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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTAREA/Network Working Group J. Zhu 2 Internet Draft Intel 3 Intended status: Informational S. Kanugovi 4 Expires: June 16,2020 Nokia 5 December 16, 2019 7 Generic Multi-Access (GMA) Convergence Encapsulation Protocols 8 draft-zhu-intarea-gma-05 10 Status of this Memo 12 This Internet-Draft is submitted in full conformance with the 13 provisions of BCP 78 and BCP 79. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six 21 months and may be updated, replaced, or obsoleted by other 22 documents at any time. It is inappropriate to use Internet-Drafts 23 as reference material or to cite them other than as "work in 24 progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html 32 This Internet-Draft will expire on June 16, 2019. 34 Copyright Notice 36 Copyright (c) 2019 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with 44 respect to this document. Code Components extracted from this 45 document must include Simplified BSD License text as described in 46 Section 4.e of the Trust Legal Provisions and are provided without 47 warranty as described in the Simplified BSD License. 49 Abstract 51 Today, a device can be simultaneously connected to multiple 52 networks, e.g. Wi-Fi, LTE, 5G, and DSL. It is desirable to combine 53 them seamlessly to improve quality of experience. Such 54 optimization requires additional control information, e.g. 55 Sequence Number, in each (IP) data packet. This document presents 56 a new light-weight and flexible encapsulation protocol for this 57 need. The solution has been developed by the authors based on 58 their experiences in multiple standards bodies including the IETF 59 and 3GPP, is not an Internet Standard and does not represent the 60 consensus opinion of the IETF. This document will enable other 61 developers to build interoperable implementations. 63 Table of Contents 65 1. Introduction ................................................. 2 66 2. Conventions used in this document ............................ 3 67 3. Use Case ..................................................... 4 68 4. GMA Encapsulation Format ..................................... 5 69 5. Fragmentation ................................................ 8 70 6. Concatenation ................................................ 9 71 7. Security Considerations ..................................... 10 72 8. IANA Considerations ......................................... 11 73 9. References .................................................. 11 74 9.1. Normative References ..................................11 75 9.2. Informative References ................................11 77 1. Introduction 79 Figure 1 shows the user-plane Generic Multi-Access (GMA) protocol 80 stack, which has been used in today's multi-access solutions 81 [ATSSS] [MAMS] [LWIPEP] [GRE]. 83 +-----------------------------------------------------+ 84 | IP PDU | 85 |-----------------------------------------------------| 86 | Convergence Sublayer | 87 |-----------------------------------------------------| 88 | Adaptation | Adaptation | Adaptation | 89 | Sublayer | Sublayer | Sublayer | 90 | (optional) | (optional) | (optional) | 91 |-----------------------------------------------------| 92 | Access #1 IP | Access #2 IP | Access #3 IP | 93 +-----------------------------------------------------+ 94 Figure 1: GMA User-Plane Protocol Stack 96 It consists of the following two Sublayers: 98 o Convergence sublayer: This layer performs multi-access 99 specific tasks, e.g., multi-link (path) aggregation, 100 splitting/reordering, lossless switching/retransmission, 101 fragmentation, concatenation, etc. 102 o Adaptation sublayer: This layer performs functions to handle 103 tunnelling, network layer security, and NAT (network address 104 translation). 106 The convergence sublayer operates on top of the adaptation 107 sublayer in the protocol stack. From the Transmitter perspective, 108 a User Payload (e.g. IP packet) is processed by the convergence 109 sublayer first, and then by the adaptation sublayer before being 110 transported over a delivery connection; from the Receiver 111 perspective, an IP packet received over a delivery connection is 112 processed by the adaptation sublayer first, and then by the 113 convergence sublayer. 