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Forward Information Base The information that is maintained by each ATN router and contains the set of forwarding paths reflecting the various policy and QOS rankings available to reach each known destination. Frame The basic unit of data transfer at link level. A frame can include from one to four Comm-A or Comm-B segments, or from two to sixteen Comm-C segments, or from one to sixteen Comm-D segments. Framing Pulses The pulses which frame the data pulses (code) of SSR Mode A and C replies (described as F1 and F2 respectively). Also known as bracket pulses. Free Route The preferred trajectory flown by an aircraft between an entry point and exit point without reference to an ATS route in free route airspace. Free Route Airspace Specific airspace of defined dimensions within which airspace users shall freely plan their routes between an entry point and an exit point without reference to the ATS network. Frequency Band The C-Band includes 3900 to 6200 MHz. A part of the band is used for aeronautical services; satellite feeder links and MLS. Frequency Division Multiple Access Frequency Division Multiple Access is a technique in which each user can transmit all of the time in a channels of the total available bandwidth. FDMA is efficient as long as each user requires the use of the network a large percentage of the time. If such is not the case, available bandwidth is being wasted since other users could have transmitted on these channels. Frequency Modulation A modulation technique where the frequency of the carrier signal is changed by the amplitude of the information signal. Fringe Envelope The Fringe envelope is the intersection of the vertical plane passing from the Radar Sensor and the actual coverage. It defines the limits within which the system satisfies the specified performance and availability requirements. Fruit Unwanted SSR replies received by an interrogator, which have been triggered by other SSR interrogators. Full Load (AMAN) The system state that is reached during run-time when the arrival traffic reaches the system designed maxima. Full Operational Capability For GIPS, this is defined as the capability that will occur when 24 operational (Block If/IIA) satellites are operating in their assigned orbits and have been tested for military functionality and met military requirements.