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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RTGWG Working Group C. Li 3 Internet-Draft Z. Hu 4 Intended status: Standards Track Huawei Technologies 5 Expires: February 4, 2021 August 3, 2020 7 Enhanced Topology Independent Loop-free Alternate Fast Re-route 8 draft-li-rtgwg-enhanced-ti-lfa-02 10 Abstract 12 Topology Independent Loop-free Alternate Fast Re-route (TI-LFA) aims 13 at providing protection of node and adjacency segments within the 14 Segment Routing (SR) framework. A key aspect of TI-LFA is the FRR 15 path selection approach establishing protection over the expected 16 post-convergence paths from the point of local repair. However, the 17 TI-LFA FRR path may skip the node even if it is specified in the SID 18 list to be traveled. 20 This document defines Enhanced TI-LFA(TI-LFA+) by adding a No-bypass 21 indicator for segments to ensure that the FRR route will not bypass 22 the specific node, such as firewall. Also, this document defines No- 23 bypass flag and No-FRR flag in SRH to indicate not to bypass nodes 24 and not to perform FRR on all the nodes along the SRv6 path, 25 respectively. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on February 4, 2021. 44 Copyright Notice 46 Copyright (c) 2020 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 64 3. Overview of Enhanced TI-LFA . . . . . . . . . . . . . . . . . 3 65 4. IGP Protocol Extensions . . . . . . . . . . . . . . . . . . . 4 66 4.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 4.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 5. Flags in SRH . . . . . . . . . . . . . . . . . . . . . . . . 8 69 5.1. No-bypass Flag in SRH . . . . . . . . . . . . . . . . . . 8 70 5.2. No-FRR Flag in SRH . . . . . . . . . . . . . . . . . . . 9 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 72 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 73 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 74 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 75 8.2. Informative References . . . . . . . . . . . . . . . . . 10 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 78 1. Introduction 80 Segment Routing [RFC8402] enables to steer packets by explicitly 81 encoding instructions in the data packets at the source node to 82 support services like traffic engineer. Relying on SR, 83 [I-D.ietf-rtgwg-segment-routing-ti-lfa] defines Topology Independent 84 Loop-free Alternate Fast Re-route (TI-LFA), a local repair mechanism 85 for IGP shortest path that capable of restoring end-to-end 86 connectivity in the case of a sudden directly connected failure of a 87 network component. 89 TI-LFA supports to establish a loop free backup path over the 90 expected post-convergence paths from the point of local repair 91 irrespective of the topologies used in the network, which provides a 92 major improvment compared to LFA [RFC5286], and remote LFA [RFC7490] 93 which cannot be applicable in some topologies [RFC6571]. 95 However, the TI-LFA path may skip the node that the active SID points 96 to when protecting [Adjacency, Node] segment lists. For instance, 97 the node that a adjacency SID points to is a very important node and 98 can not be skipped, such as a firewall node. When the link between 99 the local repair node and firewall node fails, the packets should be 100 steered back to the firewall and then forwarding. But in TI-LFA, if 101 the next SID in the SID list is a node SID, the TI-LFA FRR path MAY 102 bypass the node that the active segment points to. Also, if the 103 firewall node is down, the packets should be dropped instead for fast 104 reroute to bypass the node. Bypassing nodes like firewall in FRR 105 brings issues of network security and reliability. 107 To enhance the security and reliability of networks, this document 108 defines an Enhanced Topology Independent Loop-free Alternate Fast Re- 109 route (TI-LFA+) based on TI-LFA by adding a No-bypass flag for 110 segments to explicitly specify what node can not be bypassed. Also, 111 this document defines No-bypass flag and No-FRR flag in SRH to 112 indicate not to bypass nodes and not to perform FRR on all the nodes 113 along the SRv6 path, respectively. 