# Two-Level Congestion Control Mechanism (2 LCCM) for Information-Centric Networking
## 1 Introduction  
The applications of 5G (Fifth Generation) networks [1] have critical requirements for end-to-end latency, especially in ultra-Reliable Low Latency Communication (uRLLC) scenarios [2]. To achieve the high-performance of 5G, researchers are working hard on a variety of supporting technologies, especially the optimization of network architectures. A new network paradigm called Information-Centric Networking (ICN) has been proposed [3]. ICN architecture and related technologies are being standardized [4] and have the potential to enhance data delivery services in 5G networks. ICN changes the Internet communication paradigm from a host-centric model to an information-centric model. It uses network-level entity identifiers (IDs) to address and retrieve the corresponding content data. By using in-network caching techniques, ICN can provide significant benefits such as faster content delivery, reduced unnecessary network traffic, and fewer duplicate transmissions of the same content. After ICN was proposed, many projects with different architectures have emerged, including Content-Centric Networking (CCN) [5], Data-Oriented Network Architecture (DONA) [6], MobilityFirst (MF) [7], Network of Information (NetInf) [8], and On-Site, Elastic, Autonomous Network (SEANet) [9]. To solve the problems faced in implementing these architectures, many related key techniques are still being investigated, such as naming,routing, caching, forwarding, security, and transport [10]. This paper focuses on the study of transport control techniques [11], in particular, congestion control mechanisms. Compared with traditional Transmission Control Protocol (TCP)/Internet Protocol (IP) architecture, ICN transmission has two main new features. One feature is the receiver-driven transmission mode, where the receiver sends the request packet carrying the content ID into the network, and the network nodes storing the corresponding content can all return the requested data by response packet. The other feature is multi-replica transmission, where the chunk requested by the receiver often has multiple copies in the network (located at the original content provider or the intermediate cache-supported ICN routers) due to the existence of the in-network caching mechanism. The new features of ICN transmission bring new opportunities for the design of congestion control. The existing ICN congestion control mechanisms are usually to first match the nearest replicas [12] by means of opportunistic cache-hits (also called happen-to-meet) [13] and then avoid network congestion by rate adjustment during data transmission. The three main mechanisms of rate adjustment include window-based congestion control mechanisms, interest-shaping methods of intermediate network nodes [14], and intermediate nodes displaying feedback congestion information [15] to assist the receiver in adjusting the request sending rate. However, these congestion control mechanisms mainly adapt to the receiver-driven characteristics and fail to take full advantage of the multi-replica feature brought by the ICN in-network caching mechanism. Considering that the content in ICN is partitioned into chunks first, and then is further partitioned into smaller packets, the authors in the literature [16] proposed a new protocol to handle the transmission of chunks in a hop-by-hop way and to perform rate adjustment inside the chunk by a loss-based algorithm. However, this approach is not very compatible with IP infrastructure. Therefore, this paper proposes a two-level congestion control mechanism (2 LCCM), where level one selects the most appropriate replica of chunk for data service by a replica selection method, and level two adjusts the request sending rate to maximize bandwidth utilization by a receiver-driven congestion control algorithm. The two levels can be switched to execute and take effect, usually by executing level one first to select a copy for data service, and then adjusting the request sending rate during the transmission process.