6LoWPAN Working Group E. Kim Internet-Draft ETRI / PEC Expires: December 13, 2007 N. Chevrollier TNO D. Kaspar ETRI / PEC June 11, 2007 Design and Application Spaces for 6LoWPANs draft-ekim-6lowpan-scenarios-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 13, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Kim, et al. Expires December 13, 2007 [Page 1] Internet-Draft 6LoWPAN Design and Applications June 2007 Abstract This document investigates potential application scenarios and use cases for low-power wireless personal area networks (LoWPANs). Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Design Space . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Application Scenarios . . . . . . . . . . . . . . . . . . . . 6 3.1. Structural Monitoring ('Intelligent Bridge') . . . . . . . 6 3.2. Agricultural Monitoring ('Vineyard') . . . . . . . . . . . 7 3.3. Patient Monitoring ('Hospital') . . . . . . . . . . . . . 9 3.4. Vehicle Telematics ('Smart Roads') . . . . . . . . . . . . 9 4. 6LoWPAN benefits . . . . . . . . . . . . . . . . . . . . . . . 11 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . . . 16 Kim, et al. Expires December 13, 2007 [Page 2] Internet-Draft 6LoWPAN Design and Applications June 2007 1. Introduction LoWPANs are inexpensive, low-performance, wireless communication networks, and are formed by devices complying with the IEEE 802.15.4 standard [1]. Their typical characteristics can be summarized as follows: o Low power: depending on country regulations and used frequency band, the maximum transmit power levels can be up to 1000 mW [1]. However, typical wireless radios for LoWPANs are battery-operated and consume between 10 mW and 20 mW [2]. o Short range: The Personal Operating Space (POS) defined by IEEE 802.15.4 implies a range of 10 meters. For real implementations, the range of LoWPAN radios is typically measured in tens of meters, but can go far beyond that in non line-of-sight situations [2]. o Low bit rate: the IEEE 802.15.4 standard defines a maximum over- the-air rate of 250 kb/s, as well as lower data rates of 40 kb/s and 20 kb/s for each of the currently defined physical layers (2.4 GHz, 915 MHz and 868 MHz, respectively). o Small memory capacity: common RAM sizes for LoWPAN devices consist of a few kilobytes, such as 4 KB. o Limited processing capability: current LoWPAN nodes usually have 8-bit processors with clock rates around 10 MHz. The IEEE 802.15.4 standard distinguishes between two types of nodes, reduced-function devices (RFDs) and full-function devices (FFDs). Through their inability to transmit MAC layer beacons, RFDs can only communicate with FFDs in a resulting "master/slave" star topology. FFDs are able to communicate with peer FFDs and with RFDs in the aforementioned relation. FFDs can therefore assume arbitrary network topologies, such as multi-hop meshes. A LoWPAN network can be seen as a network of small star-networks, each consisting of a single FFD connected to zero or more RFDs. The FFDs themselves act as packet forwarders or routers and connect the entire LoWPAN in a multi-hop fashion. A LoWPAN domain is defined by the number of devices controlled by the LoWPAN coordinator. Each LoWPAN has a single coordinator, which must be of FFD type and it is responsible for address allocation. One can note that a LoWPAN coordinator is responsible for a single LoWPAN. Kim, et al. Expires December 13, 2007 [Page 3] Internet-Draft 6LoWPAN Design and Applications June 2007 O X | | O --- O --- X O: FFD / \ \ X: RFD X X X Figure 1: A simple LoWPAN. Furthermore, communication to corresponding nodes outside of the LoWPAN is becoming increasingly important. The distinction between RFDs and FFDs and the introduction of additional functional elements, such as gateways or border routers, increase the complexity on how basic network functionality (e.g., routing and mobility) can be designed for LoWPANs. After describing the characteristics of a LoWPAN, this draft provides a list of use cases and market domains that may benefit and motivate the work currently done in the 6LoWPAN WG. Kim, et al. Expires December 13, 2007 [Page 4] Internet-Draft 6LoWPAN Design and Applications June 2007 2. Design Space From [3], this section describes the potential dimensions that could be used to describe the design space of wireless sensor networks in the context of the 6LoWPAN WG. The design space is already limited by the characteristics of a 6LoWPAN (e.g., low-power, short range, low-bit rate) as described in [4]. Hence, this section highlights the dimensions that are inherent to the nature of LoWPANs. The possible dimensions for scenario categorization used in this draft are described as follows: o Deployment: In a LoWPAN, sensor nodes can be scattered randomly or deployed in an organized manner. The deployment can occur at once, or as an iterative process. The