Here, we will describe the solution request by request and instruction by instruction. Pay attention to the request number and the corresponding process on the script.
Note the following request and reply numbers. We will show the relevant requests only. Pay special attention to the IP present on the headers, Via, Contact, and the
c= line of the SDP header. These are the fields modified by the NAT algorithms. Check the Contact header of the INVITE relayed (2) for the presence of
nat=yes in the Contact header as well. In the ACK, pay close attention to the
nat=yes parameter, now in the Request-URI. ACK is a sequential ...