---
title: Invite
---
sequenceDiagram
UE1->>P-CSCF: SIP - INVITE
P-CSCF->>S-CSCF: SIP - INVITE
S-CSCF->>OCS: initial CCR
OCS->>S-CSCF: initial CCA
Note over S-CSCF: rewrite request URI to registered address
S-CSCF->>P-CSCF: SIP - INVITE
P-CSCF->>UE2: SIP - INVITE
alt
UE1->>P-CSCF: SIP - CANCEL
P-CSCF->>S-CSCF: SIP - CANCEL
S-CSCF->>P-CSCF: SIP - CANCEL
P-CSCF->>UE2: SIP - CANCEL
else
UE2->>P-CSCF: SIP 183 - Session Progress
P-CSCF->>S-CSCF: SIP 183 - Session Progress
S-CSCF->>P-CSCF: SIP 183 - Session Progress
P-CSCF->>UE1: SIP 183 - Session Progress
P-CSCF->>PCRF: AAR
PCRF->>P-CSCF: AAA
UE1->>P-CSCF: SIP - PRACK
P-CSCF->>S-CSCF: SIP - PRACK
S-CSCF->>P-CSCF: SIP - PRACK
P-CSCF->>UE2: SIP - PRACK
UE2->>P-CSCF: SIP 200 - OK (PRACK)
P-CSCF->>S-CSCF: SIP 200 - OK (PRACK)
S-CSCF->>P-CSCF: SIP 200 - OK (PRACK)
P-CSCF->>UE1: SIP 200 - OK (PRACK)
UE2->>P-CSCF: SIP 180 - Ringing
P-CSCF->>S-CSCF: SIP 180 - Ringing
S-CSCF->>P-CSCF: SIP 180 - Ringing
P-CSCF->>UE1: SIP 180 - Ringing
UE1->>P-CSCF: SIP - PRACK
P-CSCF->>S-CSCF: SIP - PRACK
S-CSCF->>P-CSCF: SIP - PRACK
P-CSCF->>UE2: SIP - PRACK
UE2->>P-CSCF: SIP 200 - OK (PRACK)
P-CSCF->>S-CSCF: SIP 200 - OK (PRACK)
S-CSCF->>P-CSCF: SIP 200 - OK (PRACK)
P-CSCF->>UE1: SIP 200 - OK (PRACK)
UE2->>P-CSCF: SIP 200 - OK (INVITE)
P-CSCF->>S-CSCF: SIP 200 - OK (INVITE)
S-CSCF->>P-CSCF: SIP 200 - OK (INVITE)
P-CSCF->>UE1: SIP 200 - OK (INVITE)
UE1->>P-CSCF: ACK
P-CSCF->>S-CSCF: ACK
S-CSCF->>P-CSCF: ACK
P-CSCF->>UE2: ACK
loop Every 30s
S-CSCF->>OCS: CCR
OCS->>S-CSCF: CCA
end
alt
S-CSCF->>P-CSCF: BYE
P-CSCF->>UE1: BYE
UE1->>P-CSCF: OK (BYE)
P-CSCF->>S-CSCF: OK (BYE)
S-CSCF->>P-CSCF: BYE
P-CSCF->>UE2: BYE
UE2->>P-CSCF: OK (BYE)
P-CSCF->>S-CSCF: OK (BYE)
else
UE1->>P-CSCF: BYE
P-CSCF->>S-CSCF: BYE
S-CSCF->>P-CSCF: BYE
P-CSCF->>UE2: BYE
UE2->>P-CSCF: OK (BYE)
P-CSCF->>S-CSCF: OK (BYE)
S-CSCF->>P-CSCF: OK (BYE)
P-CSCF->>UE1: OK (BYE)
else
UE2->>P-CSCF: BYE
P-CSCF->>S-CSCF: BYE
S-CSCF->>P-CSCF: BYE
P-CSCF->>UE1: BYE
UE1->>P-CSCF: OK (BYE)
P-CSCF->>S-CSCF: OK (BYE)
S-CSCF->>P-CSCF: OK (BYE)
P-CSCF->>UE2: OK (BYE)
end
S-CSCF->>OCS: final CCR
OCS->>S-CSCF: final CCA
end