115 IP-over-IP tunneling has been used in today's multi-access 116 solutions, e.g. [LWIPEP] [GRE], to insert the GRE header, and then 117 encode additional control information in the GRE header fields, 118 e.g. Key, Sequence Number. However, there are two main drawbacks 119 with this approach: 1) IP-over-IP tunneling leads to higher 120 overhead especially for small packet. For example, the overhead of 121 IP-over-IP/GRE tunneling with both Key and Sequence Number is 32 122 Bytes, which is 80% of a 40 Bytes TCP ACK packet; 2) It is 123 difficult to introduce new control fields with the GRE header 124 format. 126 This document presents a light-weight GMA encapsulation protocol 127 for the convergence sublayer. It avoids IP-over-IP tunneling to 128 minimize overhead and introduces new control fields to support 129 fragmentation and concatenation at the convergence sublayer, which 130 are not available in today's GRE-based solutions [LWIPEP] [GRE]. 132 GMA protocol SHALL only operate between endpoints that have been 133 configured to operate with GMA through additional control messages 134 and procedures, for example [MAMS]. Moreover, UDP or IPSec 135 tunneling MAY be used at the adaptation sublayer to protect GMA 136 operation from intermediate nodes. 138 2. Conventions used in this document 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 141 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", 142 "MAY", and "OPTIONAL" in this document are to be interpreted as 143 described in BCP 14 [RFC2119] [RFC8174] when, and only when, they 144 appear in all capitals, as shown here. 146 3. Use Case 148 Multi-Access Aggregation 150 +---+ +---+ 151 | |A|--- LTE Connection -----|C| | 152 |U|-| |-|S| Internet 153 | |B|--- Wi-Fi Connection ---|D| | 154 +---+ +---+ 155 Client Multi-Access Gateway 157 A: The adaptation sublayer endpoint of the LTE connection 158 resides in the client 160 B: The adaptation sublayer endpoint of the Wi-Fi connection 161 resides in the client 163 C: The adaptation sublayer endpoint of the LTE connection 164 resides in the Multi-Access Gateway, aka N-MADP (Network 165 Multi-Access Data Proxy) in [MAMS] 167 D: The adaptation sublayer endpoint of the Wi-Fi connection 168 resides in the Multi-Access Gateway 170 U: The convergence sublayer endpoint resides in the client 172 S: The convergence sublayer endpoint resides in the Multi- 173 Access Gateway 175 Figure 2: GMA-based Multi-Access Aggregation 177 As shown in Figure 2, a client device (e.g. Smartphone, Laptop, 178 etc.) may connect to Internet via both Wi-Fi and LTE connections, 179 one of which (e.g. LTE) may operate as the anchor connection, and 180 the other (e.g. Wi-Fi) may operate as the delivery connection. The 181 anchor connection provides the IP address and connectivity for 182 end-to-end Internet access, and the delivery connection provides 183 additional path between client and Multi-Access Gateway for multi- 184 access optimizations. 186 For example, per-packet aggregation allows a single IP flow to use 187 the combined bandwidth of the two connections. In another example, 188 packets lost due to temporarily link outage may be retransmitted. 189 Moreover, packets may be duplicated over multiple connections to 190 achieve high reliability and low latency, and duplicated packets 191 should be eliminated by the receiving side. Such multi-access 192 optimization requires additional control information, e.g. 193 Sequence Number, in each IP data packet, which can be supported by 194 the GMA encapsulation protocol described in this document. 196 The GMA protocol in this document is designed for multiple 197 connections, but it may also be used when there is only one 198 connection between two end-points. For example, it may be used for 199 loss detection and recovery. In another example, it may be used to 200 concatenate multiple small packets and reduce per packet overhead. 202 4. GMA Encapsulation Format 204 +------------------------------------------------------+ 205 | IP hdr | IP payload | GMA Trailer | 206 +------------------------------------------------------+ 207 Figure 3: Trailer-based Encapsulation Format 209 Figure 3 shows the trailer-based encapsulation GMA PDU (protocol 210 data unit) format for the convergence sublayer. A (GMA) PDU may 211 carry one or multiple IP packets, aka (GMA) SDUs (service data 212 unit), in the payload, or a fragment of the SDU. 214 The Protocol Type field in the IP header of the GMA PDU MUST be 215 changed to 114 (Any 0-Hop Protocol) [IANA] to indicate the 216 presence of the GMA trailer. The following three IP header fields 217 SHOULD also be changed: 219 o IP Length: add the length of "GMA Trailer" to the length of 220 the original IP packet 221 o Time To Live (TTL) or Hop-Limit (HL): set the HL field to "0" 222 if the original IP packet is IPv6, and set the TTL field to "1" 223 if the original IP packet is IPv4. 