Some newly emerging physical-layer cooperative communication techniques (e.g. physical-layer network coding (PNC), interference alignment, and virtual multiple-input multiple-output (VMIMO) schemes) provide high spectral efficiency and have attracted much attention. To implement these physical-layer techniques, the support from appropriate upper-layer mechanisms is required. This article takes PNC as an example to show how an upper layer mechanism can work appropriately to support PNC in a multihop network. We present a media access control (MAC) centric cross-layer collaboration mechanism for PNC, aiming at scheduling different relaying methods adaptively and allocating the correspondingly needed resources (e.g. transmission powers and channels) efficiently. Our numerical results affirm the efficiency of this mechanism, highlighting the importance of cross-layer collaboration for the implementation of physical-layer cooperative communication techniques.