Independent Submission Wu,Xu Internet Draft CEDRI Intended status: Informational July 31, 2010 Expires: January 2011 Convergence framework of Internet and WSN draft-wu-convergence-internet-wsn-00.txt Abstract This Internet Draft provides a detailed description of the convergence framework of Internet and WSN so far, including 4 main solutions and 2 additional technologies. The main aim of this document is to serve as a general reference for the convergence solution space, to take advantage of the two networks the advantages of diversity and meet the needs of network users. Furthermore, each solution is analyzed based on a number of evaluation considerations. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction ................................................ 2 2. Conventions used in this document............................ 2 2.1. WSN .................................................... 2 2.2. DTN .................................................... 3 3. Proxy ....................................................... 3 4. Protocol Overlay ............................................ 4 5. Delay Tolerant Network....................................... 5 6. Full IP ..................................................... 6 7. Other technologies .......................................... 8 8. Security Considerations...................................... 8 9. IANA Considerations ......................................... 8 10. References ................................................. 8 10.1. Normative References................................... 8 10.2. Informative References................................. 9 11. Acknowledgments ............................................ 9 1. Introduction With large-scale, integrated, flat Internet and small-scale, diverse, mobile wireless sensor network, a converged network is coming into existence, which is efficient, flexible and secure [1]. Network adopting the integration of mutual collaboration and effective management of resources and rational allocation can effectively improve network throughput ,reduce the energy consumption of wireless devices , reduce the information transmission delay, and provide technical support for rapid decision-making; we can take advantage of the two networks the advantages of diversity and meet the needs of network users better, effectively improve network security, provide a basis for the reliable platform for access to information and expand the network coverage, so the network is more scalable. 2. Conventions used in this document 2.1. WSN A wireless sensor network (WSN) consists of spatially distributed autonomous sensors to cooperatively monitor physical or environmental Wu,Xu Expires January 31, 2011 [Page 2] Internet-Draft WSN convergence framework July 2010 conditions, such as temperature, sound, vibration, pressure, motion or pollutants [2]. 2.2. DTN A disruption-tolerant network (DTN) is a network designed so that temporary or intermittent communications problems, limitations and anomalies have the least possible adverse impact. 3. Proxy Proxy nodes between heterogeneous networks are mounted in this mode, which can simultaneously implement WSN protocols and TCP / IP, and translate protocols at the different levels. Communications between Internet and WSN need the proxy. So a WSN can use different protocols with respect to the requirements and environment. This is the simplest mode of network convergence, as shown in Figure 1. +--------+ +-------+ +-----+ |Internet|-------| Proxy |-----| WSN | +--------+ +-------+ +-----+ Figure 1 Proxy mode Proxy mode includes two different operating sub-modes: relay agent and front-end. Relay agent simply forwards the packets between the WSN and Internet, equivalent to a special router at application and network levels. Agents can also act as the front-end of WSN. Sensor nodes push data to the proxy, periodically or event-driven based. The proxy stored the information into a database, with capacity of large database and powerful processing. Internet users can query all kinds of information in various ways, through SQL or Web-based interface. Without the required information, an agent can start the collection of information. As the front-end, an agent can integrate the processing and storage of data, and can return data to the user as quickly as possible, with key management, user authentication, data encryption and other security measures at the same time. A proxy node can be integrated by user agent, application agent, register agent and resource manager, acting as the bridge between Internet and WSN, with resource storage and access control functions, and provides a quick query of WSN information services. WSN can access Internet through a proxy node, and Internet users can easily visit the WSN. Wu,Xu Expires January 31, 2011 [Page 3] Internet-Draft WSN convergence framework July 2010 In contrast, proxy mode has an obvious disadvantage of single point failure. Most functions are concentrated in the proxy node, such as network protocol conversion, information processing and storage. Once the agent fails, the Internet can not communicate with the WSN. In addition, an agent is application-oriented, usually dedicated to specific tasks and agreement. Applications need special agent design. Without proper routing mechanism, Internet and WSN can not converged; result in lack of flexibility and scalability. 