224 o IP checksum: recalculate after changing "Protocol Type", "TTL 225 or HL" and "IP Length" 227 However, if UDP tunnelling is used at the adaptation sublayer to 228 carry the GMA PDU, the above three IP header fields MAY remain 229 unchanged, and the receiver will determine the GMA PDU length 230 based on the UDP packet length. 232 The GMA (Generic Multi-Access) trailer MUST consist of the 233 following two mandatory fields. The Flags field is at the end of 234 the PDU, and the Next Header field is the second last. The 235 Receiver SHOULD first decode the Flags field to determine the 236 length of the GMA trailer, and then decode each optional field 237 accordingly. 239 o Next Header (1 Byte): the IP protocol type of the (first) SDU 240 in a PDU 241 o Flags (2 Bytes): Bit 0 is the most significant bit (MSB), and 242 Bit 15 is the least significant bit (LSB). 243 + Checksum Present (bit 0): If the Checksum Present bit is set 244 to 1, then the Checksum field is present and contains valid 245 information. 246 + Concatenation Present (bit 1): If the Concatenation Present 247 bit is set to 1, then the PDU carries multiple SDUs, and the 248 First SDU Length field is present and contains valid 249 information. 250 + Connection ID Present (bit 2): If the Connection ID Present 251 bit is set to 1, then the Connection ID field is present and 252 contains valid information. 253 + Flow ID Present (bit 3): If the Flow ID Present bit is set 254 to 1, then the Flow ID field is present and contains valid 255 information. 256 + Fragmentation Present (bit 4): If the Fragmentation Present 257 bit is set to 1, then the PDU carry a fragment of the SDU and 258 the Fragmentation Control field is present and contains valid 259 information. 260 + Sequence Number Present (bit 5): If the Sequence Number 261 Present bit is set to 1, then the Sequence Number field is 262 present and contains valid information. 263 + Timestamp Present (bit 6): If the Timestamp Present bit is 264 set to 1, then the Timestamp field is present and contains 265 valid information. 266 + TTL Present (bit 7): If the TTL Present bit is set to 1, 267 then the TTL field is present and contains the valid 268 information. 269 + Reserved (bit 8-12) 270 + Version (bit 13~15): GMA version number, this is set to 0. 272 The GMA (Generic Multi-Access) trailer MAY consist of the 273 following optional fields: 275 o Checksum (1 Byte): to contain the (one's complement) checksum 276 sum of all the 8 bits in the trailer. For purposes of 277 computing the checksum, the value of the checksum field is 278 zero. This field is present only if the Checksum Present bit 279 is set to one. 280 o First SDU Length (2 Bytes): the length of the first IP packet 281 in the PDU, only included if a PDU contains multiple IP 282 packets. 284 o Connection ID (1 Byte): an unsigned integer to identify the 285 anchor and delivery connection of the GMA PDU. 286 + Anchor Connection ID (MSB 4 Bits): an unsigned integer to 287 identify the anchor connection 288 + Delivery Connection ID (LSB 4 Bits): an unsigned integer to 289 identify the delivery connection 290 o Flow ID (1 Byte): an unsigned integer to identify the IP flow 291 that a PDU belongs to, for example Data Radio Bearer (DRB) ID 292 [LWIPEP] for a cellular (e.g. LTE) connection. 293 o Fragmentation Control (FC) (e.g. 1 Byte): to provide necessary 294 information for re-assembly, only needed if a PDU carries 295 fragments. 296 o Sequence Number (4 Bytes): an auto-incremented integer to 297 indicate order of transmission of the SDU (e.g. IP packet), 298 needed for lossless switching or multi-link (path) aggregation 299 or fragmentation. Sequence Number SHALL be generated per flow. 300 o Timestamp (4 Bytes): to contain the current value of the 301 timestamp clock of the transmitter in the unit of 100 302 microseconds. 303 o TTL (1 Byte): to contain the TTL value of the original IP 304 header if the GMA SDU is an IPv4 packet, and the Hop-Limit 305 value of the IP header if the GMA SDU is an IPv6 packet. 307 Figure 4 shows the GMA trailer format with all the fields present. 