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Minaburo 5 Expires: 3 September 2022 Acklio 6 March 2022 8 Transmission of SCHC-compressed packets over IEEE 802.15.4 networks 9 draft-gomez-6lo-schc-15dot4-02 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 2 September 2022. 41 Copyright Notice 43 Copyright (c) 2022 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 Revised BSD License text as 52 described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Revised 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 5.2. SCHC compression for CoAP headers . . . . . . . . . . . . 7 72 5.3. Header compression examples . . . . . . . . . . . . . . . 8 73 6. Fragmentation and reassembly . . . . . . . . . . . . . . . . 8 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 75 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 76 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 77 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 78 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 79 10.2. Informative References . . . . . . . . . . . . . . . . . 10 80 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 82 1. Introduction 84 RFC 6282 is the main specification for IPv6 over Low power Wireless 85 Personal Area Network (6LoWPAN) IPv6 header compression [RFC6282]. 86 This RFC was designed assuming IEEE 802.15.4 as the layer below the 87 6LoWPAN adaptation layer, and it has also been reused (with proper 88 adaptations) for IPv6 header compression over many other technologies 89 relatively similar to IEEE 802.15.4 in terms of characteristics such 90 as physical layer bit rate, layer 2 maximum payload size, etc. 91 Examples of such technologies comprise BLE, DECT-ULE, ITU G.9959, MS/ 92 TP, NFC, and PLC. RFC 6282 provides additional functionality, such 93 as a mechanism for UDP header compression. 95 In the best cases, RFC 6282 allows to compress a 40-byte IPv6 header 96 down to a 2-byte compressed header (for link-local interactions) or a 97 3-byte compressed header (when global IPv6 addresses are used). On 98 the other hand, an RFC 6282 compressed UDP header has a typical size 99 of 4 bytes. Therefore, in advantageous conditions, a 48-byte 100 uncompressed IPv6/UDP header may be compressed down to a 6-byte 101 format (when using link-local addresses) or a 7-byte format (for 102 global interactions) by using RFC 6282. 104 Recently, a framework called Static Context Header Compression (SCHC) 105 has been designed with the primary goal of supporting IPv6 over Low 106 Power Wide Area Network (LPWAN) technologies [RFC8724]. SCHC 107 comprises header compression and fragmentation functionality tailored 108 to the extraordinary constraints of LPWAN technologies, which are 109 more severe than those exhibited by IEEE 802.15.4 or other relatively 110 similar technologies. SCHC header compression allows a greater 111 compression ratio than that of RFC 6282. If used properly, SCHC 112 allows to compress an IPv6/UDP header down to e.g. a single byte. In 113 addition, SCHC can be used to compress Constrained Application 114 Protocol (CoAP) headers as well [RFC7252][RFC8824], which further 115 increases the achievable performance improvement of using SCHC header 116 compression, since there is no 6LoWPAN header compression defined for 117 CoAP. Therefore, it may make sense to use SCHC header compression in 118 some 6LoWPAN environments [I-D.toutain-6lo-6lo-and-schc], including 119 IEEE 802.15.4 networks, considering its greater efficiency. 121 If SCHC header compression is added to the panoply of header 122 compression mechanisms used in 6LoWPAN environments, then there is a 123 need to signal when a packet header has been compressed by using 124 SCHC. To this end, the present document specifies a 6LoWPAN Dispatch 125 Type for SCHC header compression [RFC4944]. 127 This document specifies how a SCHC-compressed packet can be carried 128 over IEEE 802.15.4 networks. Note that, as per this document, and 129 while SCHC defines fragmentation mechanisms as well, 6LoWPAN/6Lo 130 fragmentation is used when necessary to transport SCHC-compressed 131 packets over IEEE 802.15.4 networks [RFC4944][RFC8930][RFC8931]. 