We are developing a next-generation power grid in the low-carbon era, which operates and controls demand-side equipment as well as that on the power generation and transmission sides. For these operations and controls, a computer unit, called a customer gateway in this paper, exchanges data with devices in customer premises and those in this grid. To ensure interoperability for communications with the customer gateway, a standard protocol such as IEC 62056 could be applied. The applicability of the latter for the customer gateway, however, remains to be ascertained. We specify the requirements for customer gateway communications in this paper. In addition, we show performance results measured using an experimental system with IEC 62056. Based on the requirements and results, we argue that IEC 62056 has no problem with respect to the transfer of data in bulk. In terms of latency, we must develop some methods to shorten the elapsed time and thus fulfill the requirements.