[Serusers] About "Expire" header in INVITE method

[ZHANG, YI2 -HCHBJ]

hello,
   As a basic call flow like below.
   UAC                       (SER)
     |                        |
     |       INVITE F1        |
     |----------------------->|
     |    100 Trying F2       |
     |<-----------------------|
     |                        |
     |       200 OK F3        |
     |<-----------------------|
     |         ACK F4         |
     |----------------------->| 
  if the UAC request INVITE method contain a "Expire" field with the value of 120.
  and after 120 second the final response ACK reach the SER. in this scenarios, Would SER think this ACK is valid respone from UAC? and would SER correctly proxy this message to corresponding UAS?


Regards

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