133 TO-DO: indicate here any specific updates of RFC 8724 for use over 134 IEEE 802.15.4. 136 2. Terminology 137 2.1. Requirements language 139 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 140 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 141 "OPTIONAL" in this document are to be interpreted as described in 142 BCP14 [RFC2119], [RFC8174], when, and only when, they appear in all 143 capitals, as shown here. 145 2.2. Background on SCHC 147 The reader is expected to be familiar with the terms and concepts 148 defined in the specification of SCHC (RFC 8724). 150 3. Architecture 152 3.1. Network topologies 154 IEEE 802.15.4 supports two main network topologies: the star 155 topology, and the peer-to-peer (i.e., mesh) topology. 157 SCHC has been designed for LPWAN technologies, which are typically 158 based on a star topology where constrained devices (e.g., sensors) 159 communicate with a less constrained, central network gateway [RFC 160 8376]. However, as stated in [draft-ietf-lpwan-architecture], SCHC 161 is generic and it can also be used in networking environments beyond 162 the ones originally considered for SCHC. 164 SCHC compression is applicable to both star topology and mesh 165 topology IEEE 802.15.4 networks. 167 3.2. Protocol stack 169 The traditional 6LoWPAN-based protocol stack for constrained devices 170 (Figure 1, left) places the 6LoWPAN adaptation layer between IPv6 and 171 an underlying technology such as IEEE 802.15.4. Suitable upper layer 172 protocols include CoAP [RFC7252] and UDP. (Note that, while CoAP has 173 also been specified over TCP, and TCP may play a significant role in 174 IoT environments [RFC9006], 6LoWPAN header compression has not been 175 defined for TCP.) 177 6LoWPAN can be envisioned as a set of two main sublayers, where the 178 upper one provides header compression, while the lower one offers 179 fragmentation. 181 This document defines an alternative approach for packet header 182 compression over IEEE 802.15.4, which leads to a modified protocol 183 stack (Figure 1, right). 185 +------------+ +------------+ 186 | CoAP, other| | CoAP, other| 187 +------------+ +------------+ 188 | UDP, other | | UDP, other | 189 +------------+ +------------+ 190 | IPv6 | | IPv6 | 191 +------------+ +------------+ 192 | 6LoWPAN HC | | SCHC HC | <-- NEW 193 +------------+ +------------+ 194 |6LoWPAN Frag| |6LoWPAN Frag| 195 +------------+ +------------+ 196 | 802.15.4 | | 802.15.4 | 197 +------------+ +------------+ 199 Figure 1: Traditional 6LoWPAN-based protocol stack over IEEE 200 802.15.4 (left) and alternative protocol stack using SCHC for 201 header compression (right). HC and Frag stand for Header 202 Compression and Fragmentation, respectively. 204 SCHC header compression may be applied to the headers of different 205 protocols or sets of protocols. Some examples include: i) IPv6 206 packet headers, ii) joint IPv6 and UDP packet headers, iii) joint 207 IPv6, UDP and CoAP packet headers, etc. 209 4. Frame Format 211 This document defines the frame format to be used when a SCHC- 212 compressed packet is carried over IEEE 802.15.4. Such format is 213 carried as IEEE 802.15.4 frame payload. The format comprises a SCHC 214 Dispatch Type, a SCHC Packet (i.e. a SCHC-compressed packet (RFC 215 8724), and Padding bits, if any). Figure 2 illustrates the described 216 frame format. 218 <---------- IEEE 802.15.4 frame payload ----------> 220 <----- SCHC Packet -----> 221 +---------------+-------------+---------+ - - - - + 222 | SCHC Dispatch | SCHC Header | Payload | Padding | 223 +---------------+-------------+---------+ - - - - + 225 Figure 2: Encapsulated, SCHC-compressed packet. Padding bits are 226 added if needed. 228 4.1. SCHC Dispatch 230 Adding SCHC header compression to the panoply of header compression 231 mechanisms used in 6LoWPAN/6Lo environments creates the need to 232 signal when a packet header has been compressed by using SCHC. To 233 this end, the present document specifies the SCHC Dispatch. The SCHC 234 Dispatch indicates that the next field in the frame format is a SCHC- 235 compressed header (SCHC Header in Figure 2, see 4.2)). 