Hy,
I have a question about the following situation:
UAC sends INVITE, UAS ansueres with 200 OK and UAC sends ACK. In rfc 3261 (13.2.2.4) is said that:
Once the ACK has been constructed, the procedures of [4] are used to determine the destination address, port and transport. However, the request is passed to the transport layer directly for transmission, rather than a client transaction. This is because the UAC core handles retransmissions of the ACK, not the transaction layer.
Let suggest that whe have more then one posible destination to which to send the ACK. When we sending ACK we can easily find out when there is error in sending the pocket. We go to the next possible destination. But if we received an ICMP host unreachable for that destination, how we are going to retransmit the ACK. In transport layer as i now there is no retransmission interval in that case. May idea is to save a copy of the packet and retransmit it to the next destination but i don't now for how long to keep the copy.
What is yor opinion?
You should keep it for 64*T1=32 seconds. After this the server will send a BYE.
But be aware that you cannot resend the SIP packet as it on a different destination. As per RFC3263 if you try the next destination you need also to change the branch in the Via even if in this case this is not strictly needed, as there is no transaction.
Thanks.
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