Thanks Neels, It is it is necessary to mention that I have used an IP access module as HNB and it is connected to my core. So the RTP packets are received from HNB and I send my RTP packets to HNB (call connection is established before). I have attached my RTP pcap file. I don't know how I can convert this log (RTP packet payloads which you said has IuUP header) to an AMR file.
I have removed the IuUP header (4 bytes) from payload and concatenated all payloads but the result is not a valid AMR bytes!
Also I think osmo-mgw will not be able to convert IuUP bytes to AMR in offline mode.
Can you help me more?