rdisp/sna_gw_service is a SAP Parameter attribute which is used to control SNA Gateway service 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 .
Name of the service where the SNA Gateway can be reached. The service
must be defined in the services database.
UNIX
Must be entered in the /etc/services file
NT
Must be entered in the file C:\WINNT\SYSTEM32\DRIVERS\ETC\SERVICES
See SAP Parameter Documentation for full SAP documentation for this profile parameter.