gw/internal_timeout is a SAP Parameter attribute which is used to control Timeout for read/write calls 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 .
The parameter specifies the timeout value for NiRead and NiWrite calls
in milliseconds. If not all the data has been sent or received within
this time interval, the action concerned is interrupted and reinitiated
later on. Thus slow connections cannot block the gateway.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.