idnits 2.17.1 draft-ietf-alto-path-vector-05.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 : ---------------------------------------------------------------------------- ** The abstract seems to contain references ([RFC7285]), which it shouldn't. Please replace those with straight textual mentions of the documents in question. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 517 has weird spacing: '...SONBool allo...' -- The document date (March 11, 2019) is 1870 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'TBD' is mentioned on line 912, but not defined == Outdated reference: A later version (-21) exists of draft-ietf-alto-cost-calendar-01 == Outdated reference: A later version (-22) exists of draft-ietf-alto-incr-update-sse-15 == Outdated reference: A later version (-24) exists of draft-ietf-alto-unified-props-new-01 Summary: 1 error (**), 0 flaws (~~), 6 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ALTO WG K. Gao 3 Internet-Draft Tsinghua University 4 Intended status: Standards Track Y. Lee 5 Expires: September 12, 2019 Huawei 6 S. Randriamasy 7 Nokia Bell Labs 8 Y. Yang 9 Yale University 10 J. Zhang 11 Tongji University 12 March 11, 2019 14 ALTO Extension: Path Vector Cost Type 15 draft-ietf-alto-path-vector-05 17 Abstract 19 The Application-Layer Traffic Optimization (ALTO) protocol [RFC7285] 20 has defined cost maps and endpoint cost maps to provide basic network 21 information. However, they provide only scalar (numerical or 22 ordinal) cost mode values, which are insufficient to satisfy the 23 demands of solving more complex network optimization problems. This 24 document introduces an extension to the base ALTO protocol, namely 25 the path-vector extension, which allows ALTO clients to query 26 information such as the capacity region for a given set of flows 27 (called co-flows). A non-normative example called co-flow scheduling 28 is presented to illustrate the limitations of existing ALTO endpoint 29 cost maps. After that, details of the extension are defined. 31 Requirements Language 33 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 34 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 35 document are to be interpreted as described in RFC 2119 [RFC2119]. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at http://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on September 12, 2019. 54 Copyright Notice 56 Copyright (c) 2019 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (http://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 72 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 73 3. Use Case: Capacity Region for Co-Flow Scheduling . . . . . . 5 74 4. Overview of Path Vector Extensions . . . . . . . . . . . . . 7 75 4.1. New Cost Type to Encode Path Vectors . . . . . . . . . . 7 76 4.2. New ALTO Entity Domain to Provide ANE Properties . . . . 8 77 4.3. Extended Cost Map/Endpoint Cost Service for Compound 78 Resources . . . . . . . . . . . . . . . . . . . . . . . . 8 79 5. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . . . 8 80 5.1. Cost Mode: array . . . . . . . . . . . . . . . . . . . . 9 81 5.2. Cost Metric: ane-path . . . . . . . . . . . . . . . . . . 9 82 5.3. Path Vector Cost Type Semantics . . . . . . . . . . . . . 9 83 6. ANE Domain . . . . . . . . . . . . . . . . . . . . . . . . . 10 84 6.1. Domain Name . . . . . . . . . . . . . . . . . . . . . . . 10 85 6.2. Domain-Specific Entity Addresses . . . . . . . . . . . . 10 86 6.3. Hierarchy and Inheritance . . . . . . . . . . . . . . . . 10 87 7. Protocol Extensions for Path Vector . . . . . . . . . . . . . 10 88 7.1. Filtered Cost Map Extensions . . . . . . . . . . . . . . 11 89 7.1.1. Accept Input Parameters . . . . . . . . . . . . . . . 11 90 7.1.2. Capabilities . . . . . . . . . . . . . . . . . . . . 11 91 7.1.3. Response . . . . . . . . . . . . . . . . . . . . . . 12 92 7.2. Endpoint Cost Service Extensions . . . . . . . . . . . . 12 93 7.2.1. Accept Input Parameters . . . . . . . . . . . . . . . 13 94 7.2.2. Capabilities . . . . . . . . . . . . . . . . . . . . 13 95 7.2.3. Response . . . . . . . . . . . . . . . . . . . . . . 13 96 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 13 97 8.1. Workflow . . . . . . . . . . . . . . . . . . . . . . . . 13 98 8.2. Information Resource Directory Example . . . . . . . . . 14 99 8.3. Example # 1 . . . . . . . . . . . . . . . . . . . . . . . 16 100 8.4. Example # 2 . . . . . . . . . . . . . . . . . . . . . . . 18 101 8.5. Example #3 . . . . . . . . . . . . . . . . . . . . . . . 20 102 9. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 22 103 9.1. Compatibility with Base ALTO Clients/Servers . . . . . . 22 104 9.2. Compatibility with Multi-Cost Extension . . . . . . . . . 23 105 9.3. Compatibility with Incremental Update . . . . . . . . . . 23 106 10. General Discussions . . . . . . . . . . . . . . . . . . . . . 23 107 10.1. Provide Calendar for Property Map . . . . . . . . . . . 23 108 10.2. Constraint Tests for General Cost Types . . . . . . . . 24 109 10.3. General Compound Resources Query . . . . . . . . . . . . 24 110 11. Security Considerations . . . . . . . . . . . . . . . . . . . 24 111 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 112 12.1. ALTO Cost Mode Registry . . . . . . . . . . . . . . . . 25 113 12.2. ALTO Cost Metric Registry . . . . . . . . . . . . . . . 26 114 12.3. ALTO Entity Domain Registry . . . . . . . . . . . . . . 26 115 12.4. ALTO Network Element Property Type Registry . . . . . . 26 116 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 26 117 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 118 14.1. Normative References . . . . . . . . . . . . . . . . . . 27 119 14.2. Informative References . . . . . . . . . . . . . . . . . 