Patent ID: 6947674
Filing Date: 2005-09-20
Classification: H04J,H04L

Abstract:
1. A circuit for preventing transmission of a fixed pattern of an optical digital transmission equipment, comprising: a memory for temporarily accumulating a low-order group signal; a multiplexing circuit for multiplexing an output signal output by said memory with an overhead bit necessary for optical digital transmission; a pattern generation circuit for generating an unfixed pattern having no fixed value and outputting the pattern to said multiplexing circuit; a selection circuit coupled to said multiplexing circuit, said pattern generating circuit, and said memory, wherein in response to reception of said fixed pattern output by said memory said selection circuit selects said unfixed pattern generated by said pattern generating circuit; a phase comparator coupled to said selection circuit, said phase comparator outputting a reset signal that resets said memory based on a phase difference between a phase of write to said memory and a phase of read from the memory, wherein in response to said phase comparator, said selection circuit selects said unfixed pattern based on said reset signal output by said phase comparator; and a reset signal detection circuit for outputting a switching signal based on a read address signal applied to said memory from when said memory is reset until when a signal first written into said memory is read from said memory, wherein said selection circuit selects said unfixed pattern based on said reset signal and said switching signal.