IMS is the buzz word in today’s telecom industry and believed to be the strongest candidate for the next generation all IP networks. Since it converge the traditional cellular network and global internet, it inherits all the IP based network security issues and exposed to a verity of threats in term of access and traffic security. In this thesis we will elaborate the IMS security architecture in term of inter-domain traffic security and will propose a security model for IMS network domain security. IMS Network Domain Security/Internet Protocol NDS/IP is based on Security Gateways (SEGs) implemented at the edge of each IMS core. There are security associations maintained by SEGs between each communicating entity to ensure ESP protocol tunneled links. A detailed study is taken on SEGs structure, protocols and security parameters implemented. The authentication and encryption algorithms implemented on SEGs for source authentication and data confidentiality are studied in detail. The performance of all supported algorithms is analyzed and compared to propose suitable algorithms. IMS Security model is implemented in a network simulator called OPNET. Due to the technology limitations traffic generation between the two interworked IMS networks using IMS Security model can not be completely simulated. In this report I also tried to point out the known attributes and parameters that are not functional in OPNET preventing the traffic generation.