Hi,
This scenario can happen at either the proxy or the user agent i.e., the TU could be a proxy core or it could be a UA core.
If it is a proxy core, after it sends a 2xx, it drops the transaction and has no more knowledge of it. So, when it receives a retransmitted INVITE, it creates a new server transaction and continues its processing as if it were a new request. There is nothing more it can do and nothing more it needs to do. Handling it like a completely new request will not cause any harm.
If it is a UA core, the handling is different. A new server transaction is created in this case too. This is because the transaction layer has no way to know that it is a retransmission. When the UA core receives it, it sees that it does not contain a 'to-tag'. Hence, it is a out of dialog request. Then it can check that the 'callid' and 'from-tag' match one of the ongoing dialogs and in this case, also find that it has already sent one or more 2xx responses for it. It MUST then send the same 2xx response. This is because the lost 2xx may eventually find its way. The 2xx can be sent as part of the newly created server transaction so as that it can be deleted.
Hope this helps.
Regards, A. N. Gautham
Since you say that the TU will handle retransmissions of 3xx, we are talking about the UA core and not proxy core. For a proxy core, there is no way it will detect this situation. It will create another server transaction and proceed as usual.
Since both the '100 Trying' and the first '200 OK' are lost/dropped, the UAC is still retransmitting the INVITE. KrishnaKanthT 70508 wrote:
Hi,
I need one clarification on INVITE server transaction.
After UAS gets INVITE, when TU sends 2xx response, then UAS immediately transits to "Terminated" state and gets deleted. From then onwards, TU will handle the retransmissions of 2xx response and its corresponding ACK.
Now, if we assume that, after UAS receives INVITE, the 100 sent by it is dropped in the network. Similarly when UAS sends 2xx, lets assume that 2xx is also dropped. Since 2xx is sent, UAS transaction is deleted. Since UAC has not received any response, it will again retransmit INVITE. Now, when this retransmitted INVITE comes to the destination, will a new server transaction be created. If so, how is this retransmitted INVITE handled??
Thanks & Regards Krishna
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