Translate the following English sentence to French:
"Firstly, we must establish a better definition of what public service means, failing which we will not be able to make progress, and for the same reason we must also define what the general interest in the field of telecommunications really means."
Tout d' abord, il est nécessaire de mieux définir les notions de service public et d' intérêt général en matière de télécommunications sous peine de ne pouvoir avancer.