Fault determination and information sending methods and apparatuses, a source end device, and a sink end device. The fault determination method comprises: receiving OMS-O (overhead) information sent by an optical multiplex section (OMS) source end device, the OMS-O (overhead) information comprising a trail trace identifier (TTI) field (S302); according to the OMS-O (overhead) information, determining whether an OMS layer connection is faulty (S304).