vmcj/debug_proxy/cfg/defaultPort is a SAP Parameter attribute which is used to control Line to define the default port for the Java Debug Proxy information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Line of the Java debug proxy configuration file to define the default
port.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.