237 This document defines the SCHC Dispatch as a 6LoWPAN Dispatch Type 238 for SCHC header compression [RFC4944]. With the aim to minimize 239 [RFC8025] for the SCHC Dispatch Type: 241 SCHC Dispatch Type bit pattern: 01000100 (Page 0) (Note: to be 242 confirmed by IANA)) 244 4.2. SCHC Header 246 SCHC Header (Figure 2) corresponds to a packet header that has been 247 compressed by using SCHC. As defined in [RFC8724], the SCHC Header 248 comprises a RuleID, and a compression residue. As per the present 249 specification, a RuleID size between 1 and 16 bits is RECOMMENDED. 250 In order to decide the RuleID size to be used in a network, the 251 trade-off between (compressed) header overhead and the number of 252 Rules needs to be carefully assessed. 254 4.3. Padding 256 If SCHC header compression leads to a SCHC Packet size of a non- 257 integer number of bytes, padding bits of value equal to zero MUST be 258 appended to the SCHC Packet as appropriate to align to an octet 259 boundary. 261 5. SCHC compression for IPv6, UDP, and CoAP headers 263 SCHC header compression may be applied to the headers of different 264 protocols or sets of protocols. Some examples include: i) IPv6 265 packet headers, ii) joint IPv6 and UDP packet headers, iii) joint 266 IPv6, UDP and CoAP packet headers, etc. 268 5.1. SCHC compression for IPv6 and UDP headers 270 IPv6 and UDP header fields MUST be compressed as per Section 10 of 271 RFC 8724. 273 IPv6 addresses are split into two 64-bit-long fields; one for the 274 prefix and one for the Interface Identifier (IID). 276 To allow for a single Rule being used for both directions, RFC 8724 277 identifies IPv6 addresses and UDP ports by their role (Dev or App) 278 and not by their position in the header (source or destination). 279 This optimization can be used as is in some IEEE 802.15.4 networks 280 (e.g., an IEEE 802.15.4 star topology where the peripheral devices 281 (Devs) send/receive packets to/from a network-side entity (App)). 283 However, in some types of 6LoWPAN environments (e.g., when a sender 284 and its destination are both peer nodes in a mesh topology network), 285 additional functionality (TBD) is needed to allow use of the Dev and 286 App roles for C/D. In this case, each SCHC C/D entity needs to know 287 its role (Dev or App) for each endpoint it communicates with. In 288 such cases, the terms Uplink and Downlink that have been defined in 289 RFC 8724 need to be understood in the context of each specific pair 290 of endpoints. 292 5.1.1. Compression of IPv6 addresses 294 Compression of IPv6 source and destination prefixes MUST be performed 295 as per Section 10.7.1 of RFC 8724. 297 Compression of IPv6 source and destination IIDs MUST be performed as 298 per Section 10.7.2 of RFC 8724. One particular consideration when 299 SCHC C/D is used in IEEE 802.15.4 networks is that, in contrast with 300 some LPWAN technologies, IEEE 802.15.4 data frame headers include 301 both source and destination fields. If the Dev or App IID are based 302 on an L2 address, in some cases the IID can be reconstructed with 303 information coming from the L2 header. Therefore, in those cases, 304 DevIID and AppIID CDAs can be used. 306 5.2. SCHC compression for CoAP headers 308 CoAP header fields MUST be compressed as per Sections 4 to 6 of RFC 309 8824. 311 For CoAP header compression/decompression, the SCHC Rules description 312 uses direction information in order to reduce the number of Rules 313 needed to compress headers. 315 As stated in 5.1, in some types of 6LoWPAN environments (e.g., when a 316 sender and its destination are both peer nodes in a mesh topology 317 network), each SCHC C/D entity needs to know its role (Dev or App) 318 for each endpoint it communicates with. Therefore, in such cases, 319 direction information will be specific for each pair of endpoints. 321 5.3. Header compression examples 323 TO-DO: provide examples for IPv6-only, IPv6/UDP and IPv6/UDP/CoAP. 325 6. Fragmentation and reassembly 327 After applying SCHC header compression to a packet intended for 328 transmission, if the size of the resulting frame format (Section 4) 329 exceeds the IEEE 802.15.4 frame payload space available, such frame 330 format MUST be fragmented, carried and reassembled by means of 331 6LoWPAN fragmentation and reassembly [RFC4944][RFC8930][RFC8931]. 