第12章电子信息类专业英语(第二版)课本李白萍.ppt

　　[3]? The rapid evolution of LANs and metropolitan area network (MANs) to high speeds, efficient inter-working, and wider availability, together with advances in software control, is making possible most of the services currently envisioned as supported by ISDN and others beyond the capabilities of narrowband ISDN.　　局域网和城域网在向高速、高效互连和更广泛应用方面飞速发展，并且与先进的软件控制相结合，使当前大多数业务通过ISDN和窄带ISDN之外的其他技术的支持正在成为可能。　　· 本句的主句结构为The rapid evolution…，is making possible…。as supported by…为条件状语。 　　[4]? It is essential that ISDN, if it is to achieve the ubiquity needed for low cost, inter-work with these alternative architectures and exist within them as “virtual ISDN” when appropriate.　　如果是为了普遍满足低价的需要，那么ISDN的实质应该是与不同结构的网络相连，并在恰当的时候作为这些网络的“虚拟ISDN”存在。　　· 逻辑上的主语是ISDN inter-work…and exist…，中间插入if it…是条件状语从句。 Unit Five ISDN Unit Five ISDN Passage A Introduction of ISDN Passage B ISDN Multimedia Services Passage C ISDN Evolution and its Benefits Passage A Introduction of ISDN 　　Imagine a network that would break down the walls of classrooms, letting teachers, students, and staff directly access computer-based resources and other communications facilities. This network could enhance communications between teachers and staff, allowing students to gain more of their teachers time for instruction, personal attention, and an enriched curriculum.[1] Computer-aided instruction (CAI) and computer-based teaching and grading could be enhanced, allowing better tailor-made courses and tracking of an individual student’s progress. Teleconferencing could provide courses to the sick or homebound students, courses to student spread over a wide geographic area, and continuing education for teachers and other staff members. Community or state-wide databases could allow the sharing of scarce educational resources. Student attendance and teacher availability could all be tracked via centralized databases. PC-to-PC networking could be easily accomplished between buildings on a campus or between ca