急求高质量英译汉,15天有效,给100分.机器译的也行.

急求高质量英译汉,15天有效,给100分.机器译的也行.如果没有正确答案,将把分给翻译质量最好那位,不一定是翻译的最多那位!Abstract:The Asymmetric Digital Subscriber Line (ADSL) draft standard is nearing completion by ANSI and should become finalized as a standard in 1995.Commercially available products will be appearing later in 1995.As specified in this standard,ADSL technology will provide over a single twisted-pair loop a number of simplex channels (up to 6 Mb/s total capacity) from the central office to a subscriber and a number of duplex channels (up to 640 kb/s total capacity) while leaving POTS service unaffected.Although the intention of the downstream data rates prescribed in the standard are to provide compressed video services,we believe a compelling case may also be made for data services over ADSL.This paper provides an overview of the ADSL standard,discusses video provisioning issues and how ADSL may compare to hybrid fiber-coax in this regard,and introduces a number of concepts for offering new data services using ADSL and existing LAN and WAN technology.The ADSL standardA number of years ago ISDN was standardized with a basic rate access of 160 kb/s [2].This digital transport technology was designed to operate over the existing public switched telephone network,including the copper loop plant,and made the ubiquitous twisted-pair into a Digital Subscriber Line (DSL).More recently,advances in signal processing techniques and processing power have enabled an increase in data rates.As embodied in High-bit-rate DSL (HDSL) technology,bi-directional T1 rates (1.5 Mb/s) are achieved over two pairs of unconditioned lines up to a range of 12,000 feet of 24 AWG cable [31.HDSL presents an alternative for providing standard T1 service over copper twisted-pairs.By requiring no repeaters,loop conditioning or pair selection (allowing the existence of bridged-taps),HDSL allows for faster and lower-cost provisioning of TI service.By limiting high-rate transmission to one direction only,near-end crosstalk (NEXT) from the same service is reduced,allowing a further increase in the data rate.Given that many service applications such as entertainment video,information services and telecommuting do not require bidirectional high-rate transmission,the concept of Asymmetric DSL (ADSL) arose.As specified in the draft ANSI standard,ADSL will support four loop range options,defined as transport classes,over a single twisted-pair (Table 1).A number of optional rates (such as those based on multiples of 2,048 Mb/s and rates that include ATM overhead) are also specified.