Defects noticed by APS protocol could be either none or a composition of the bits (0-3): fullyIncompatibleProvisioning(0) - occures by the reception of three APS frames with the incompatible 'B' bit value during the period of 22.5 seconds; protectionSwitchingIncomplete(1) - occures if the transmitted 'Requested Signal' and the received 'Bridged Signal' do not match for a period of 50ms or longer; protectionConfigurationMismatch(2) - working/protection configuration mismatch, occures by the reception of three APS frames from the working transport entity during the period of 22.5 seconds; epsConfigurationMismatch(3) - provisioning mismatch - for example the local side is set in revertive mode, the remote side is set in non revertive mode.