1. A system for remote loopback testing across two or more networks with dissimilar transport technologies, the system comprising: an interface gateway providing an interface between a first network and a second network, wherein control of gateways at an edge of a first network is based upon Media Gateway Control Protocol/Network-based Call Signaling (MGCP/NCS) protocol, data is transported on the first network using the MGCP/NCS protocol, and data is transported on a second network using a second traffic protocol different from the MGCP/NCS protocol; a test probe coupled to the interface gateway over the second network; an adapter coupled to the interface gateway over the first network, the adapter operable to loop back data from the interface gateway and define a remote address of the adapter; and a switch for controlling establishing a loopback connection mode between the test probe and the remote address of the adapter via the interface gateway and across the first and second networks using the MGCP/NCS protocol, wherein during loopback connection mode, the MGCP/NCS protocol is used in the second network by attaching a prefix or a suffix to the remote address.