Embodiments describe transceiver architectures to enable ‘loopback’ operation, thereby allowing or on-chip or intra module characterization of the transceiver. This includes but is not limited to tests such as bit error rate (BER) characterization, received power characterization and calibration of filters (MUX, DMUX etc.) present in the transceiver. Embodiments may also describe architectures for superimposing low-speed data on to the signal coming out of a transmitter, which in turn enables low frequency communication between network elements in the external link.