VoLTE : Apart from the LTE standard nodes like SGW, PGW and PCRF , what are all nodes involve to provide VoLTE ?

Question

Sometimes due to coverage hole issue in the LTE network, the ongoing VoLTE is continued to UE by using the CS network like GSM network. This is known as SRVCC (Single Radio Voice Call continuity). What messages are exchanged between network nodes when UE moves from LTE to GSM ?

Answer 1

Similar to LTE core network, IMS has its own network.
LTE core network has various nodes such as MME, SGW, PGW/PCEF, PCRF, HSS.
IMS core network has various nodes such as P-CSCF, I-CSCF, S-CSCF , SLF , HSS.

Each node belongs either to LTE network or IMS network, has specific set of functions that it performs.