| 单词 | dedicated circuit |
| 释义 | dedicated circuit A distinct physical circuit dedicated to directly connecting devices, such as multi- plexers, PBXs, and host computers. A dedicated circuit, also known as a leased line, can be provisioned over a private network comprising facilities owned by the end user organization, although it more typically is in the form of a leased line provisioned over a public network. In the latter case, the circuit includes an access circuit, or local loop, that connects the originating device at the customer premises to the service provider’s point of presence (POP) at the edge of the carrier network. In the case of an incumbent local exchange carrier (ILEC), the POP typically is housed in a central office (CO). At the POP, the access circuit terminates in a wire center, where it is cross-connected directly to a long-haul transport circuit, bypassing any switching devices. The long haul portion of the dedicated circuit typically comprises multiple interconnected links and terminates in a POP at the egress edge of the network, where it is crossconnected to another access circuit that connects to the premises housing the destination device. A dedicated circuit offers the advantages of dedicated availability, dedicated bandwidth, and excellent performance overall. Because a dedicated circuit is not in shared public use but is dedicated to the requirements of a specific customer, it tends to be expensive, with the cost sensitive to bandwidth and distance. The cost, however, is typically a flat rate, with no usage-sensitive component; therefore, the end user organization can use the circuit constantly to maximum capacity at the same cost as if it were to not use the circuit at all. The nature of the traffic over a dedicated circuit generally is not restricted, and can include voice, computer data, facsimile, image, video, and multimedia traffic. The ability to integrate such a wide variety of traffic over a single facility offers considerable efficiencies. A multi-site user organization might consider a private, leased line network to interconnect the sites. However, the process of designing such a network can be difficult, as it is necessary to determine the points of termination in the optimal topology, the correct number of circuits, and the bandwidth requirements of each.When the design is established, the provisioning time required by the carrier can be quite lengthy. As a dedicated circuit involves a specific set of network elements, the circuit is susceptible to disruption. Therefore, backup circuits or services are required to ensure connectivity in the event of either a catastrophic failure or serious performance degradation. Organizations with intense communications requirements commonly consider dedicated circuits to be viable alternatives to switched circuits. Large data centers that communicate intensively in support of applications such as data backup traditionally have opted for dedicated circuits. Large multi-site end user organizations often use dedicated circuits known as tie trunks to tie together multiple PBXs. In such applications, the advantages of assured availability, capacity, and performance in support of mission-critical, time-sensitive applications, particularly when coupled with low comparative cost, can outweigh considerations of configuration difficulty and risk of circuit failure. Dedicated circuits sometimes are referred to as 74570c04.qxd 9/11/07 12:19 PM Page 130 |
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