309 0 1 2 3 310 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | TTL | Timestamp 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 | Sequence Number 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 | FC | Flow ID | Connection ID | 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 318 | First SDU Length (FSL) | Checksum | Next Header | 319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 320 | Flags | 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 Figure 4: GMA Trailer Format 325 +-----------------------------------------------------+ 326 |GMA Header | IP hdr | IP payload | 327 +-----------------------------------------------------+ 328 Figure 5: Header-based Non-IP Encapsulation Format 330 The trailer-based GMA PDU format SHOULD be used as long as 331 implementation allows. However, if the GMA control fields can't be 332 added at the end due to any reason, e.g. implementation 333 constraints, one may use the header-based encapsulation (Figure 5) 334 with the GMA header format (Figure 6). "Flags" is moved to the 335 front. Moreover, "TTL", "FSL", and "Next Header" are removed from 336 the GMA control fields since the IP header fields of the GMA SDU 337 remain unchanged during encapsulation. 339 +--------------------------------------------------+ 340 | Flags | GMA control fields | 341 +--------------------------------------------------+ 342 Figure 6: GMA Header Format 344 If the adaptation sublayer, e.g. UDP tunnelling, supports non-IP 345 packet format, the GMA PDU format as shown in Figure 5 may be used 346 without any modification. Otherwise, the GMA PDU format SHOULD be 347 modified as shown in Figure 7. The IP header of the GMA SDU is 348 moved to the front so that the GMA PDU becomes an IP packet. The 349 IP header fields SHOULD be changed in the same way as the 350 Trailered-based encapsulation (Figure 3) and the GMA control 351 fields may carry "Next Header", "TTL", and "FSL". 353 +-----------------------------------------------------+ 354 |IP hdr | GMA Header | IP payload | 355 +-----------------------------------------------------+ 356 Figure 7: Header-based IP Encapsulation Format 358 The GMA endpoints MAY choose the GMA PDU format (header or 359 trailer) through control signalling or pre-configuration. 361 5. Fragmentation 363 The convergence sublayer MAY support fragmentation if a delivery 364 connection has a smaller maximum transmission unit (MTU) than the 365 original IP packet (SDU). The fragmentation procedure at the 366 convergence sublayer is similar to IP fragmentation [RFC791] in 367 principle, but with the following two differences for less 368 overhead: 370 o The fragment offset field is expressed in number of fragments 371 not 8-bytes blocks 372 o The maximum number of fragments per SDU is 2^7 (=128) 374 The Fragmentation Control (FC) field in the GMA trailer (or 375 header) contains the following bits: 377 o Bit #7: a More Fragment (MF) flag to indicate if the fragment 378 is the last one (0) or not (1) 379 o Bit #0~#6: Fragment Offset (in units of fragments) to specify 380 the offset of a particular fragment relative to the beginning 381 of the SDU 383 A PDU carries a whole SDU without fragmentation if the FC field is 384 set to all "0"s or the FC field is not present in the trailer. 385 Otherwise, the PDU contains a fragment of the SDU. 387 The Sequence Number (SN) field in the trailer is used to 388 distinguish the fragments of one SDU from those of another. The 389 Fragment Offset (FO) field tells the receiver the position of a 390 fragment in the original SDU. The More Fragment (MF) flag 391 indicates the last fragment. 393 To fragment a long SDU, the transmitter creates two PDUs and 394 copies the content of the IP header fields from the long PDU into 395 the IP header of both PDUs. The length field in the IP header of 396 PDU SHOULD be changed to the length of the PDU, and the protocol 397 type SHOULD be changed to 114. 399 The data of the long SDU is divided into two portions based on the 400 MTU size of the delivery connection. The first portion of the data 401 is placed in the first PDU. The MF flag is set to "1", and the FO 402 field is set to "0". The second portion of the data is placed in 403 the second PDU. The MF flag is set to "0", and the FO field is set 404 to "1". This procedure can be generalized for an n-way split, 405 rather than the two-way split described the above. 407 To assemble the fragments of a SDU, the receiver combines PDUs 408 that all have the same Sequence Number (in the trailer). The 409 combination is done by placing the data portion of each fragment 410 in the relative order indicated by the Fragment Offset in that 411 fragment's trailer. The first fragment will have the Fragment 412 Offset set to "0", and the last fragment will have the More- 413 Fragments flag reset to "0". 415 6. Concatenation 417 The convergence sublayer MAY support concatenation if a delivery 418 connection has a larger maximum transmission unit (MTU) than the 419 original IP packet (SDU). Only the SDUs with the same client IP 420 address, and the same Flow ID MAY be concatenated. 