6LoWPAN Working Group D. Kaspar Internet-Draft E. Kim Expires: August 29, 2007 M. Shin H. Kim ETRI / PEC February 25, 2007 Design Goals and Requirements for 6LoWPAN Mesh Routing draft-dokaspar-6lowpan-routreq-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 August 29, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Kaspar, et al. Expires August 29, 2007 [Page 1] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 Abstract This document defines the problem statement, design goals, and requirements for mesh routing in low-power wireless personal area networks (LoWPANs). Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Scenario Considerations . . . . . . . . . . . . . . . . . 3 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 3. LoWPAN Mesh Routing Design Goals . . . . . . . . . . . . . . . 6 3.1. Reuse of Existing MANET Protocols . . . . . . . . . . . . 6 3.2. Adaptation Layer Routing . . . . . . . . . . . . . . . . . 6 3.3. Minimizing Overhead and Complexity . . . . . . . . . . . . 6 3.4. Power Conservation . . . . . . . . . . . . . . . . . . . . 6 3.5. Reliability and Robustness . . . . . . . . . . . . . . . . 7 3.6. Connectivity . . . . . . . . . . . . . . . . . . . . . . . 7 3.7. Neighbor Discovery . . . . . . . . . . . . . . . . . . . . 7 3.8. Bootstrapping . . . . . . . . . . . . . . . . . . . . . . 8 3.9. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.10. Scalability . . . . . . . . . . . . . . . . . . . . . . . 8 3.11. Addressing . . . . . . . . . . . . . . . . . . . . . . . . 8 3.12. Security . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.13. Implementation Considerations . . . . . . . . . . . . . . 9 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Analysis of Existing Mesh Routing Candidates . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15 Kaspar, et al. Expires August 29, 2007 [Page 2] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 1. Introduction Low-power wireless personal area networks (LoWPANs) are formed by devices complying to the IEEE 802.15.4 standard [1]. LoWPAN devices are distinguished by their low bandwidth, short range, scarce memory capacity, limited processing capability and other attributes of inexpensive hardware. In this document, the characteristics of nodes participating in LoWPANs are assumed to be those described in [2]. IEEE 802.15.4 networks support star and mesh topologies and consist of two different device types: reduced-function devices (RFDs) and full-function devices (FFDs). RFDs have the most limited capabilities and are intended to perform only simple and basic tasks. RFDs may only associate with a single FFD at a time, but FFDs may form arbitrary topologies among each other and accomplish more advanced functions, such as multi-hop routing. Neither the IEEE 802.15.4 standard nor the "IPv6 over IEEE 802.15.4" [3] specification provide any information as to how mesh topologies could be obtained and maintained. However, routing in mesh networks has been the subject of much research in the IETF. A number of experimental protocols have been developed in the Mobile Ad-hoc Networks (MANET) working group, such as AODV [4], OLSR [5], or DYMO [6]. This document defines the problem statement of mesh routing in LoWPAN environments and outlines the relevant design goals and requirements. 1.1. Scenario Considerations Low-power WPAN technology is still in its early stage of development, but the range of conceivable usage scenarios is tremendous. The numerous possible applications of sensor networks make it obvious that mesh topologies will be prevalent in LoWPAN environments and routing will be a necessity for expedient communication. In general, the requirements on a routing protocol are depending on the hardware parameters of the participating nodes and the properties of the network; 1. Network properties: * Device number and density * Network scale and topology * Mobility issues Kaspar, et al. Expires August 29, 2007 [Page 3] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 * ... etc. 2. Node parameters: * Physical dimensions * Hardware Cost * Processing speed and memory size * Power consumption and source * Transmission range, rate and bandwidth * ... etc. Network properties may vary arbitrarily for application scenarios in both LoWPAN or MANET contexts. For instance, even though LoWPANs are often regarded as more dense and consisting of more nodes than MANET networks, it might as well occur that a MANET consists of more devices than a LoWPAN. On the other hand, the node parameters themselves define whether a certain node is a LoWPAN device, a MANET device or neither of both. The classification boundaries are only vaguely defined. However, it is clear that pure LoWPAN devices enable services that MANET devices can not provide because of their nature of being more expensive, occupying greater physical space or requiring too much battery power. We might think that the characteristics of LoWPANs are device features only, but they enable a whole new segment of services that MANET devices are not always able to satisfy. And for implementing these specialized LoWPAN services, the reuse of routing protocols tailored for MANET purposes might not suffice. Kaspar, et al. Expires August 29, 2007 [Page 4] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 2. Problem Statement If possible, the easiest way to achieve LoWPAN mesh routing is by reusing existing MANET protocols without making any modifications. However, the modification or simplification of existing MANET routing