115 2. Terminology 117 This document makes use of the terms defined in 118 [I-D.ietf-rtgwg-segment-routing-ti-lfa] and [RFC8402]. The reader is 119 assumed to be familiar with the terminology defined in 120 [I-D.ietf-rtgwg-segment-routing-ti-lfa] and [RFC8402]. 122 2.1. Requirements Language 124 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 125 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 126 "OPTIONAL" in this document are to be interpreted as described in BCP 127 14 [RFC2119] [RFC8174] when, and only when, they appear in all 128 capitals, as shown here. 130 3. Overview of Enhanced TI-LFA 132 Enhanced Topology Independent Loop-free Alternate Fast Re-route (TI- 133 LFA+) is an enhancement of TI-LFA to explicitly indicate whether a 134 node that segment points to can not be bypassed in FRR scenarios. 136 TI-LFA+ will not change the main process and algorithm of TI-LFA. 137 Instead, in TI-LFA+, when generating repair SID list for a SID, the 138 node should consider whether the SID endpoint can be baseed or not, 139 which is explicitly encoded in IGP messages. If the node that 140 segment points to can not be bypassed, then the repair SID MUST lead 141 the packets to that node. This document defines a No-bypass flag for 142 segments in IS-IS and OSPF. Details will be discussed in section 4. 144 A node should advertise two kinds of segment to meet various service 145 policy requirements. 147 o Bypassing capable segment with No-bypass flag unset 149 o No-bypassing segment with No-bypass flag set. 151 A controller or control plane should choose specific segment 152 according to the service policy. 154 [Editors' note] If the TI-LFA result is generated based on Locator 155 route instead of SIDs, then the No-bypass Flag can be applied to the 156 Locator. 158 Also, this document defines No-bypass flag and No-FRR flag in SRH to 159 indicate not to bypass nodes and not to perform FRR on all the nodes 160 along the SRv6 path, respectively. Details will be discussed in 161 section 5. 163 4. IGP Protocol Extensions 165 4.1. IS-IS 167 [I-D.ietf-isis-segment-routing-extensions] describes the necessary 168 IS-IS extensions that need to be introduced for Segment 169 Routing.[I-D.ietf-lsr-isis-srv6-extensions] defines the IS-IS 170 extensions required to support Segment Routing over an IPv6 data 171 plane. This documment defines a No-bypass flag in flag filed of the 172 following IS-IS sub-TLV/TLV. 174 o Prefix Segment Identifier sub-TLV (Prefix-SID sub-TLV) 175 [I-D.ietf-isis-segment-routing-extensions] 177 o Adjacency Segment Identifier sub- TLV (Adj-SID sub- 178 TLV).[I-D.ietf-isis-segment-routing-extensions] 180 o Locator entry in SRv6 Locator TLV 181 [I-D.ietf-lsr-isis-srv6-extensions] 183 The following figures are included here for reference and will be 184 deleted in the future version. 186 0 1 2 3 187 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 1 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | Type | Length | Flags | Algorithm | 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 191 | SID/Index/Label (variable) | 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 0 1 2 3 4 5 6 7 195 +--+--+--+--+--+--+--+--+ 196 |R | N| P| E| V| L|NB| | 197 +--+--+--+--+--+--+--+--+ 199 Figure 1. Prefix-SID sub-TLV and No-bypass Flag 201 0 1 2 3 202 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 1 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | Type | Length | Flags | Weight | 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 206 | SID/Label/Index (variable) | 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 209 0 1 2 3 4 5 6 7 210 +--+--+--+--+--+--+--+--+ 211 |F | B| V| L| S|NB| | | 212 +--+--+--+--+--+--+--+--+ 213 Figure 2. Adj-SID sub-TLV and No-bypass Flag 215 0 1 2 3 216 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 1 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 | Metric | 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 | Flags | Algorithm | 221 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 222 | Loc Size | Locator (variable)... 