4. Protocol Overlay Instead of protocol conversion, heterogeneous networks with different protocol stacks use protocol overlay for the protocol interconnection. There are two modes of WSN and Internet overlay: WSN over TCP / IP and TCP / IP over WSN. WSN over TCP / IP mode is similar to the private network implemented on the Internet via VPN (virtual private network). In this mode, Internet computers communicating with the WSN are called virtual WSN nodes (virtual node), so are the gateway nodes connecting heterogeneous networks. A network composite of virtual nodes is called WSN virtual network, which is an extension of WSN over the Internet. Each WSN node has its own private protocols dedicated to the characteristics of WSN, and communication between nodes is based on the private protocols. In the virtual part of the networks, WSN traffic is carried over TCP / UDP / IP as protocol payload. TCP / UDP / IP transfer data in a tunnel between the virtual nodes. WSN over TCP / IP protocol stack is shown in Figure 2. Internet Overlay gateway WSN +--------+ +-----------------+ +--------+ | APP-S | | APP-S | | APP-S | +--------+ +-----------------+ +--------+ |Trans-S | | Trans-S | |Trans-S | +--------+ +-----------------+ +--------+ | NET-S | | NET-S | | NET-S | +--------+ +--------+--------+ +--------+ |TCP/UDP | |TCP/UDP | LLC-S | | LLC-S | +--------+ +--------+--------+ +--------+ | IP | | IP | MAC-S | | MAC-S | +--------+ +--------+--------+ +--------+ ^ ^ ^ ^ | | | | +----------+ +-----------+ Figure 2 WSN over TCP / IP Wu,Xu Expires January 31, 2011 [Page 4] Internet-Draft WSN convergence framework July 2010 Internet users may need to access and control some special nodes in the WSN, like nodes with the execution (actuator) or performing certain important functions as cluster head nodes. These special nodes support TCP / IP protocol. Because of communication capacity constraints, these nodes and gateway nodes can not reach each other in one hop. For data transfer between them, a tunnel over WSN is introduced, that is TCP/IP over WSN. The private protocols are used by the majority of WSN, and IP is only extended to the special nodes. So it is not proposed that all WSN nodes support TCP / IP protocol. Protocol stacks and data flows of this mode are shown in Figure 3. Internet WSN host TCP/IP node +--------+ +--------+ | APP | | APP | +--------+ Common +--------+ |TCP/UDP | Tunnel node |TCP/UDP | +--------+ +--------+--------+ +--------+ +--------+ | IP | | IP | | APP-S | | APP-S | +--------+ +--------+--------+ +--------+ +--------+ ^ ^ |Trans-S | |Trans-S | |Trans-S | | | +--------+ +--------+ +--------+ +-----------+ ^ ^ ^ ^ | | | | +---------+----+---------+ Figure 3 TCP / IP over WSN 5. Delay Tolerant Network Internet protocols are inefficient in the environment of long communication path, variable delay, frequent network structure, high error rate and asynchronous transfer. Delay tolerant network (DTN) is proposed for this kind of network environment, as shown in figure 4. +--------+ +-------+ +-----+ |Internet| | DTN | | WSN | | host |<----->|Gateway|<--->| node| +--------+ +-------+ +-----+ Figure 4 DTN gateway A bundle layer is introduced at the top layer of DTN, to achieve interoperability for heterogeneous network domains. DTN is suitable for WSN, and every node has storage function. Due to node sleep or failure, WSN will frequently change its division structures, breaking all end to end paths through the network. Packet loss rate is very Wu,Xu Expires January 31, 2011 [Page 5] Internet-Draft WSN convergence framework July 2010 high in WSN, and the data routes are asymmetric too. DTN system is more powerful than the simple agent-based approach. When a DTN gateway is in a WSN, the WSN is mapped to multiple DTN regions. In a WSN with frequent network division change and less end to end communications, this network design is more appropriate to ensure the communication reliability in the DTN layer. There are one or more DTN gateways in each DTN region, which are responsible for message forwarding between the regions, and message transfer from other regions to the local area, without single point failure like in the proxy system. With one or more DTN gateways connecting to Internet, the WSN can easily be extended to the Internet via DTN. More cost is needed to deploy Bundle in the existing network protocol stack, which is the disadvantage of the DTN mode. 6. Full IP Adoption of TCP / IP protocols for all WSN nodes is a direct approach for seamless convergence of WSN and Internet, result in the same network layer protocol for heterogeneous networks, and protocol conversion or overlay through special nodes is not needed. With one or more WSN nodes connecting to the Internet, two networks can exchange information by any node, through direct physical connection (Ethernet cable) or wireless link (GPRS). In the network we can use the network link to communicate through the