IMS — TS 24.228's signalling flows
R1.
Registration: user not registered R2.
Re-registration R3.
UE subscription for registration state R4.
P-CSCF subscription for registration state R5.
Deregistration in S-CSCF R6.
Deregistration in HSS R7.
Deregistration upon UE roaming and registration to a new network R8.
Re-authentication S1.
Session-Initiation: mobile origination and termination roaming, with different network operators S2.
Session-Initiation: mobile origination and termination in home network S3.
Session-Initiation: origination in CS Network, and mobile termination in home network S4.
Session-Initiation: mobile origination in home network, termination in CS network S5.
Session-Initiation: mobile origination and termination in home network, but terminating UE roaming and busy
Registration: user not registered R2.
Re-registration R3.
UE subscription for registration state R4.
P-CSCF subscription for registration state R5.
Deregistration in S-CSCF R6.
Deregistration in HSS R7.
Deregistration upon UE roaming and registration to a new network R8.
Re-authentication S1.
Session-Initiation: mobile origination and termination roaming, with different network operators S2.
Session-Initiation: mobile origination and termination in home network S3.
Session-Initiation: origination in CS Network, and mobile termination in home network S4.
Session-Initiation: mobile origination in home network, termination in CS network S5.
Session-Initiation: mobile origination and termination in home network, but terminating UE roaming and busy