223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 224 | Sub-tlv-len | Sub-TLVs (variable) . . . | 225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 227 0 1 2 3 4 5 6 7 228 +--+--+--+--+--+--+--+--+ 229 |D |NB| | | | | | | 230 +--+--+--+--+--+--+--+--+ 231 Figure 3. SRv6 Locator Entry and No-bypass Flag 233 If the No-bypass(NB) flag is set, means the node that the SID/Label/ 234 Locator points to can not be bypassed. Oterwise, the node can be 235 bypassed. 237 4.2. OSPF 239 [I-D.ietf-ospf-segment-routing-extensions] describes the necessary 240 OSPF extensions that need to be introduced for Segment 241 Routing.[I-D.ietf-lsr-ospfv3-srv6-extensions] defines the OSPF 242 extensions required to support Segment Routing over an IPv6 data 243 plane. This documment defines a No-bypass flag in flag filed of the 244 following OSPF sub-TLV/TLV. 246 o Prefix SID Sub-TLV [I-D.ietf-ospf-segment-routing-extensions] 248 o Adj-SID sub-TLV [I-D.ietf-ospf-segment-routing-extensions] 250 o SRv6 Node SID TLV [I-D.ietf-lsr-ospfv3-srv6-extensions] 252 o SRv6 SID Link Attribute Sub-TLV 253 [I-D.ietf-lsr-ospfv3-srv6-extensions] 255 The following figures are included here for reference and will be 256 deleted in the future version. 258 0 1 2 3 259 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 1 260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 261 | Type | Length | 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 | Flags | Reserved | MT-ID | Algorithm | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 | SID/Index/Label (variable) | 266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 268 0 1 2 3 4 5 6 7 269 +--+--+--+--+--+--+--+--+ 270 | |NP|M |E |V |L |NB| | 271 +--+--+--+--+--+--+--+--+ 273 Figure 4. Prefix-SID sub-TLV and No-bypass Flag 275 0 1 2 3 276 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 1 277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 278 | Type | Length | 279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 280 | Flags | Reserved | MT-ID | Weight | 281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 282 | SID/Label/Index (variable) | 283 +---------------------------------------------------------------+ 285 0 1 2 3 4 5 6 7 286 +--+--+--+--+--+--+--+--+ 287 |B | V| L| G| P|NB| | | 288 +--+--+--+--+--+--+--+--+ 290 Figure 5. Adj-SID sub-TLV and No-bypass Flag 292 0 1 2 3 293 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 1 294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 295 | Type | Length | 296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 297 | Reserved | Function-Flags| Function Code | 298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 299 | Reserved | SID Flags | SID-size | 300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 | SID (variable - 32 bit aligned) ... 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | Sub-TLVs (variable) . . . 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 0 1 2 3 4 5 6 7 307 +--+--+--+--+--+--+--+--+ 308 |D |NB| | | | | | | 309 +--+--+--+--+--+--+--+--+ 310 Figure 6. SRv6 Node SID TLV and No-bypass Flag 312 0 1 2 3 313 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 1 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 | Type | Length | 316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 | Reserved | Function-Flags| Function Code | 318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 | Reserved | SID Flags | SID-size | 320 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 321 | SID (variable - 32 bit aligned) ... 322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 | Sub-TLVs (variable) . . . 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 326 0 1 2 3 4 5 6 7 327 +--+--+--+--+--+--+--+--+ 328 |NB| | | | | | | | 329 +--+--+--+--+--+--+--+--+ 330 Figure 7. SRv6 Adj-SID TLV and No-bypass Flag 332 If the No-bypass(NB) flag is set, means the node that the SID/Label/ 333 Locator points to can not be bypassed. Oterwise, the node can be 334 bypassed. 336 5. Flags in SRH 338 This section describes two flags in SRH. 340 5.1. No-bypass Flag in SRH 342 This document defines a No-bypass Flag in SRH [RFC8754]. 344 0 1 2 3 4 5 6 7 345 +--+--+--+--+--+--+--+--+ 346 |NB| | | | | | | | 347 +--+--+--+--+--+--+--+--+ 349 o NB Flag: No-Bypass flag, when the flag is set, the repair segment 350 endpoint nodes MUST NOT bypass any nodes when link or node 351 failures occur. When a link is down, the packet MUST be forwarded 352 to the next segment endpoint node through the repair path. When 353 the node identified by the active SID in IPv6 destination address 354 is down, the SID can not be skipped, and the traffic MUST be 355 forwarded to the node. 357 The flag can be set when the SID list containing service SIDs like 358 firewall SID, so that the traffic will not bypass the service nodes. 