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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6lo Working Group C.G. Gomez 3 Internet-Draft UPC 4 Intended status: Standards Track A.M. Minaburo 5 Expires: 26 April 2022 Acklio 6 October 2021 8 Transmission of SCHC-compressed packets over IEEE 802.15.4 networks 9 draft-gomez-6lo-schc-15dot4-01 11 Abstract 13 A framework called Static Context Header Compression and 14 fragmentation (SCHC) has been designed with the primary goal of 15 supporting IPv6 over Low Power Wide Area Network (LPWAN) technologies 16 [RFC8724]. One of the SCHC components is a header compression 17 mechanism. If used properly, SCHC header compression allows a 18 greater compression ratio than that achievable with traditional 19 6LoWPAN header compression [RFC6282]. For this reason, it may make 20 sense to use SCHC header compression in some 6LoWPAN environments, 21 including IEEE 802.15.4 networks. This document specifies how a 22 SCHC-compressed packet can be carried over IEEE 802.15.4 networks. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on 4 April 2022. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 48 license-info) in effect on the date of publication of this document. 49 Please review these documents carefully, as they describe your rights 50 and restrictions with respect to this document. Code Components 51 extracted from this document must include Simplified BSD License text 52 as described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2.1. Requirements language . . . . . . . . . . . . . . . . . . 4 60 2.2. Background on SCHC . . . . . . . . . . . . . . . . . . . 4 61 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4 62 3.1. Network topologies . . . . . . . . . . . . . . . . . . . 4 63 3.2. Protocol stack . . . . . . . . . . . . . . . . . . . . . 4 64 4. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 5 65 4.1. SCHC Dispatch . . . . . . . . . . . . . . . . . . . . . . 6 66 4.2. SCHC Header . . . . . . . . . . . . . . . . . . . . . . . 6 67 4.3. Padding . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 5. SCHC compression for IPv6, UDP, and CoAP headers . . . . . . 6 69 5.1. SCHC compression for IPv6 and UDP headers . . . . . . . . 6 70 5.1.1. Compression of IPv6 addresses . . . . . . . . . . . . 7 71 5.1.2. Compression of UDP ports . . . . . . . . . . . . . . 7 72 5.2. SCHC compression for CoAP headers . . . . . . . . . . . . 7 73 5.3. Header compression examples . . . . . . . . . . . . . . . 8 74 6. Fragmentation and reassembly . . . . . . . . . . . . . . . . 8 75 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 76 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 77 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 78 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 79 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 80 10.2. Informative References . . . . . . . . . . . . . . . . . 10 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 83 1. Introduction 85 RFC 6282 is the main specification for IPv6 over Low power Wireless 86 Personal Area Network (6LoWPAN) IPv6 header compression [RFC6282]. 87 This RFC was designed assuming IEEE 802.15.4 as the layer below the 88 6LoWPAN adaptation layer, and it has also been reused (with proper 89 adaptations) for IPv6 header compression over many other technologies 90 relatively similar to IEEE 802.15.4 in terms of characteristics such 91 as physical layer bit rate, layer 2 maximum payload size, etc. 92 Examples of such technologies comprise BLE, DECT-ULE, ITU G.9959, MS/ 93 TP, NFC, and PLC. RFC 6282 provides additional functionality, such 94 as a mechanism for UDP header compression. 96 In the best cases, RFC 6282 allows to compress a 40-byte IPv6 header 97 down to a 2-byte compressed header (for link-local interactions) or a 98 3-byte compressed header (when global IPv6 addresses are used). On 99 the other hand, an RFC 6282 compressed UDP header has a typical size 100 of 4 bytes. Therefore, in advantageous conditions, a 48-byte 101 uncompressed IPv6/UDP header may be compressed down to a 6-byte 102 format (when using link-local addresses) or a 7-byte format (for 103 global interactions) by using RFC 6282. 