and so on. This kind of convergence is more flexible. WSN nodes can access the Internet nodes closely, relaying real-time data to the end user with minimal delay, and the Internet users can visit any WSN node. Wu,Xu Expires January 31, 2011 [Page 6] Internet-Draft WSN convergence framework July 2010 +-----+ | WSN |TCP/IP | node| +-----+ | | TCP/IP +--------+ +-----+ +-----+ |Internet|<--->| WSN |------| WSN |TCP/IP | | | node| | node| +--------+ +-----+ +-----+ ^ | | | | | v | | +-----+ +-----+ +-----+ | WSN |------| WSN |------| WSN | | node| | node| | node| +-----+ +-----+ +-----+ TCP/IP TCP/IP TCP/IP Figure 5 Full IP mode The data transmitted between WSN nodes is small-sized, usually a few dozen bytes or even a few bytes. The header of TCP / IP protocol is at least 40 bytes, 20 bytes for TCP protocol and 20 bytes for IP protocol, which seriously affect the data transmission efficiency and waste node's energy. To use WSN TCP / IP protocol efficiently, a protocol header compression algorithm must be used. In addition, TCP / IP protocol is also too complicated for WSN nodes with limited resource. Many enhanced algorithms have been proposed, such as protocol mapping, homeostasis, and probability searching methods, but these methods cost great time and space complexity. IP address auto-configuration for WSN nodes is also an important research area, which is useful for WSN with dispersion and the static structure, but there are still some obstacles for the dense nodes and mobile nodes. With the introduction of protocol header compression, the new model of two nodes and two stacks is presented for WSN nodes TCP / IP protocol, containing a small amount of additional super nodes in addition to ordinary nodes. The ordinary nodes use compressed TCP / IP protocol. The super nodes achieve conversion between the compressed and standard TCP / IP protocol, and interact with the external Internet seamlessly and efficiently. However, without efficient routing mechanism, the super node does not have universal applicability. IPv6 protocol is brought to WSN after efficient simplification, which is basis of WSN routing protocol. The algorithm Wu,Xu Expires January 31, 2011 [Page 7] Internet-Draft WSN convergence framework July 2010 of protocol stack has a good scalability, but not a best routing algorithm to solve energy problems and slow convergence. The network has primary nodes with large storage capacity and powerful processing capabality, and other nodes cluster around the primary node. The primary node is assigned with fixed IP address, and has a mapping table of member ID and IP address. This approach is only suitable for heterogeneous WSN, and the scalability is not good. 7. Other technologies There are other modes for the convergence of Internet and WSN, such as virtual IP and mobile agent technologies [3]. Virtual IP is an IP address mapping technology. For computer network users, only the gateway is assigned with a virtual IP address, and the sensor node does not have one. This technology can realize the address mapping between sensor node ID / location and gateway IP address. Mobile agent is encapsulated in the WSN node, capable of interacting with Internet. When running out of energy, the agent disconnects from the Internet, and travels to the appropriate neighbor with useful information, which is then an access node. Internet user can pack the required data for long-term interaction in the mobile agent. The agent moves to WSN with the information, and interacts with the gateway or access node. Connection failure between the Internet and WSN will not affect the mobile agent. After the connection's resuming, the proxy will return the results to Internet user. 8. Security Considerations Due to the open wireless environment of WSN, the convergence framework mechanisms are susceptible to a number of information attacks. 9. IANA Considerations This document includes no IANA actions. 10. References 10.1. Normative References [1] S. Corson, J. Macker, " Mobile Ad hoc Networking (MANET): Routing Protocol Performance Issues and Evaluation Considerations ", RFC 2501, January 1999. Wu,Xu Expires January 31, 2011 [Page 8] Internet-Draft WSN convergence framework July 2010 10.2. Informative References [2] Kay; Friedemann Mattern, "The Design Space of Wireless Sensor Networks", IEEE Wireless Communications 11 (6): 54-61, doi:10.1109/MWC.2004.1368897. [3] Thomas Haenselmann. Sensor networks. GFDL Wireless Sensor Network textbook. Retrieved 2006-08-29. 11. Acknowledgments The author wishes to acknowledge the following for their review and constructive criticism of this document: Zhiwei Cai. This document was prepared using 2-Word-v2.0.template.dot. Wu,Xu Expires January 31, 2011 [Page 9] Internet-Draft WSN convergence framework July 2010 Authors' Addresses Zuoshun Wu China Electronic Device Research Insititue(CEDRI) No.13 Road Dacheng, District Fengtai, Beijing, China Phone: +86 010 68693712 Email: wuzuoshun@163.com Qijian Xu China Electronic Device Research Insititue(CEDRI) No.13 Road Dacheng, District Fengtai, Beijing, China Phone: +86 010 68693730 Email: xuqijian@sina.com Wu,Xu Expires January 31, 2011 [Page 10]