636 is connectionless and does not guarantee reliable communication; it's up to the application that received the message on Port 636 to process any errors and verify correct delivery.