27 120 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 122 1. Introduction 124 The base ALTO protocol [RFC7285] is designed to expose network 125 information through services such as cost maps and endpoint cost 126 service. These services use an extreme "single-node" network 127 abstraction, which represents a whole network as a single node and 128 hosts as "endpoint groups" directly connected to the node. 130 Although the "single-node" abstraction works well in many settings, 131 it lacks the ability to support emerging use cases, such as co-flow 132 scheduling for large-scale data analytics. For such a use case, 133 applications require a more powerful network view abstraction beyond 134 the "single-node" abstraction. 136 To support capabilities like co-flow scheduling, this document uses a 137 "path vector" abstraction to represent more detailed network graph 138 information like capacity regions. The path vector abstraction uses 139 path vectors with abstract network elements to provide network graph 140 view for applications. A path vector consists of a sequence of 141 abstract network elements (ANEs) that end-to-end traffic goes 142 through. Example ANEs include links, switches, middleboxes, and 143 their aggregations. An ANE can have properties such as "bandwidth", 144 "delay". Providing such information can help both applications to 145 achieve better application performance and networks to avoid network 146 congestion. 148 Providing path vector abstraction using ALTO introduces the following 149 additional requirements (ARs): 151 AR-1: The path vector abstraction requires the encoding of array- 152 like cost values rather than scalar cost values in cost maps or 153 endpoint cost maps. 155 Specifically, the path vector abstraction requires the 156 specification of the sequence of ANEs between sources and 157 destinations. Such a sequence, however, cannot be encoded by the 158 scalar types (numerical or ordinal) which the base ALTO protocol 159 supports. 161 AR-2: The path vector abstraction requires the encoding of the 162 properties of aforementioned ANEs. 164 Specifically, only the sequences of ANEs are not enough for 165 existing use cases. Properties of ANEs such as "bandwidth" and 166 "delay" are needed by applications to properly construct capacity 167 regions. 169 AR-3: The path vector abstraction requires consistent encoding of 170 path vectors (AR-1) and the properties of the elements in a path 171 vector (AR-2). 173 Specifically, path vectors and the properties of abstract network 174 elements in the vectors are dependent. A mechanism to query both 175 of them consistently is necessary. 177 This document proposes the path vector extension which satisfies 178 these additional requirements to the ALTO protocol. Specifically, 179 the ALTO protocol encodes the array of ANEs over an end-to-end path 180 using a new cost type, and conveys the properties of ANEs using 181 unified property map [I-D.ietf-alto-unified-props-new]. We also 182 provide an optional solution to query separated path vectors and 183 properties of ANEs in a consistent way. But querying general 184 separated resources consistently is not the scope in this document. 186 The rest of this document is organized as follows. Section 3 gives 187 an example of co-flow scheduling and illustrates the limitations of 188 the base ALTO protocol in such a use case. Section 4 gives an 189 overview of the path vector extension. Section 5 introduces a new 190 cost type. Section 6 registers a new domain in Domain Registry. 191 Section 7 extends Filtered Cost Map and Endpoint Cost Service to 192 support the compound resource query. Section 8 presents several 193 examples. Section 9 and Section 10 discusses compatibility issues 194 with other existing ALTO extensions and design decisions. Section 11 195 and Section 12 review the security and IANA considerations. 197 2. Terminology 199 Besides the terms defined in [RFC7285] and 200 [I-D.ietf-alto-unified-props-new], this document also uses the 201 following additional terms: Abstract Network Element, Path Vector. 203 o Abstract Network Element (ANE): An abstract network element is an 204 abstraction of network components; it can be an aggregation of 205 links, middle boxes, virtualized network function (VNF), etc. An 206 abstract network element has two types of attributes: a name and a 207 set of properties. 209 o Path Vector: A path vector is an array of ANEs. It presents an 210 abstract network path between source/destination points such as 211 PIDs or endpoints. 213 3. Use Case: Capacity Region for Co-Flow Scheduling 215 Assume that an application has control over a set of flows, which may 216 go through shared links or switches and share a bottleneck. The 217 application hopes to schedule the traffic among multiple flows to get 218 better performance. The capacity region information for those flows 219 will benefit the scheduling. However, existing cost maps can not 220 reveal such information. 222 Specifically, consider a network as shown in Figure 1. The network 223 has 7 switches (sw1 to sw7) forming a dumb-bell topology. Switches 224 sw1/sw3 provide access on one side, sw2/sw4 provide access on the 225 other side, and sw5-sw7 form the backbone. Endhosts eh1 to eh4 are 226 connected to access switches sw1 to sw4 respectively. Assume that 227 the bandwidth of link eh1 -> sw1 and link sw1 -> sw5 are 150 Mbps, 228 and the bandwidth of the rest links are 100 Mbps. 230 +------+ 231 | | 232 --+ sw6 +-- 233 / | | \ 234 PID1 +-----+ / +------+ \ +-----+ PID2 235 eh1__| |_ / \ ____| |__eh2 236 | sw1 | \ +--|---+ +---|--+ / | sw2 | 237 +-----+ \ | | | |/ +-----+ 238 \_| sw5 +---------+ sw7 | 239 PID3 +-----+ / | | | |\ +-----+ PID4 240 eh3__| |__/ +------+ +------+ \____| |__eh4 241 | sw3 | | sw4 | 242 +-----+ +-----+ 244 Figure 1: Raw Network Topology. 246 The single-node ALTO topology abstraction of the network is shown in 247 Figure 2. 249 +----------------------+ 250 {eh1} | | {eh2} 251 PID1 | | PID2 252 +------+ +------+ 253 | | 254 | | 255 {eh3} | | {eh4} 256 PID3 | | PID4 257 +------+ +------+ 258 | | 259 +----------------------+ 261 Figure 2: Base Single-Node Topology Abstraction. 