A method of detecting media plane faults within a communications network. The method comprises, following the establishment of a media plane connection between first and second end point nodes within the network, where the connection transits one or more intermediate nodes within the media plane, sending session test requests from the first end point towards the second end point across a supervision session established over the media plane, and sending session test acknowledgements from the second end point to the first end point, the session test acknowledgements identifying a first border of the supervision session. The method further comprises, in the event of a media plane fault, responding to the sending of a further session test request by returning a further session test acknowledgement identifying a second border of the supervision session. The media plane fault can be detected by comparing the first and second supervision session borders contained in session test acknowledgements.