In this paper, a formal method for automated transformation of an SDL specification into a corresponding Lotos specification is presented. The method is applicable to various SDL specifications and to various communications protocols for various ISO (International Standards Organization) OSI (Open Systems Interconnections) layers. This formal automated transformation facilitates immediate indirect applicability of future formal methods for derivation of testing sequences for Lotos specifications to SDL specifications. Firstly, the formal automated transformation method is applied to generate a Lotos version. Then, the Lotos-based derivation method is applied. This facilitates the best coverage of the testing sequences for SDL specifications as the formal test derivation method with the best coverage can be applied. This also facilitates comparison of various test derivation methods in terms of coverage. We develop an algorithm for constructing the Lotos specifications.