360 5.2. No-FRR Flag in SRH 362 This document defines a No-FRR Flag in SRH [RFC8754]. 364 0 1 2 3 4 5 6 7 365 +--+--+--+--+--+--+--+--+ 366 | |NF| | | | | | | 367 +--+--+--+--+--+--+--+--+ 369 o NF Flag: No-FRR flag, when the flag is set, the FRR is disable for 370 the packet, thus the packet will not be protected by the Local 371 protection mechanism, such as TI-LFA. 373 The flag can be set when the SID list containing service SIDs like 374 firewall SID, so that the traffic will not bypass the service nodes. 375 In this case, E2E protection mechanism should be deployed. 377 6. IANA Considerations 379 TBD. 381 7. Security Considerations 383 TBD. 385 8. References 387 8.1. Normative References 389 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 390 Requirement Levels", BCP 14, RFC 2119, 391 DOI 10.17487/RFC2119, March 1997, 392 . 394 [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for 395 IP Fast Reroute: Loop-Free Alternates", RFC 5286, 396 DOI 10.17487/RFC5286, September 2008, 397 . 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 [RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N. 404 So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)", 405 RFC 7490, DOI 10.17487/RFC7490, April 2015, 406 . 408 [RFC6571] Filsfils, C., Ed., Francois, P., Ed., Shand, M., Decraene, 409 B., Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free 410 Alternate (LFA) Applicability in Service Provider (SP) 411 Networks", RFC 6571, DOI 10.17487/RFC6571, June 2012, 412 . 414 [I-D.ietf-rtgwg-segment-routing-ti-lfa] 415 Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B., 416 Francois, P., Voyer, D., Clad, F., and P. Camarillo, 417 "Topology Independent Fast Reroute using Segment Routing", 418 draft-ietf-rtgwg-segment-routing-ti-lfa-03 (work in 419 progress), March 2020. 421 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 422 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 423 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 424 . 426 8.2. Informative References 428 [RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation 429 Element (PCE) Communication Protocol Generic 430 Requirements", RFC 4657, DOI 10.17487/RFC4657, September 431 2006, . 433 [RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody, 434 "PCEPS: Usage of TLS to Provide a Secure Transport for the 435 Path Computation Element Communication Protocol (PCEP)", 436 RFC 8253, DOI 10.17487/RFC8253, October 2017, 437 . 439 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 440 Decraene, B., Litkowski, S., and R. Shakir, "Segment 441 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 442 July 2018, . 444 [I-D.ietf-isis-segment-routing-extensions] 445 Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., 446 Gredler, H., and B. Decraene, "IS-IS Extensions for 447 Segment Routing", draft-ietf-isis-segment-routing- 448 extensions-25 (work in progress), May 2019. 450 [I-D.ietf-ospf-segment-routing-extensions] 451 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 452 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 453 Extensions for Segment Routing", draft-ietf-ospf-segment- 454 routing-extensions-27 (work in progress), December 2018. 456 [I-D.ietf-lsr-ospfv3-srv6-extensions] 457 Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak, 458 "OSPFv3 Extensions for SRv6", draft-ietf-lsr- 459 ospfv3-srv6-extensions-00 (work in progress), February 460 2020. 462 [I-D.ietf-lsr-isis-srv6-extensions] 463 Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and 464 Z. Hu, "IS-IS Extension to Support Segment Routing over 465 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 466 (work in progress), April 2020. 468 Authors' Addresses 470 Cheng Li 471 Huawei Technologies 472 Huawei Campus, No. 156 Beiqing Rd. 473 Beijing 100095 474 China 476 Email: c.l@huawei.com 478 Zhibo Hu 479 Huawei Technologies 480 Huawei Campus, No. 156 Beiqing Rd. 481 Beijing 100095 482 China 484 Email: huzhibo@huawei.com