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为了核对主叫用户的服务类别(COS),用户线信令(SLSA)将占用发端的全部信息送至呼叫控制(SGCA),查证主叫用户话机是何种拨号方式,以便考虑接上多频收码器,使呼叫程序进入呼叫控制的预测呼叫性质(Preseleetion Call Control—PRE.CC)阶段。由于用户线信令(SLSA)在低一级的L/TCE的控制单元里,信令控制在高一级的呼叫控制ACE的控制单元里,这两种控制单元要进行通信必须经由数字交换网。因此对网络结构、数字交换单元、交换端口的工作情况、数字交换网络、建立通路等均有介绍。但就1240系统的呼叫程序而言,在开局时L/TCE与L/TCE之间早已建有“用户”控制通路,可作为SLSA向SGCA传送信息之用。
In order to check the caller’s service class (COS), subscriber line signaling (SLSA) sends the outgoing full message to the call control (SGCA) to check the caller’s dialing method in order to consider connecting multiple frequencies Receivers, the call program into the call control of the nature of the call (Preseleetion Call Control-PRE.CC) phase. Because subscriber line signaling (SLSA) in the lower level of the L / TCE control unit, the signaling control in a higher level of call control ACE control unit, the two control units to communicate must be through the digital switching network . Therefore, the network structure, digital switching unit, switching port work, digital switching network, the establishment of access and so on are introduced. However, for the 1240 system’s calling procedure, a “user” control path has been established between the L / TCE and the L / TCE at the outset for transmitting information to the SGCA as an SLSA.