The Citrix ADC service monitor that a Citrix Administrator can use to test the three-way handshake between the Citrix ADC and the backend server is TCP. The three-way handshake, also known as SYN, SYN-ACK, and ACK, is a process used by TCP to establish a connection between a client and a server. Neither PING, UDP, nor LDAP involves the three-way handshake.