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目前数字网络的基础是由CCITT建议G.702(1972年)所定义的准同步系列。CCITT建议G.702形成了两套不同的世界通用的标准,常称为欧洲标准和北美标准。 欧洲标准包括: ——64kb/s基本数字流,利用同步帧复用为2048kb/s基群数字流; ——8448,34 368和139 264kb/s高次群数字流,从基群开始4个分支为一组,依次准同步多路复用获得。 现今两种数字系列共同的基本特点是利用脉冲填充技术进行准同步复用。此技术利用增加调整比特和相关控制比特来实现分支
The current digital network is based on a plesiochronous series as defined by CCITT Recommendation G.702 (1972). CCITT recommends that G.702 form two different sets of world-wide standards, often referred to as European and North American standards. The European standard consists of: a 64kb / s elementary digital stream multiplexed into 2048kb / s elementary digital streams using synchronous frames; - 8448,34 368 and 139 264kb / s higher sub-group digital streams, starting from 4 A group, followed by quasi-synchronous multiplexing obtained. The basic feature common to both digital families today is the use of pulse-filling techniques for quasi-synchronous multiplexing. This technique uses the addition of adjustment bits and associated control bits to achieve the branch