IP Multimedia Subsystem (IMS core)

• P-CSCF: acts as an Access SBC with full transcoding support and other features. Interfacts with the PCRF to provide quality of service management
• I-CSCF: provides full Cx/Dx interface support and selects S-CSCF based on user capabilities and load
• S-CSCF: provides flexible application execution using a standards-based ISC interface and allows optional charging integration with standard Ro/Rf interfaces

Application servers:

• IP-SM-GW: provides SMS services for VoLTE and legacy devices and allows interworking towards other networks based on SMPP
• MRF: provides network announcements and conferencing
• LI: Provides X1 to X3 interfaces for lawful interception.