selected type of deployment has an impact on node density and location. This feature affects how to organize - manually or automatically - the sensor network, and how to allocate addresses in the network. o Mobility: Inherent to the wireless characteristics of LoWPANs, sensor nodes could move or be moved around. Mobility can be an induced factor (e.g., sensors in an automobile), hence not predictable, or a controlled characteristic (e.g., pre-planned movement in a supply chain). o Network size: This number takes into account nodes that provide the intended network capability (i.e., FFD). The number of nodes involved in a LoWPAN could be small (10 nodes), moderate (several 100s), or large (over a 1000). o Routing: The routing factor highlights the number of hops that has to be traversed to reach the edge of the network or a destination node within it. A single hop may be needed for simple star- topologies or a multi-hop communication scheme for more elaborate topologies, such as meshes or trees. From previous work on LoWPANs from academia and industry, various routing mechanisms have been introduced, such as data-centric, event-driven, address- centric, localization-based, or geographical routing. We do not use such a fine granularity in our draft but rather use topologies and single/multi-hop communication when referring to the routing categorization. o Connectivity: Nodes within a LoWPAN are considered "always connected" when there is a network connection between any two given nodes. However, due to external factors (e.g., extreme environment, mobility) or programmed disconnections (e.g., sleeping mode), the network connectivity can be "intermittent" (i.e., regular disconnection) to "sporadic" (i.e., almost always disconnected network). Kim, et al. Expires December 13, 2007 [Page 5] Internet-Draft 6LoWPAN Design and Applications June 2007 3. Application Scenarios This section lists a fundamental set of LoWPAN application scenarios in terms of system design. A complete list of practical use cases is not the goal of this draft. The intention is to define a minimal set of LoWPAN configurations to which any other scenario can be abstracted to. Also, the characteristics of the scenarios described in this section do not reflect the characteristics that every LoWPAN must have in a particular use case (e.g., healthcare). 3.1. Structural Monitoring ('Intelligent Bridge') Intelligent monitoring in facility management can make safety checks and periodic monitoring of the architecture status highly efficient. Mains powered nodes can be included in the design phase of a construction or battery-equipped nodes can be added afterwards. Dominant parameters: o static deployment o small size of networks (dozens of nodes) o star topology (potentialy with hierarchy) o all battery-powered except LoWPAN coordinators X X X \ | / X --- O --- X / | \ O: LoWPAN coordinator (FFD) X X X X: FFD or RFD Figure 2: A LoWPAN with a simple star topology. Example: A 1000m long bridge with 10 pillars. Each pillar contains 5 sensors to measure the water level, and 5 vibration sensors to monitor its structural health. On the top part of each pillar, an "infrastructure" FFD sink node is placed to collect the sensor data. The FFD is the LoWPAN coordinator of the sensors for each pillar which can be FFD or RFD. All nodes are static, and manually configured with a single-hop connection to the coordinator. All sensor nodes do not move while the service is provided. The network configuration and routing table are changed only in case of node failure. Except from the pillar itself, there are no special obstacles of attenuation to the sensor signals, but careful configuration is needed to prevent signal interference between Kim, et al. Expires December 13, 2007 [Page 6] Internet-Draft 6LoWPAN Design and Applications June 2007 sensors. A logical entity of data gathering can lie with each LoWPAN coordinator. Communication schedules must be set up between leaf nodes and their LoWPAN coordinator, to efficiently gather the different types of sensed data. Each data packet may include meta- information about its data, or the type of sensors could be encoded in its address during the address allocation. This type of application works based on event-driven notifications. The data over or under a pre-defined threshold is meaningful to report. The event- driven data sensed on abnormal occurances is time-critical and required secure and reliable transmission. For energy saving, all sensors could have periodic and long sleep modes but wake up on certain events. The LoWPAN coordinators can play the role of a gateway, so that a third party with internet access can check the status of the specific pillar. Due to the contents of the data, only authenticated users should be allowed to access the data. This use case can be extended to a medium size sensor network to monitor a building for instance. They still have similar characteristics such as static nodes, manually deployed networks, and mostly star (or multi-level of star) topology, and event-driven real- time data gathering. 