In recent years, low-rate wireless personal area network (LR-WPAN) technology integrating network technology, embedded technology and sensor technology has become a research hotspot. LR-WPAN is a network designed for short-range, low-rate, low-power wireless communication, and can be widely used in smart home appliances and industrial control. The IETF organization formally established the IPv6 overLR-WPAN (6LowPan) working group in November 2004, and set out to develop an IPv6-based low-speed wireless personal area network standard, namely IPv6over IEEE 802.15.4, which aims to introduce IPv6 into IEEE 802.15.4. The underlying standard wireless personal area network. Its emergence has driven the development of short-range, low-rate, low-power wireless personal area networks. IEEE 802.15.4 is a typical representative of LR-WPAN, and its application prospects are very broad. The research based on it is in the ascendant.
However, IEEE802 15.4 only specifies the physical layer (PHY) and media access control (MAC) layer standards, and does not cover the above network layer specifications, and the IEEE 802 15.4 device density is very large, and it is urgent to implement networking. At the same time, in order to meet the interconnection and interoperability between devices of different equipment manufacturers, it is necessary to establish a unified network layer standard. With its unprecedented address space and openness, IPv6 has a great appeal to LR-WPAN.
1. Overview of IEEE 882.15.4 Technology
IEEE 802.15.4 defines the PHY and MAC layers.
The main features of the IEEE802.15.4 standard: 1 low rate, for the 2.4GHz, 828MHz, 915MHz three frequency bands corresponding to 250Kb / s, 20Kb / s and 40Kb / s three rates; 2 low power consumption, can be used in standby mode 2 Section 5 dry battery drive for more than 6 months; 3 low cost, generally using bottom-end embedded devices with very limited hardware resources or smaller special equipment; 4 short distance, node signal coverage is limited, generally 10-100m; Low complexity, lower than the existing standard; 6 short frame length, maximum frame length is 127 bytes; 7 multi-topology, rich network topology, support two basic topologies and hybrid networking of star topology and point-to-point topology .
2, 6LowPan technology overview
2.1 Introduction to 6LowPan Technology
The research focus of 6LowPan working group is adaptation layer, routing, header compression, fragmentation, IPv6, network access and network management. Currently, the adaptation layer technology draft has been proposed. Other technologies are still under discussion.
The 6LowPan technology uses the PHY layer and the MAC layer defined by IEEE 802.15.4, and the network layer adopts the IPv6 protocol. Due to the payload length supported by the MAC in IPv6, the payload length of the 6LowPan bottom layer can be provided. In order to achieve seamless link between the MAC layer and the network layer, the 6Low-Pan working group proposes to add a network between the network layer and the MAC layer. The layer is used to complete the header compression, fragmentation and reassembly, and mesh routing and forwarding.
2.2 Advantages of 6LowPan technology
(1) Popularity: IP networks are widely used, and IPv6, which is the core technology of the next generation Internet, is also accelerating its popularity. It is more acceptable to use IPv6 in LR-WPAN networks.
(2) Applicability: The IP network protocol stack architecture is widely recognized, and the LR-WPAN network can be developed simply and efficiently based on this architecture.
(3) More address space: The biggest highlight of IPv6 applied to LR-WPAN is the huge address space. This is precisely the need to deploy large-scale, high-density LR-WPAN network equipment.
(4) Support stateless automatic address configuration: when the node is started in IPv6. The MAC address can be read automatically and the required IPv6 address can be configured according to the relevant rules. This feature is very attractive for sensor networks because in most cases it is not possible to configure the user interface for the sensor nodes, and the nodes must have automatic configuration capabilities.
(5) Easy access: LR-WPAN uses IPv6 technology to make it easier to access other IP-based networks and next-generation Internet, enabling it to take advantage of IP network technologies.
(6) Easy development: At present, many technologies based on IPv6 are relatively mature and widely accepted. The characteristics of LR-WPAN are appropriately simplified and trade-offs for these technologies, simplifying the process of protocol development.
It can be seen that the application of IPv6 technology on the LR-WPAN network has a broad space for development, and the access of the LR-WPAN to the Internet will greatly expand its application, making the realization of a large-scale sensing control network possible.
2.3 6LowPan key technology analysis
The 6LowPan working group has conducted active research and discussion on the key technologies of IPv6 and IEEE805.15.4. The key technologies for transmitting IPv6 data packets on IEEE 802.15.4 are as follows:
(1) Coordination of IPv6 and IEEE 802.15.4. The maximum frame length defined by the IEEE 802.15.4 standard is 127 bytes. The maximum length of the MAC header is 25 bytes, and the maximum length of the remaining MAC payload is 102 bytes. If safe mode is used, different security algorithms occupy different numbers of bytes. For example, AES-CCM-128 requires 21 bytes, AES-CCM-64 requires 13 bytes, and AES-CCM-32 requires 8 bytes. This leaves the MAC payload with a minimum of 81 bytes. And in IPv6. The MAC payload is up to 1280 bytes. IEEE 802.15.4 frames cannot encapsulate complete IPv6 packets. Therefore, to coordinate the relationship between the two, an adaptation layer is introduced between the network layer and the MAC layer to perform the functions of fragmentation and reassembly.
(2) Address configuration and address management. IPv6 supports stateless address autoconfiguration. Compared to stateful autoconfiguration, the configuration requires less overhead, which is suitable for LR-WPAN device features. At the same time, since LR-WPAN devices may be distributed in large quantities and densely in places that are difficult for people to reach, it is more important to implement stateless address autoconfiguration.
(3) Network management. Network management technology is critical to the LR-WPAN network. Due to the large scale of the network and the location of some devices that are not accessible to personnel, the LR-WPAN network should have self-healing capabilities, requiring LR-WPAN network management technology to manage highly densely distributed networks at very low overhead. device. Since forwarding IPv6 data on IEEE802.15.4 advocates using existing protocols as much as possible, and Simple Network Management Protocol (SNMP) provides a good network management framework and implementation method for lP networks, 6LowPan tends to be in LR. - Network management using SNMPv3 on WPAN. However, since the original intention of SNMP was to manage the IP-based Internet, it was applied to the LR-WPAN network with limited hardware resources. Further research and improvement are still needed. For example: limiting data types, simplifying basic encoding rules, and more.
(4) Security issues. Because the use of security mechanisms requires additional processing and bandwidth resources, it is not suitable for LR-WPAN devices, and the AES security mechanism provided by IEEE802.15.4 at the link layer is relatively loose and needs to be further strengthened, so it is suitable for LR-WPAN. Security mechanisms have become one of the key issues in the 6LowPan study.
As a new research hotspot in the information field today, 6Low-Pan has many key technologies to be discovered and studied, such as service discovery technology, device discovery technology, application programming interface technology, and data fusion technology.
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