| 摘要 |
<p>PURPOSE:To protect synchronization by using a pointer value and a reference value Pr so as to take cell synchronization. CONSTITUTION:A pointer value and a reference value Pr are written respectively in registers 401, 402 by using a frame pulse 414 received for each frame, they are compared for each frame at a comparator 403, its output and an inverted output of an inverter 411 are given as an input and a reset signal of counters 404, 405, the counter 404 counts a consecutive coincidence number and the counter 405 counts a consecutive dissident number. When a decided threshold is counted, an RS flip-flop 406 represents the synchronization state and out of synchronism state. A residue of (Pr+Lc-M)/Lc is used for a reference value Pr 416 by using adders 407, 408 and a selector 409 for each frame. A selector 410 is switched in response to the synchronization state represented by an FF 406 as to whether the Pr 416 is used or the reception pointer 415 is used for the reference value Pr in a succeeding frame. Thus, the cell location is recognized and the synchronization protection method is realized, in which cell out of synchronism in one frame is prevented.</p> |
