Transmission quality monitoring system for a digital communication network

A digital communication network transmission quality monitoring system for a digital communication network having a first end office which includes a first multiplexer unit and a second end office which includes a second multiplexer unit, add which performs transmission and reception of multiplexed signals between said first end office and said second end office, said transmission quality monitoring system having first monitor means within said first end office, and second monitor means in said second end office for performing monitoring of signal accuracy of a signal received from said first end office, information with regard to said signal accuracy monitored by said second monitor means being included as sub-signalling information in an input signal which is sent to said first end office from said second end office, said sub-signalling information being extracted by said first monitor means at said first end office from said input signal, to enable monitoring of signal accuracy of said input signal,

• wherein said sub-signalling information is information which is periodically inserted into main signal information which is to be communicated between said first end office and said second end office, and wherein said first monitor means comprises a sub-synchronizing unit which establishes synchronization with said sub-signalling information after synchronization is established with said main signal information,
• wherein said sub-signalling information is various types of transmission quality monitoring data which are mapped in a prescribed data format, and wherein said first monitor means includes a timing generation unit which generates timing signals for the purpose of individually extracting the various transmission quality monitoring data from said various transmission quality data included in said data format, monitoring of the input signal received by said first end office from said second end office being performed according to said extracted transmission quality monitoring data,
• wherein said sub-signalling information is composed of multiframes according to ESF (Extended Super Frame), said sub-signalling information being composed by means of a data link which is formed by collecting bits which are assigned to each frame which makes up said multiframe, and said format which comprises the sub-signalling information being the LAPD (Link Access procedure of the D-channel) format which is comprised of the bit groups which make up said data link, said sub-synchronizing unit detecting the head pattern of said LAPD format, so as to establish synchronization of said LAPD format,
• wherein said timing generation unit, based on said generated timing signals, extracts a One-Second Report area which is mapped onto a prescribed location in said LAPD format, and further individually extracts various transmission quality monitoring data from within said One-Second Report area.