We propose a test selection method that provides efficient test sets for systems based on SDL specifications. Our approach builds on previous results of Voung et al. and Feijs et al. on string edit distance based coverage metrics. The method reduces a set of test cases represented in the MSC (Message Sequence Chart) notation, while maintaining the highest possible distance between all pairs of traces defined by the given test set. The algorithm is tunable by a parameter representing the threshold distance for test redundancy. We show that the algorithm runs in polynomial time of the size of the input test set and that it is independent of the size of the system. We implemented and incorporated the algorithm into our SDL-based test selection framework, and evaluated against existing symbol coverage and fault coverage based test selection approaches by conducting experiments on the well-known INRES and Conference Protocol. Results indicate that the string edit distance based method yields similar results in terms of reduction-capability and coverage as the other approaches, but with significantly less complexity.