![]() The “5G” referred to here consists of the 5G radio network and 5G core network (5GC), and the IMS nodes are interconnected with the 5GC. The goal of Release 15 was developing the basic specification for 5G (Phase 1), that of Release 16 was the completion of the 5G specification (Phase 2), and that of Release 17 is additional enhancements related to 5G. The 3GPP specifications are implemented by mobile operators.ģGPP is now vigorously developing technical specifications related to 5G and studies the progress in units called Releases. Latest trends in 3GPP standardizationģGPP was organized to promote the standardization of 3rd-generation and later mobile communications and related technologies (e.g., 3G, 4G, 5G, IMS). Currently, the IP Multimedia Subsystem (IMS) specified by 3GPP is the global standard for telecommunication operator networks using SIP. To solve this problem, international standards developing organizations, such as the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) and the 3rd Generation Partnership Project (3GPP), have deliberated service requirements and the network architecture for telecommunication operators to provide their services and published profiles of signaling protocols as international standards. Telecommunication operators need to select technical specifications among the numerous RFCs to be implemented for providing their VoIP services. RFC 5411, which is a guide for understanding SIP-related RFCs, indicates that there were over 100 related RFCs even in 2009. In addition to the basic specification of RFC 3261, many extensions to the basic SIP have also been developed. The basic specification of SIP is defined in Request for Comment (RFC) 3261 developed by the Internet Engineering Task Force (IETF), an organization that develops technical standards for the Internet. ![]() Today, SIP is widely used as a protocol for VoIP session control (e.g., connecting and disconnecting communications with the other party). Standards developing organizations for IP interconnection NTT Network Service Systems Laboratories has worked on developing new SIP common interface specifications to ensure interoperability of IP telephone networks through domestic and international standardization activities. The conventional interconnection through the PSTN is achieved with the mature signaling protocol called Integrated Services Digital Network User Part (ISUP), but direct IP interconnection needs to be achieved with the Session Initiation Protocol (SIP), which is excessively complex for telephone services and has a wide variety of usage. Architecture of interconnection for VoIP services. However, telecommunication operators in Japan and the Ministry of Internal Affairs and Communications are planning to change the via-PSTN interconnections to direct VoIP interconnections due to the inefficiency of IP-to-STM (Synchronous Transport Module) conversions and maintenance limits of some PSTN nodes ( Fig. With conventional voice over Internet protocol (VoIP) services, each telecommunication operator’s network is connected to the public switched telephone network (PSTN), and phone calls between VoIP users are provided through the PSTN. To enable users served by different telecommunication operators to talk with each other, the network of each operator needs to be interconnected with one another.
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