Link-11 employs netted communications techniques and a standard message format for exchanging digital information among airborne, land-based and shipboard tactical data systems. Link-11 data communications must be capable of operation in either the high frequency (HF) or ultrahigh frequency (UHF) bands. When operating in the HF band, Link-11 provides gapless omnidirectional coverage of up to 300 nautical miles (NM) from the transmitting site. When operating in the UHF band, the link provides omnidirectional gapless coverage to approximately 25 NM ship-to-ship, or 150 NM ship-to-air. The messages used to exchange information over Link-11 are known as the M-series messages. Link-11B employs a dedicated, point-to-point, full duplex digital data link using serial transmission frame characteristics and standard message format for exchanging digital information. Link-11B data is exchanged over a fully automatic, phase-continuous, full duplex, frequency modulated data link operating at a rate of 1200 bps with an alternate capability of 600 bps. Link-11B data communications must be capable of operation in either the UHF or VHF bands.