Cache Invalidation-Based Optimization in Next Generation Wireless Network: Taxonomy, Review, and Future Directions

Caching has emerged as a common approach utilized to optimize the performance of applications on wireless networks, with the objective of enhancing Quality-of-Service (QoS) metrics. However, as data undergoes frequent updates across most of the wireless network applications, it becomes challenging to provide updated data to the clients due to frequent disconnections and the inherent mobility of nodes. Cache Invalidation (CI) emerges as a promising mechanism to address these issues. In this paradigm, the servers broadcast, multicast or unicast the changes made in the cached data, prompting the clients to update their cached data and serve the requests efficiently. However, frequent disconnections and power-saving strategies of Mobile Terminals (MTs) can cause data loss and inconsistencies in the network. Recently, various researchers have extensively analyzed Cache Invalidation Techniques (CIT), and several CIT techniques are proposed to maintain the validity of cache contents in the MTs. This paper presents a novel taxonomy to categorize different CIT techniques that systematically optimize client query response times. Most of the reviewed techniques extend the permissible disconnection time for MTs, thus optimizing power consumption and enhance QoS by satisfying client requests with consistent data. The proposed taxonomy categorizes the existing CIT techniques based on several dimensions, notably: i) Traditional approaches, ii) contents of Invalidation Report (IR), iii) the IR-based Broadcast Time (BT), and the Disconnection Times (DT). Furthermore, this paper also presents an extensive comparative analysis of the existing techniques to examine their defining characteristics. The work also discuss the cache invalidation mechanisms for data-centric networks. This comprehensive review will provide future directions toward further exploration of CIT techniques and assist in selecting the appropriate CIT mechanism based on the requirements of the wireless application.