## 2 Background
### Comparison with Standard Mobility Management Protocols  
To support the mobility management protocol, several mobility protocols have been proposed for wireless Internet [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19]. These protocols can be broadly classified based on the layer of their operation, such as those operating in the network layer, transport layer and application layer. The dependency of these mobility protocols on the access networks reduces progressively as we move up on the protocol stack. Among them, Internet Engineering Task Force (IETF) has standardized Mobile IP (MIP) and Session Initiation Protocol (SIP) as the mobility solution for the network layer and application layer, respectively. Table 1 shows the comparison of CoMP with the Mobile IP and SIP MM. Mobile IP allows the mobile node to acquire and register a new IP address in each visited network. Mobile IP [6] is the main protocol for mobility management at the IP layer, which allows a mobile node to remain reachable despite of its movement within the IP environment. The Mobile IP uses the tunnel mechanism to prevent the packet loss during the handover between the access router and the mobile node or between access routers. Mobile IP, however, requires significant changes in the underlying networking infrastructure. Furthermore, the mobile node requires the routing function and tunneling function in order to support the tunneling scheme. In IoT network environment, the routing function and the tunneling function at the mobile node requires the high processing capability, high power consumption, high memory, etc. Mobile IP may not be suitable for IP mobility management at IoT/WoT networks. SIP is an application level signaling protocol that controls communication sessions for multimedia flows in the Internet, such as voice or video calls. Through SIP's name mapping and redirection services, it can be used for personal mobility. Application layer protocols however, are transparent to the lower layer characteristics and they maintain end-to-end semantics of a connection. The application layer protocols are also expected to be the right candidate for handling mobility in a heterogeneous environment. SIP is capable of supporting not only terminal mobility but also session mobility, personal mobility and service mobility. In addition, SIP can support IP mobility without the tunneling scheme. Therefore, SIP has been considered as an attractive candidate at the application layer mobility management protocol for heterogeneous 5G wireless networks [21]. However, SIP may not be suitable for IoT network environments with network constraints such as the limited packet size, low bandwidth and resource constraints such as low power, low CPU processing capacity, and small memory. In particular, SIP requires an additional application header to carry its signaling messages, and hence is limited by the performance of TCP or UDP over constrained wireless links. More specifically, in SIP, the maximum transmission unit (MTU) of a packet requires 1500 bytes. However, the MTU of IEEE 802.15.4 standard is limited to 127 bytes. Hence, SIP may not effectively provide the mobility management at IoT network environment. In Mobile IP and SIP, the session initiation agent is the mobile node. On the contrary, in WoT network environment, the Web client performs the session initiation. In addition, the sensor node in IoT environment usually operates either in sleep or wakeup mode. Hence, the Web client may not get the required data from the senor node in sleep mode operation. Therefore, the protocols mentioned previously may not be suitable for mobility management in a IoT environment with constrained device and network characteristics; for example, with low signaling overhead, low processing and energy constraints, or in sleep mode operation. Therefore, the novel mobility protocol is required to solve the previous problems. To solve the mentioned previous problems, we propose the CoAP-based mobility management protocol, called CoMP, for IoT network environment.