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由于受到信息传输速率的限制，窄带ＩＳＤＮ（Ｎ－ＩＳＤＮ）不能提供许多新的业务。为了克服Ｎ－ＩＳＤＮ的局限性，在２０世纪８０年代初Ｎ－ＩＳＤＮ刚问世不久，人们便在寻求一种更新的网络，该网络能够提供传送全部现有的和将来可能出现的业务，传输速率从低到≤１０ｂｉ
Narrowband ISDN (N-ISDN) can not provide many new services due to the limitation of information transmission rate. In order to overcome the limitations of N-ISDN, shortly after the advent of N-ISDN in the early 1980s, people are seeking a newer network that can deliver all existing and future possible services, transmission rates From low to ≤ 10bi