Network Address and Port Translators (NATs) have the potential to
interrupt the end-to-end nature of Internet applications, thereby
threatening end-to-end security and other end-to-end functions. Thus it
is important to be able to discover the existence of NATs and their type.
Accordingly there is provided a method of discovering the existence and
type of NAT that involves instigating a test call between media endpoints
on a Media Gateway (MG) and a Media Gateway Controller (MGC). The MGC is
able to deduce the existence of a NAT by examining the media packets sent
to its endpoint. If a NAT is determined to be present the MGC instructs
the endpoint on the MG to send media packets to another endpoint on the
MGC. By comparing the IP addresses and ports of the media packets
received at the endpoints of the MGC, the MGC is able to deduce whether
the type of NAT is Cone or Symmetric.