That WIKI aims to provide information describing how the SAP GUI connection/communication with the application server is done.
That WIKI discusses the steps used by the client software to initiate connection with the backend system.
SAP GUI connection to Backend
• SAP GUI uses the TCP/IP protocol to connect to the SAP system
• Connections are established from the front-end, and never from the SAP Server.
• SAP GUI will start making a TCP connection to the Message Server to determine the most suitable (responsive) application server. The connection to the message server is subject to a timeout defaulted to 10 seconds. That timeout value can be changed in the SAP Logon options -> General -> "Message server Timeout in seconds"
• SAP GUI then establishes a TCP connection to the dispatcher under the TCP port sapdp <nr> on the application server. The default value is sapdp00 and the corresponding TCP port number is 3200. If the timeout is exceeded, SAP GUI raises an error and terminates the connection.