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本文对目前CCITT ISD用户一网路接口的无源总线实现方案推荐另一种方法。我们的新方法称力相位对准的无源总线(PAB)方案。终端设备采取利用监视比特的自动相位调整机理。这种方案使终端能在无源总线上按完全相位同步方式来工作。从这种技术得到的好处是:(1)原则上消除了由于往返延迟时间引起的总线长度限制。如果保持192kb/s的线路比特率,则对终端分布不受限制的实际总线长度约700m。(2)允许各种延伸总线的配置。例如,简单中继延伸,光链路连接,以及多个分支的无源总线。(3)提供备用比特传输能力,方便了总线内通信和维护。作为另一种方法,它保持了目前CCITTI系列标准总线的结构。例如B+B+D通路结构以及LAP—D规程。实现长无源总线的多次试验均证实了所推荐结构的可行性。这种概念证明,适用于二线全双工用户一网络接口在采用时间压缩传输的现有局环境中也是有利的。
In this paper, another method is recommended for the implementation of the passive bus in the network interface of CCITT ISD users. Our new method calls for a passive phase-aligned passive bus (PAB) scheme. The terminal device takes the automatic phase adjustment mechanism that utilizes monitoring bits. This solution enables the terminal to operate in full phase synchronization on a passive bus. The benefits from this technique are: (1) The bus length limitations due to round-trip delay are, in principle, eliminated. If the line rate of 192kb / s is maintained, the actual bus length, which is not limited to the terminal distribution, is about 700m. (2) Allows extended bus configuration. For example, simple relay extensions, optical link connections, and passive multi-branch buses. (3) Backup bit transmission capability to facilitate the bus communication and maintenance. As an alternative, it maintains the current CCITTI family of standard bus structures. Such as the B + B + D path structure and the LAP-D protocol. Multiple experiments to achieve a long passive bus confirmed the feasibility of the proposed structure. This concept proves that it is also advantageous for a second-line full-duplex user-network interface to be present in an existing office environment that uses time-compressed transmission.