| 单词 | virtual circuit |
| 释义 | virtual circuit A circuit that exists in essence or effect, although not in the reality of dedicated compo- nents. In other words, a virtual circuit is a logical, rather than a physical, circuit.A virtual circuit commonly exists in the form of channel capacity provided over high-capacity, multichannel physical circuits, such as fiber optic transmission facilities, in a packet network.Virtual circuits are established end-to-end through a packet network, such as X.25 and Frame Relay, based on options and instructions defined in software routing tables. Permanent Virtual Circuits (PVCs) are permanently defined in routing tables, until such time as the carrier permanently redefines them. Switched Virtual Circuits (SVCs) are determined at the moment in time the connection is requested, with the specific path selection made in consideration of factors such as the level of congestion, level of error performance, geographic distance, and number of hops. A virtual circuit provides connectivity much as though it were a physical circuit, with all data traveling the same path. See also circuit, PVC, and SVC. |
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