## 1 Introduction  
Recent advancement in micro-electro-mechanical and wireless communication systems have enabled the development of low cost, low power, multifunctional sensor nodes that are small in size and can communicate over short distances [1, 2]. A sensor network is a special type of communication network that is composed of a large number of tiny sensor nodes that are densely deployed either inside the phenomenon or very close to it [1]. Sensors are generally equipped with data processing and communication capabilities. The sensing circuitry senses the environment surrounding the sensor and transforms them into an electric signal. The sensor sends such signal, usually via radio transmitter, to the sink node either directly or through other sensor nodes. In the past, applications of sensor networks were thought to be very specific. The communication protocol of sensor network was also very simple and straightforward. Some researchers were even against the use of the internetworking concept in WSNs for reasons such as the resource constraints for layered architecture, the configuration problems of large numbers of devices, the essence of sensor nodes' distinct identity, _etc_. But with the advent of the Internet of things and federated IP-WSNs, this demand is going to be blurred. The huge number of IPv6 addresses, the necessity for end to end communication and advancement of micro-electronics have changed the concept of the research community. Now a tiny sensor node can hold a compatible TCP/IP protocol stack [3], so we can now think of using the concept of internetworking protocols in IP-WSNs [4]. We can easily think of providing IPv6 address to individual sensor nodes since it provides around \(6\times 10^{23}\) addresses per square meter of the Earth's space. The IPv6 over low power wireless personal area network (6 LoWPAN) working group of the Internet Engineering Task Force (IETF) defines the manner in which IPv6 communication is to be carried out over IEEE 802.15.4 interface [5, 6]. Although 6 LoWPAN helps making the wide implementation of IP-WSN a reality and its end to end communication to the external world feasible, excessive signaling costs for sensor nodes because of too much tunneling through the air makes it difficult. Excessive signaling costs therefore become a barrier for the application of IP-WSNs especially in the case of the mobility scenario of individual sensor nodes or groups of nodes in different areas such as in a patient's body sensor network, in industrial automation, _etc_. [7]. Nowadays most of the communication protocols are host based, which is practically infeasible for IP-WSNs since individual nodes need to participate in mobility related signaling. PMIPv6 which is a network based protocol, provides mobility support to any IPv6 host within a restricted and topologically localized portion of the network, without requiring the host to participate in any mobility-related signaling. 6 LoWPAN based IP-WSNs may use the sensor network compatible PMIPv6 to introduce and to enhance the mobility scenario in a localized domain. With this thinking in mind, in this work we focus on the mobility in IP-WSNs with attention paid to an energy efficient network based communication protocol for IP-WSNs. In this regard, we have proposed the SPMIPv6 for IP-WSNs. In our proposed scheme we use sensor network-based localized mobility anchors, mobile access gateways, and multiple smart and fully functional sensor nodes which are IPv6 header stack-enabled. These all IP devices including the sensor nodes make it feasible to implement the SPMIPv6 protocol over IP-WSNs. There are different application areas where IP-WSNs can be used such as industrial control, structural monitoring, healthcare, smart home, vehicle telematics, agricultural monitoring _etc_. [8]. In these scenarios, node to node communication is very important since these are the collaborative functions.