A watertight connector has a housing with terminal fittings therein. In one embodiment, the circuit is represented as a directed, partitioned graph. One of intermediate layers has the p-type conduction and comes in directly contact with the mesa stripe, while, the other intermediate layer has the n-type conduction and put between the former intermediate layer and the current blocking layer. The method also includes, sending frames that have resided in a memory slot for a greater period compared to frames residing in at least another memory slot; and setting age bits in plural memory slots when frames are written and the relative age is determined based on the age bits.