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 A wave that has been reflected or otherwise returned with sufficient magnitude and delay to be perceived. Echoes are frequently measured in dB relative to the directly transmitted wave. Echoes may be desirable (as in radar) or undesirable (as in telephone systems).
 
  
 A check to determine the integrity of transmission of data, whereby the received data are returned to the source for comparison with the originally transmitted data. Synonym: loop check.
 
  
 To append redundant check symbols to a message for the purpose of generating an error detection and correction code.
 
  
 Any technique that will detect or correct errors by introducing more signal elements than are necessary to convey the basic information. Error control is divided in two main categories:

Error Detection: Redundancy allows a receiver to check whether the received data has been corrupted during transmission. He can for example request a retransmission.

Error Correction: This type of error control allows a receiver to reconstruct the original information when it has been corrupted during transmission. This is especially useful when there is only one-way communication.
 
  
 A code in which each data signal conforms to specific rules of construction so that departures from this construction in the received signal can generally be automatically detected and corrected. If the number of errors is less than or equal to the maximum correctable threshold of the code, all errors will be corrected. The two main classes of error-correcting codes are block codes and convolutional codes.
 
  
 A code in which each data signal conforms to specific rules of construction, so that departures from this construction in the received signal can generally be detected automatically. The two main classes of error-detecting codes are block codes and convolutional codes.
 
  
 Ethernet (this name comes from the physical concept of ether) is a frame based computer networking technology for local area networks (LANs). It defines wiring and signaling for the physical layer, and frame formats and protocols for the media access control (MAC)/data link layer of the OSI model. Ethernet is mostly standardized as IEEEs 802.3. It has become the most widespread LAN technology in use during the 1990s to the present, and has largely replaced all other LAN standards such as token ring, FDDI, and ARCNET.
 
  
 In ASCII, ETX is a short name for the "End of Text" control character (code 3). It is often used as a "break" character (Ctrl-C). On MS-DOS systems, however, the "end of text" is marked by the Ctrl-Z character (code 26, "Substitute").