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Wang 7 Chongqing University of 8 Posts and Telecommunications 9 February 21, 2017 11 An energy optimization routing scheme for LLSs 12 draft-wang-roll-energy-optimization-scheme-00 14 Abstract 16 Low-Power and Lossy Networks (LLNs) are composed of devices that 17 have constraints on processing power, memory, and energy (battery 18 power). It is obvious that conserving energy is especially important 19 in the LLNs. This document is aimed at proposing an efficient and 20 effective scheme to optimize the energy in the process of seeking 21 the DAG root node. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF), its areas, and its working groups. Note that 30 other groups may also distribute working documents as Internet- 31 Drafts. 33 Internet-Drafts are draft documents valid for a maximum of six 34 months and may be updated, replaced, or obsoleted by other documents 35 at any time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 The list of current Internet-Drafts can be accessed at 39 http://www.ietf.org/ietf/1id-abstracts.txt 41 The list of Internet-Draft Shadow Directories can be accessed at 42 http://www.ietf.org/shadow.html 44 This Internet-Draft will expire on August 25, 2017. 46 Copyright Notice 48 Copyright (c) 2017 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with 56 respect to this document. Code Components extracted from this 57 document must include Simplified BSD License text as described in 58 Section 4.e of the Trust Legal Provisions and are provided without 59 warranty as described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction ................................................ 2 64 1.1. Requirements Notation................................... 3 65 1.2. Terms Used ............................................. 3 66 2. Requirements ................................................ 3 67 3. An Energy Optimization Routing Scheme ........................4 68 3.1. The network topology.................................... 4 69 3.2. Increasing Broadcast.................................... 5 70 3.3. The implementation of the scheme ........................7 71 4. Security Considerations...................................... 8 72 5. IANA Considerations ......................................... 8 73 6. Acknowledgements ............................................ 8 74 7. References .................................................. 9 75 7.1. Normative References.................................... 9 76 7.2. Informative References.................................. 9 78 1. Introduction 80 IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) is 81 specified in [RFC6550], which provides a mechanism whereby 82 multipoint-to-point traffic from devices inside the LLN towards a 83 central control point as well as point-to-multipoint traffic from 84 the central control point to the devices inside the LLN are 85 supported. The routing metrics and constraints are specified in 86 [RFC6551], which provides a high degree of flexibility and a set of 87 routing metrics and constraints. A variety of node 88 constraints/metrics must be possible taken into account during path 89 computation (see RFC[6551]). 91 Low-Power and Lossy Networks (LLNs) have recently attracted a lot of 92 interest to the researchers due to its wide range of applications 93 such as military implementations in a battlefield, an environmental 94 monitoring, and multifunction in health sector. However, due to the 95 characteristics of LLNs, it has such limitations as limited battery 96 power, finite computing and memory capability, the large scale of 97 deployment and narrow communication bandwidth. Therefore, there is 98 an urgent need for conserving energy in the LLNs so as to ensure 99 long term operation. 101 1.1. Requirements Notation 103 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 104 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 105 document are to be interpreted as described in [RFC2119]. 107 1.2. Terms Used 109 DAG: Directed Acyclic Graph. A directed graph has the property that 110 all edges are oriented in such a way that no cycles exist. All edges 111 are contained in paths oriented toward and terminating at one or 112 more root nodes. 114 DAG root: A DAG root is a node within the DAG that has no outgoing 115 edge. Because the graph is acyclic, by definition, all DAGs MUST 116 have at least one DAG root and all paths terminate at a DAG root. 118 Increasing broadcast: Increasing broadcast is a routing scheme used 119 for energy optimization. In the process of seeking the DAG root node, 120 the routing request message will be sent to the nodes which have the 121 most neighbors. And the number of nodes is increasing order. 123 2. Requirements 125 Due to the restrained hardware resource and energy of LLNs, its data 126 processing and transmission ability is weak. Therefore, how to make 127 full use of energy becomes an important research area of routing 128 protocol. LLNs is a multiple hops self-organizing networks, that the 129 data is forwarded along the optimal path is main function of routing 130 protocol. In order to make full use of limited resource, the current 131 routing protocols attempt to find the path that consumes the least 132 energy. However, it is not comprehensive to merely focus on the 133 efficiency of energy when designing the routing protocol, the 134 balance of energy consumption and the security can also affect the 135 performance of the networks. Studies have shown that the nodes close 136 to DAG root node are faced with more data transmission tasks due to 137 the influence of RPL (Routing Protocol for Low Power and Lossy 138 Networks), so the energy consumption is much faster than the nodes 139 far away from DAG root node. With the frequent data transmission to 140 DAG root node, the closer nodes will have a shorter lifetime. As a 141 result, it leads to an energy hole around the DAG root node. And it 142 makes the data of other nodes cannot be transmitted to the DAG root 143 node through multiple hops, which seriously influence the functions 144 and the lifetime of networks. However, the nodes outside the energy 145 hole still have much residual energy. 