## 3 Enhanced Name Resolution System
### Partitioning-Based Registration and Resolution
#### 3.2.2 Name Registration and Name Resolution Schemes  
The name resolution function in ENRS follows the Publish/Subscribe paradigm, i.e., publishers (content providers) and subscribers (content consumers) will interact with ENRS through a set of HMs. Publishers and subscribers will interact with ENRS via different local HMs, which are designated through network attachment. Name resolution is developed based on the following control messages. We define three types of massages in ENRS as follows:* REGISTER (_Serv\({}_{t}\)_, EID, NA, \(T_{d}\), \(T_{send}\));
* QUERY (_EID_, _Serv\({}_{t}\)_, \(T_{d}\), \(T_{remain}\), \(T_{send}\));
* UPDATE (_Serv\({}_{t}\)_, EID, NA, \(T_{d}\), \(T_{send}\)). (A) Customized Parameters  
These parameters are defined to assist the selections of HMs and to decide the diffusion scopes of registration and resolution messages. The definition of parameters as follows:  
(i) Service Type Option (STO) parameter: represented as _Serv\({}_{t}\)_, 8 bits, which is used to distinguish the service type to decide the scopes of latency requirements. The service type can be factory automatic, vehicular networking service, mobile video service, etc. (ii) Enhanced Name Resolution Threshold (ENRT) parameter: represented as \(T_{n}\), 8 bits, it ranges from 0-255 ms; \(T_{n}\) is the latency requirement threshold provided by ENRS. (iii) Name Resolution Delay Requirement (NDRR) parameter: represented as \(T_{d}\), 8 bits. \(T_{d}\) ranges from 0 to 255 ms. \(T_{d}\) is a service-oriented and predetermined round-trip response time requirement parameter of name registration and resolution, which is utilized to assist the strategy selection. If there is no special delay requirement for an EID, then \(T_{d}=0\). Usually, the EIDs generated by the same application or service have the same \(T_{d}\). \(T_{d}\) is set based on the requestor's criteria or the contextual information. (v) Timestamp parameter: represented as \(T_{send}\), 32 bits, \(T_{send}\) is the timestamp when the message is sent. (vi) Remaining Tolerable Latency (RTL) optional parameter: represented as \(T_{remain}\), 8 bits. \(T_{remain}\) is the remaining available time to query a name. \(T_{remain}\) will decide whether to forward the request to the peer neighbors of HM when the Tolerable Latency Based Peer HM Forwarding algorithm is available, which will be discussed further below. (B) Name Registration and Name Resolution  
Name registration is aimed at publishing the bindings of EIDs and NAs in the ENRS's distributed resolvers. Name resolution finds the residing place of one copy of a name binding. Hierarchical NRSs have different name resolution approaches. For example, in CURLING, Content Resolution Servers (CRS) propagate registration and resolution requests only to their provider AS, which is the root of the tree structure of hierarchical resolution nodes, as shown in Figure 3a. Figure 3: The examples of name resolution processes. (**a**) shows the name registration and query message forwarding processes of CURING. (**b–d**) shows the message forwarding processes of three situations of name registration and query in ENRS  
Similar to CURLING, ENRS only forwards the registration and resolution requests to certain HMs by single-hop, but is not limited to AS-level. ENRS develops area-partitioning based registration and resolution request schemes according to the response time requirements, not only to realize constant query hops, but also to achieve local resolution and forwarding locality. In ENRS, the REGISTER message will be forwarded to proper HMs in different hierarchical HEA the requestor belongs to by quantitative comparison results of the round-trip response time requirement \(T_{d}\) and the transmission latency constraints \(T_{i}\) between the user nodes to the i-th level HM. The message forwarding conditions are divided into three cases as below.