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来源：百度知道 编辑：UC知道 时间：2024/05/10 06:17:14
单板上的恒温晶振，系统锁相环设置在 SSUB 单板上，锁相环根据4 个外部时钟源的输入情况，依上述次序选择其中某一个作为系统时钟，故系统设计要求ODT1/2/3 的第一个 E1 要作为上连 LE 的V5 中继链路。S SUB 板优先同步于外部独立时钟源，产 生系统所需时钟，可 从 BITS 时钟系统或其它独立时钟系统的2Mbps或 2MHz 信号中提取定时基准。当外部独立时钟源无信号时，SSUB 板可同步于与交换机相连的 V5 接口内的时钟。为可靠起见，最多由三块ODT 板提供三路参考时钟到 SSUB 板的时钟提取电路，SSUB 按顺序自动选取一路为同步时钟源。当所有外部时钟基准信号消失时，可自动切换为内部时钟工作模式，时钟精度至少为三级时钟标准，此时接入网设备可继续工作，业务质量可能有某种程度的下降。
The system altogether establishes 5 clocks sources: BITS (2Mbps),ODT1/ODT2/ODT3 first E1 perhaps SSUB
On the veneer constant temperature crystal oscillator, thesystem phase-lock link establishes on the SSUB veneer, the phase-locklink acts according to 4 exterior clocks sources the input situation,chooses some achievement system clock according to the above order,therefore the system design requests ODT1/2/3 first E1 to need to takeon links LE the V5 relaying link. S SUB board first synchronization tothe exterior independent clock source, produces the system to need theclock, may withdraws fixed time the datum from the BITS clock systemeither other independent clock systems 2Mbps or in the 2MHz signal.When exterior the independent clock source does not have the signal,the SSUB board may synchronization in and the switchboard connected V5connection clock. For reliable in order to, are most from three ODTboard provides to withdraw the electric circuit three groups referenceclocks