home  exhibition  quizzes  tour 
   A - E   F - J    K - O   P - T   U - Z  
  F - J

F | G | H | I | J |
 
search  
glossary  
projects  
sitemap  
contact  
  
 An online file that contains frequently asked questions with answers provided to assist new users and avoid repetitive offline inquiries.
 
  
 Is a standard for data transmission in a local area network that can extend in range up to 200 km. The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users. The underlying medium is optical fibre (though it can be copper cable, in which case it may be called CDDI) and the topology is a dual-attached, counter-rotating token ring.
 
  
 Frequency-division multiplexing is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal.

FDM can also be used to combine multiple signals before final modulation onto a carrier wave. In this case the carrier signals are referred to as subcarriers: an example is stereo FM transmission, where a 38 KHz subcarrier is used to separate the left-right difference signal from the central left-right sum channel, prior to the frequency modulation of the composite signal.

Where frequency-division multiplexing is used as to allow multiple users to share a physical communications channel, it is called frequency-division multiple access (FDMA).
 
  
 FDMA is the oldest and most important of the three main ways for multiple radio transmitters to share the radio spectrum. The other two methods are Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA).

In FDMA, each transmitter is assigned a distinct frequency channel so that receivers can discriminate among them by tuning to the desired channel. TDMA and CDMA are always used in combination with FDMA, i.e., a given frequency channel may be used for either TDMA or CDMA independently of signals on other frequency channels.
 
  
 In data transmission or processing, a flag is an indicator such as a signal, a symbol, a character or a digit, used for identification. A flag may be a bit, a byte or a letter that signals the occurrence of some condition or event. For example, it can be a Boolean variable that can be set to either 1 (Set, Raised, True) or 0 (Unset, False).
 
  
 Frequency modulation (FM) is a form of modulation which represents information as variations in the instantaneous frequency of a carrier wave (Contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant).

In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Digital data can be represented by shifting the carrier frequency among a set of discrete values, a technique known as frequency-shift keying.
 
  
 Forward error correction (FEC) is a system of error control for data transmission wherein the receiving device has the capability to detect and correct fewer than a predetermined number or fraction of bits or symbols corrupted by transmission errors.

FEC is accomplished by adding redundancy to the transmitted information using a predetermined algorithm. Each redundant bit is invariably a complex function of many original information bits. The original information may or may not appear in the encoded output; codes that include the unmodified input in the output are systematic, while those that do not are nonsystematic.

The two main categories of FEC are block coding and convolutional coding. Block codes work on fixed-size blocks of bits or symbols of predetermined size, while convolutional codes work on bit or symbol streams of arbitrary length.
 
  
 In telecommunications, a frame is a packet which has been encoded for transmission over a particular link:

  - In data transmission, the sequence of contiguous bits delimited by, and including, beginning and ending flag sequences.
  - In pulse-code modulation (PCM) systems, a set of consecutive time slots in which the position of each digit can be identified by reference to a frame-alignment signal.
  - In a time-division multiplexing (TDM) system, a repetitive group of signals resulting from a single sampling of all channels, including any required system information, such as additional synchronizing signals.
  - In ISDN, a block of variable length, labeled at the Data Link Layer of the OSI-Reference Model.
 
  
 Frame Relay is a high-performance WAN protocol that operates at the physical and data link layers of the OSI reference model. It was originally designed for use across Integrated Services Digital Network (ISDN) interfaces. Today, it is used over a variety of other network interfaces as well. Frame Relay is an example of a packet-switched technology, which enables end stations to dynamically share network resources.
 
  
 FTP or file transfer protocol is an application protocol, part of the TCP/IP protocol stack, used for transferring files between network nodes. FTP is defined in the RFC 959.
 
  
 A fully connected topology, also called complete topology or full mesh topology, is a network topology in which there is a direct link between all pairs of nodes. In a fully connected network with n nodes, there are n(n-1)/2 direct links. Networks designed with this topology are usually very expensive to set up, but have a high amount of reliability due to multiple paths data can travel on.