. flat rate A fixed cost for service. Additional charges may be applied for additional services or usage if so specified. Glossary flow control flow control A system that uses buffering and other mechanisms, such as controls that turn a device on and off, to prevent data loss during transmission. FM (frequency modulation) One of three ways to modify a sine wave signal to carry dig- ital bits. The sine wave, or carrier, has its frequency modified in accordance with the informa- tion to be transmitted. The frequency function of the modulated wave may be continuous or discontinuous. (fixed-mobile convergence) The vision of being able to use one phone with one number, address book, and voicemail bank while enjoying the benefits of low-cost, high-speed connectivity in the office or fixed-line residential environment, while still enjoying the freedom of mobility in the WAN. FMC features seamless handoff between fixed and mobile networks. FOMA (Freedom of Mobile Multimedia Access) The proprietary 3G standard Japanese mobile phone operator NTT DoCoMo. forward channel The communications path that carries voice or data from the call initiator to the network. four-wire circuit A circuit that contains two pairs of wire (or their logical equivalent) for simultaneous (i.e., full-duplex) two-way transmission. Two pairs of conductors, one for the inbound channel and one for the outbound channel, are connected to the station equipment. FQ (Fair Queuing) A queuing mechanism whose objectives are to provide fair access to band- width, resources, and routers and to ensure that no one flow receives more than its fair share. FQDN (fully qualified domain name) An unambiguous domain name that specifies a node's position in the DNS tree hierarchy absolutely. fractional T-1/E-1 T-1/E-1 lines that have apportioned bandwidth for separate transmission channels (DS-0/64Kbps subchannels), generally in increments of four channels. fragmentation The process of splitting a packet into pieces when it is larger than the MTU it must transmit. frame (