al Redundancy Check. (Parity method used on Address. Within the context of a telecommunication network, it is transmitted data for error checking.) a sequence of bits or characters which uniquely identifies a Vertical Radiation Pattern. (Of an antenna.) user, element or application. Its most common application is the Very Small Aperture Terminal. (Satellite receiver.) number which is entered by a caller to identify the called party. Vestigial Sideband modulation. (A method for am- Adjacent channel interference. Interference arising between two plitude modulation of a signal.) transmission channels which are adjacent to each other. Voltage Standing Wave Ratio. Agent mode. The mode which makes only managed objects Virtual Tributary. (SONET terminology for a virtual visible to other network elements in a network management container.) system. Virtual Terminal Protocol. Agent process. An application which performs operations on managed objects within a network management system and issues events on their behalf. Alarm category. Grouping of alarms to indicate their severity. Wait Acknowledgement. (Control signal returned by Usually these are classified as critical, major, or minor. receiver to indicate to the sender that it is tempo- Alarms. Events within a network management system which have rarily unable to accept any more data.) been designated as having special significance, usually because Wide Area Network. they indicate a fault. World Administrative Radio Conference. ITU.) A-law. Companding technique for PCM, used in Europe. WATTC World Administrative Telephone and Telegraph Alert. Usually refers to the act of indicating to an operator that Conference. (Of ITU.) there is an incoming call. For example by ringing a bell. WBLLN Wideband Leased Line Network. ALOHA. An algorithm used for multiple access of a medium, Wavelength Division Multiplexing. (Multiplexing where a station will begin transmission when ready, and will technique used with optical communications sys- retransmit if a collision occurs. tems.) Alph