As per definition of "person liable to pay service tax',consignor or consignrr , as the case may be, is liable to pay tax. If definition absolves them, then the transporter is liable to pay.
As per the provisions, consignor or consignee is liable to pay service tax and register themselves as service receiver and pay tax,even if transporter pays the liablity is not absolved to consignor or consignee.