IPv6 and Wireless Sensor Networks

Introduction

Sensor networks are becoming increasingly important in various applications such as inventory to disaster management. To realize the full potential, these sensor networks require connectivity to the Internet.

When sensor networks connect to the Internet using IPv6, it delivers further benefits because it can now take advantages of the huge (132-bit) address space of IPv6.

Preparing sensor networks for IP communication and integrating them into the Internet, however, requires certain features and specification to work, for example, in the adaptation of the respective link technology, specification of ad hoc networking, handling the security issues, and auto configuration to support ad hoc deployment.

Further, depending upon the application scenario, if the sensor networks are moving from the IP point of view, mobility management is also required. As mentioned, the deployment of IPv6 provides a huge address space for networking purposes to address the large sensor networks on a global scale, providing built-in auto configuration via IPv6 neighbor discovery and IPv6 stateless address auto configuration features, and providing support for NEtwork MObility (NEMO).

v6 Wireless Sensor Networks

For wireless sensor networks, the goal is to design, develop and implement IP6-enabled sensor networks over the wireless environment. The realization of IPv6-enabled sensor networks and their integration in an IPv6-enabled WAN infrastructure puts some requirements on the architecture and its functional blocks. Following are the functional blocks and their respective requirements:

Specification of IPv6 over Sensor Network Technologies

An IP-enabled sensor network requires the implementation of an IP stack in the sensor nodes and appropriate inter-working between the IP layer and the link layer. IP operation has to be specified for each specific sensor link technology, covering encapsulation and decapsulation including fragmentation and reassembling of IP packets, address resolution, compression, etc. For example, the Bluetooth Network Encapsulation Protocol (BNEP) realizes IPv6 packet transport over a Bluetooth network. A new promising link layer technology for sensor networks is IEEE 802.15.4, especially designed for low power wireless sensor networks.


Ad Hoc Networking

In order to increase the reachable range within the sensor network, IPv6-enabled sensor networks are expected to form a multihop network in which IPv6 data packets are forwarded by the intermediate nodes on the route towards the packet's destination. Moreover, sensor networks could be dynamic concerning the topology, i.e. nodes may enter or leave the network or just move around.

Even in case sensor nodes do not change their respective position, in various scenarios sensor networks are setup in an ad hoc fashion and by deploying ad hoc routing protocols like OSLR, AODV, DYMO, DSR the initial routing configuration can be generated automatically. However, MANET routing protocols could be implemented at link layer as well, performing multihop routing at link layer, adapted to the resource poor environment.

Auto Configuration

Sensor network nodes need to be configured with several parameters (IP addresses) to make them ready for communication at the network layer. The human machine interfaces (HMI) can be used to configure the sensor networks manually or they can be configured through the manufacturer provided default configuration, or through the auto configuration route that requires no user involvement. Auto configuration offers several advantages. For example, sensor nodes provide limited HMI and this makes manual configuration of nodes a difficult task indeed. Moreover, sensor networks may consist of hundreds of nodes, making manual configuration extremely hard if not outright impossible to achieve. As stated above, sensor networks are deployed in an ad hoc fashion and the actual position and function of a node within the network is not known a priori, excluding the option of manufacturer provided default configuration. In contrast, auto configuration allows IP nodes to become communication ready without any user involvement.

Mobility Management

The point of attachment of the sensor network to the Internet could be fixed or dynamic. A dynamic point of attachment is required in case the sensor network is mobile, e.g. the sensor network is attached to a rescue worker (body area network) or a vehicle that moves around. The roaming of moving networks between different geographic locations is often handled by the subnet technology in use. For example, cellular networks allow a seamless roaming and wireless Local Area Networks (WLAN) support roaming between different access points at link layer. However, when roaming takes place between different communication technologies such as a WLAN connection to a mobile connection, it becomes difficult to resolve at the link layer and has to be handled at the IP layer. In order to keep running session and to inform other nodes in the Internet about the current IP address of a mobile node, mobility management is required. In case of an IPv6 enabled sensor network without the NAT functionality between sensor network and the Internet, NEtwork MObility (NEMO) provides a solution for mobility management.

Security Issues

Security is a major concern in every part of the Internet, covering areas like encryption, detection of intrusion, access control, authentication, authorization, integrity protection, prevention of denial of service etc. In principle, in IP-enabled sensor networks standard security mechanisms based on IP could be applied. However, especially sensor networks are resource constraint concerning processing power and network bandwidth, putting limits on security. Therefore, new lightweight security mechanisms appropriate for sensor networks have to be used.