idnits 2.17.1 draft-baccelli-manet-multihop-communication-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 3, 2014) is 3669 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC4903' is defined on line 396, but no explicit reference was found in the text Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Mobile Ad-hoc Networks (MANET) E. Baccelli 3 Internet-Draft INRIA 4 Intended status: Informational C. Perkins 5 Expires: September 4, 2014 Futurewei 6 March 3, 2014 8 Multi-hop Ad Hoc Wireless Communication 9 draft-baccelli-manet-multihop-communication-03 11 Abstract 13 This document describes characteristics of communication between 14 nodes in a multi-hop ad hoc wireless network, that protocol engineers 15 and system analysts should be aware of when designing solutions for 16 ad hoc networks at the IP layer. 18 Status of This Memo 20 This Internet-Draft is submitted to IETF in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on September 4, 2014. 35 Copyright Notice 37 Copyright (c) 2014 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. 47 Table of Contents 49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 50 2. Multi-hop Ad Hoc Wireless Networks . . . . . . . . . . . . . 2 51 3. Common Packet Transmission Characteristics in Multi-hop Ad 52 Hoc Wireless Networks . . . . . . . . . . . . . . . . . . . . 3 53 3.1. Asymmetry, Time-Variation, and Non-Transitivity . . . . . 3 54 3.2. Radio Range and Wireless Irregularities . . . . . . . . . 4 55 4. Alternative Terminology . . . . . . . . . . . . . . . . . . . 7 56 5. IP over Multi-hop Ad Hoc Wireless . . . . . . . . . . . . . . 8 57 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 58 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 59 8. Informative References . . . . . . . . . . . . . . . . . . . 9 60 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11 62 1. Introduction 64 Experience gathered with ad hoc routing protocol development, 65 deployment and operation, shows that wireless communication presents 66 specific challenges [RFC2501] [DoD01], which Internet protocol 67 designers should be aware of, when designing solutions for ad hoc 68 networks at the IP layer. This document briefly describes these 69 challenges. 71 2. Multi-hop Ad Hoc Wireless Networks 73 For the purposes of this document, a multi-hop ad hoc wireless 74 network will be considered to be a collection of devices that each 75 have a radio transceiver (i.e., a wireless network interface), that 76 are using the same physical and medium access protocols on their 77 respective wireless network interfaces, and that are moreover 78 configured to self-organize and provide store-and-forward 79 functionality on top of these protocols as needed to enable 80 communications. The devices providing network connectivity are 81 considered to be routers. Other non-routing wireless devices, if 82 present in the ad hoc network, are considered to be "end-hosts". The 83 considerations in this document apply equally to routers or end- 84 hosts; we use the term "node" to refer to any such network device in 85 the ad hoc network. 87 Examples of multi-hop ad hoc wireless network deployment and 88 operation include wireless community networks such as 89 Funkfeuer[FUNKFEUER] and Freifunk[FREIFUNK]; these use routers 90 running OLSR (Optimized Link State Routing [RFC3626]) on IEEE 802.11 91 in ad hoc mode with the same ESSID (Extended Service Set 92 Identification) at the link layer. Multi-hop ad hoc wireless 93 networks may also run on link layers other than 802.11, and may use 94 routing protocols other than OLSR (for instance, AODV[RFC3561], 95 TBRPF[RFC3684], DSR[RFC4728], or OSPF-MPR[RFC5449]). 97 In contrast, simple hosts communicating through an 802.11 access 98 point in infrastructure mode do not form a multi-hop ad hoc wireless 99 network, since the central role of the access point is predetermined, 100 and since nodes other than the access point do not generally provide 101 store-and-forward functionality. 