The power to rule on the jurisdiction of arbitral tribunal rests with?

As per s.16 of the Act. S. 16. Competence of arbitral tribunal to rule on its jurisdiction.—(1) The arbitral tribunal may rule  on its own jurisdiction, including ruling on any objections with respect to the existence or validity of the  arbitration agreement, and for that purpose,— (a) an arbitration clause which forms part of a contract shall be treated as an agreement  independent of the other terms of the contract; and (b) a decision by the arbitral tribunal that the contract is null and void shall not entail ipso jure the  invalidity of the arbitration clause.