This invention relates to a system and method of monitoring, by establishing end to end loopback testing across one or more networks with dissimilar transport technologies. The system allows for connection in loopback mode from a standard interface on a test device to a media adaptor located on an IP-based access network, such as a standard multimedia terminal adapter (“MTA”). End-to-End Quality of service delivered over the transmit and receive path can thus be monitored. Loopback tests are initiated from designated endpoints on the network and made operational by attaching a tag to a telephone number, to allow the gateway to signal connection mode to a call agent. The system and method overcome certain inherent limitations of the MGCP/NCS architecture.