When a RAS clients NetBIOS application issues multiple NCB.CALL commands simultaneously, you can improve performance by allowing more than the defaut 3 connections.
Use Regedt32 to navigate to:
Double-click the NumRecvQueryIndications value name in the right hand pane and enter the number of connections using the Decimal Radix. The range for this REG_DWORD entry is 1 - 32.
You will need to shutdown and restart your computer for the setting to take effect.