 the long-term evolution (LTE) radio access network (RAN) archi- tecture, telecom operators adopted LTE as the most viable access option for maximizing system coverage, throughput, and capacity. The LTE/EPC infrastructures were developed and launched around 2010. LTE/EPC supports data rates beyond 3G high speed packet access (HSPA), provides higher efficiency for the spectrum, and makes all IP services possible. The LTE implementation required a new LTE radio network supported by the EPC. The voice and short messaging services (SMS) were mapped to an IP-based application to effectively use the all-IP LTE network for all voice and data services. IMS data and VoIP solutions were integrated for service continuity with existing networks. On the VoIP service platforms side, in the early 2000s, many telecom operators started looking into migrating their entire infrastructure to IP. At that time, there was no generally known architecture avail- able that would support all possible applications, specifically VoIP and multimedia. VoIP was primarily viewed as a technology to either provide an enterprise with the ability to use the existing data network to also carry voice, or provide carriers with a way of bypassing access or egress charges. There was no known comprehensive architecture in the industry that a large service provider could potentially use to support all of its services across an IP network. Telecom operators started to define several major char- acteristics of the desired architecture and contained within it the key architectural principles that IMS is based on. Separation of access, session management, and service logic layers were the most critical requirements. The ability to support access technologies of the future without impacting the rest of the architecture was also deemed critical. The ability for application logic to be totally independent of the access technology being used at the time of a service call, the ability for an application to be applied to a session over various access technologies, a