263 Consider an application overlay (e.g., a large data analysis system) 264 which wants to schedule the traffic among a set of end host source- 265 destination pairs, say eh1 -> eh2 and eh1 -> eh4. The application 266 can request a cost map providing end-to-end available bandwidth, 267 using 'availbw' as cost-metric and 'numerical' as cost-mode. 269 The application will receive from ALTO server that the bandwidth of 270 eh1 -> eh2 and eh1 -> eh4 are both 100 Mbps. But this information is 271 not enough. Consider the following two cases: 273 o Case 1: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw6 -> 274 sw7 -> sw2 -> eh2 and eh1 -> eh4 uses path eh1 -> sw1 -> sw5 -> 275 sw7 -> sw4 -> eh4, then the application will obtain 150 Mbps at 276 most. 278 o Case 2: If eh1 -> eh2 uses the path eh1 -> sw1 -> sw5 -> sw7 -> 279 sw2 -> eh2 and eh1 -> eh4 uses the path eh1 -> sw1 -> sw5 -> sw7 280 -> sw4 -> eh4, then the application will obtain only 100 Mbps at 281 most. 283 To allow applications to distinguish the two aforementioned cases, 284 the network needs to provide more details. In particular: 286 o The network needs to expose more detailed routing information to 287 show the shared bottlenecks. 289 o The network needs to provide the necessary abstraction to hide the 290 real topology information while providing enough information to 291 applications. 293 The path vector extension defined in this document propose a solution 294 to provide these details. 296 See [I-D.bernstein-alto-topo] for a more comprehensive survey of use 297 cases where extended network topology information is needed. 299 4. Overview of Path Vector Extensions 301 This section presents an overview of approaches adopted by the path 302 vector extension. It assumes the readers are familiar with cost map 303 and endpoint cost service defined in [RFC7285]. The path vector 304 extension also requires the support of Filtered Property Map defined 305 in [I-D.ietf-alto-unified-props-new]. 307 The path vector extension is composed of three building blocks: (1) a 308 new cost type to encode path vectors; (2) a new ALTO entity domain 309 for unified property extension [I-D.ietf-alto-unified-props-new] to 310 encode properties of ANEs; and (3) an extension to the cost map and 311 endpoint cost resource to provide path vectors and properties of ANEs 312 in a single response. 314 4.1. New Cost Type to Encode Path Vectors 316 Existing cost types defined in [RFC7285] allow only scalar cost 317 values. However, the "path vector" abstraction requires to convey 318 vector format information. To achieve this requirement, this 319 document defines a new cost mode to enable the cost value to carry an 320 array of elements, and a new cost metric to take names of ANEs as 321 elements in the array. We call such an array of ANEs a path vector. 322 In this way, the cost map and endpoint cost service can convey the 323 path vector to represent the routing information. Detailed 324 information and specifications are given in Section 5.1 and 325 Section 5.2. 327 4.2. New ALTO Entity Domain to Provide ANE Properties 329 The path vector can only represent the route between the source and 330 the destination. Although the application can find the shared ANEs 331 among different paths, it is not enough for most use cases, which 332 requires the bandwidth or delay information of the ANEs. So this 333 document adopts the property map defined in 334 [I-D.ietf-alto-unified-props-new] to provide the general properties 335 of ANEs. The document registers a new entity domain called "ane" to 336 represent the ANE. The address of the ANE entity is just the ANE 337 name used by the path vector. By requesting the property map of 338 entities in the "ane" domain, the client can retrieve the properties 339 of ANEs in path vectors. 341 4.3. Extended Cost Map/Endpoint Cost Service for Compound Resources 343 Providing the path vector information and the ANE properties by 344 separated resources have several known benefits: (1) can be better 345 compatible with the base ALTO protocol; (2) can make different 346 property map resources reuse the same cost map or endpoint cost 347 resource. However, it conducts two issues: 349 o Efficiency: The separated resources will require the ALTO client 350 to invoke multiple requests/responses to collect all needed 351 information. It increases the communication overhead. 353 o Consistency: The path vectors and properties of ANEs are 354 correlated. So querying them one by one may conduct consistency 355 issue. Once the path vector changes during the client requests 356 the ANE properties, the ANE properties may be inconsistent with 357 the previous path vector. 359 To solve these issues, this document introduces an extension to cost 360 map and endpoint cost service, which allows the ALTO server to attach 361 a property map in the data entry of a cost map or an endpoint cost 362 service response. 364 These issues may exist in all general cases for querying separated 365 ALTO information resources. But solving this general problem is not 366 in the scope of this document. 368 5. Cost Type 370 This document extends the cost types defined in Section 6.1 of 371 [RFC7285] by introducing a new cost mode "array" and a new cost 372 metric "ane-path". In the rest content, this document uses "path- 373 vector" to indicate the combination cost type of the cost mode 374 "array" and the cost metric "ane-path". 376 5.1. Cost Mode: array 378 This document extends the CostMode defined in Section 10.5 of 379 [RFC7285] with a new cost mode: "array". This cost mode indicates 380 that every cost value in a cost map represents an array rather than a 381 simple value. The values are arrays of JSONValue. The specific type 382 of each element in the array depends on the cost metric. 384 5.2. Cost Metric: ane-path 386 This document specifies a new cost metric: "ane-path". This cost 387 metric indicates that the cost value is a list of ANEs which the path 388 from a source to a destination goes across. The values are arrays of 389 ANE names which are defined in Section 6.2. 