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Forwarding Strategies for 6Lowpan-Fragmented Ipv6 Datagrams

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Forwarding Strategies for 6Lowpan-Fragmented Ipv6 Datagrams Forwarding Strategies for 6LoWPAN-Fragmented IPv6 Datagrams Vom Promotionsausschuss der Technischen Universit¨atHamburg-Harburg zur Erlangung des akademischen Grades Doktor-Ingenieur (Dr.-Ing.) genehmigte Dissertation von Andreas Weigel aus Potsdam, Deutschland 2017 Date of Oral Examination September 05th, 2017 Chair of Examination Board Prof. Dr. Heiko Falk Institute of Embedded Systems Hamburg University of Technology First Examiner Prof. Dr. Volker Turau Institute of Telematics Hamburg University of Technology Second Examiner Prof. Dr. Andreas Timm-Giel Institute of Communication Networks Hamburg University of Technology Acknowledgment Several people supported me in the long, difficult and sometimes frustrating process of finishing this dissertation. I want to seize the opportunity to express my deeply felt gratitude towards them. First, I would like to thank my supervisor Prof. Turau for his guidance, encourage- ment and intellectual input, but also for being the kind of superior he is. I would like to thank my colleagues, who made everydays work at the institute a pleasant experience. Special thanks go to my \roommates" Bernd-Christian Renner, Martin Ringwelski and Florian Kauer for bearing with me and my curses and com- plains and for providing so much valuable input. Further, I'd like to thank Stefan Untersch¨utzand Martin Ringwelski for their implementation work on CometOS and its 6LoWPAN module and the numerous fruitful discussions. I want to thank my parents for their genes and the continuous support I experienced throughout my life. And finally: Thanks Susanne, for your encouragement and help and for taking on life together with me. Andreas Weigel L¨uneburg,November 2017 Abstract Recent efforts towards a fully standardized protocol stack (RPL, CoAP, 6LoWPAN) for \low power and lossy networks" (LLNs) contribute to realize the vision of the Internet of Things. 6LoWPAN is a central building block among these protocols, enabling the transmission of IPv6 datagrams using the IEEE 802.15.4 protocol for wireless mesh networks. To provide IPv6' minimal MTU of 1280 bytes by means of the 127 byte frames of IEEE 802.15.4, 6LoWPAN defines a fragmentation mechanism. However, the use of fragmentation is suspected to amplify existing problems for the communication in LLNs and thereby decrease reliability. This dissertation explores the impact of 6LoWPAN fragmentation on the reliabil- ity of transmissions for the LLN-typical collection traffic pattern and implementation strategies to improve this reliability. The two route-over forwarding methods \Assem- bly" and \Direct" are considered as basic implementations. The former reassembles a datagram at every IPv6 hop, the latter uses a cross-layer approach to forward indi- vidual fragments as soon as they arrive. An extension to a bit-error-based analytical model for fragmented 6LoWPAN trans- missions is developed to estimate the number of created frames and to better reflect current implementation realities. Furthermore, simulative and testbed studies are car- ried out to evaluate the basic implementations and the extension developed as part of the dissertation, adaptive rate-restriction. Based on the results of these parameter studies, the author proposes a mechanism called \6LoWPAN Ordered Forwarding" (6LoOF), which is designed to prevent local short-term congestion by suspending transmissions at nodes that overhear ongoing transmissions in the neighborhood. Evaluation of 6LoOf in simulation and two dif- ferent testbeds show that { especially in combination with adaptive rate restriction { it significantly improves the reliability of the transmission for large 6LoWPAN- fragmented IPv6 datagrams, in some cases reducing the number of dropped datagrams by 50 %. Furthermore, inconsistent results between simulation and testbed