The value of tnOamTrProbeHistoryAddressType indicates the type of binding address information returned in response to a test. When the test has the tnOamTrCtlTestMode value 'ethCfmLinkTrace', 'unknown' is returned. For 'macTraceRoute', three types of address are applicable - 'sapId', 'localCpu', and 'sdpId'. Address type of 'sdpId' is a special case used specifically to indicate that the probe was traversing a b-vpls node in a PBB network (but where destination MAC is not necessarily known to the b-vpls node).