Patent ID: 7359382

Claim:
A method of detecting a type of network address translator (NAT) for a user agent at a call manager, the call manager having a first network address, a second network address, a first connection port, a second connection port, a third connection port and a fourth connection port; the first connection port and the second connection port corresponding to the first network address, the third connection port and the fourth connection port corresponding to the second network address, the method comprising: sending a first request message from the user agent to the first connection port of the first network address of the call manager; sending a reply message from the call manager to the user agent to enable the user agent to register at the fourth connection port of the second network address of the call manager, wherein the call manager records as a first address an address of the first request message sent from the user agent; sending a second request message from the user agent to the fourth connection port of the second network address of the call manager; and receiving the second request message by the call manager and recording an address of the second request massage sent from the user agent to obtain a second address, and then comparing the first address and the second address; if the first address and the second address are identical, the call manager sends a first error message to the user agent, and the first error message has a first tag to indicate a first NAT type.