## 1 Introduction  
The rapid increase of the scale of the power system, coupled with concerns about an energy crisis and environmental pollution, spurred the progressive application of new-generation and transmission elements, such as cross-regional ultra-high-voltage (UHV) transmission, concentrated or distributed renewable generating, electricity markets, and so on. In order to maintain the reliability and security of power system operation, control resources on the demand side are expected to make more important contributions to power system control. Therefore, demand response (DR) is absorbing more and more attention from researchers and utilities around the world [1; 2]. The traditional DR system tends to be based on the advanced metering infrastructure (AMI) with good performances in accuracy, stability, and speed on load control, benefiting from the highly universal and centralized architecture and control strategies [2; 3; 4]. This routine is suitable in a modern and automated power system environment with adequate budget for construction and maintenance cost. However, for developing countries, there are two significant limitations of this routine: (1) considerable expense is expected to achieve DR through this routine, as massive updates and adjustments need to be applied in the communication infrastructure and physical infrastructure [3]; (2) loads are supposed to be well aggregated in the form of smarting buildings, central air conditioning, etc., which are accessible to DR appliances [2]. Unfortunately, the loads in developing countries are mostly heterogeneous and non-zoned with weak central management. Therefore, the purpose of our work is to find a justifiable approach to resolve the conflicts between the operation demands and economy constraints, while fully utilizing the existing communication facilities and attracting social funds, to establish a bidirectional, evolution-accessible, and highly adaptable DR system proven to be valuable and practicable [4; 5]. Given that broadband internet connections already exist in fundamental power facilities and appreciable households in most countries, some researches followed an internet-based control approach to satisfy DR task requirements [4; 5; 6; 7]. However, there are some limitations in these researches: (1) the coverage of the internet-based system is limited by internet access points (APs); (2) the system is mainly optimized for customer requirements, while there is a lack of consideration of the influences on the grid [6; 7]. In this paper, the physical equilibrium of the grid is considered in the system architecture and control strategies to ensure system practicality. Internet of things (IoT) technologies are expected to address the shortage of internet coverage. IoT retains the management ability of massive device access, with significantly lower power consumption and plug-and-play function [8; 9; 10]. Reference [8] reviewed the prospects and challenges of IoT in power system appliances, and concluded that the efficiency, reliability, flexibility, security, and sustainability of power systems could be highly improved by applying IoT. However, previous studies about IoT in power systems mainly concentrated on theorical or device-level problems, and the achievements and effectiveness were mainly limited to micro-grids [4; 9; 10]. This paper addresses these gaps by providing a multi-communication-based DR system integrating IoT and existing internet connections into a power system, to provide a lower implementation budget and operating energy cost. In addition, the multi-scale and multi-target characteristics of grids and customer tasks are considered through the deployment of agents and corresponding strategies. Specifically, a local check-and-action strategy is described in detail as a case of the proposed DR system providing short-time control for power system regulation. All the elements involved were implemented, including a smart terminal which could support the deployment and operation of the DR system.