103 3. Common Packet Transmission Characteristics in Multi-hop Ad Hoc 104 Wireless Networks 106 Let A and B be two nodes in a multi-hop ad hoc wireless network N. 107 Suppose that, when node A transmits an IP packet through its 108 interface on network N, that packet is correctly and directly 109 received by node B without requiring storage and/or forwarding by any 110 other device. We will then say that B can "detect" A. Note that 111 therefore, when B detects A, an IP packet transmitted by A will be 112 rigorously identical to the corresponding IP packet received by B. 114 Let S be the set of nodes that detect node A through its interface on 115 network N. The following section gathers common characteristics 116 concerning packet transmission over such networks, which were 117 observed through experience with MANET routing protocol development 118 (OLSR[RFC3626], AODV[RFC3561], TBRPF[RFC3684], DSR[RFC4728], or OSPF- 119 MPR[RFC5449]), as well as deployment and operation 120 (Freifunk[FREIFUNK], Funkfeuer[FUNKFEUER]). 122 3.1. Asymmetry, Time-Variation, and Non-Transitivity 124 First, even though a node C in set S can (by definition) detect A, 125 there is no guarantee that node C can, conversely, send IP packets 126 directly to node A. In other words, even though C can detect A (since 127 it is a member of set S), there is no guarantee that A can detect C. 128 Thus, multi-hop ad hoc wireless communications may be "asymmetric". 129 Such cases are common. 131 Second, there is no guarantee that, as a set, S is at all stable, 132 i.e. the membership of set S may in fact change at any rate, at any 133 time. Thus, multi-hop ad hoc wireless communications may be "time- 134 variant". Time variation is often observed in multi-hop ad hoc 135 wireless networks due to variability of the wireless medium, and to 136 node mobility. 138 Now, conversely, let V be the set of nodes which A detects. Suppose 139 that node A is communicating at time t0 through its interface on 140 network N. As a consequence of time variation and asymmetry, we 141 observe that A: 143 1. cannot assume that S = V, 145 2. cannot assume that S and/or V are unchanged at time t1 later than 146 t0. 148 Furthermore, transitivity is not guaranteed over multi-hop ad hoc 149 wireless networks. Indeed, let's assume that, through their 150 respective interfaces within network N: 152 1. node B and node A can detect one another (i.e. node B is a member 153 of sets S and V), and, 155 2. node A and node C can also detect one another (i.e. node C is a 156 also a member of sets S and V). 158 These assumptions do not imply that node B can detect node C, nor 159 that node C can detect node B (through their interface on network N). 160 Such "non-transitivity" is common on multi-hop ad hoc wireless 161 networks. 163 In a nutshell: multi-hop ad hoc wireless communications can be 164 asymmetric, non-transitive, and time-varying. 166 3.2. Radio Range and Wireless Irregularities 168 Section 3.1 presents an abstract description of some common 169 characteristics concerning packet transmission over multi-hop ad hoc 170 wireless networks. This section describes practical examples, which 171 illustrate the characteristics listed in Section 3.1 as well as other 172 common effects. 174 Wireless communication links are subject to limitations to the 175 distance across which they may be established. The range-limitation 176 factor creates specific problems on multi-hop ad hoc wireless 177 networks. In this context, the radio ranges of several nodes often 178 partially overlap. Such partial overlap causes communication to be 179 non-transitive and/or asymmetric, as described in Section 3.1. 180 Moreover, the range varies from one node to another, depending on 181 location and environmental factors. This is in addition to the time 182 variation of range and signal strength caused by variability in the 183 local environment. 185 For example, as depicted in Figure 1, it may happen that a node B 186 detects a node A which transmits at high power, whereas B transmits 187 at lower power. In such cases, B detects A, but A cannot detect B. 188 This examplifies the asymmetry in multi-hop ad hoc wireless 189 communications as defined in Section 3.1. 