391 The cost metric "ane-path" SHOULD NOT be used when the cost mode is 392 not "array" unless it is explicitly specified by a future extension. 393 If an ALTO client send queries with the cost metric "ane-path" and a 394 non "array" cost mode, the ALTO server SHOULD return an error with 395 the error code "E_INVALID_FIELD_VALUE"; If an ALTO server declares 396 the support of a cost type with the cost metric "ane-path" and a non 397 "array" cost mode, the ALTO client SHOULD assume such a cost type is 398 invalid and ignore it. 400 5.3. Path Vector Cost Type Semantics 402 The new cost type follows the convention of the cost types in the 403 base ALTO protocol. Table 1 lists some of the current defined cost 404 types and their semantics. 406 +------------+--------------+---------------------------------------+ 407 | Cost Mode | Cost Metric | Semantics | 408 +------------+--------------+---------------------------------------+ 409 | numerical | routingcost | a number representing the routing | 410 | | | cost | 411 | numerical | hopcount | a number representing the hop count | 412 | ordinal | routingcost | a ranking representing the routing | 413 | | | cost | 414 | ordinal | hopcount | a ranking representing the hop count | 415 | array | ane-path | a list representing the ane path | 416 +------------+--------------+---------------------------------------+ 418 Table 1: Cost Types and Their Semantics 420 The "routingcost" and "hopcount" can encoded in "numerical" or 421 "ordinal", however, the cost metric "ane-path" can only be applied to 422 the cost mode "array" defined in this document to convey path vector 423 information. The cost metric "ane-path" can not be used in 424 "numerical" or "ordinal" unless it is defined in future extensions. 425 If the ALTO server declares that it support cost type with cost 426 metric being "ane-path" and cost mode not being "array", the ALTO 427 client SHOULD ignore them. 429 6. ANE Domain 431 This document specifies a new ALTO entity domain called "ane" in 432 addition to the ones in [I-D.ietf-alto-unified-props-new]. The ANE 433 domain associates property values with the ANEs in a network. The 434 entity in ANE domain is often used in the path vector by cost maps or 435 endpoint cost resources. Accordingly, the ANE domain always depends 436 on a cost map or an endpoint cost map. 438 6.1. Domain Name 440 ane 442 6.2. Domain-Specific Entity Addresses 444 The entity address of ane domain is encoded as a JSON string. The 445 string MUST be no more than 64 characters, and it MUST NOT contain 446 characters other than US-ASCII alphanumeric characters 447 (U+0030-U+0039, U+0041-U+005A, and U+0061-U+007A), the hyphen ("-", 448 U+002D), the colon (":", U+003A), the at sign ("@", code point 449 U+0040), the low line ("_", U+005F), or the "." separator (U+002E). 450 The "." separator is reserved for future use and MUST NOT be used 451 unless specifically indicated in this document, or an extension 452 document. 454 To simplify the description, we use "ANE name" to indicate the 455 address of an entity in ANE domain in this document. 457 The ANE name is usually unrelated to the physical device information. 458 It is usually generated by the ALTO server on demand and used to 459 distinguish from other ANEs in its dependent cost map or endpoint 460 cost map. 462 6.3. Hierarchy and Inheritance 464 There is no hierarchy or inheritance for properties associated with 465 ANEs. 467 7. Protocol Extensions for Path Vector 469 To make the ALTO client query the path vectors and properties of ANEs 470 efficiently and consistently, this document extends the Filtered Cost 471 Map and Endpoint Cost Service. 473 7.1. Filtered Cost Map Extensions 475 This document extends Filtered Cost Map, as defined in Section 11.3.2 476 of [RFC7285], by adding new input parameters and capabilities, and by 477 augmenting the property map into the data entry of the response. 479 The "media type", "HTTP method", and "uses" specifications (described 480 in Sections 11.3.2.1, 11.3.2.2, and 11.3.2.5 of [RFC7285], 481 respectively) remain the same. 483 7.1.1. Accept Input Parameters 485 The ReqFilteredCostMap object in Section 11.3.2.3 of [RFC7285] is 486 extended as follows: 488 object { 489 [PropertyName compound-properties<1..*>;] 490 } ReqPVFilteredCostMap : ReqFilteredCostMap; 492 compound-properties: If the capability "allow-compound-response" is 493 false, the ALTO client MUST NOT specify this field, and the ALTO 494 server MUST reject the request and return "E_INVALID_FILED_VALUE" 495 error when it receives a request including this field. If this 496 field is specified and accepted, the ALTO server MUST augment the 497 dependent property map with the properties in this field into the 498 response automatically. 500 7.1.2. Capabilities 502 The Filtered Cost Map capabilities are extended with two new members: 504 o dependent-property-map 506 o allow-compound-response 508 The capability "dependent-property-map" indicates which property map 509 this resource depends on, and the capability "allow-compound- 510 response" indicates whether the ALTO server supports the resource to 511 compound the property map with its own response data. With these two 512 additional members, the FilteredCostMapCapabilities object in 513 Section 11.3.2.4 of [RFC7285] is extended as follows: 515 object { 516 [ResourceID dependent-property-map;] 517 [JSONBool allow-compound-response;] 518 } PVFCMCapabilities : FilteredCostMapCapabilities; 520 dependent-property-map: This field MUST be specified when the "cost- 521 type-names" includes a cost type name indicating a "ane-path" 522 metric. Its value MUST be a resource id indicating a property map 523 including "ane" domain. If not, the ALTO client SHOULD consider 524 this resource is invalid. 