Conformance testing of protocols is the process of checking whether an
implementation under test conforms to the standards. In this paper we
prove that the multilevel method (M method) [which splits the specifi
cation graph into a basic subgraph and one or more higher level subgra
ph(s)] is capable of diagnosing any number of faults in the higher lev
el subgraph(s), if the basic subgraph is error-free, Heuristics for ob
taining the basic subgraph and higher level subgraphs from the specifi
cation graph are also given. The advantage of the M method is that it
has error recovery and, in addition, it does not assume the presence o
f reliable reset in the implementation under test. We additionally pro
pose an incremental test sequence generation method, which produces a
shorter test sequence and whose fault coverage is same as that of the
hi method. Finally, we compare the M method with other fault detection
and fault diagnostic methods.