However, most buses use a centralized control protocol because it is faster and does not deteriorate under heavy use. In one widely used scheme, would-be bus initiators have to request and get permission to use the bus. Each bus initiator has two wires between it and a special circuit called the arbiter. One wire is called bus request and the other bus grant. When a device wants to use the bus, it asserts bus request. If the bus is free and no one else also has their bus request wire asserted, the arbiter automatically grants control to the requester by asserting bus grant to that device. Fig. 16.5.1 shows this process.