Data communication in modern systems involves the exchange of information between independent components over networks, which is crucial for distributed architectures that rely on network-based interactions like APIs and event brokers. This communication is foundational for ensuring service independence, global responsiveness, and the seamless integration of diverse systems. It requires addressing challenges such as latency, reliability, and coupling through a well-defined Data Communication Interface (DCI) that includes messaging, protocol, and transport layers. As microservices and IoT proliferate, robust inter-service communication layers must be designed to handle retries, circuit breaking, and backpressure, ensuring reliability and fault tolerance. Tools like PubNub facilitate real-time data communication by providing a global, low-latency network that abstracts infrastructure concerns and supports features like presence tracking, state storage, and fine-grained access control. Effective communication strategies enable scalability, real-time analytics, and system observability, while maintaining security and compliance across layers. As systems grow more complex, thoughtful communication design is essential for resilience and agility.