3GPP 38.300 v19.3.0 — the document's own text
16.21.2 Protocol Architecture
From L2 MP Remote UE perspective, three bearer types exist: direct bearer, indirect bearer, and split bearer. For direct bearer, only Uu radio resources are involved, and for indirect bearer, only PC5 or N3C radio resources are involved. For split bearer, both Uu and PC5/N3C radio resources are involved.