A.20ms B.80ms C.160ms D.40ms E.320ms
A.SCCAS B.PCRF C.IP D.P-CSCF
A.10ms B.20ms C.5ms D.1ms
A.2～3 B.3～5 C.0.5～2
A.UPDATE B.re-INVITE C.100Trying D.183response