3.2. Agricultural Monitoring ('Vineyard') Accurate temporal and spatial monitoring can significantly increase agricultural productivity. Due to natural limitations, such as a farmers' inability to check the crop at all times of day or inadequate measurement tools, luck often plays a too large role in the success of harvests. Using a network of strategically placed sensors, indicators such as temperature, humidity, soil condition, can be automatically monitored without labor intensive field measurements. For example, sensor networks could provide precise information about crops in real time, enabling businesses to reduce water, energy, and pesticide usage and enhancing environment protection. Dominant parameters: o static mesh topology with local star topologies o medium to large number of nodes o all nodes are battery-powered, except sink Kim, et al. Expires December 13, 2007 [Page 7] Internet-Draft 6LoWPAN Design and Applications June 2007 X X X X X X X X X X X X +---------+ \|/ \|/ \|/ \|/ | Gateway | ---- O ---- O ---- O ---- O +---------+ /|\ /|\ /|\ /|\ X: RFD X X X X X X X X X X X X O: FFD Figure 3: An aligned multi-hop LoWPAN. Example: In a vineyard with medium to large geographical size, a number of 50 to 100 FFDs nodes are manually deployed in order to provide full signal coverage over the study area. These FFD nodes support a multi-hop routing scheme to enable data forwarding to a sink node at the edge of the vineyard. An additional number of 100 to 1000 (possibly different) specialized RFD sensors (i.e., humidity, temperature, soil condition, sunlight) are attached to the FFDs in local wireless star topologies, periodically reporting measurements to the associated master FFD. For example, in a 20-acres vineyard, 8 parcels of land with each 10 sensors to provide readings on temperature and soil moisture. Each of the 8 parcels contains 1 FFD sink to collect the sensor data. 10 intermediate FFD "routers" are used to connect the sinks to the main gateway. Sensor nodes may send event-driven notifications when readings exceed certain thresholds, such as low soil humidity; which may automatically trigger a water sprinkler in the local environment. For increased energy efficiency, all sensors are in periodic sleep state. However, FDD nodes need to be aware of sudden events from RFDs. Their sleep periods should therefore be set to shorter intervals. Communication schedules must be set up between RFDs and FFDs and global time synchronization is needed to account for clock drift. Sensor localization is important for geographical routing, for pinning down where an event occurred, and for combining gathered data with their actual position. Using manual deployment, device addresses can be used. For randomly deployed nodes, a localization algorithm needs to be applied. There might be various types of sensor devices deployed in a single WPAN, each providing raw data with different semantics. Thus, an additional method is required to correctly interpret sensor readings. Each data packet may include meta-information about its data, or a type of a sensor could be encoded in its address during address allocation. Kim, et al. Expires December 13, 2007 [Page 8] Internet-Draft 6LoWPAN Design and Applications June 2007 3.3. Patient Monitoring ('Hospital') LoWPANs are envisioned to be heavily used in healthcare environments. They would ease the deployment of new services by getting rid of cumbersome wires and ease the patient care and life in hospitals. In this environment, delay or lost information may be a matter of life or death, therefore LoWPANs have to reliably cope with a highly mobile environment. Dominant parameters: o small star topologies in static infrastucture o mobility o always connected o programmed deployment +-------+ | Sinks | (in hospital walls) +-------+ | +-----------+ | O | (on patient's body) | /|\ | | X X X | O: FFD +-----------+ X: RFD (could be replaced with FFDs) Figure 4: A mobile star-shaped LoWPAN. Example: a small number (e.g, less than 10) of sensors are deployed on a patient body for medical surveillance. They monitor vital signs such as heart beats (electrocardiogram-ECG) or blood pressure, and provide localization information. The patient is able to move in his room or within the hospital. The collected data is sent to sinks placed onto hospital's walls. Sinks in the hospital's walls are mains powered. Devices carried by the patient run on battery. Localization-based services are provided in this scenario. Furthermore, the stringent requirements of medical applications imply highly reliable communications over a robust network. 