Optimal channel graphs (least blocking probability), so far confined to those derived by parallel operations", are generalized for a simple 4-stage case. An optimum is materialized, and is assured to be superior to the former optimum.

A method to obtain optimal channel graphs (least blocking probability) is described, for a class of 4-stage link systems without parallel" limitation. Slip notation, introduced to classify and identify channel graphs effectively, makes their comparison tractable. General blocking probability calculation procedure is obtained for this purpose. Generalized optimums are concretely determined for a range of small link sizes, and assured by the comparison with every non-slip type. Former parallel" optimums are proved to be inferior, but practically sufficient according to numerical results. Necessary conditions for generalized optimums are shown based on a theorem.