0-9  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z valuation techniques Placing a value or worth on an asset. There are several methods of valuation including discounted cash flow (DCF) and comparable company relative valuation. value-added reseller (VAR) A company which sells something (e.g., computers) made by another company (an OEM) with extra components added (e.g., specialist software or other services). vapor-phase axial deposition (VAD) An oxidation process for fabricating graded-index optical fibers in which the preform is developed radially rather than longitudinally. variable optical attenuator (VOA) This device attenuates (reduces the intensity of) a light signal by a level detremined by an external input. vertical-cavity surface-emitting lasers (VCSEL) A type laser diode that emits light in a vertical direction with respect to the plane of the active region, as compared to edge-emitting lasers. Benefits include simpler scaling for high volume manufacture, circular output beams, high power conversion efficiency and the ease of fabrication into arrays. vertical marketplace An online intermediary that links buyers and sellers. Vertical markets streamline purchasing by aggregating offerings from multiple sellers or by matching buyers and sellers in an exchange or auction. very-high-data-rate digital subscriber line (VDSL) A technology in the very early stages of definition, initial VDSL implementation is likely to be in asymmetric form, essentially being very high speed variations on the ADSL theme. virtual connection A data path between two terminals that performs as if the two devices were connected directly to each other, although in reality the are not connected. virtual private network (VPN) An enclosed and privatized network that is logically, but not physically, separated from the public Internet. virtual topology See logical topology. voice access equipment Primarily class 4/5 switches; used for traditional voice networks. voice extensible markup language (voiceXML) (VXML) An extension to extensible markup language (XML) that enables access to the Internet via telephones and other voice-activated devices. voice over IP (VoIP) The transmission of voice over a network using Internet protocols (IP).