The Windows NT and Windows 2000 implementation of NetBIOS over TCP/IP is referred to as NetBT. NetBT uses the following TCP and UDP ports: UDP port 137 (name services) UDP port 138 (datagram services) TCP port 139 (session services) NetBIOS over TCP/IP is specified by RFC 1001 and RFC 1002. The NetBT.sys driver is a kernel-mode component that supports the Transport Driver Interface (TDI) interface. Services such as Workstation and Server use the TDI interface directly, but traditional NetBIOS applications have their calls mapped to TDI calls by the Netbios.sys driver. Using TDI to make calls to NetBT is a more difficult programming task, but can provide higher performance and freedom from historical NetBIOS limitations. NetBIOS concepts are discussed further in the "Network Application Interfaces" section of this document.