147 Worse still, in current technology, multiple DAG root nodes can move 148 randomly and make up routing topology to accomplish data collection 149 in a small area. The nodes in the routing topology transmit data to 150 the DAG root node directly, while the nodes outside the routing 151 topology need to seek the DAG root node firstly and then finish the 152 data transmission. Many researches show that the nodes outside the 153 routing topology seek the DAG root node by flooding broadcast, which 154 makes the nodes consume energy vastly. Meanwhile, when the nodes 155 transmit the data to the DAG root node after finding it, the DAG 156 root node may move to another place, thus causing the loss of data. 158 Consequently, the balance of energy is important to routing protocol, 159 thus avoiding some nodes die quickly because of excessive energy 160 cost. And it is an important technology to prolong the life cycle of 161 LLNs. The document proposes an energy optimization routing scheme 162 based on increasing broadcast for LLNs. 164 3. An Energy Optimization Routing Scheme 166 3.1. The network topology 168 The scheme proposed by this document is applied to the network 169 topology shown in the figure 1. The mobile DAG root node builds a 170 DAG by using the RPL in a range of limited hops. And the member 171 nodes that belong to the DAG send data to the DAG root node directly. 172 However, the nodes outside the DAG need to seek the DAG root node 173 firstly and then send data to the DAG root node found by them. 174 Meanwhile, the mobile DAG root node will move to another place after 175 staying for a period of time and set up a new DAG through the RPL. 177 +--------------------+ +--------------------+ 178 | | -- | | 179 | +--+ | |SN| | +--+ | 180 | ---| R |--- | -- | ---| R |--- | 181 | | +--+ | | | | +--+ | | 182 | | | | -- | | | | 183 | -- -- | |SN| | -- -- | 184 | |SN| |SN| | -- | |SN| |SN| | 185 | -- -- | | -- -- | 186 | | | | -- | | | | 187 | | | | |SN| | | | | 188 | -- -- | -- | -- -- | 189 | |SN| |SN| | | |SN| |SN| | 190 | -- -- | | -- -- | 191 | | | | 192 +--------------------+ +--------------------+ 193 Figure 1 The network topology 195 As shown in the figure above, the root node builds a DAG in some 196 area. Some nodes are in the DAG, while others are outside of the DAG. 198 3.2. Increasing Broadcast 200 For the purpose of lowering the energy consumption used for seeking 201 the DAG root node, the document proposes a method named increasing 202 broadcast to forward the routing request message instead of using 203 the previous flooding broadcast. The detailed process of the 204 increasing broadcast is shown as figure 2. 206 +-------------------------------------------+ 207 |The node chooses its neighbor node which | 208 |has the most neighbor nodes and sends the | 209 |routing request message to it. | 210 +-------------------------------------------+ 211 | 212 V 213 +-------------------------------------------+ 214 |The node receiving the above routing | 215 |request message chooses two neighbor nodes | 216 |which have the most neighbor nodes and | 217 |sends the routing request message to them. | 218 +-------------------------------------------+ 219 | 220 V 221 +-------------------------------------------+ 222 |The nodes receiving the above routing | 223 |request message choose three neighbor nodes| 224 |which have the most neighbor nodes and send| 225 |the routing request message to them. And | 226 |these three nodes respectively broadcast | 227 |the message according to this rule. | 228 +-------------------------------------------+ 229 | 230 V 231 +-------------------------------------------+ 232 |The process ends until the increasing | 233 |broadcast reaches the largest hop or the | 234 |DAG root node (the member of a DAG) has | 235 |been found. | 236 +-------------------------------------------+ 237 Figure 2 The process of the increasing broadcast 239 (1) Firstly, the node determines which neighbor node has the most 240 neighbor nodes, and then sends the routing request message to it. 241 Because the node chooses one of its neighbor nodes, which has the 242 most neighbor nodes to forward the routing request message, the odds 243 of finding the DAG root node or the member of a DAG (directed 244 acyclic graph) is much larger. 246 (2) The nodes receiving the above message choose two of its neighbor 247 nodes, which have the most neighbor nodes and send the routing 248 request message to them. It is noted that the node SHOULD choose 249 other nodes except for the source nodes, thus avoiding the situation 250 that the routing request message is sent back to them. 252 (3) The above two nodes which receive the routing request message 253 choose three neighbor nodes which have the most neighbor nodes and 254 broadcast routing request message to them. All the nodes broadcast 255 the message according to the aforementioned rule. To put it simply, 256 the nodes broadcast the routing request message after receiving it 257 through the increasing broadcast. When the node chooses the neighbor 258 nodes with the most neighbors, the number will be increased by one 259 on the basis of the prior choice. The energy can be saved and the 260 area of seeking the DAG root node is also expanded at the same time. 262 (4) When the increasing broadcast reaches the largest hop and the 263 last hop is not the DAG root node or the member of a DAG, the 264 routing request