Smart city services like smart water management, smart energy, smart mobility, smart buildings, etc., are based on a centralized system. A web of sensors spread across the city feeds data to this centralized system or control center by sensing activities in the physical environment. At the control center, the data is processed and stored as meaningful information. This information is shared across various departments of the city government for better coordination and data-driven decision-making.
This sounds pretty easy to implement, doesn't it?
But practically, it is not easy. Why?
Integrating various devices with different technologies with the existing communication infrastructure is one of the biggest challenges in developing a sustainable and efficient smart city.
ICT Architecture of a Smart City
The Information and Communication Technology (ICT) architecture of a smart city has four layers:
- Sensing
- Communication
- Data
- Service

Sensing Layer
This layer contains a varied set of IoT nodes deployed across an urban area. These nodes collect data about physical environment activities. An IoT node includes sensors, microchips, power supply, and network elements. Nodes are categorized as:
- Constrained node: Operates in low-power environments with limited processing and data-transfer capabilities.
- Unconstrained node: Has no constraints in power, processing, or data-transfer capabilities.
A node may function as constrained or unconstrained based on operational conditions. For example, a proximity sensor in a small office parking lot may be constrained, while the same in a large complex may be unconstrained.
Constrained nodes struggle with XML data due to overhead and parsing complexity. To address this, the W3C proposed the Efficient XML Interchange (EXI) format, which supports constrained devices.
EXI includes two encoding methods:
- Schema-less encoding: Data is encoded directly and decoded without needing prior knowledge of the schema.
- Schema-informed encoding: An XML schema is shared between processors, allowing optimized tag representation.
Schema-informed EXI enables constrained IoT nodes to become multipurpose by understanding and generating structured data formats efficiently.
Communication Layer
Every smart city system involves millions of IoT nodes. Each node requires a unique address, facilitated by IPv6 (128-bit address). However, IPv6 overhead is too high for constrained devices. Enter 6LoWPAN—a low-power protocol designed for these nodes.
Bridge routers convert IPv6 packets to 6LoWPAN and vice versa, enabling seamless communication.
Communication technologies include:
- Unconstrained nodes: Wi-Fi, optic fiber, Ethernet, LTE, UMTS, and powerline communication.
- Constrained nodes: IEEE 802.11 Low Power, Bluetooth Low Energy, IEEE 802.15.4, RFID, NFC, and PLC.
Data Layer
This is the intelligence layer of a smart city. It involves structured storage and processing of data from IoT nodes. Databases track:
- All IoT nodes
- Departments managing the nodes (e.g., water management)
- Associated departmental data
Statistical models used include:
- Predictive models: Analyze past and current data to forecast future events.
- Descriptive models: Explain the relationship between events and their causes.
- Decision models: Evaluate outcomes of decisions based on influencing factors.
ERP systems also play a role in managing interdepartmental data flows within this layer.
Service Layer
This cross-departmental layer integrates data from various city services (e.g., water, power, pollution, transport) through web and mobile applications. The layer supports not only internal government collaboration but also provides public access to subsets of data for transparency and innovation.
Many cities have addressed urban challenges successfully through smart technology. Notable examples include Barcelona, Tel Aviv, Amsterdam, Seoul, and Stockholm.