# A Hierarchical Mapping System for Flat Identifier to Locator Resolution Based on Active Degree
## 2 Hierarchical Mapping Architecture on Active-Degree (HMAA) for Identifier Resolution  
Reference [11] points out that the activity of an IP subnet prefix meets the heavy-tailed distribution, in which the underlying reason is related to the psychological characteristics and social life habits of network users such as usage habits that do not change usually. So, by taking advantage of the character in the existing network, we \"push\" the active mapping items to network users under the ID/Locator separation architecture.  
The mapping structure is divided into three levels: active local level, neutral transfer level, and inert global level. Their corresponding mapping servers are AMS (Active Mapping Server), NMS (Neutral Mapping Server), and IMS (Inert Mapping Server), respectively. Figure 2 shows the entire resolving system, which is called HMAA (Hierarchical Mapping Architecture on Active-Degree).  
Here we use active-degree to indicate the activity of mapping items. The nearer to endpoint, the higher the active-degree. The mapping item which is used frequently will be assumed a higher active-degree to a special user and will be stored at the mapping server with the higher activity layer.  
AMS provides services for one or a group of AR(s), stores related copies of frequently-used mapping items, and allocates appropriate RIDs to the corresponding endpoint AIDs if necessary. That is, it produces the original mapping item. The purpose of using AMS is to ensure the queries of mapping are quickly replied for most users communication; NMS stores less frequently used mapping items which are related to a group of ARs, and performs the Policy Report (PR) of mapping items, which aims to reduce the frequent mapping item updates caused by the numerous endpoint frequently move; IMS stores all the copies of mapping items, and every mapping item which is allocated by AMS should be reported to IMS. Storing all mapping items in IMS is to ensure the robustness of query for identifier-to-locator; mapping items are placed and dynamically flow between the three levels according to their activity.  
Policy Report occurs in a special area we call GROUP. The so-called GROUP refers to a set consisting of several ARs, neutral services routers, AMSs and NMSs in the same geographical range. A neutral service router is a special core router, which directly associates with the corresponding NMSlogically within the GROUP. A neutral service router deals with the first several packets sent to the mobile endpoints in the same GROUP, and informs the fact RIDs of mobile endpoints to communicate to peers. Within each GROUP there is one or more NMS, and each NMS is responsible for the storage of less frequently used communicating peers' identifier mapping items corresponding of several AMSs in the GROUP and local endpoint mapping items reported by the ARs. In this paper, we consider the case that each GROUP has only one NMS, because we can regard each region as a group, which corresponds with an NMS and its several corresponding AMSs, as shown in Figure 2.  
It should be noted that, in order to prevent the mapping system from possible user attacks, we deploy the mapping system in the routing identifier space, that is, every mapping server is identified by RID.