333 7. IANA Considerations 335 This document requests the allocation of the Dispatch Type Field bit 336 pattern 01000100 (Page 0) as SCHC Dispatch Type. 338 8. Security Considerations 340 This document does not define SCHC header compression functionality 341 beyond the one defined in RFC 8724. Therefore, the security 342 considerations in section 12.1 of RFC 8724 and in section 9 of RFC 343 8824 apply. 345 As a safety measure, a SCHC decompressor implementing the present 346 specification MUST NOT reconstruct a packet larger than 1500 bytes 347 [RFC8724]. 349 IEEE 802.15.4 networks support link-layer security mechanisms such as 350 encryption and authentication. As in RFC 8824, the use of a 351 cryptographic integrity-protection mechanism to protect the SCHC 352 headers is REQUIRED. 354 9. Acknowledgments 356 Ana Minaburo and Laurent Toutain suggested for the first time the use 357 of SCHC in environments where 6LoWPAN has traditionally been used. 358 Laurent Toutain, Pascal Thubert, Dominique Barthel, and Guangpeng Li 359 made comments that helped shape this document. 361 Carles Gomez has been funded in part by the Spanish Government 362 through project PID2019-106808RA-I00, and by Secretaria 363 d'Universitats i Recerca del Departament d'Empresa i Coneixement de 364 la Generalitat de Catalunya 2017 through grant SGR 376. 366 10. References 368 10.1. Normative References 370 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 371 Requirement Levels", BCP 14, RFC 2119, 372 DOI 10.17487/RFC2119, March 1997, 373 . 375 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 376 "Transmission of IPv6 Packets over IEEE 802.15.4 377 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 378 . 380 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 381 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 382 DOI 10.17487/RFC6282, September 2011, 383 . 385 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 386 Application Protocol (CoAP)", RFC 7252, 387 DOI 10.17487/RFC7252, June 2014, 388 . 390 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 391 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 392 RFC 8025, DOI 10.17487/RFC8025, November 2016, 393 . 395 [RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation- 396 Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065, 397 February 2017, . 399 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 400 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 401 May 2017, . 403 [RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. 404 Zuniga, "SCHC: Generic Framework for Static Context Header 405 Compression and Fragmentation", RFC 8724, 406 DOI 10.17487/RFC8724, April 2020, 407 . 409 [RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static 410 Context Header Compression (SCHC) for the Constrained 411 Application Protocol (CoAP)", RFC 8824, 412 DOI 10.17487/RFC8824, June 2021, 413 . 415 [RFC8930] Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On 416 Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6 417 Network", RFC 8930, DOI 10.17487/RFC8930, November 2020, 418 . 420 [RFC8931] Thubert, P., Ed., "IPv6 over Low-Power Wireless Personal 421 Area Network (6LoWPAN) Selective Fragment Recovery", 422 RFC 8931, DOI 10.17487/RFC8931, November 2020, 423 . 425 10.2. Informative References 427 [I-D.toutain-6lo-6lo-and-schc] 428 Minaburo, A. and L. Toutain, "Comparison of 6lo and SCHC", 429 Work in Progress, Internet-Draft, draft-toutain-6lo-6lo- 430 and-schc-00, 4 November 2019, 431 . 434 [RFC9006] Gomez, C., Crowcroft, J., and M. Scharf, "TCP Usage 435 Guidance in the Internet of Things (IoT)", RFC 9006, 436 DOI 10.17487/RFC9006, March 2021, 437 . 439 Authors' Addresses 441 Carles Gomez 442 UPC 443 C/Esteve Terradas, 7 444 08860 Castelldefels 445 Spain 446 Email: carlesgo@entel.upc.edu 448 Ana Minaburo 449 Acklio 450 1137A avenue des Champs Blancs 451 35510 Cesson-Sevigne Cedex 452 France 453 Email: ana@ackl.io