Insertion unit for fibre=optic transmission system - converts HDB3 code signals into line code for error detection in regeneration unit at receiver side

摘要

Prim. signals in HDB3 code enter a module of the insertion unit at the sender. This converts them into line code HDB3/CMI, which does not use the configuration 1-0. A sec. signal in binary code enters another unit; the duration of 1 in this code is a large multiple (n) of 1 in HDB3. Whenever a 1 in the coded sec. signals coincides with 0 in the HDB3 coded signals the first 0-1 in HDB3 (equiv. to 0) becomes 1-0. 0 in binary code is the absence of 1-0 in line code. The extn. unit at the receiver recovers the 2 original coded signals. A unit in the regeneration device along the fibre-optic link detects the erroneous presence of 1-0 in the absence of sec. signals, presenting it as a percentage of error. The sec. signalling rate is a function of the multiple (n) and is typically 1/20th of the prim. signalling rate.