ISDN signal transmission performance monitoring

A method for determining if a signal transmission error has occurred during signal transmission between an access line and a network trunk line, the access line terminating at a line card mounted in an access line shelf, the access line shelf also including common equipment wherein the network trunkline terminates, wherein words on the network trunk line each correspond to a data byte and a performance monitoring byte on the line card, said data byte containing data to be transmitted between the access line and the network trunk line and said performance monitoring byte containing performance monitoring data for determination of whether or not a signal transmission error has occurred;

• the method comprising the steps of:
• performing signal transmission from the network trunk line to the access line, including:
• receiving said words from the network trunk line, breaking each one of said words into two corresponding bytes including said data byte and said performance monitoring byte, transmitting said corresponding bytes to the line card, and performing performance monitoring to determine if a signal transmission error has occurred;
• and
• performing signal transmission from the access line to the network trunk line, including:
• receiving pairs of data bits from the access line, combining said pairs of data bits into data bytes, generating pairs of performance monitoring bits combining said pairs of performance monitoring bits into performance monitoring bytes, transmitting corresponding pairs of data bytes and performance monitoring bytes to the common equipment, and performing performance monitoring to determine if a signal transmitting error has occurred.