EMS can send zxAnPonRmOnuRetrieveCmd to retrieve ONU monitoring metrics which are not defined by ME of OMCI or OAM. Otherwise, EMS can retrieve error messages of excution of zxAnPonRmOnuConfCmd in ONU. The action is divided into two steps. Step one: EMS sends zxAnPonRmOnuRetrieveCmdSessionId and zxAnPonRmOnuRetrieveCmd to OLT. The format of zxAnPonRmOnuRetrieveCmd is: 'command head::[parameter 1]=P1,[parameter 2]=P2, ...[parameter n]=Pn;' the command head represents a configuration function which is defined by EMS and ONU. parameters are followed by '::' and separated by ',', the end of the command must be ';'. Example: GET_WAN_CONF::WANID=1; Step two: The result is saved in zxAnPonRmOnuRetrieveCmdReply. EMS can retrieve result by zxAnPonRmOnuRetrieveCmdSessionId. The format of zxAnPonRmOnuRetrieveCmdReply is: 'command head::[parameter 1]=P1,[parameter 2]=P2, ...[parameter n]=Pn;' the command head represents a configuration function which is defined by EMS and ONU. parameters are followed by '::' and separated by ',', the end of the command must be ';'. Example: GET_WAN_CONF_RESULT::WANID=1,HOST=1,MODE=1,PPPUser=test, PPPPassword=test;