When I was setting this up for an ISP a few years ago the TDM was just a SFP that has its own MAC address inside. Its doing the TDM part inside the SPF itself. When we configured a new customer it was just adding the MAC to the config of an interface on an alcatel router at the hub side. You might not be able to transmit without interference but I bet you could spoof the MAC of a neighbor on the same fiber and listen in.