## 2 Related Work
### Resolution Latency  
Resolution latency is another key indicator of the NRS. The name resolution itself does not require much bandwidth, while the query latency is critical. In 5G and emerging networks, as the network capacity increases, \"milliseconds count\" [34]. For distributed ICN NRSs, low latency demands that the NRSs complete the name resolution procedures with minimal delay, thus efficient routing and load balancing methods are needed. For an NRS with low latency characteristics, the complexity of resolution latency should be O (1), i.e., should not depend on the number of nodes in the network [34]. At the same time, the name resolution system should support the forwarding locality, which is contributed to reduce the inter-domain traffic and resolution delay [26]. Resolution message forwarding locality means that if two communication endpoints (i.e., sender and receiver) are in the same network domain, the resolution path should also be included in that domain to minimize inter-domain traffic [22]. [PERSON] et al. proposed a generic hierarchical global NRS framework HDHT with flat naming [26]. The request registration and forwarding paths in the framework can match with the underlying network topologies. The domain (i.e., subsystem) of HDHT is autonomous, the locality of the request is exploited, the name resolution of the constant hop count is supported, and the scopes of publications are limited, which effectively reduce the resolution latency and the system control overhead. [PERSON] et al. proposed an \"Efficient yet Simple\" (ES) model for constructing a DHT-based ICN NRS topology with a self-organizing feature to achieve low latency resolution and reduce the control overhead of the NRS, as well as adapting to highly dynamic environments [35]. The ES model had a small diameter. Thus, the number of routing hops of the query message was reduced, which can effectively shorten the query latency and save network resources. [PERSON] and [PERSON] proposed a distributed ICN name resolution method for IoT scenarios [36; 37]. A specialized ICN router was selected as the Home Node for collecting and maintaining all the necessary information for name resolution, and a decision-tree-based classification model was utilized to assign the Home Node for newly published content. Leaving multiple replicas of names in the distributed NRS is an effective way to reduce the resolution delay and enable the localization of query traffic. [PERSON] et al. proposed a distributed resolution mechanism Direct Mapping(DMap) [38] for GUID and NA mapping in GNRS [18]. DMap maps the GUIDs to the NAs of AS-level gateway routers through \(K\) (\(K\geq 1\)) consistent hash functions and cachesthe GUID in the gateway routers. Caching \(K\) (\(K\geq 1\)) GUID replicas in multiple ASs ensures that requestors can obtain resolution responses through a single-hop, which is beneficial for low-latency name resolution. Research [39; 40; 41; 42] has shown that network size, content location dynamics, and content popularity have a great impact on name resolution performance. However, when selecting the storage location of the GUID replicas, DMap does not consider the popularity and the location distribution of contents. A hierarchical method GMap [35] for multi-replica placement of GUID and NA mappings in GMRS was proposed. GMap was developed based on DMap. It utilizes hierarchical replica caching method to make full use of query localization to achieve fast name resolution. GMap caches \(K\) replicas for each GUID, similar to DMap. However, GMap divides the global network into finer granularity, such as global, national, and urban networks, thus leaving \(K_{1}\), \(K_{2}\), and \(K_{3}\) replicas at different levels, with \(K_{1}\), \(K_{2}\), \(K_{3}\) satisfying \(K_{1}+K_{2}+K_{3}=K\). GMap retains the advantage of DMap to exploit single-hop querying and GMap significantly reduces the resolution latency compared with DMap.