In global mobility networks (GLOMONET), offering secure communication with privacy to the authorized mobile users is a challenge in roaming services.Authentication is an identification mechanism of legal user, which is highly desirable to have a secure and authorized communication in GLOMONET. Additionally, the privacy of the user would undoubtedly throw more concentre for roaming services in GLOMONET. Thus, security along with the privacy should be addressed in the design of security protocols for GLOMONET. In recent years, most of the works are focused on one way authentication or do not have desirable security attributes. In this paper, we discuss the development on authentication protocol for GLOMONET. To address the security and privacy issues in authorized communication, we proposed an probably secure authentication protocol for GLOMONET. To strengthen the proposed protocol, we have also presented the analysis of the scheme with respect to all known attacks. The analysis of proposed scheme demonstrates that the proposed scheme address the security and privacy challenges. Results show that our scheme reaches the level of security requirements and also has suitable cost in performance.