Considering that the running theme of the Arbitration and Conciliation Act is the consent or agreement between the parties at every stage, Section 21 performs an important function of forging such consensus on several aspects viz., the scope of the disputes, the determination of which disputes remain unresolved; of which disputes are time-barred; of identification of the claims and counter claims and most importantly, on the choice of arbitrator. Thus, the inescapable conclusion on a proper interpretation of Section 21 of the Act is that in the absence of an agreement to the contrary, the notice under Section 21 of the Act by the claimant invoking the arbitration clause, preceding the reference of disputes to arbitration, is mandatory. In other words, without such notice, the arbitration proceedings that are commenced would be unsustainable in law. Alupro Building Systems Pvt. Ltd. v. Ozone Overseas Pvt. Ltd., 2017 SCC Online Del 7228.