The Transport Expresso Windows client software communicates with the Transport Expresso domain controller via SAP’s remote function call (RFC) protocol. RFC is a TCP/IP sockets-based protocol that uses TCP ports in the range 3300-3399.
The specific port number that is used will depend on the application server configuration of the SAP system that you select as the Transport Expresso domain controller. If we assume that the chosen SAP system has only one application server with system number 10, then the TCP port number 3310 will be used. In this manner, the RFC protocol works in the same manner as the SAPGUI, except that it utilises the port number range 3300-3399 instead of the port number range 3200-3299. It follows that the network configuration must allow the necessary port numbers to be used.