526 allow-compound-response: If present, the true value means the ALTO 527 client can request the resource to augment its dependent property 528 map into the response automatically; the false value means the 529 ALTO client cannot request the compound response. If omitted, the 530 default value is false; 532 To be noticed that the capability "cost-constraints" is unexpected 533 for the "array" cost mode. The syntax and semantics of constraint 534 tests on the "array" cost mode depends on the implementation and can 535 be defined in the future documents. But it is not in the scope of 536 this document. 538 7.1.3. Response 540 If the ALTO client specifies the "cost-type" input parameter with 541 "ane-path" metric, the "dependent-vtags" field in the "meta" field of 542 the response MUST include the version tag of its dependent property 543 map following its dependent network map. 545 If the ALTO client specifies the "compound-properties" input 546 parameter which is accepted by the ALTO server, the response MUST 547 include a "property-map" field following the "cost-map" field, and 548 its value MUST be a PropertyMapData object. This PropertyMapData 549 object MUST be equivalent to the result when query the dependent 550 property map resource using the following request: the "entities" 551 field includes all the ANE names appearing in the cost values of the 552 "cost-map" field, the "properties" field has the same value as the 553 "compound-properties" field does. The properties shown in the 554 "compound-properties" input parameter but are not supported by the 555 dependent property map SHOULD be omitted from the response. 557 7.2. Endpoint Cost Service Extensions 559 This document extends the Endpoint Cost Service, as defined in 560 Section 11.5.1 of [RFC7285], by adding new input parameters and 561 capabilities and by augmenting the property map into the data entry 562 of the response. 564 The media type, HTTP method, and "uses" specifications (described in 565 Sections 11.5.1.1, 11.5.1.2, and 11.5.1.5 of [RFC7285], respectively) 566 are unchanged. 568 7.2.1. Accept Input Parameters 570 The ReqEndpointCostMap object in Section 11.5.1.3 of [RFC7285] is 571 extended as follows: 573 object { 574 [PropertyName compound-properties<1..*>;] 575 } ReqPVEndpointCostMap : ReqEndpointCostMap; 577 The "compound-properties" has the same interpretation as defined in 578 Section 7.1.1. 580 7.2.2. Capabilities 582 The extensions to the Endpoint Cost Service capabilities are 583 identical to the extensions to the Filtered Cost Map (see 584 Section 7.1.2). 586 7.2.3. Response 588 If the ALTO client specifies the "cost-type" input parameter with 589 "ane-path" metric, the response MUST include the "meta" field with 590 the "dependent-vtags" in it, and the "dependent-vtags" field MUST 591 include the version tag of its dependent property map. 593 If the ALTO client specifies the "compound-properties" input 594 parameter which is accepted by the ALTO server, the response MUST 595 include a "property-map" field following the "endpoint-cost-map" 596 field, and its value MUST be a PropertyMapData object. This 597 PropertyMapData object MUST be equivalent to the result when query 598 the dependent property map resource using the following request: the 599 "entities" field includes all the ANE names appearing in the cost 600 values of the "endpoint-cost-map" field, the "properties" field has 601 the same value as the "compound-properties" field does. The 602 properties shown in the "compound-properties" input parameter but are 603 not supported by the dependent property map SHOULD be omitted from 604 the response. 606 8. Examples 608 This section lists some examples of path vector queries and the 609 corresponding responses. 611 8.1. Workflow 613 This section gives a typical workflow of how an ALTO client query 614 path vectors using the extension. 616 1. Send a GET request for the whole Information Resource Directory. 618 2. Look for the resource of the (Filtered) Cost Map/Endpoint Cost 619 Service which supports the "ane-path" cost metric and get the 620 resource ID of the dependent property map. 622 3. Check whether the capabilities of the property map includes the 623 desired "prop-types". 625 4. Check whether the (Filtered) Cost Map/Endpoint Cost Service 626 allows the compound response. 628 5. If allowed, the ALTO client can send a request including the 629 desired ANE properties to the ALTO server and receive a compound 630 response with the cost map/endpoint cost map and the property 631 map. 633 6. If not allowed, the ALTO client sends a query for the cost map/ 634 endpoint cost map first. After receiving the response, the ALTO 635 client interprets all the ANE names appearing in the response and 636 sends another query for the property map on those ANE names. 638 8.2. Information Resource Directory Example 640 Here is an example of an Information Resource Directory. In this 641 example, filtered cost map "cost-map-pv" doesn't support the multi- 642 cost extension but support the path-vector extension, "endpoint- 643 multicost-map" supports both multi-cost extension and path-vector 644 extension. Filtered Property Map "propmap-availbw-delay" supports 645 properties "availbw" and "delay". 647 { 648 "meta": { 649 "cost-types": { 650 "path-vector": { 651 "cost-mode": "array", 652 "cost-metric": "ane-path" 653 }, 654 "num-routingcost": { 655 "cost-mode": "numerical", 656 "cost-metric": "routingcost" 657 }, 658 "num-hopcount": { 659 "cost-mode": "numerical", 660 "cost-metric": "hopcount" 661 } 662 } 663 }, 664 "resources": { 665 "my-default-networkmap": { 666 "uri" : "http://alto.example.com/networkmap", 667 "media-type" : "application/alto-networkmap+json" 668 }, 669 "my-default-cost-map": { 670 "uri": "http://alto.example.com/costmap/pv", 671 "media-type": "application/alto-costmap+json", 672 "accepts": "application/alto-costmapfilter+json", 673 "capabilities": { 674 "cost-type-names": [ "num-hopcount", 675 "num-routingcost" ] 676 }, 677 "uses": [ "my-default-networkmap" ] 678 }, 679 "cost-map-pv": { 680 "uri": "http://alto.example.com/costmap/pv", 681 "media-type": "application/alto-costmap+json", 682 "accepts": "application/alto-costmapfilter+json", 