# IMU: A Content Replacement Policy for CCN, Based on Immutance Content Selection
###### Abstract
Content replacement policy is responsible for choosing the right content against defined criteria [13]. The network performance and cache hit ratio decreases if popular content is removed from the cache or unpopular content remains in cache for a long time [14, 15, 16, 17]. Although cached contents at all nodes, along with the routing path, increase the network performance and cache hit ratio, it is not a practical approach due to the finite cache space. That is, if the cache space is full and new content arrives, one of the cached content needs to be removed from the cache space. However, most existing replacement policies follow the concept of the Least Frequently Used (LFU) or Least Recently Used (LRU) policy to replace the content which is not effective for CNN [18]. The newly arrived content may become popular over time due to high demand. When popular content loses its popularity, it stays in the cache due to previous popularity. Therefore, the network performance may decrease due to the overstay of previous popular content that is currently unpopular or the eviction of currently popular content. To solve this issue and improve network performance, we introduced a new concept of content maturity and immaturity to deal with the aforementioned issues. The content that loses its popularity over a specific time frame and stays in the cache for a long time is called immature content. In contrast, the content will be considered mature if it has high popularity and is also recently requested in the network within a specific time frame. Every new content is neither popular nor mature. Content should stay in the cache for some time to know its maturity level. Hence, such content is not evicted from the cache, which is yet to become popular. In addition, this concept removes content from the cache that loses its popularity after being highly popular for some time. A content replacement policy is proposed in this work called IMU (Immaturity used). This policy removes content from the cache that is immature within a limited time frame. Therefore, most of the contents in the cache are recently used and highly popular, leading to a better cache hit ratio and network performance. The key contributions are summarized below:  
* A new concept of content maturity/immaturity has been introduced to design and develop an effective content eviction policy. The proposed content eviction policy evicts the content from cache through the immature content selection to improve the cache hit ratio, latency, path stretch, and link load. * A mechanism to calculate the maturity level of the content has been designed and developed using the content frequency and arrival time of the content. * Icarus [19] has been used to verify the performance of the proposed policy with existing state-of-the-art content replacement policies. Subsequently, we gained substantial improvement in cache hit ratio, latency, path stretch, and link load. The rest of this paper is organized as follows: We discuss the related work in Section 2. The proposed policy is described in Section 3, which highlights its contribution. Section 4 describes the simulation environment and parameters as well as the result analysis and discussion. Finally, the conclusion and future work are in Section 5.