message will be discarded directly. If the DAG root 265 node or the member of a DAG is found in the process of finding, the 266 routing request message will be stopped to forward to other nodes 267 and the routing response message will be sent back to source node. 269 3.3. The implementation of the scheme 271 Because the nodes seek DAG root node or the member of a DAG by using 272 flooding broadcast in the original routing scheme, the energy is 273 consumed largely. Worse still, the DAG root node is mobile in lots 274 of mobile routing algorithms which focus on the balance of the 275 energy in the LLNs. When the nodes outside the topology find the DAG 276 root node, it may move to another place when the data is transmitted 277 to it, thus causing the loss of the data. The document proposes an 278 energy optimization routing scheme based on above-mentioned 279 increasing broadcast. It can be used to seek DAG root node with low 280 energy consumption, meanwhile, it guarantees the success of data 281 transmission. As a result, the overhead of the network energy is 282 lowered and the reliability of data transmission is ensured. The 283 detailed scheme is shown as follows: 285 (1) Due to the fact that the DAG root node only maintains a DAG in 286 an area of limited hops and there exist many DAGs with the mobile 287 DAG root node in the network, a part of nodes in the network belong 288 to the DAG while others are outside of the DAG. Firstly, the node 289 SHOULD be determined whether it is a member of a DAG. 291 (2) When the node that is going to transmit the data is a member of 292 a DAG, the data will be transmitted to its father node directly. And 293 the father node will finally transmit the data to the DAG root node. 295 (3) When the node that is going to transmit the data is not a member 296 of a DAG, it will send routing request message to neighbor nodes by 297 means of increasing broadcast so as to find the DAG root node and 298 transmit data to it. It needs to be noted that the node is pre- 299 configured a largest hop before sending the routing request message. 300 When the increasing broadcast reaches the largest hop and the node 301 of the last hop is not the DAG root node or a member of a DAG, the 302 routing request message will be discarded. In addition, the node of 303 last hop will send a message of failure back to the source node, and 304 the source node directly broadcast the routing request message to 305 every node in the network. 307 (4) If the DAG root node or the member of a DAG is found through the 308 increasing broadcast, the routing request message is sent to it by 309 the source node. And the source node will receive a routing response 310 message from the DAG root node or the member of a DAG. The routing 311 response message includes the time for which the DAG root node stays 312 in the present DAG and the number of hops between the DAG root node 313 and the source node. 315 (5) The source node selects the DAG root node whose standing time is 316 greater than the transmission time according to the routing response 317 message. And then the source node continues selecting the closest 318 DAG root node to transmit the data. The transmission time (Tn) is 319 obtained by the formula Tn=nT1, where n means the hops between the 320 source node and the DAG root node, and T1 denotes the mean 321 transmission time per hop. 323 4. Security Considerations 325 TBD. 327 5. IANA Considerations 329 This memo includes no request to IANA. 331 6. Acknowledgements 333 Thanks to the authors of RFC 6550 RFC 6551 RFC 6554 and RFC 6552. 334 The authors would like to acknowledge the review, feedback, and 335 comments. 337 7. References 339 7.1. Normative References 341 7.2. Informative References 343 [RFC6550] 344 Winter, T., P. Thuber, and B. Brandt. "RFC 6550: IPv6 Routing 345 Protocol for Low-Power and Lossy Networks." Internet 346 Engineering Task Force (IETF) Request For Comments (2008). 348 [RFC6551] 349 Vasseur, J. P., et al. "RFC 6551: Routing Metrics Used for 350 Path Calculation in Low-Power and Lossy Networks." Internet 351 Engineering Task Force (IETF) Request For Comments (2012). 353 [RFC2119] 354 RFC2119, RFC2119. "Key words for use in RFCs to Indicate 355 Requirement Levels." (1997). 357 Authors' Addresses 359 Hao Wang 360 Key Laboratory of Industrial Internet of Things & Networked Control 361 Ministry of Education 362 Chongqing University of Posts and Telecommunications 363 2 Chongwen Road 364 Chongqing, 400065 365 China 367 Email: wanghao@cqupt.edu.cn 369 Min Wei 370 Key Laboratory of Industrial Internet of Things & Networked Control 371 Ministry of Education 372 Chongqing University of Posts and Telecommunications 373 2 Chongwen Road 374 Chongqing, 400065 375 China 377 Email: weimin@cqupt.edu.cn 379 Shuaiyong Li 380 Key Laboratory of Industrial Internet of Things & Networked Control 381 Ministry of Education 382 Chongqing University of Posts and Telecommunications 383 2 Chongwen Road 384 Chongqing, 400065 385 China 387 Email: lishuaiyong@cqupt.edu.cn 389 Qingqing Huang 390 Key Laboratory of Industrial Internet of Things & Networked Control 391 Ministry of Education 392 Chongqing University of Posts and Telecommunications 393 2 Chongwen Road 394 Chongqing, 400065 395 China 397 Email: huangqq@cqupt.edu.cn 399 Ping Wang 400 Key Laboratory of Industrial Internet of Things & Networked Control 401 Ministry of Education 402 Chongqing University of Posts and Telecommunications 403 2 Chongwen Road 404 Chongqing, 400065 405 China 407 Phone: (86)-23-6246-1061 408 Email: wangping@cqupt.edu.cn 410 Chaomei Wang 411 Key Laboratory of Industrial Internet of Things & Networked Control 412 Ministry of Education 413 Chongqing University of Posts and Telecommunications 414 2 Chongwen Road 415 Chongqing, 400065 416 China 418 Email: wangcm24@126.com