683 "capabilities": { 684 "cost-type-names": [ "path-vector" ], 685 "dependent-property-map": "propmap-availbw-delay" 686 }, 687 "uses": [ "my-default-networkmap" ] 688 }, 689 "endpoint-cost-pv": { 690 "uri": "http://alto.exmaple.com/endpointcost/pv", 691 "media-type": "application/alto-endpointcost+json", 692 "accepts": "application/alto-endpointcostparams+json", 693 "capabilities": { 694 "cost-type-names": [ "path-vector" ], 695 "dependent-property-map": "propmap-availbw-delay", 696 "allow-compound-response": true 697 } 698 }, 699 "invalid-cost-map" : { 700 "uri": "http://alto.example.com/costmap/invalid", 701 "media-type": "application/alto-costmap+json", 702 "accepts": "application/alto-costmapfilter+json", 703 "capabilities": { 704 "cost-type-names": [ "path-vector" ], 705 "allow-compound-response": true 706 }, 707 "uses": [ "my-default-networkmap" ] 708 }, 709 "propmap-availbw-delay": { 710 "uri": "http://alto.exmaple.com/propmap/ane-prop", 711 "media-type": "application/alto-propmap+json", 712 "accepts": "application/alto-propmapparams+json", 713 "capabilities": { 714 "domain-types": [ "ane" ], 715 "prop-types": [ "availbw", "delay" ] 716 }, 717 "uses": [ "cost-map-pv", "endpoint-cost-pv" ] 718 } 719 } 720 } 722 8.3. Example # 1 724 Query filtered cost map to get the path vectors. 726 POST /costmap/pv HTTP/1.1 727 Host: alto.example.com 728 Accept: application/alto-costmap+json, 729 application/alto-error+json 730 Content-Length: [TBD] 731 Content-Type: application/alto-costmapfilter+json 733 { 734 "cost-type": { 735 "cost-mode": "array", 736 "cost-metric": "ane-path" 737 }, 738 "pids": { 739 "srcs": [ "PID1" ], 740 "dsts": [ "PID2", "PID3" ] 741 } 742 } 743 HTTP/1.1 200 OK 744 Content-Length: [TBD] 745 Content-Type: application/alto-costmap+json 747 { 748 "meta": { 749 "dependent-vtags": [ 750 { 751 "resource-id": "my-default-networkmap", 752 "tag": "75ed013b3cb58f896e839582504f622838ce670f" 753 } 754 ], 755 "cost-type": { 756 "cost-mode": "array", 757 "cost-metric": "ane-path" 758 } 759 }, 760 "cost-map": { 761 "PID1": { 762 "PID2": [ "ane:L001", "ane:L003" ], 763 "PID3": [ "ane:L001", "ane:L004" ] 764 } 765 } 766 } 768 Then query the properties of ANEs in path vectors. 770 POST /propmap/ane-prop HTTP/1.1 771 Host: alto.example.com 772 Accept: application/alto-propmap+json, 773 application/alto-error+json 774 Content-Length: [TBD] 775 Content-Type: application/alto-propmapparams+json 777 { 778 "entities": [ "ane:L001", "ane:L003", "ane:L004" ], 779 "properties": [ "delay" ] 780 } 781 HTTP/1.1 200 OK 782 Content-Length: [TBD] 783 Content-Type: application/alto-propmap+json 785 { 786 "meta": { 787 "dependent-vtags": [ 788 { 789 "resource-id": "cost-map-pv", 790 "tag": "a7d57e120ab63124e3c9a82f7a54bc120fc96216" 791 } 792 ] 793 }, 794 "property-map": { 795 "ane:L001": { "delay": 46}, 796 "ane:L003": { "delay": 50}, 797 "ane:L004": { "delay": 70} 798 } 799 } 801 8.4. Example # 2 803 POST /endpointcost/pv HTTP/1.1 804 Host: alto.example.com 805 Accept: application/alto-endpointcost+json, 806 application/alto-error+json 807 Content-Length: [TBD] 808 Content-Type: application/alto-endpointcostparams+json 810 { 811 "multi-cost-types": [ 812 { 813 "cost-mode": "array", 814 "cost-metric": "ane-path" 815 }, 816 { 817 "cost-mode": "numerical", 818 "cost-metric": "routingcost" 819 } 820 ], 821 "endpoints": { 822 "srcs": [ "ipv4:192.0.2.2" ], 823 "dsts": [ "ipv4:192.0.2.89", 824 "ipv4:203.0.113.45", 825 "ipv6:2001:db8::10" ] 826 } 827 } 828 HTTP/1.1 200 OK 829 Content-Length: [TBD] 830 Content-Type: application/alto-endpointcost+json 832 { 833 "meta": { 834 "cost-type": [ 835 {"cost-mode": "array", "cost-metric": "ane-path"} 836 ] 837 }, 838 "endpoint-cost-map": { 839 "ipv4:192.0.2.2": { 840 "ipv4:192.0.2.89": [ "ane:L001", "ane:L003", 841 "ane:L004" ], 842 "ipv4:203.0.113.45": [ "ane:L001", "ane:L004", 843 "ane:L005" ], 844 "ipv6:2001:db8::10": [ "ane:L001", "ane:L005", 845 "ane:L007" ] 846 } 847 } 848 } 850 POST /endpointcost/pv HTTP/1.1 851 Host: alto.example.com 852 Accept: application/alto-endpointcost+json, 853 application/alto-error+json 854 Content-Length: [TBD] 855 Content-Type: application/alto-endpointcostparams+json 857 { 858 "entities": [ "ane:L001", "ane:L003", "ane:L004", 859 "ane:L005", "ane:L007" ], 860 "properties": [ "availbw" ] 861 } 862 HTTP/1.1 200 OK 863 Content-Length: [TBD] 864 Content-Type: application/alto-propmap+json 866 { 867 "meta": { 868 "dependent-vtags": [ 869 { 870 "resource-id": "endpoint-cost-pv", 871 "tag": "12c0889c3c0892bb67df561ed16d93f5d1fa75cf" 872 } 873 ] 874 }, 875 "property-map": { 876 "ane:L001": { "availbw": 50 }, 877 "ane:L003": { "availbw": 48 }, 878 "ane:L004": { "availbw": 55 }, 879 "ane:L005": { "availbw": 60 }, 880 "ane:L007": { "availbw": 35 } 881 } 882 } 884 8.5. Example #3 885 POST /endpointcost/pv HTTP/1.1 886 Host: alto.example.com 887 Accept: application/alto-endpointcost+json, 888 application/alto-error+json 889 Content-Length: [TBD] 890 Content-Type: application/alto-endpointcostparams+json 892 { 893 "multi-cost-types": [ 894 { 895 "cost-mode": "array", 896 "cost-metric": "ane-path" 897 }, 898 { 899 "cost-mode": "numerical", 900 "cost-metric": "routingcost" 901 } 902 ], 903 "endpoints": { 904 "srcs": [ "ipv4:192.0.2.2" ], 905 "dsts": [ "ipv4:192.0.2.89", 906 "ipv4:203.0.113.45", 907 "ipv6:2001:db8::10" ] 908 }, 909 "properties": [ "delay", "availbw" ] 910 } 911 HTTP/1.1 200 OK 912 Content-Length: [TBD] 913 Content-Type: application/alto-endpointcost+json 915 { 916 "meta": { 917 "dependent-vtags": [ 918 { 919 "resource-id": "propmap-availbw-delay", 920 "tag": "bb6bb72eafe8f9bdc4f335c7ed3b10822a391cef" 921 } 922 ], 923 "cost-type": [ 924 {"cost-mode": "array", "cost-metric": "ane-path"} 925 ] 926 }, 927 "endpoint-cost-map": { 928 "ipv4:192.0.2.2": { 929 "ipv4:192.0.2.89": [ "ane:L001", "ane:L003", 930 "ane:L004" ], 931 "ipv4:203.0.113.45": [ "ane:L001", "ane:L004", 932 "ane:L005" ], 933 "ipv6:2001:db8::10": [ "ane:L001", "ane:L005", 934 "ane:L007" ] 935 } 936 }, 937 "property-map": { 938 "ane:L001": { "availbw": 50, "delay": 46 }, 939 "ane:L003": { "availbw": 48, "delay": 50 }, 940 "ane:L004": { "availbw": 55, "delay": 70 }, 941 "ane:L005": { "availbw": 60, "delay": 100 }, 942 "ane:L007": { "availbw": 35, "delay": 100 } 943 } 944 } 946 9. Compatibility 948 9.1. Compatibility with Base ALTO Clients/Servers 950 The path vector extension on Filtered Cost Map and Endpoint Cost 951 Service is backward compatible with the base ALTO protocol: 953 o If the ALTO server provides extended capabilities "dependent- 954 property-map" and "allow-compound-response" for Filtered Cost Map 955 or Endpoint Cost Service, but the client only supports the base 956 ALTO protocol, then the client will ignore those capabilities 957 without conducting any incompatibility. 