105 Recently, a framework called Static Context Header Compression (SCHC) 106 has been designed with the primary goal of supporting IPv6 over Low 107 Power Wide Area Network (LPWAN) technologies [RFC8724]. SCHC 108 comprises header compression and fragmentation functionality tailored 109 to the extraordinary constraints of LPWAN technologies, which are 110 more severe than those exhibited by IEEE 802.15.4 or other relatively 111 similar technologies. SCHC header compression allows a greater 112 compression ratio than that of RFC 6282. If used properly, SCHC 113 allows to compress an IPv6/UDP header down to e.g. a single byte. In 114 addition, SCHC can be used to compress Constrained Application 115 Protocol (CoAP) headers as well [RFC7252][RFC8824], which further 116 increases the achievable performance improvement of using SCHC header 117 compression, since there is no 6LoWPAN header compression defined for 118 CoAP. Therefore, it may make sense to use SCHC header compression in 119 some 6LoWPAN environments [I-D.toutain-6lo-6lo-and-schc], including 120 IEEE 802.15.4 networks, considering its greater efficiency. 122 If SCHC header compression is added to the panoply of header 123 compression mechanisms used in 6LoWPAN environments, then there is a 124 need to signal when a packet header has been compressed by using 125 SCHC. To this end, the present document specifies a 6LoWPAN Dispatch 126 Type for SCHC header compression [RFC4944]. 128 This document specifies how a SCHC-compressed packet can be carried 129 over IEEE 802.15.4 networks. Note that, as per this document, and 130 while SCHC defines fragmentation mechanisms as well, 6LoWPAN/6Lo 131 fragmentation is used when necessary to transport SCHC-compressed 132 packets over IEEE 802.15.4 networks [RFC4944][RFC8930][RFC8931]. 134 TO-DO: indicate here any specific updates of RFC 8724 for use over 135 IEEE 802.15.4. 137 2. Terminology 138 2.1. Requirements language 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 141 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 142 "OPTIONAL" in this document are to be interpreted as described in 143 BCP14 [RFC2119], [RFC8174], when, and only when, they appear in all 144 capitals, as shown here. 146 2.2. Background on SCHC 148 The reader is expected to be familiar with the terms and concepts 149 defined in the specification of SCHC (RFC 8724). 151 3. Architecture 153 3.1. Network topologies 155 IEEE 802.15.4 supports two main network topologies: the star 156 topology, and the peer-to-peer (i.e., mesh) topology. 158 SCHC has been designed for LPWAN technologies, which are typically 159 based on a star topology where constrained devices (e.g., sensors) 160 communicate with a less constrained, central network gateway [RFC 161 8376]. However, as stated in [draft-ietf-lpwan-architecture], SCHC 162 is generic and it can also be used in networking environments beyond 163 the ones originally considered for SCHC. 165 SCHC compression is applicable to both star topology and mesh 166 topology IEEE 802.15.4 networks. 168 3.2. Protocol stack 170 The traditional 6LoWPAN-based protocol stack for constrained devices 171 (Figure 1, left) places the 6LoWPAN adaptation layer between IPv6 and 172 an underlying technology such as IEEE 802.15.4. Suitable upper layer 173 protocols include CoAP [RFC7252] and UDP. (Note that, while CoAP has 174 also been specified over TCP, and TCP may play a significant role in 175 IoT environments [RFC9006], 6LoWPAN header compression has not been 176 defined for TCP.) 178 6LoWPAN can be envisioned as a set of two main sublayers, where the 179 upper one provides header compression, while the lower one offers 180 fragmentation. 182 This document defines an alternative approach for packet header 183 compression over IEEE 802.15.4, which leads to a modified protocol 184 stack (Figure 1, right). 186 +------------+ +------------+ 187 | CoAP, other| | CoAP, other| 188 +------------+ +------------+ 189 | UDP, other | | UDP, other | 190 +------------+ +------------+ 191 | IPv6 | | IPv6 | 192 +------------+ +------------+ 193 | 6LoWPAN HC | | SCHC HC | <-- NEW 194 +------------+ +------------+ 195 |6LoWPAN Frag| |6LoWPAN Frag| 196 +------------+ +------------+ 197 | 802.15.4 | | 802.15.4 | 198 +------------+ +------------+ 200 Figure 1: Traditional 6LoWPAN-based protocol stack over IEEE 201 802.15.4 (left) and alternative protocol stack using SCHC for 202 header compression (right). HC and Frag stand for Header 203 Compression and Fragmentation, respectively. 