MSEPONs aim to provide customers with multiservice broad access of telecom carriers’ QoS

which can support Ethernet and TDM traffic （E1）. As a carrierclass system

it is very important and necessary to monitor the error of the system. In this paper

a novel scheme of online error monitoring is proposed

which utilizes the bit interleaved parity （BIP） technique

with a byte in the preamble of Ethernet frame. Furthermore the performance of the scheme is analyzed and the feasibility of the scheme is proved.