959 o If the client sends a request with the input parameter 960 "properties", but the server only supports the base ALTO protocol, 961 the server will ignore this field. 963 9.2. Compatibility with Multi-Cost Extension 965 This document does not specify how to integrate the "array" cost mode 966 and the "ane-path" cost metric with the multi-cost extension 967 [RFC8189]. Although there is no reason why somebody has to compound 968 the path vectors with other cost types in a single query, there is no 969 compatible issue doing it without constraint tests. 971 As Section 7.1.2 mentions, the syntax and semantics of whether 972 "constraints" or "or-constraints" field for the "array" cost mode is 973 not specified in this document. So if an ALTO server provides a 974 resource with the "array" cost mode and the capability "cost- 975 constraints" or "testable-cost-types-names", the ALTO client MAY 976 ignore the capability "cost-constraints" or "testable-cost-types- 977 names" unless the implementation or future documents specify the 978 behavior. 980 9.3. Compatibility with Incremental Update 982 As this document still follows the basic request/response protocol 983 with JSON encoding, it is surely compatible with the incremental 984 update service as defined by [I-D.ietf-alto-incr-update-sse]. But 985 the following details are to be noticed: 987 o When using the compound response, updates on both cost map and 988 property map SHOULD be notified. 990 o When not using the compound response, because the cost map is in 991 the "uses" attribute of the property map, once the path vectors in 992 the cost map change, the ALTO server MUST send the updates of the 993 cost map before the updates of the property map. 995 10. General Discussions 997 10.1. Provide Calendar for Property Map 999 Fetching the historical network information is useful for many 1000 traffic optimization problem. [I-D.ietf-alto-cost-calendar] already 1001 proposes an ALTO extension called Cost Calendar which provides the 1002 historical cost values using Filtered Cost Map and Endpoint Cost 1003 Service. However, the calendar for only path costs is not enough. 1005 For example, as the properties of ANEs (e.g., available bandwidth and 1006 link delay) are usually the real-time network states, they change 1007 frequently in the real network. It is very helpful to get the 1008 historical value of these properties. Applications may predicate the 1009 network status using these information to better optimize their 1010 performance. 1012 So the coming requirement may be a general calendar service for the 1013 ALTO information resources. 1015 10.2. Constraint Tests for General Cost Types 1017 The constraint test is a simple approach to query the data. It 1018 allows users to filter the query result by specifying some boolean 1019 tests. This approach is already used in the ALTO protocol. 1020 [RFC7285] and [RFC8189] allow ALTO clients to specify the 1021 "constraints" and "or-constraints" tests to better filter the result. 1023 However, the current defined syntax is too simple and can only be 1024 used to test the scalar cost value. For more complex cost types, 1025 like the "array" mode defined in this document, it does not work 1026 well. It will be helpful to propose more general constraint tests to 1027 better perform the query. 1029 In practice, it is too complex to customize a language for the 1030 general-purpose boolean tests, and can be a duplicated work. So it 1031 may be a good idea to integrate some already defined and widely used 1032 query languages (or their subset) to solve this problem. The 1033 candidates can be XQuery and JSONiq. 1035 10.3. General Compound Resources Query 1037 As the last paragraph of Section 4.3 mentions, querying multiple ALTO 1038 information resources continuously is a general requirement. And the 1039 coming issues like inefficiency and inconsistency are also general. 1040 There is no standard solving these issues yet. So we need some 1041 approach to make the ALTO client request the compound ALTO 1042 information resources in a single query. 1044 11. Security Considerations 1046 This document is an extension of the base ALTO protocol, so the 1047 Security Considerations of the base ALTO protocol fully apply when 1048 this extension is provided by an ALTO server. 1050 The path vector extension requires additional considerations on two 1051 security considerations discussed in the base protocol: 1052 confidentiality of ALTO information (Section 15.3 of [RFC7285]) and 1053 availability of ALTO service (Section 15.5 of [RFC7285]). 1055 For confidentiality of ALTO information, a network operator should be 1056 aware of that this extension may introduce a new risk: the path 1057 vector information may make network attacks easier. For example, as 1058 the path vector information may reveal more network internal 1059 structures than the more abstract single-node abstraction, an ALTO 1060 client may detect the bottleneck link and start a distributed denial- 1061 of-service (DDoS) attack involving minimal flows to conduct the in- 1062 network congestion. 