In today's complex computer networks, we are constantly facing a risk of data loss, system compromise, or intellectual property theft. The complexity of the networks hinders their effective defense. A Network-wide Cyber Situational Awareness (NwCSA) has been introduced to assist a network security administrator with network security. The concept, however, faces several challenges that hinder an efficient application of the NwCSA in a real-world environment. The challenges include the overload of raw data, low speed of reaction, and a lack of context and unified view on a network. In this paper, we present a novel framework that faces above mentioned challenges. The framework leverages a distributed data stream processing system and methods for real-time big data processing. The framework is evaluated with respect to stated requirements on systems for NwCSA. Moreover, we present a prototype framework implementation and provide lessons learned from its real-world deployment.