protocols may be required for mesh routing to be feasible in a LoWPAN domain, because other requirements apply to LoWPAN devices. Unlike MANET devices, LoWPAN nodes are characterized by much lower power supplies, smaller memory sizes, and lower processing power, which creates new challenges on obtaining robust and reliable mesh routing within LoWPANs. Therefore, the modification and simplification of existing mesh routing protocols have to be done in such a way as to ensure efficient and robust packet delivery within LoWPAN networks. This document also outlines the fundamental design goals, which mesh routing will intend to accomplish for LoWPANs. There exists a trade-off relationship between routing effectiveness and the requirements posed upon the devices participating in a mesh network. The challenge is to create a balance between protocol simplicity and routing performance. But stripping down existing protocols to power-aware, low-overhead protocols decreases the efficacy and functionality of their sophisticated routing techniques, or possibly even endangers the goals they were designed for. Kaspar, et al. Expires August 29, 2007 [Page 5] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 3. LoWPAN Mesh Routing Design Goals This section outlines the fundamental design goals, which mesh routing implementations will intend to accomplish for LoWPANs. 3.1. Reuse of Existing MANET Protocols If the application of MANET routing protocols is feasible in LoWPAN environments, existing specifications should be simplified and modified to the smallest extent possible, in order to fit their low- power requirements. 3.2. Adaptation Layer Routing Because network layer routing imposes too much overhead for LoWPANs and link layer techniques are out of scope of IETF, LoWPAN mesh routing should be performed within the adaptation layer defined in [3]. 3.3. Minimizing Overhead and Complexity Because energy-efficient routing is important in LoWPANs, control messages must be trimmed from overhead to the highest degree possible. Routing overhead must be minimized in order to prevent fragmentation of frames on the physical layer, reducing the energy required for transmission and preventing the need for packet reassembly. Routing protocols should be designed to minimize the required number of control messages, memory size and computational complexity. Possible techniques might include the omission of routing tables or local repair procedures, but the actual details are left to the protocol designers. 3.4. Power Conservation Saving energy is crucially important to LoWPAN devices that are not mains-powered but have to rely on a depleting source, such as a battery. The lifetime of a LoWPAN node depends on the energy it can store and harvest. Compared to functions such as performing memory operations or taking sensor samples, radio communications is by far the dominant factor of power consumption [7]. Therefore, optimization of mesh routing protocols in terms of achieving a minimal number of control messages is essential for the longevity of battery-powered nodes. Many nodes in LoWPAN environments might periodically hibernate (i.e. Kaspar, et al. Expires August 29, 2007 [Page 6] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 disable their transceiver activity) to save energy. Therefore, mesh routing protocols must ensure robust packet delivery despite of nodes frequently shutting off their radio transmission interface. In order to find energy-optimal routing paths, LoWPAN mesh routing protocols should minimize power consumption by utilizing the link quality indication (LQI) provided by the MAC layer. 3.5. Reliability and Robustness An important characteristic of LoWPAN devices is their unreliability due to limited system capabilities, and also because they might be closely coupled to the physical world with all its unpredictable variation, noise, and asynchrony. It is predicted that LoWPANs will be comprised of significantly higher numbers of devices than counted in current networks, causing user interaction and maintenance to become impractical and therefore requiring robustness and self-healing capabilities in their fundamental network structure. Mesh routing must be aware of unreliable nodes. One method to estimate the reliability of a node is to use the link quality indication (LQI) provided by the MAC layer. Route repair and route error messages should be avoided for minimizing the overall number of control messages and the required energy for sending them. Loop-freedom is a desirable property of any routing protocol. 3.6. Connectivity IP routing between LoWPAN domains and higher layer networks must be provided bidirectionally. A LoWPAN mesh routing protocol must allow for gateways to forward packets out of the local domain and it must be possible to query a LoWPAN device from outside of the local domain. Strategies must be considered to avoid battery depletion of nodes by too many queries from higher level networks. End-to-end communication is not a design goal of LoWPAN. 3.7. Neighbor Discovery Neighbor discovery is a major precondition to allow routing in a network. Especially in a low-power environment, where nodes might be in periodic sleeping states, it is difficult to define whether a node Kaspar, et al. Expires August 29, 2007 [Page 7] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 is a neighbor of another or not. In addition to that, LoWPAN devices must be very economical in terms of power consumption and should avoid sending "Hello" messages. Instead, link layer mechanisms (such as acknowledgments or beacon responses) could be utilized to keep track of active neighbors. 