1064 To mitigate this risk, the ALTO server should consider protection 1065 mechanisms to reduce information exposure or obfuscate the real 1066 information, in particular, in settings where the network and the 1067 application do not belong to the same trust domain. But the 1068 implementation of path vector extension involving reduction or 1069 obfuscation should guarantees the constraints on the requested 1070 properties are still accurate. 1072 For availability of ALTO service, an ALTO server should be cognizant 1073 that using path vector extension might have a new risk: frequent 1074 requesting for path vectors might conduct intolerable increment of 1075 the server-side storage and break the ALTO server. It is known that 1076 the computation of path vectors is unlikely to be cacheable, in that 1077 the results will depend on the particular requests (e.g., where the 1078 flows are distributed). Hence, the service providing path vectors 1079 may become an entry point for denial-of-service attacks on the 1080 availability of an ALTO server. To avoid this risk, authenticity and 1081 authorization of this ALTO service may need to be better protected. 1083 Even if there is no intentional attack, the dependent property map of 1084 path vector might be still dynamically enriched, in that every new 1085 request for path vectors will make the ALTO server generate a new 1086 property map. So the properties of the abstract network elements can 1087 consume a large amount of resources when cached. To avoid this, the 1088 ALTO server providing the path vector extension should support a 1089 time-to-live configuration for the property map, so that the outdated 1090 entries can be removed from the property map resource. 1092 12. IANA Considerations 1094 12.1. ALTO Cost Mode Registry 1096 This document specifies a new cost mode "array". However, the base 1097 ALTO protocol does not have a Cost Mode Registry where new cost mode 1098 can be registered. This new cost mode will be registered once the 1099 registry is defined either in a revised version of [RFC7285] or in 1100 another future extension. 1102 12.2. ALTO Cost Metric Registry 1104 A new cost metric needs to be registered in the "ALTO Cost Metric 1105 Registry", listed in Table 2. 1107 +-------------+---------------------+ 1108 | Identifier | Intended Semantics | 1109 +-------------+---------------------+ 1110 | ane-path | See Section 5.2 | 1111 +-------------+---------------------+ 1113 Table 2: ALTO Cost Metrics 1115 12.3. ALTO Entity Domain Registry 1117 As proposed in Section 9.2 of [I-D.ietf-alto-unified-props-new], 1118 "ALTO Domain Entity Registry" is requested. Besides, a new domain is 1119 to be registered, listed in Table 3. 1121 +-------------+--------------------------+--------------------------+ 1122 | Identifier | Entity Address Encoding | Hierarchy & Inheritance | 1123 +-------------+--------------------------+--------------------------+ 1124 | ane | See Section 6.2 | None | 1125 +-------------+--------------------------+--------------------------+ 1127 Table 3: ALTO Entity Domain 1129 12.4. ALTO Network Element Property Type Registry 1131 The "ALTO Abstract Network Element Property Type Registry" is 1132 required by the ALTO Domain "ane", listed in Table 4. 1134 +-------------+--------------------------+ 1135 | Identifier | Intended Semantics | 1136 +-------------+--------------------------+ 1137 | availbw | The available bandwidth | 1138 | delay | The transmission delay | 1139 +-------------+--------------------------+ 1141 Table 4: ALTO Abstract Network Element Property Types 1143 13. Acknowledgments 1145 The authors would like to thank discussions with Andreas Voellmy, 1146 Erran Li, Haibin Son, Haizhou Du, Jiayuan Hu, Qiao Xiang, Tianyuan 1147 Liu, Xiao Shi, Xin Wang, and Yan Luo. The authors thank Greg 1148 Bernstein (Grotto Networks), Dawn Chen (Tongji University), Wendy 1149 Roome, and Michael Scharf for their contributions to earlier drafts. 1151 14. References 1153 14.1. Normative References 1155 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1156 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 1157 RFC2119, March 1997, . 1160 14.2. Informative References 1162 [I-D.bernstein-alto-topo] 1163 Bernstein, G., Yang, Y., and Y. Lee, "ALTO Topology 1164 Service: Uses Cases, Requirements, and Framework", draft- 1165 bernstein-alto-topo-00 (work in progress), October 2013. 1167 [I-D.ietf-alto-cost-calendar] 1168 Randriamasy, S., Yang, Y., Wu, Q., Lingli, D., and N. 1169 Schwan, "ALTO Cost Calendar", draft-ietf-alto-cost- 1170 calendar-01 (work in progress), February 2017. 1172 [I-D.ietf-alto-incr-update-sse] 1173 Roome, W., Yang, Y., and S. Chen, "ALTO Incremental 1174 Updates Using Server-Sent Events (SSE)", draft-ietf-alto- 1175 incr-update-sse-15 (work in progress), December 2018. 1177 [I-D.ietf-alto-unified-props-new] 1178 Roome, W., Chen, S., xinwang2014@hotmail.com, x., Yang, 1179 Y., and J. Zhang, "Extensible Property Maps for the ALTO 1180 Protocol", draft-ietf-alto-unified-props-new-01 (work in 1181 progress), December 2017. 1183 [RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S., 1184 Previdi, S., Roome, W., Shalunov, S., and R. Woundy, 1185 "Application-Layer Traffic Optimization (ALTO) Protocol", 1186 RFC 7285, DOI 10.17487/RFC7285, September 2014, 1187 . 1189 [RFC8189] Randriamasy, S., Roome, W., and N. Schwan, "Multi-Cost 1190 Application-Layer Traffic Optimization (ALTO)", RFC 8189, 1191 DOI 10.17487/RFC8189, October 2017, . 1194 Authors' Addresses 1195 Kai Gao 1196 Tsinghua University 1197 Beijing Beijing 1198 China 1200 Email: gaok12@mails.tsinghua.edu.cn 1202 Young Lee 1203 Huawei 1204 TX 1205 USA 1207 Email: leeyoung@huawei.com 1209 Sabine Randriamasy 1210 Nokia Bell Labs 1211 Route de Villejust 1212 NOZAY 91460 1213 FRANCE 1215 Email: Sabine.Randriamasy@nokia-bell-labs.com 1217 Y. Richard Yang 1218 Yale University 1219 51 Prospect St 1220 New Haven CT 1221 USA 1223 Email: yry@cs.yale.edu 1225 Jingxuan Jensen Zhang 1226 Tongji University 1227 4800 Caoan Road 1228 Shanghai 201804 1229 China 1231 Email: jingxuan.n.zhang@gmail.com