학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 박세웅.Transmission power is an important factor which impacts on routing topology in low power and lossy networks (LLNs). LLNs have been designed for low rate traffic where use of maximum transmission power is the best choice for performance maximization since it results in reduced hop distance and transmission overhead. However, large scale applications also require LLNs to deliver very high rate traffic. In such large scale applications, the nodes which are near the root node will incur heavy traffic even though each node generates low rate traffic. As a result, it will cause severe link congestion. In this paper, we first investigate the effect of transmission power control on the performance of the routing protocol for LLNs (RPL) at heavy traffic load through testbed experiments. Our experiments show that, unlike LLNs in low rate applications, packet delivery performance at heavy load first increases and then decreases with transmission power. And we further investigate the reasons of what makes packet loss rate have a convex curve according to transmission power by per node analysis. We classify packet losses into link loss and queue loss. From the experiment results, we observe that link and queue losses are significantly unbalanced among nodes, which causes the load balancing problem of RPL. Furthermore, queue losses occur at the nodes which experience severe link loss. To solve this problem, we propose a simple power control mechanism, which allows each node to adaptively control its transmission power according to its own link and queue losses. Our proposal significantly improves the packet delivery performance by balancing the traffic load within a routing tree. We show performance improvement through experimental measurements on a real mutihop LLN testbed running RPL over IEEE 802.15.4.Contents
Abstract i
Contents iii
List of Figures iii
List of Tables v
Chap 1 Introduction 1
Chap 2 Experimental Environments 4
2.1. IPv6 routing protocol for low power and lossy networks (RPL) 4
2.2. Experimental environments 5
Chap 3 Load Balancing Problem of RPL 7
3.1. Packet loss rate 7
3.2. Queue loss and link loss 8
3.3. Topology analysis 11
3.4. Per node analysis 12
Chap 4 Transmission Power Control Mechanism 15
4.1. Effect of proposed power control on load balancing 15
4.2. Power control mechanism 17
Chap 5 Experimental Results 20
5.1. Packet loss rate 20
5.2. Queue loss and link loss 22
5.3. Packet loss rate 23
Chap 6 Conclusions 25
References 26
초 록 30
감사의 글 32Maste
