| 单词 | B-ISDN (Broadband Integrated Services Digital Network) |
| 释义 | B-ISDN (Broadband Integrated Services Digital Network) A set of specifications from the ITU- T for an integrated services digital network (ISDN) requiring transmission channels capable of supporting rates greater than the primary rate, which is defined in the North American primary rate interface (PRI) standard as 1.544 Mbps and in the European primary rate access (PRA) standard as 2.048 Mbps.There are three underlying sets of technologies and standards critical to B-ISDN: • Signaling and control: Signaling System 7 (SS7) supports B-ISDN, just as it supports narrowband ISDN (N-ISDN). • Switching and multiplexing: Asynchronous transfer mode (ATM). • Transmission: SDH/SONET fiber optics transmission system (FOTS). B-ISDN user access is specified at two SDH/SONET levels. User network interface A (UNI A) operates at OC-3 rates of 155 Mbps, whereas user network interface B (UNI B) operates at OC-12 rates of 622 Mbps. A network-to-network interface (NNI) is required for network access to B-ISDN from frame relay and N-ISDN networks. B-ISDN defines interactive services and distribution services. • Interactive services involve bidirectional transmission and include three classes of service. Conversational services include voice, interactive data, and interactive video. Messaging services include compound document mail and video mail. Retrieval services include text retrieval, data retrieval, image retrieval, video retrieval, and compound document retrieval. • Distribution services may or may not involve user presentation control. For example, interactive TV is a service requiring presentation control. Interactive TV actually enables the viewer to interact with the program, perhaps to select a product marketed over TV or to change the camera angle to view a sporting event from a different perspective. Conventional broadcast TV exemplifies a service requiring no presentation control. B-ISDN user equipment is an extension of that described for N-ISDN. Broadband terminal equipment type 1 (B-TE1) is defined as B-ISDN compatible. Broadband terminal equipment type 2 (B-TE2) is defined as terminal equipment that supports a broadband interface other than B-ISDN and must interface with the network through a broadband terminal adapter (B-TA). Cost and complexity issues forestalled the deployment of B-ISDN, in favor of broadband public networking based variously on ATM, Ethernet, frame relay, and Internet Protocol (IP). B-ISDN seems to have little future other than as an evolutionary dead end. See also ATM, BRI, broadband, channel, Ethernet, FOTS, frame relay, IP, ISDN, ITU-T, narrowband, NNI, OC, SDH, SONET, SS7, and UNI. |
| 随便看 |
|
科学参考收录了5291条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。