triggered a de- tailed analysis of the used MAC layer, which relied on the CSMA/CA mechanism provided by the transceiver hardware. This experimental analysis shows that the re- alization of IEEE 802.15.4 in hardware on many current transceivers severely impacts the reliability of transmissions in multi-hop traffic scenarios, potentially biasing results of research obtained with communication stacks using these realizations. Contents 1 Introduction 1 2 Problem Statement 5 2.1 IEEE 802.15.4 . .5 2.2 6LoWPAN . .6 2.2.1 Compression and Fragmentation . .6 2.2.2 6LoWPAN Routing Schemes . .8 2.2.3 Basic Route-Over Forwarding Techniques . .8 2.2.4 Adjacent Protocols . .9 2.2.5 LFFR . 11 2.2.6 6TiSCH . 11 2.3 Applications . 11 2.4 Energy Availability . 12 2.5 Goals of Evaluation . 13 3 Analytic Model for 6LoWPAN-Fragmented Forwarding 15 3.1 Motivation and State of The Art . 15 3.1.1 Motivation . 15 3.1.2 State of the Art . 16 3.2 Model . 17 3.2.1 Link-Layer Model . 17 3.2.2 Multi-Hop Model . 18 3.3 Evaluation . 21 3.3.1 Persistent vs. Non-Persistent . 21 3.3.2 Multi-Hop Transmissions . 22 3.3.3 Additional Bits in Direct Mode . 23 3.4 Conclusions . 24 4 Simulation Model and Environment 27 4.1 Frameworks and Tools . 27 4.1.1 OMNeT++ . 27 4.1.2 MiXiM . 28 4.1.3 CometOS . 29 4.2 Physical Layer Model . 29 4.2.1 Available Models for Wireless Sensor Networks . 29 4.2.2 Choosing an Appropriate Model . 31 4.2.3 A Measurement-Based Physical Layer . 31 4.3 Automated Model Creation . 34 4.3.1 Topology Monitor . 34 4.3.2 Post-Processing . 35 i Contents 4.4 Confidence Intervals . 38 5 Basic Forwarding Techniques for 6LoWPAN-Fragmented Datagrams 39 5.1 Related Work . 39 5.2 Modes . 41 5.2.1 Enhanced Direct Modes . 41 5.2.2 Retry Control . 42 5.3 6LoWPAN Implementation . 42 5.4 Experiment Setup . 44 5.4.1 Testbed . 44 5.4.2 Simulation . 47 5.4.3 Network Topologies . 48 5.4.4 Traffic . 50 5.4.5 Link Layer Configuration . 50 5.5 Evaluation . 51 5.5.1 First Set of Experiments . 51 5.5.2 Second Set of Experiments . 56 5.5.3 Explanation of Results . 58 6 Hardware-Assisted IEEE 802.15.4 Transmissions 61 6.1 Hypothesis . 61 6.2 Capturing Node State in Real-Time . 62 6.3 Experiment Setup . 64 6.4 Evaluation . 66 6.4.1 Direct Mode . 66 6.4.2 Direct-ARR Mode . 68 6.5 Conclusions . 70 7 Basis Forwarding Techniques Revisited { a Parameter Study 73 7.1 Experiment and Simulation Setup . 73 7.1.1 Testbed . 73 7.1.2 Simulation . 74 7.2 Validation of RS-C . 75 7.2.1 PRR . 75 7.2.2 Drop Causes { 6LoWPAN Layer . 76 7.2.3 Drop Causes { Link Layer . 77 7.3 6LoWPAN Forwarding Modes and IEEE 802.15.4 Parameters . 79 7.3.1 macMaxFrameRetries . 81 7.3.2 macMinBe . 82 7.3.3 macCcaMode . 84 7.3.4 macMaxBe . 86 7.3.5 UDP packet size LUDP ...................... 86 7.3.6 Latency . 90 7.3.7 Pull-Based Collection . 90 7.4 Summary . 91 8 6LoWPAN Ordered Forwarding - 6LoOF 93 8.1 The 6LoOF Mechanism . 93 ii Contents 8.1.1 Snooping . 94 8.1.2 Probing . 94 8.1.3 6LoOF Definition . 96 8.2 Implementation . 105 8.3 Experiment setup . 106 8.3.1 Testbeds . 106 8.3.2 Memory Usage . 111 8.3.3 Simulation Environment . 113 8.4 Evaluation: 6LoOF vs Plain Forwarding . 113 8.4.1 6LoOF Parameters . 113 8.4.2 TB-IoT Experiments . 118 8.4.3 TB-D Experiments . 123 8.4.4 Simulation . 126 8.4.5 Summary . 137 9 Conclusion and Outlook 139 Bibliography 143 iii List of Figures 2.1 6LoWPAN fragmentation headers . .7 2.2 Message flow in Assembly and Direct . .9 2.3 Standard protocol stack for low-power lossy networks . 10 2.4 Application scenario example . 14 3.1 Direct forwarding: enumeration of cases . 20 3.2 Model evaluation: expected number of bits persisting/non-persisting . 22 3.3 Model evaluation: path length and retransmissions . 22 3.4 Model evaluation: expected number of bits Assembly/Direct . 23 3.5 Model evaluation: number of fragments . 24 4.1 Extension of MiXiM classes . 33 4.2 Determination of thermal noise . 34 4.3 pe;frame against SINR . 35 4.4 Derivation of normal distribution (first step) . ..
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