205 SCHC header compression may be applied to the headers of different 206 protocols or sets of protocols. Some examples include: i) IPv6 207 packet headers, ii) joint IPv6 and UDP packet headers, iii) joint 208 IPv6, UDP and CoAP packet headers, etc. 210 4. Frame Format 212 This document defines the frame format to be used when a SCHC- 213 compressed packet is carried over IEEE 802.15.4. Such format is 214 carried as IEEE 802.15.4 frame payload. The format comprises a SCHC 215 Dispatch Type, a SCHC Packet (i.e. a SCHC-compressed packet (RFC 216 8724), and Padding bits, if any). Figure 2 illustrates the described 217 frame format. 219 <---------- IEEE 802.15.4 frame payload ----------> 221 <----- SCHC Packet -----> 222 +---------------+-------------+---------+ - - - - + 223 | SCHC Dispatch | SCHC Header | Payload | Padding | 224 +---------------+-------------+---------+ - - - - + 226 Figure 2: Encapsulated, SCHC-compressed packet. Padding bits are 227 added if needed. 229 4.1. SCHC Dispatch 231 Adding SCHC header compression to the panoply of header compression 232 mechanisms used in 6LoWPAN/6Lo environments creates the need to 233 signal when a packet header has been compressed by using SCHC. To 234 this end, the present document specifies the SCHC Dispatch. The SCHC 235 Dispatch indicates that the next field in the frame format is a SCHC- 236 compressed header (SCHC Header in Figure 2, see 4.2)). 238 This document defines the SCHC Dispatch as a 6LoWPAN Dispatch Type 239 for SCHC header compression [RFC4944]. With the aim to minimize 240 [RFC8025] for the SCHC Dispatch Type: 242 SCHC Dispatch Type bit pattern: 01000100 (Page 0) (Note: to be 243 confirmed by IANA)) 245 4.2. SCHC Header 247 SCHC Header (Figure 2) corresponds to a packet header that has been 248 compressed by using SCHC. As defined in [RFC8724], the SCHC Header 249 comprises a RuleID, and a compression residue. The present 250 specification defines a RuleID size of 8 bits. 252 4.3. Padding 254 If SCHC header compression leads to a SCHC Packet size of a non- 255 integer number of bytes, padding bits of value equal to zero MUST be 256 appended to the SCHC Packet as appropriate to align to an octet 257 boundary. 259 5. SCHC compression for IPv6, UDP, and CoAP headers 261 SCHC header compression may be applied to the headers of different 262 protocols or sets of protocols. Some examples include: i) IPv6 263 packet headers, ii) joint IPv6 and UDP packet headers, iii) joint 264 IPv6, UDP and CoAP packet headers, etc. 266 5.1. SCHC compression for IPv6 and UDP headers 268 With the exception of IPv6 addresses and UDP ports, IPv6 and UDP 269 header fields MUST be compressed as per Section 10 of RFC 8724. 271 IPv6 addresses are split into two 64-bit-long fields; one for the 272 prefix and one for the Interface Identifier (IID). 274 To allow for a single Rule being used for both directions, RFC 8724 275 identifies IPv6 addresses and UDP ports by their role (Dev or App) 276 and not by their position in the header (source or destination). 277 However, such roles are not applicable in some types of 6LoWPAN 278 environments (e.g., when a sender and its destination are both nodes 279 in a mesh topology network). In such cases, the terms Uplink and 280 Downlink as they have been defined in RFC 8724 are not applicable 281 either. 283 The present specification identifies IPv6 addresses and UDP ports by 284 their position in the header (source or destination). Accordingly, 285 the present specification defines two new values for the Direction 286 Indicator: Transmit (Tx) and Receive (Rx). 288 5.1.1. Compression of IPv6 addresses 290 Compression of IPv6 source and destination prefixes MUST be performed 291 as per Section 10.7.1 of RFC 8724. 293 If the source or destination IID are based on an L2 address, then the 294 IID can be reconstructed with information coming from the L2 header. 295 In that case, the TV is not set, the MO is set to "ignore" and the 296 CDA is set to compute-IID. 298 As described in [RFC8065], it may be undesirable to build the source 299 IPv6 IID of a device out of the device address. Another static value 300 is used instead. In that case, the TV contains the static value, the 301 MO operator is set to "equal" and the CDA is set to "not-sent". 303 If several IIDs are possible, then the TV contains the list of 304 possible IIDs, the MO is set to "match-mapping" and the CDA is set to 305 "mapping-sent". 307 It may also happen that the IID variability only expresses itself on 308 a few bytes. In that case, the TV is set to the stable part of the 309 IID, the MO is set to "MSB" and the CDA is set to "LSB". 