191 Radio Ranges for Nodes A and B 193 <~~~~~~~~~~~~~+~~~~~~~~~~~~~> 194 | <~~~~~~+~~~~~~> 195 +--|--+ +--|--+ 196 | A |======>| B | 197 +-----+ +-----+ 199 Figure 1: Asymmetric Link example. Node A can communicate with 200 node B, but B cannot communicate with A. 202 Another example, depicted in Figure 2, is known as the "hidden node" 203 problem. Even though the nodes all have equal power for their radio 204 transmissions, they cannot all detect one another. In the figure, 205 nodes A and B can detect one another, and A and C can also detect one 206 another. On the other hand, nodes B and C cannot detect one another. 207 When nodes B and C simultaneously try to communicate with node A, 208 their radio signals may collide. Node A may receive incoherent 209 noise, and may even be unable to determine the source of the noise. 210 The hidden terminal problem illustrates the property of non- 211 transitivity in multi-hop ad hoc wireless communications as described 212 in Section 3.1. 214 Radio Ranges for Nodes A, B, C 216 <~~~~~~~~~~~~~+~~~~~~~~~~~~~> <~~~~~~~~~~~~~+~~~~~~~~~~~~~> 217 |<~~~~~~~~~~~~~+~~~~~~~~~~~~~>| 218 +--|--+ +--|--+ +--|--+ 219 | B |=======>| A |<=======| C | 220 +-----+ +-----+ +-----+ 222 Figure 2: The hidden node problem. Nodes C and B 223 try to communicate with node A at the same time, 224 and their radio signals collide. 226 Another situation, shown in Figure 3, is known as the "exposed node" 227 problem. In the figure, node A and node B can detect each other, and 228 node A is transmitting packets to node B, thus node A cannot detect 229 node C -- but node C can detect node A. As shown in Figure 3, during 230 the on-going transmission of node A, node C cannot reliably 231 communicate with node D because of interference within C's radio 232 range due to A 's transmissions. Node C is then called an "exposed 233 node", because it is exposed to co-channel interference from node A 234 and is thereby prevented from reliably exchanging protocol messages 235 with node D -- even though these transmissions would not interfere 236 with the reception of data sent from node A destined to node B. 238 Radio Ranges for Nodes A, B, C, D 240 <~~~~~~~~~~~~+~~~~~~~~~~~~> <~~~~~~~~~~+~~~~~~~~~~~> 241 |<~~~~~~~~~~~~+~~~~~~~~~~~~>|<~~~~~~~~~~~~+~~~~~~~~~> 242 +--|--+ +--|--+ +--|--+ +--|--+ 243 | B |<======| A | | C |======>| D | 244 +-----+ +-----+ +-----+ +-----+ 246 Figure 3: The exposed node problem. When node A is communicating 247 with node B, node C is an "exposed node". 249 Hidden and exposed node situations are often observed in multi-hop ad 250 hoc wireless networks. Problems with asymmetric links may also arise 251 for reasons other than power inequality (e.g., multipath 252 interference). Such problems are often resolved by specific 253 mechanisms below the IP layer, for example, CSMA/CA, which ensures 254 transmission in periods perceived to be unoccupied by other 255 transmissions. However, depending on the link layer technology in 256 use and the position of the nodes, such problems may affect the IP 257 layer due to range-limitation and partial overlap . 259 Besides radio range limitations, wireless communications are affected 260 by irregularities in the shape of the geographical area over which 261 nodes may effectively communicate (see for instance [MC03], [MI03]). 262 For example, even omnidirectional wireless transmission is typically 263 non-isotropic (i.e. non-circular). Signal strength often suffers 264 frequent and significant variations, which are not a simple function 265 of distance. Instead, it is a complex function of the environment 266 including obstacles, weather conditions, interference, and other 267 factors that change over time. Because each individual link has to 268 encounter different terrain, path, obstructions, atmospheric 269 conditions and other phenomena, analytical formulation of signal 270 strength is considered intractable [VTC99], and the radio engineering 271 community has thus developed numerous radio propagation models, 272 relying on median values observed in specific environments [SAR03]. 