## 1 Introduction
As a result, the load of middle agent can be dramatically increased when the number of mobile nodes increases and the triangular routing problem can be incurred. Hence, the process of control packet and real packet may be separated. This lightweight Mobile IPv6 does not consider the sleep mode operation of IoT devices and requires the modification of infrastructure such as home agent and foreign agent because it is based on Mobile IPv6. [PERSON] _et al._ proposed the Sensor Networks for an All-IP World (SNAIL) based on MARIO [14]. In this research, the sensor is composed of PAN coordinator, static node, partner node, mobile node, and gateway. SNIL uses the ancestral concept to perform the handover. More specifically, the mobile node retrieves the domain information of next static node, _i.e._, node ID and IP address, through the partner node before the mobile node performs the handover. After that, in the next domain, the mobile node performs the binding update with next domain information. As a result, the handover delay can be reduced. However, as the mobile node does not move into pre-defined location of next static node, the handover delay and packet loss can be large. Also, a PAN coordinator may always manage and update the information of near sensor. It can occur a large signaling overhead in the network domain. [PERSON] _et al._ presented a protocol to carry out inter-WSN mobility inside of the architecture that has been defined at a hospital [15]. It can decrease the number of interchanged messages of mobile nodes when the mobile nodes move within pre-defined regions. However, it is not suitable for IoT global mobility protocol because this mobility protocol cannot support the global mobility and the modification of network infrastructure is required. [PERSON] _et al._ presented the Care-of Address Pool for Hierarchical MIPv6 (CoAP-HMIPv6) to reduce the handover latency by reducing influence caused by the DAD procedure [16]. However authors have not considered the mobile network with the constrained resource. [PERSON] _et al._ have proposed the Open Mobile Alliance device management protocol for reliable Device Management (OMA-DM) and have analyzed and compared the efficient XML interchange (EXI), CoRE Link format, and protobuf for efficient message format [17]. The authors proposed EXI is efficient as the payload format in use of CoAP. [PERSON] _et al._ presented a mobility management scheme for 6 LoWPAN sensor nodes [18]. The authors proposed the fast handover proxy mobile IPv6 for sensor network (FPMIPv6 S) protocol, an improved version of the Proxy Mobile IPv6 (PMIPv6) protocol, to reduce the number of messages exchanged and the handover latency. However, they did not consider the complexity of FMIPv6, with respect to CPU processing overhead and energy consumption. [PERSON] _et al._ presented a resource mobility scheme for service continuity in an IoT environment [19]. They proposed a resource mobility scheme using two operating modes, caching and tunneling, to enable applications to access the sensory data when a resource becomes temporarily unavailable. The sensor gateway caches the measured data, and transmits the data in response to a service provider's request instead of the sensor. The tunneling method reduces the amount of packet loss during the handover of a sensor by creating a tunnel between the sensor gateways. However, as both sensor gateway and sensor itself can move between different wireless networks, the connectivity might be disrupted during their movement. In summary, most current mobility management protocols may not be suitable for supporting the mobility of CoAP sensor nodes in WoT environments because the sensor nodes in such an environment generally have constrained CPU processing power and memory capacities and they must have low energy consumption. They have other characteristics such as sleep mode operation and a constrained network of wireless sensor networks.