When modeling a 2-d quantum network by a 1-d quantum graph one usually substitutes the 2-d vertex domains by the point-wise junctions with appropriate boundary conditions imposed on the boundary values ψ(a) = (ψ ₁ (a), ψ ₂ (a), ψ ₃ (a), ...ψ _n (a)), ψ′ = ψ′ ₁ (a), ψ′ ₂ (a), ψ′ ₃ (a),... ψ′ _n (a)) of the wave-function on the leads ω ₁ , ω ₂ ,...ω _n at the junction a. In particular Datta proposed parametrization of the boundary condition, for symmetric T-junction, by some orthogonal 1-d projection P ₀ : R _n → R _n P ₀ ^⊥ ψ(a) = 0, P ₀ ψ′(a) = 0. We consider an arbitrary junction, n ≥ 3 of 2-d leads attached to a 2-d vertex domain Ω _int , in case, when there exist a resonance eigenvalue λ = 2m* E∫ ℏ ^-2 of the Schrödinger operator L _int . We derive, from the first principles, energy-dependent boundary conditions for thin, quasi-1-d, network, and obtain from it, in the limit of zero temperature, Datta-type boundary condition, interpreting the projection P ₀ in terms of the resonance eigenfunction ψ ₀ : L _int ψ ₀ = λ ₀ ψ ₀ and geometry of the leads.