274 The above irregularities also cause communications on multi-hop ad 275 hoc wireless networks to be non-transitive, asymmetric, or time- 276 varying, as described in Section 3.1, and may impact protocols at the 277 IP layer and above. There may be no indication to the IP layer when 278 a previously established communication channel becomes unusable; 279 "link down" triggers are generally absent in multi-hop ad hoc 280 wireless networks, since the absence of detectable radio energy 281 (e.g., in carrier waves) may simply indicate that neighboring nodes 282 are not currently transmitting. Such an absence of detectable radio 283 energy does not therefore indicate whether or not transmissions have 284 failed to reach the intended destination. 286 4. Alternative Terminology 288 Many terms have been used in the past to describe the relationship of 289 nodes in a multi-hop ad hoc wireless network based on their ability 290 to send or receive packets to/from each other. The terms used in 291 this document have been selected because the authors believe they are 292 unambiguous, with respect to the goal of this document (see 293 Section 1). 295 Nevertheless, here are a few other terms that describe the same 296 relationship between nodes in multi-hop ad hoc wireless networks. In 297 the following, let network N be, again, a multi-hop ad hoc wireless 298 network. Let the set S be, as before, the set of nodes that can 299 directly receive packets transmitted by node A through its interface 300 on network N. In other words, any node B belonging to S can detect 301 packets transmitted by A. Then, due to the asymmetry characteristic 302 of wireless links: 304 - We may say that node A "reaches" node B. In this terminology, 305 there is no guarantee that node B reaches node A, even if node A 306 reaches node B. 308 - We may say that node B "hears" node A. In this terminology, 309 there is no guarantee that node A hears node B, even if node B 310 hears node A. 312 - We may say that node A "has a link" to node B. In this 313 terminology, there is no guarantee that node B has a link to node 314 A, even if node A has a link to node B. 316 - We may say that node B "is adjacent to" node A. In this 317 terminology, there is no guarantee that node A is adjacent to node 318 B, even if node B is adjacent to node A. 320 - We may say that node B "is downstream from" node A. In this 321 terminology, there is no guarantee that node A is downstream from 322 node B, even if node B is downstream from node A. 324 - We may say that node B "is a neighbor of" node A. In this 325 terminology, there is no guarantee that node A is a neighbor of 326 node B, even if node B a neighbor of node A. As it happens, the 327 terminology for "neighborhood" is quite confusing for asymmetric 328 links. When B can detect A, but A cannot detect B, it is not 329 clear whether B should be considered a neighbor of A at all, since 330 A would not necessarily be aware that B was a neighbor, as it 331 cannot detect B. Perhaps it is thus best to avoid the "neighbor" 332 terminology except for symmetric links. 334 This list of alternative terminologies is given here for illustrative 335 purposes only, and is not suggested to be complete or even 336 representative of the breadth of terminologies that have been used in 337 various ways to explain the properties mentioned in Section 3. 339 5. IP over Multi-hop Ad Hoc Wireless 341 The characteristics of packet transmission over multi-hop ad hoc 342 wireless networks, described in previous sections, are not the 343 typical characteristics expected by IP [RFC6250]. Nevertheless, it 344 is possible and desirable to run IP over such networks, through the 345 use of: 347 IP interface configuration, such as described in RFC 5889 348 [RFC5889], or 350 routing protocols designed for operation over wireless interfaces, 351 for example OLSR[RFC3626], AODV[RFC3561], or OSPF-MPR[RFC5449]. 