Hi,
I have the following setup: a B2BUA based on sipstack "A" and a mediaserver,
based on sipstack "B".
Themediaserver sends a REFER to the B2BUA which starts to send NOTIFYs
according to the progress of the REFERred call: for example: 100, 183,. 180,
200. One of the NOTIFY gets lost on the network, lets say the 183, the "A"
stack retransmits it, but before the retransmittion, the 180 is sent and
replied:
100->
<--OK(100)
183->
180->
<-OK(180)
183(r)->
<-500
("A" stack terminates the subscription)
The "B" stack refuses the retransmitted 183 NOTIFY with 500, because it's cseq
is smaller than the 180's, which seems correct as per 12.2.2 of RFC3261:
"
If the remote sequence number was not empty, but the sequence number
of the request is lower than the remote sequence number, the request
is out of order and MUST be rejected with a 500 (Server Internal
Error) response.
"
The "A" stack in turn terminates the subscription and the transaction dies,
because the mediaserver application expects to receive more NOTIFYs, at least
one with "subscription-state: terminated", but it never comes. The "B" stack
doesn't notify the mediaserver application, so has no way of knowing something
went wrong.
What would be the correct behavior?
Should the B2BUA hold the sending of the next NOTIFY until it doesn't receive
reply to the last one?
Should the "A" stack marshall the NOTIFYs and make sure they don't get out of
order?
Should the "B" stack accept out-of-order NOTIFYs?
Thank you in advance!
br
Szo
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