Hi All,
If retransmissted INVITE is received after exchanging
PRACK-200 OK (but before 200 OK of INVITE), what
should be the behavior?
User A User B
| |
|INVITE F1 Cseq:1|
|--------------->|
| |
|(100 Trying) F2 |
|<---------------|
| |
| 180 Ringing F3 Cseq:1
|<---------------|
| PRACK F4 Cseq:2
|--------------->|
| |
| 200 PRACK F5 Cseq:2
|<---------------|
| |
|INVITE F6 Cseq:1|
|--------------->|
| |
| 180 Ringing F7 Cseq:1
|<---------------| ??????
| |
| |
| 500 F7 CSeq:1
|<---------------| ??????
| |
The F6 in the above example is exactly copy of F1.
What should UserB send in this case? 180 with (last
provisional response) or 500 Server internal error as
CSeq is less than last received Request i.e., PRACK.
As per me, User B should send 180 provisional response
even if PRACK and 200 OK of PRACK is exchnaged. I am
refering sec 17.2.1 of RFC3261
If a request retransmission is received while in the
Proceeding state, the most recent provisional
response that was received from the TU MUST be passed
to the transport layer for retransmission.
Can anybody confirm the same?
Some of the SIP vendors are using retransmissted
INVITE like above as the tools to keep alive the
signaling pinhole. I need to know whether this
retransmitted INVITE shall be rejected by 500 or not.
If not, then possibly those network vendors are doing
anything wrong. Though, they are sending re-INVITE
with updated Cseq after initial INVITE transction is
over. My question is only for the time duration when
INVITE transction is not over.
Thanks in advance.
Siddhartha
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