3.4. Vehicle Telematics ('Smart Roads') LoWPANs play an important role in intelligent transportation systems. Incorporated in roads or/and, they contribute to the improvement of safety of transporting systems. Through traffic or air-quality Kim, et al. Expires December 13, 2007 [Page 9] Internet-Draft 6LoWPAN Design and Applications June 2007 monitoring, they increase the possibilities in terms of traffic flow optimization and help reducing road congestion. Dominant parameters: o static multi-hop topology o large network o scattered deployment o intermittent connectivity +-------+ | Sinks | (at the road side) +-------+ -------|------------------------------ O --- O --- O ----- O +---|---+ / \ | | X-O-X | (cars) O O --- O +---|---+ O: FFD -------------------------------------- X: RFD Figure 5: Multi-hop LoWPAN combined with mobile star LoWPAN. Example: Scattered sensors are included in roads during their construction for motion monitoring. When a car passes on top of these sensors, the possibility is then given to track the trajectory and velocity of the car for safety purpose. The lifetime of sensors devices incorporated into roads is expected to be as long as the life time of the roads (10 years). Multihop communication is possible between sensors, and the network should be able to cope with the deterioration over time of the node density due to power failure. Sinks place at the road side are mains powered, sensor nodes in the roads run on battery. Power savings schemes might disconnect intermittently sensors nodes. A rough estimate of 4 sensors per square meter is needed. Kim, et al. Expires December 13, 2007 [Page 10] Internet-Draft 6LoWPAN Design and Applications June 2007 4. 6LoWPAN benefits Sensor networks have been implemented in various industrial fields and there are many application scenarios that can be listed [3]. Thus, one could question the relevance of providing 6LoWPAN scenarios so many sensor application scenarios already exist using non-IP based communications, and proprietary routing or configuration mechanisms. While not a preliminary goal of this draft, we enumerate few motivations. First, 6LoWPAN will make pervasive internet communication with sensors, using standard IP protocols, without changing underling MAC/ PHY which has been used for sensor networks. Some emerging sensor network applications in health care or in intelligent transportation systems can benefit of the end-to-end communication paradigm of IP networks. It is noted that 6LoWPAN sensors need light version of IPv6 that could be used in low-powered, low-cost LoWPANs, but it is out of the scope of this document. Second, 6LoWPAN will give interoperability capability to LoWPANs. If company X is developing its own network stack for LoWPAN and company Y another one, thousand of different implementations will have to coexist. Third, using IP for LoWPANs will leverage existing protocols [5]. Established security protocols, naming and addressing schemes, to name only a few, could be reused to some extend in the context of a LoWPAN. Kim, et al. Expires December 13, 2007 [Page 11] Internet-Draft 6LoWPAN Design and Applications June 2007 5. Acknowledgements Thanks to David Cypher for giving more insight on the IEEE 802.15.4 standard and to Irene Fernandez for her review and valuable comments. Kim, et al. Expires December 13, 2007 [Page 12] Internet-Draft 6LoWPAN Design and Applications June 2007 6. Security Considerations Security issues are not within the scope of this document. Kim, et al. Expires December 13, 2007 [Page 13] Internet-Draft 6LoWPAN Design and Applications June 2007 7. References [1] IEEE Computer Society, "IEEE Std. 802.15.4-2003", October 2003. [2] Bulusu, N. and S. Jha, "Wireless Sensor Networks", July 2005. [3] Roemer, K. and F. Mattern, "The Design Space of Wireless Sensor Networks", December 2004. [4] Kushalnagar, N., Montenegro, G., and C. Schumacher, "6LoWPAN: Overview, Assumptions, Problem Statement and Goals, draft-ietf-6LoWPAN-problem-08 (work in progress)", February 2007. [5] Culler, D. and J. Hui, "6lowPAN Tutorial: IP on IEEE 802.15.4 Low Power Wireless Networks", May 2007. Kim, et al. Expires December 13, 2007 [Page 14] Internet-Draft 6LoWPAN Design and Applications June 2007 Authors' Addresses Eunsook Kim ETRI / PEC 161 Gajeong-dong Yuseong-gu Daejeon 305-700 Korea Phone: +82-42-860-6124 Email: eunah.ietf@gmail.com Nicolas G. Chevrollier TNO Brassersplein 2 P.O. Box 5050 Delft 2600 The Netherlands Phone: +31-15-285-7354 Email: nicolas.chevrollier@tno.nl Dominik Kaspar ETRI / PEC 161 Gajeong-dong Yuseong-gu Daejeon 305-700 Korea Phone: +82-42-860-1072 Email: dominik.ietf@gmail.com Kim, et al. Expires December 13, 2007 [Page 15] Internet-Draft 6LoWPAN Design and Applications June 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Kim, et al. Expires December 13, 2007 [Page 16]