Link 11

Link 11 (TADIL-A) is a secure half-duplex TADIL radio link used by NATO that receives or transmits--but not both simultaneously--a sequential data exchange digital link. It exchanges digital information among airborne, land-based, and ship-board tactical data systems. It is the primary means to exchange data such as radar tracking information beyond line of sight. TADIL-A can be used on either high frequency (HF) or ultrahigh frequency (UHF). However, the U.S. Army uses only HF. Link 11 relies on a single platform to report positional information on sensor detections. This positional information can be amplified with additional data to qualify the identity of the detected track.

Link 11 will be replaced by Link 22.

Link 11 is defined by the United States Department of Defense as MIL-STD-6011.
http://en.wikipedia.org/wiki/MIL-STD-6011