# A Replica-Selection Algorithm Based on Transmission Completion Time Estimation in ICN
## 1 Introduction  
As the number of users increases, the huge demand for higher data rates and bandwidth puts the current Internet under increasing pressure. The communication model of the Internet is changing from a host-centric to a content-centric paradigm [1]. The user's motivation is to obtain the requested content, not to establish a connection with the service provider's device. In the current end-to-end communication model, users need to know the IP of the service provider to establish a connection to transmit content. When a large number of users obtain the same content, all users need to communicate with the server provider's device. Duplicate transmission of content causes a lot of wasted bandwidth. Many ICN architectures have been proposed, such as CCN [2], NDN [3], Mobilityfirst [4], NetInf [5], DONA [6], and SEANet [7]. In recent years, the feasibility of combining ICN with software-defined network (SDN) [8], intent-based networking (IBN) [9], and other technologies has also attracted new attention to ICN. ICN separates content from its producer's location [10]. Users can complete content acquisition from any node in the network that caches that replica based on the content's name. The caching of replica nodes in the network puts the content closer to the user. Therefore, the traffic in the core network can be effectively alleviated. In ICN, the content is a named data chunk (NDC) with a globally unique name. As the routers in the ICN network can cache the content, there are multiple replicas of content in the network. When a user requests content, how to find and select a suitable replica node to improve the user download rate and network throughput is an important issue, which has been studied by many researchers [11, 12]. According to the approach of name resolution, ICN can be divided into two types: the approach of name-based routing (NBR), in which the processof name routing is the process of replica selection, and the approach of standalone name resolution (SNR). NDN belongs to the former. It forwards the request to the content producer. The replica node can only be selected when it is on the forwarding path, and the replica node outside the path cannot be used. Although many works have been studied, the NBR-based approach is more complex for the process of discovering replica nodes. These approaches either require a cluster head for decision making, or forwarding based on ICN router local information [11]. SNR-based approaches such as [4] can easily obtain a list of network addresses (NA) of replica nodes in the name resolution system (NRS), and then select a replica node in the list. However, the existing replica-selection algorithm does not consider the expected transmission time of NDC. What users need most is to obtain a high and stable transmission rate, so as to have a low transmission completion time. In this paper, we proposed the novel replica-selection algorithm based on transmission completion time estimation (TCTE). When the replica node is in the ENRS [13] domain, TCTE selects the replica node with the shortest transmission completion time; when the replica node is outside the domain, TCTE selects the nearest replica node. Therefore, TCTE mainly affects the traffic distribution within the ENRS domain without increasing the traffic in the core network. The main contributions of this paper are as follows:  
* To solve the problem of replica node selection in ICN network, we propose the replica-selection algorithm based on the transmission completion time estimation. The transmission completion time of NDC is related to the size of NDC, the expected transmission rate, and the round-trip time (RTT). Therefore, we designed a method to obtain the expected transmission rate, RTT, and NDC size. * To solve the problem that the replica nodes may not be selected again due to bad performance in a short time, we design an \"activation\" mechanism. * We conducted experiments on the proposed algorithm.