3.8. Bootstrapping Bootstrapping a LoWPAN network may be a prerequisite for mesh routing. 3.9. Mobility Routing must be allowed both for fixed and dynamically adaptive topologies. Mesh networks are likely to consist of nodes with a certain degree of mobility. Due to the low performance characteristics of LoWPAN devices, fast mobility detection will be a huge challenge. Nodes might even change their location while being in state of hibernation. Routing must be robust and remain energy- efficient in all such cases. Also, as recently seen in discussions related to MANEMO (Network mobility for MANET), a similar point was stated regarding network mobility in LoWPAN environments. 3.10. Scalability Low-power WPAN topologies are foreseen to comprise of significantly more devices than current networks. Therefore, the design of mesh routing protocols must consider the fact that packets are to be reliably delivered over a much higher number of hops, too. 3.11. Addressing Both addressing modes provided by the IEEE 802.15.4 standard, 16 bit short addresses and 64 bit extended addresses, must be considered by LoWPAN mesh routing protocols. It is assumed that nodes participating in LoWPAN mesh routing are assigned a single address/identifier and do not support multiple interfaces. 3.12. Security Security threats within LoWPANs may be different from existing threat models in MANET environments. Neighbor Discovery in IEEE 802.15.4 links may be susceptible to threats as listed in RFC3756 [8]. Bootstrapping may also impose additional threats. Nevertheless, Kaspar, et al. Expires August 29, 2007 [Page 8] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 security should not cause significant transmission overhead. 3.13. Implementation Considerations Even though implementation details are out of IETF scope, due to the hardware restrictions of LoWPAN devices, code length should be considered to fit within their small memory size. Kaspar, et al. Expires August 29, 2007 [Page 9] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 4. Requirements This section lists the requirements on mesh routing protocols for LoWPANs; R01: Protocol control messages must not create fragmentation of PHY layer frames. R02: Shortest path calculation must be based on minimal energy usage. R03: Connectivity to higher layer networks must be provided by seamless IP routing. R04: Routing must be aware of sleeping nodes. R05: The solution must be simple and robust, despite of unreliable or sleeping nodes. R06: The solution must allow for dynamically adaptive topologies. It may support local mobility and global mobility. R07: The solution should support self-organization on deployment. R08: Neighbor discovery should be based on link layer mechanisms. R09: The solution should support high scalability. R10: Protocol control messages must be secured (TBD). Kaspar, et al. Expires August 29, 2007 [Page 10] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 5. Analysis of Existing Mesh Routing Candidates This section is still to be defined. An objective analysis on existing MANET routing protocols should be carried out to evaluate their suitability within LoWPANs. Kaspar, et al. Expires August 29, 2007 [Page 11] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 6. Security Considerations Security issues are handled as described in Section 3.12 Kaspar, et al. Expires August 29, 2007 [Page 12] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 7. References [1] IEEE Computer Society, "IEEE Std. 802.15.4-2003", October 2003. [2] Kushalnagar, N., Montenegro, G., and C. Schumacher, "6LoWPAN: Overview, Assumptions, Problem Statement and Goals, draft-ietf-6lowpan-problem-07 (work in progress)", February 2007. [3] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks, draft-ietf-6lowpan-format-10 (work in progress)", October 2005. [4] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-Demand Distance Vector (AODV) Routing", RFC 3561, July 2003. [5] Clausen, T. and P. Jacquet, "Optimized Link State Routing Protocol (OLSR)", RFC 3626, October 2003. [6] Chakeres, I., "Dynamic MANET On-demand (DYMO) Routing, draft-ietf-manet-dymo-06 (work in progress)", June 2005. [7] Pfister, K. and B. Boser, "Smart Dust: Wireless Networks of Millimeter-Scale Sensor Nodes". [8] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor Discovery (ND) Trust Models and Threats", RFC 3756, May 2004. [9] Bradner, S., "Intellectual Property Rights in IETF Technology", BCP 79, RFC 3979, March 2005. Kaspar, et al. Expires August 29, 2007 [Page 13] Internet-Draft 6LoWPAN Mesh Routing Requirements February 2007 Authors' Addresses Dominik Kaspar ETRI / PEC 161 Gajeong-dong Yuseong-gu Daejeon 305-700 Korea Phone: +82-42-860-1072 Email: dominik@etri.re.kr Eunsook Kim ETRI / PEC 161 Gajeong-dong Yuseong-gu Daejeon 305-700 Korea Phone: +82-42-860-6124 Email: eunah@etri.re.kr Myungki Shin ETRI / PEC 161 Gajeong-dong Yuseong-gu Daejeon 305-700 Korea Phone: +82-42-860-4847 Email: mkshin@etri.re.kr Hyoungjun Kim ETRI / PEC 161 Gajeong-dong Yuseong-gu Daejeon 305-700 Korea Phone: +82-42-860-6576 Email: hjk@etri.re.kr Kaspar, et al. Expires August 29, 2007 [Page 14] Internet-Draft 6LoWPAN Mesh Routing Requirements February 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. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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). Kaspar, et al. Expires August 29, 2007 [Page 15]