# Cache Servers Placement Based on Important Switches for SDN-Based ICN
## 2 Related Work  
We are going to discuss the working of some of the related existing approaches in this section. [PERSON] et al. [10] extended Home Router Sharing based on Trust (HORST) [32] by adopting HORST in SDN architecture. HORST [32] is an existing system to share among trusted users the access to Wi-Fi. Moreover, by utilizing the information of users from their online-social-network (OSN) profiles, HORST pre-fetches videos and caches at home routers. HORST also interconnects home routers in the peer-to-peer (P2P) overlay. This paper uses an SDN controller for content distribution and request forwarding in HORST. Furthermore, the authors introduced three tiers architecture for content sharing by using home router, caches within Internet Service Provider (ISP), and at the content distribution network (CDN) as follows. At tier-1, their proposed approach stores the data in the data center of content provider. At tier-2, their approach caches the data at edge networks and ISPs using the CDN fashion. At tier-3, their proposed approach utilizes the home routers of the user network to cache data by using HORST. Their proposed approach forwards the request of the user for video content to the closest cache in such a way to improve the quality of service and the quality of experience, and reduces the inter-domain traffic for ISP networks. However, their proposed approach does not consider path stretch, closeness centrality, and other parameters for cache server placement. [PERSON] et al. in [11] suggested a novel architecture Forwarding-Content-Caching and Routing Name Data Networking based Software Defined Networking (FCR-NS). This model resolves the three main issues related to forwarding strategy, speed of router, and cache replacement policy. The authors state that the existing architectures are using the best-route forwarding strategy that causes wastage of different resources. The reason behind the slow processing is the visiting of the Content Store (CS) table, Pending Interest Table (PIT), and Forwarding Information Base (FIB) table for searching the request message and lack of efficient cache replacement policy. The authors resolved the problems as mentioned above by using both the concept of decoupling of SDN and set bloom filter tables. The efficient cache replacement strategy is calculating the switches' popularity on a real-time basis. The SDN controller manages the fast-intra-zone routing, and the bloom filter (BF) tables are using to manage the fast inter-zone routing process. The default policy for content caching is leaving a copy of the request message on all routers on the path. This policy leads to content redundancy in the network and resource consumption. The authors suggest an architecture of several zones, as shown in Figure 1, and these are further divided into two main planes, the data plane and centralized SDN controller, which is further composed of four tables. The proposed FCR-NS has four tables in the Controller and Five Tables in the FCR-NS switch. The controller tables are Global-Top table, Global-Data table, Routing Information Base (RIB) table, and Global-Data-BF table. However, the FCR-NS switch is composed of five tables that are CS table for caching, CS-BF table, FIB table, FIB-BF table, and PIT table. The authors proposed a replacement policy for content caching that considers the popularity of data. The replacement takes place based on the FIB table, which stores the record of popular content. Furthermore, the authors improve the routing by dividing of routing into intra-zone and inter-zone. The FIB tables of switches in intra-zone and contains popular data the network, which is used for the fast reply of request messages from the nearest nodes. The controller uses Global-Data and Global-Top tables for the construction of FIB and a table for the storage for all data in that network. Then, the controller constructs the FIB table for each switch in the network.