311 5.1.2. Compression of UDP ports 313 TO-DO 315 5.2. SCHC compression for CoAP headers 317 CoAP header fields MUST be compressed as per Sections 4 to 6 of RFC 318 8824. 320 5.3. Header compression examples 322 TO-DO: provide examples for IPv6-only, IPv6/UDP and IPv6/UDP/CoAP. 324 6. Fragmentation and reassembly 326 After applying SCHC header compression to a packet intended for 327 transmission, if the size of the resulting frame format (Section 4) 328 exceeds the IEEE 802.15.4 frame payload space available, such frame 329 format MUST be fragmented, carried and reassembled by means of 330 6LoWPAN fragmentation and reassembly [RFC4944][RFC8930][RFC8931]. 332 7. IANA Considerations 334 This document requests the allocation of the Dispatch Type Field bit 335 pattern 01000100 (Page 0) as SCHC Dispatch Type. 337 8. Security Considerations 339 This document does not define SCHC header compression functionality 340 beyond the one defined in RFC 8724. Therefore, the security 341 considerations in section 12.1 of RFC 8724 apply. 343 As a safety measure, a SCHC decompressor implementing the present 344 specification MUST NOT reconstruct a packet larger than 1500 bytes 345 [RFC8724]. 347 9. Acknowledgments 349 Ana Minaburo and Laurent Toutain suggested for the first time the use 350 of SCHC in environments where 6LoWPAN has traditionally been used. 351 Laurent Toutain, Pascal Thubert, Dominique Barthel, and Guangpeng Li 352 made comments that helped shape this document. 354 Carles Gomez has been funded in part by the Spanish Government 355 through project PID2019-106808RA-I00, and by Secretaria 356 d'Universitats i Recerca del Departament d'Empresa i Coneixement de 357 la Generalitat de Catalunya 2017 through grant SGR 376. 359 10. References 361 10.1. Normative References 363 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 364 Requirement Levels", BCP 14, RFC 2119, 365 DOI 10.17487/RFC2119, March 1997, 366 . 368 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 369 "Transmission of IPv6 Packets over IEEE 802.15.4 370 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 371 . 373 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 374 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 375 DOI 10.17487/RFC6282, September 2011, 376 . 378 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 379 Application Protocol (CoAP)", RFC 7252, 380 DOI 10.17487/RFC7252, June 2014, 381 . 383 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 384 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 385 RFC 8025, DOI 10.17487/RFC8025, November 2016, 386 . 388 [RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation- 389 Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065, 390 February 2017, . 392 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 393 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 394 May 2017, . 396 [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. 397 Zuniga, "SCHC: Generic Framework for Static Context Header 398 Compression and Fragmentation", RFC 8724, 399 DOI 10.17487/RFC8724, April 2020, 400 . 402 [RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static 403 Context Header Compression (SCHC) for the Constrained 404 Application Protocol (CoAP)", RFC 8824, 405 DOI 10.17487/RFC8824, June 2021, 406 . 408 [RFC8930] Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On 409 Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 410 Network", RFC 8930, DOI 10.17487/RFC8930, November 2020, 411 . 413 [RFC8931] Thubert, P., Ed., "IPv6 over Low-Power Wireless Personal 414 Area Network (6LoWPAN) Selective Fragment Recovery", 415 RFC 8931, DOI 10.17487/RFC8931, November 2020, 416 . 418 10.2. Informative References 420 [I-D.toutain-6lo-6lo-and-schc] 421 Minaburo, A. and L. Toutain, "Comparison of 6lo and SCHC", 422 Work in Progress, Internet-Draft, draft-toutain-6lo-6lo- 423 and-schc-00, 4 November 2019, 424 . 427 [RFC9006] Gomez, C., Crowcroft, J., and M. Scharf, "TCP Usage 428 Guidance in the Internet of Things (IoT)", RFC 9006, 429 DOI 10.17487/RFC9006, March 2021, 430 . 432 Authors' Addresses 434 Carles Gomez 435 UPC 436 C/Esteve Terradas, 7 437 08860 Castelldefels 438 Spain 440 Email: carlesgo@entel.upc.edu 442 Ana Minaburo 443 Acklio 444 1137A avenue des Champs Blancs 445 35510 Cesson-Sevigne Cedex 446 France 448 Email: ana@ackl.io