Dell OptiPlex 990 (Early 2011) - Manual (Page 20)

Legacy Redirection Mode controls how the redirection works. If set to disabled, the console needs to open the redirection
ports before each session. This is meant for Enterprise consoles and new SMB consoles that support opening the redirection
ports. The old SMB consoles (before Intel AMT 6.0) which do not support opening the redirection ports function need to
manually turn on the redirection port through this Intel MEBx option.
When selecting the mode, the following message appears.
Option Description
Disabled Legacy redirection Mode is disabled.(Default)