A numerical study of the dynamics of the L-H transition in JET was done using models of anomalous transport which depend either on local or on global plasma parameters. Comparison with experimental results [1] shows that the best agreement is reached when using a global model for reducing χe, χi and D in the region where shear becomes large (e.g. outside q=l surface). Thus the L-H transition manifests itself as a sudden drop of transport coefficients everywhere outside the q=l surface, not only in a narrow layer near plasma edge. The slow improvement of plasma confinement which follows such a fast transition could then be attributed to the inverse dependence on density of the transport coefficients near the plasma centre.