# A Mechanism for Reliable Mobility Management for Internet of Things Using CoAP
## 1 Introduction
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 standard mobility management mechanisms based on MIPv6 and its variants may not be suitable for supporting the mobility of mobile sensor nodes in IoT environments because the sensor nodes in such an environment generally have constrained CPU processing power and constrained memory capacities. The sensor nodes usually have a sleep mode operation and are often connected to a unreliable wireless sensor network. Most standard mobility management methods have not addressed these constraints of sensors nodes, and do not consider packet retransmissions during handovers because the IP protocol does not support packet retransmission. In order to solve the problem mentioned above, in reference [14], we have presented the Constrained Application Protocol (CoAP)-based Mobility Management Protocol (CoMP), which can provide efficient mobility management for constrained mobile sensor nodes in IoT environments. In [14], instead of using the IP protocol, we have used the IETF CoAP [15] for the IoT mobility management. The IETF CoAP is a specialized web transfer protocol for use with constrained nodes and constrained networks in the IoT environment. The protocol is designed for machine-to-machine (M2M) applications such as smart energy and building automation. The CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as Uniform Resource Identifiers (URIs) and Internet media types. The integration of devices with contents on the Web can be easily done by the use of CoAP because it takes into account requirements such as low signaling overhead, multicast support, and simplified architecture for constrained environments with limited resources. Therefore, the requirements offered by CoAP--low signaling overhead, multicast support, and simplified architecture--suits constrained devices with limited processing capacity, low power, low memory, and poor Internet connectivity. In this paper, we have proposed a reliable mobility management mechanism for IoT using the IETF CoAP protocol. We have extended the previous work, which was published in [14]. More specifically, we have presented the detailed algorithm of the reliability mechanism for IoT mobility management. Then, we have mathematically derived the performance measures of the reliability mechanism, such as handover delay. In deriving the performance measures, we have taken into account the IoT infrastructure characteristic of packet fragmentation, which is caused by the limited packet size of the IEEE 802.15.4 low data rate personal area network. Based on this mathematical analysis, the performance of the reliability mechanism has been evaluated by simulation. It is found that the simulation results are consistent with the mathematical results. As mentioned before, there have been lots of IP mobility management protocols proposed such as MIPv6 and its variants, which are standardized by IETF [16]. However, none of these standard mobility management protocols provide any reliability mechanisms. Compared with our previous work in [14], the contributions of our research here are summarized as follows:  
* The procedure of the reliable mobility management using CoAP have been presented for the IoT environment. More specifically, a detailed signaling procedure for achieving reliable mobility management has been designed.