1) In data transmission, the sequence of contiguous bits bracketed by and including beginning and ending flag sequences. (2) In a TDM system, a repetitive group of signals resulting from a signal sampling of all channels, including any additional signals for synchronizing and other required system information. frame bandwidth allocation The sum of the committed information rates associated with all the PVCs for a specific customer. Frame Relay A packet-switching technology that is simpler and more powerful than the X.25 standard. Frame Relay provides a multiplexed channel between a router and a T-1/E-1 nodal pro- cessor. It increases bandwidth utilization while reducing overall equipment costs. The Frame Relay standard addresses data communications speeds up to 45Mbps. framing A control procedure used with multiplexed digital channels, such as T-1 carriers, in which bits are inserted so that the receiver can identify the time slots allocated to such subchan- nels. Framing bits may also carry alarm signals indicating specific alarm conditions. frequency An expression of how frequently a periodic (repetitious) waveform or signal regenerates itself at a given amplitude. Frequency can be expressed in Hertz (Hz), kilohertz (KHz), megahertz (MHz), and so on. frequency-selective fading frequency-selective fading A type of fading based on multipath time delay spread in which the bandwidth of the signal is greater than the coherence bandwidth of the channel or the delay spread is greater than the symbol period. FSK (frequency-shift keying) A modulation method that uses two different frequencies to distinguish between a mark (digital 1) and a space (digital 0) when transmitting on an analog line. FSK is used in modems that operate at 1,200bps or slower. FSO (Free Space Optics) An optical wireless networking option that uses low-powered infrared lasers. There are two options in FSO: point-to-point products, used to provide high- speed connection between two buildings, and multiple high-speed connections through the air that