422 The First SDU Length (FSL) field SHOULD be included in the trailer 423 to indicate the length of the first SDU. 425 +-----------------------------------------------------------+ 426 |IP hdr| IP payload |IP hdr| IP payload | GMA Trailer | 427 +-----------------------------------------------------------+ 428 Figure 8: GMA PDU Format with Concatenation 430 To concatenate two or more SDUs, the transmitter creates one PDU 431 and copies the content of the IP header field from the first SDU 432 into the IP header of the PDU. The data of the first SDU is placed 433 in the first portion of the data of the PDU. The whole second SDU 434 is then placed in the second portion of the data of the PDU 435 (Figure 8). The procedure continues till the PDU size reaches the 436 MTU of the delivery connection. If the FSL field is present in the 437 trailer, the IP length field of the PDU SHOULD be updated to 438 include all concatenated SDUs and the trailer, and the IP checksum 439 field SHOULD be recalculated. However, if UDP tunnelling is used 440 at the adaptation sublayer to carry the GMA PDU, both the IP 441 Length field and the checksum field of the PDU MAY remain 442 unchanged, and the receiver will determine the GMA PDU length 443 based on the UDP packet length. 445 To disaggregate a PDU, the receiver first obtains the length of 446 the first SDU from the FSL field in the trailer and decodes the 447 first SDU. If the FSL field or the trailer is not present, the 448 receiver obtains the length of the first SDU directly from the IP 449 length field of the PDU. The receiver then obtains the length of 450 the second SDU based on the length field in the second SDU IP 451 header and decodes the second SDU. The procedure continues till no 452 byte is left in the PDU. However, if the header-based Non-IP GMA 453 PDU format (Figure 5) is used, the IP header of the first SDU will 454 not change during the encapsulation process, and therefore the FSL 455 field is not used. 457 If a PDU contains multiple SDUs, the SN field in the trailer is 458 for the last SDU, and the SN of other SDU carried by the same PDU 459 can be obtained according to its order in the PDU. For example, if 460 the SN field is 6 and a PDU contains 3 SDUs (IP packets), the SN 461 is 4, 5, and 6 for the first, second, and last SDU respectively. 463 7. Security Considerations 465 Security in a network using GMA should be relatively similar to 466 security in a normal IP network. The GMA protocol at the 467 convergence sublayer is a 0-hop protocol and relies on the 468 security of the underlying network transport paths. When this 469 cannot be assumed, appropriate security protocols (IPsec, DTLS, 470 etc.) SHOULD be configured at the adaptation sublayer. On the 471 other hand, packet filtering requires either that a firewall looks 472 inside the GMA packet or that the filtering is done on the GMA 473 endpoints. In those environments in which this is considered to be 474 a security issue it may be desirable to terminate the GMA 475 operation at the firewall. 477 The balance of local-only packet leak prevention (HL=0) and 478 security (HL=255) SHOULD be on preventing the leak of the local- 479 only GMA PDUs outside the "local domain" to the Internet or to 480 another domain which could use the same IP protocol type, i.e. 481 114. 483 8. IANA Considerations 485 This draft makes no requests of IANA 487 9. References 489 9.1. Normative References 491 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 492 Requirement Levels", BCP 14, RFC 2119, DOI 493 10.17487/RFC2119, March 1997, . 496 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 497 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174 498 May 2017, . 500 9.2. Informative References 502 [MAMS] S. Kanugovi, S. Vasudevan, F. Baboescu, and J. Zhu, 503 "Multiple Access Management Protocol", 504 https://tools.ietf.org/html/draft-kanugovi-intarea-mams- 505 protocol-03 507 [IANA] https://www.iana.org/assignments/protocol- 508 numbers/protocol-numbers.xhtml 510 [LWIPEP] 3GPP TS 36.361, "Evolved Universal Terrestrial Radio 511 Access (E-UTRA); LTE-WLAN Radio Level Integration Using 512 Ipsec Tunnel (LWIP) encapsulation; Protocol 513 specification" 515 [RFC791] Internet Protocol, September 1981 517 [ATSSS] 3GPP TR 23.793, Study on access traffic steering, switch 518 and splitting support in the 5G system architecture. 520 [GRE] RFC 8157, Huawei's GRE Tunnel Bonding Protocol, May 2017 522 Authors' Addresses 524 Jing Zhu 526 Intel 528 Email: jing.z.zhu@intel.com 530 Satish Kanugovi 532 Nokia 534 Email: satish.k@nokia.com