Protocol Analysis/Testing Based on Sidhu et al in IEEE TSE 89 and TN 93 Figures from the papers.

Basic Idea Given a protocol spec, how do you know if an implementation conforms to it (conformance testing) Use black-box testing methods –Give input, see if output is “right” per spec Need a formal specification –What input / output pairs should be checked Fault coverage Automatic generation

Mealy Machine Is an FSM that produces an output on each transition. Minimal – least number of states Completely Specified – each state has a transition for every input symbol Strongly connected – if there is a transition path for each state pair Test subsequence, subsequence, test sequence, optimized test sequence

An Example Mealy Machine

Protocol Modelling Model protocol as Mealy Machine Protocol specified state/input combinations are core, others are noncore Strong vs Weak Conformance –Weak if similar behavior on core, unspeficied on noncore Analyze coverage via simulation using mutated machines –Showing that machines are equivalent ?

Basic Test generation methods T-Method –Assume minimal, strongly connected, completely specified machine –Generate random inputs till machine has traversed each transition once, eliminate loops U-Method –Assume minimal, strongly connected, completely specified machine –Derive Unique IO sequence for each state –For each transition (s i,s j ), reset, find shortest path from 0 to si, add input to cause transition to s j, add UIO –Beta sequence is concatenation of each subsequence, create optimized sequence.

More test generation methods D-Method –Assume minimal, strongly connected, completely specified machine with distinguishing sequence –Construct the same way as U method but replace UIO with DS W-Method –Assume minimal, strongly connected, completely specified machine –Derive a Characterizing set W Set of input strings a s.t the last output symbol obtained by applying these strings in a fixed order is different for different states. Use these instead of UIOs

Testing issues Finding shortest test sequence to check a given set of behaviors –How long to give complete coverage ? –Can we create a hierarchy of sequences State cardinality may differ in spec and implementation – masking behavior is different Test subsequence to test (p,q) transition can be viewed as L1.L2…Lk.CS(q) Bk test subsequence has an L sequence of length k. B0 tests a state. Every Bk is proper subsequence of some Bk+1 if machine is complete. Reset and Bridge Sequences