353 Thus, even though the physical effects described in this document 354 require robust protocol designs for routing and topology management, 355 the experience in the projects described in the cited references 356 shows that useful networks can be designed and operated using well- 357 understood techniques. Protocols running above the IP layer can be 358 shielded somewhat from the unusual characteristics experienced over 359 multi-hop ad hoc wireless networks. Note however that some protocols 360 are nevertheless more appropriate than others when interfaces to 361 multi-hop ad hoc wireless networks are involved in the communication. 362 For instance, for applications written to run over both UDP and TCP, 363 the latter choice may be preferred in situations with relatively high 364 packet loss rates. But such choices must be based on application 365 requirements. 367 6. Security Considerations 369 This document does not have any security considerations. 371 7. IANA Considerations 373 This document does not have any IANA actions. 375 8. Informative References 377 [RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking 378 (MANET): Routing Protocol Performance Issues and 379 Evaluation Considerations", RFC 2501, January 1999. 381 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 382 Demand Distance Vector (AODV) Routing", RFC 3561, July 383 2003. 385 [RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing 386 Protocol (OLSR)", RFC 3626, October 2003. 388 [RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology 389 Dissemination Based on Reverse-Path Forwarding (TBRPF)", 390 RFC 3684, February 2004. 392 [RFC4728] Johnson, D., Hu, Y., and D. Maltz, "The Dynamic Source 393 Routing Protocol (DSR) for Mobile Ad Hoc Networks for 394 IPv4", RFC 4728, February 2007. 396 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, June 397 2007. 399 [RFC5449] Baccelli, E., Jacquet, P., Nguyen, D., and T. Clausen, 400 "OSPF Multipoint Relay (MPR) Extension for Ad Hoc 401 Networks", RFC 5449, February 2009. 403 [RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad 404 Hoc Networks", RFC 5889, September 2010. 406 [RFC6250] Thaler, D., "Evolution of the IP Model", RFC 6250, May 407 2011. 409 [DoD01] Freebersyser, J. and B. Leiner, "A DoD perspective on 410 mobile ad hoc networks", Addison Wesley C. E. Perkins, 411 Ed., 2001, pp. 29--51, 2001. 413 [FUNKFEUER] 414 "Austria Wireless Community Network, 415 http://www.funkfeuer.at", 2013. 417 [MC03] Corson, S. and J. Macker, "Mobile Ad hoc Networking: 418 Routing Technology for Dynamic, Wireless Networks", IEEE 419 Press Mobile Ad hoc Networking, Chapter 9, 2003. 421 [SAR03] Sarkar, T., Ji, Z., Kim, K., Medour, A., and M. Salazar- 422 Palma, "A Survey of Various Propagation Models for Mobile 423 Communication", IEEE Press Antennas and Propagation 424 Magazine, Vol. 45, No. 3, 2003. 426 [VTC99] Kim, D., Chang, Y., and J. Lee, "Pilot power control and 427 service coverage support in CDMA mobile systems", IEEE 428 Press Proceedings of the IEEE Vehicular Technology 429 Conference (VTC), pp.1464-1468, 1999. 431 [MI03] Kotz, D., Newport, C., and C. Elliott, "The Mistaken 432 Axioms of Wireless-Network Research", Dartmouth College 433 Computer Science Technical Report TR2003-467, 2003. 435 [FREIFUNK] 436 "Freifunk Wireless Community Networks, 437 http://www.freifunk.net", 2013. 439 Appendix A. Acknowledgements 441 This document stems from discussions with the following people, in 442 alphabetical order: Jari Arkko, Teco Boot, Carlos Jesus Bernardos 443 Cano, Ian Chakeres, Thomas Clausen, Robert Cragie, Christopher 444 Dearlove, Ralph Droms, Brian Haberman, Ulrich Herberg, Paul Lambert, 445 Kenichi Mase, Thomas Narten, Erik Nordmark, Alexandru Petrescu, Stan 446 Ratliff, Zach Shelby, Shubhranshu Singh, Fred Templin, Dave Thaler, 447 Mark Townsley, Ronald Velt in't, and Seung Yi. 449 Authors' Addresses 451 Emmanuel Baccelli 452 INRIA 454 EMail: Emmanuel.Baccelli@inria.fr 455 URI: http://www.emmanuelbaccelli.org/ 457 Charles E. Perkins 458 Futurewei 460 Phone: +1-408-330-4586 461 EMail: charlie.perkins@huawei.com