Respectively use USG and TP - LINK two cases to capture packet. Then analyze. The message analysis are as following:
TPLINK and USG message contrast (NAT transition address: 188.8.131.52 public network address: 184.108.40.206) :
According to the below message to analyze:
First analyze SIP/SDP message
the Layer 2 ether header of TPLINK and USG is basically consistent, only TPLINK can't identify the source MAC address another name.
IP header of TPLINK and USG is the same, all made NAT transition
TPLINK NAT transition port since 44000, but USG since 2048
after USG make NAT transition, the port is less than before, from the beginning of 2048.
TPLINK don't do special treatment to SIP packet, output as the same, and USG make some NAT transition to SIP packet.
Through the above analysis and contrast can find that TP - LINK don't make NAT transition to SIP packet, only make NAT transition to IP header, and port value far outweigh our device. In theory: our devices don't do ASPF processing, adjust NAT transition port to be basically consistent with TP - link, should be feasible