A DDN trunk channel is interrupted much more frequently in mobile telecommunications than one in fixed telecommunications. Therefore, interrupting time of DDN equipment becomes more important in mobile telecommunications, which makes the availability of a DDN circuit much poorer than that of a DDN trunk channel. 在无线移动场合下,DDN中继信道的中断比固定场合下频繁得多,DDN设备中断恢复时间长的问题就变得突出起来,这使得DDN电路的可用性远小于DDN中继信道的可用性。