# A Replica-Selection Algorithm Based on Transmission Completion Time Estimation in ICN
## 2 Related Works  
In ICN networks, content can be cached in different locations, so each piece of content may have multiple replicas, and it is an important issue how to use multiple replicas of ICN effectively. Table 1 shows the characteristics of the related work. A name resolution service is used to help clients access content, hosts, or services using names, and there are two main approaches, the name-based routing approach (NBR) and the standalone name resolution approach (SNR) [14]. The ICN architecture has different approaches to name resolution services and different issues when performing replica selection. In the ICN architecture using the name-based routing approach, such as NDN [3], the ICN router needs to select the outgoing interface to forward the content request according to the information it maintains. The process of content request forwarding is the process of replica selection. The shortest-path routing algorithm forwards content requests to content providers, such as OSPFN [15] and NLSR [16], so only replicas on the routing path can be selected. The algorithm has lower overheads, but users have fewer replicas of the content available to them. Many algorithms have been proposed to efficiently utilize content replicas on non-shortest-routing paths. The cluster-based method [17; 18], through the cluster head node centralized caching decision and forwarding decision when receiving a content request, can realize the replica selection in the cluster. iNRR [19] explores the network in a scope-flooding approach using the first content request. In SEARCH-CNG [20],link bandwidth is defined as the ratio of the link's capacity to the number of flows over this link, and the algorithm makes forwarding decisions based on link bandwidth to avoid congested links. Both iNRR and SEARCH-CNG are flood-based methods that explore in-network replicas, thereby reducing traffic on the default forwarding path. INFORM [21] is a dynamic forwarding mechanism based on the Q-learning algorithm [22]. It discovers content replicas through flooding, and then selects forwarding paths based on indicators such as RTT. Stateful forwarding [23] is also a learning-based forwarding mechanism. The ranking value is the basis for the forwarding decision of the algorithm. It represents the priority of the forwarding path, which depends on various performance indicators, such as RTT and link state, etc. In SCAN [24], the single-hop neighbor nodes exchange the information of their cached content regularly through the Bloom filter [25]. When the content request arrives at the node, if the content exists, it will be forwarded directly to the client; if it does not exist, the content will be searched for whether it is cached in a neighbor. RFW [26] is based on random walks. A layered ICN architecture is proposed in RFW, the publisher is located in the first layer, and the client is located in the bottom layer. When the content request arrives at the layer N, the maximum random walking time is T. When the walking time exceeds T, it will be forwarded to the N \(-\) 1 layer until a replica of the content is found. In the ICN architectures that use the standalone name resolution approach, such as Mobilityfirst [4] and NetInf [5], the client first obtains the locator of the content from the name resolution system (NRS), then selects a replica, and uses the content locator for routing to complete the content acquisition [27; 28]. Compared with the ICN architecture using NBR, the ICN architecture using SNR can easily obtain the locators of multiple content replicas because of the existence of NRS, and then obtain the content. ERS [12] uses the distance-constrained-based name resolution system [13] to discover nearby replicas, and then calculates a node status value based on the maintained replica node queuing delay, outstanding requests, RTT, and the network distance for replica selection.