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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ALTO WG R. Alimi, Ed. 3 Internet-Draft Google 4 Intended status: Standards Track R. Penno, Ed. 5 Expires: March 16, 2014 Cisco Systems 6 Y. Yang, Ed. 7 Yale University 8 September 12, 2013 10 ALTO Protocol 11 draft-ietf-alto-protocol-18.txt 13 Abstract 15 Applications using the Internet already have access to some topology 16 information of Internet Service Provider (ISP) networks. For 17 example, views to Internet routing tables at looking glass servers 18 are available and can be practically downloaded to many network 19 application clients. What is missing is knowledge of the underlying 20 network topologies from the point of view of ISPs. In other words, 21 what an ISP prefers in terms of traffic optimization -- and a way to 22 distribute it. 24 The Application-Layer Traffic Optimization (ALTO) Service provides 25 network information (e.g., basic network location structure and 26 preferences of network paths) with the goal of modifying network 27 resource consumption patterns while maintaining or improving 28 application performance. The basic information of ALTO is based on 29 abstract maps of a network. These maps provide a simplified view, 30 yet enough information about a network for applications to 31 effectively utilize them. Additional services are built on top of 32 the maps. 34 This document describes a protocol implementing the ALTO Service. 35 Although the ALTO Service would primarily be provided by ISPs, other 36 entities such as content service providers could also operate an ALTO 37 Service. Applications that could use this service are those that 38 have a choice to which end points to connect. Examples of such 39 applications are peer-to-peer (P2P) and content delivery networks. 41 Requirements Language 43 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 44 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 45 document are to be interpreted as described in RFC 2119 [RFC2119]. 47 Status of this Memo 48 This Internet-Draft is submitted in full conformance with the 49 provisions of BCP 78 and BCP 79. 51 Internet-Drafts are working documents of the Internet Engineering 52 Task Force (IETF). Note that other groups may also distribute 53 working documents as Internet-Drafts. The list of current Internet- 54 Drafts is at http://datatracker.ietf.org/drafts/current/. 56 Internet-Drafts are draft documents valid for a maximum of six months 57 and may be updated, replaced, or obsoleted by other documents at any 58 time. It is inappropriate to use Internet-Drafts as reference 59 material or to cite them other than as "work in progress." 61 This Internet-Draft will expire on March 16, 2014. 63 Copyright Notice 65 Copyright (c) 2013 IETF Trust and the persons identified as the 66 document authors. All rights reserved. 68 This document is subject to BCP 78 and the IETF Trust's Legal 69 Provisions Relating to IETF Documents 70 (http://trustee.ietf.org/license-info) in effect on the date of 71 publication of this document. Please review these documents 72 carefully, as they describe your rights and restrictions with respect 73 to this document. Code Components extracted from this document must 74 include Simplified BSD License text as described in Section 4.e of 75 the Trust Legal Provisions and are provided without warranty as 76 described in the Simplified BSD License. 78 Table of Contents 80 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 7 81 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 7 82 1.2. Design Overview . . . . . . . . . . . . . . . . . . . . . 8 83 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 84 2.1. Endpoint . . . . . . . . . . . . . . . . . . . . . . . . . 8 85 2.2. Endpoint Address . . . . . . . . . . . . . . . . . . . . . 8 86 2.3. Network Location . . . . . . . . . . . . . . . . . . . . . 9 87 2.4. ALTO Information . . . . . . . . . . . . . . . . . . . . . 9 88 2.5. ALTO Information Base . . . . . . . . . . . . . . . . . . 9 89 2.6. ALTO Service . . . . . . . . . . . . . . . . . . . . . . . 9 90 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 9 91 3.1. ALTO Service and Protocol Scope . . . . . . . . . . . . . 9 92 3.2. ALTO Information Reuse and Redistribution . . . . . . . . 11 93 4. ALTO Information Service Framework . . . . . . . . . . . . . . 11 94 4.1. ALTO Information Services . . . . . . . . . . . . . . . . 12 95 4.1.1. Map Service . . . . . . . . . . . . . . . . . . . . . 12 96 4.1.2. Map Filtering Service . . . . . . . . . . . . . . . . 13 97 4.1.3. Endpoint Property Service . . . . . . . . . . . . . . 13 98 4.1.4. Endpoint Cost Service . . . . . . . . . . . . . . . . 13 99 5. Network Map . . . . . . . . . . . . . . . . . . . . . . . . . 13 100 5.1. Provider-defined Identifier (PID) . . . . . . . . . . . . 13 101 5.2. Endpoint Addresses . . . . . . . . . . . . . . . . . . . . 14 102 5.2.1. IP Addresses . . . . . . . . . . . . . . . . . . . . . 14 103 5.3. Example Network Map . . . . . . . . . . . . . . . . . . . 15 104 6. Cost Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 105 6.1. Cost Types . . . . . . . . . . . . . . . . . . . . . . . . 16 106 6.1.1. Cost Metric . . . . . . . . . . . . . . . . . . . . . 16 107 6.1.2. Cost Mode . . . . . . . . . . . . . . . . . . . . . . 17 108 6.2. Cost Map Structure . . . . . . . . . . . . . . . . . . . . 18 109 6.3. Network Map and Cost Map Dependency . . . . . . . . . . . 18 110 6.4. Cost Map Update . . . . . . . . . . . . . . . . . . . . . 19 111 7. Endpoint Properties . . . . . . . . . . . . . . . . . . . . . 19 112 7.1. Endpoint Property Type . . . . . . . . . . . . . . . . . . 19 113 7.1.1. Endpoint Property Type: pid . . . . . . . . . . . . . 19 114 8. Protocol Specification: General Processing . . . . . . . . . . 19 115 8.1. Overall Design . . . . . . . . . . . . . . . . . . . . . . 19 116 8.2. Notation . . . . . . . . . . . . . . . . . . . . . . . . . 20 117 8.3. Basic Operations . . . . . . . . . . . . . . . . . . . . . 21 118 8.3.1. Client Discovering Information Resources . . . . . . . 21 119 8.3.2. Client Requesting Information Resources . . . . . . . 21 120 8.3.3. Server Responding to IR Request . . . . . . . . . . . 22 121 8.3.4. Client Handling Server Response . . . . . . . . . . . 22 122 8.3.5. Authentication and Encryption . . . . . . . . . . . . 23 123 8.3.6. Information Refreshing . . . . . . . . . . . . . . . . 23 124 8.3.7. HTTP Cookies . . . . . . . . . . . . . . . . . . . . . 23 125 8.3.8. Parsing of Unknown Fields . . . . . . . . . . . . . . 24 127 8.4. Server Response Encoding . . . . . . . . . . . . . . . . . 24 128 8.4.1. Meta Information . . . . . . . . . . . . . . . . . . . 24 129 8.4.2. Data Information . . . . . . . . . . . . . . . . . . . 24 130 8.5. Protocol Errors . . . . . . . . . . . . . . . . . . . . . 25 131 8.5.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 25 132 8.5.2. Response Format and Error Codes . . . . . . . . . . . 25 133 8.5.3. Overload Conditions and Server Unavailability . . . . 26 134 9. Protocol Specification: Information Resource Directory . . . . 26 135 9.1. Information Resource Attributes . . . . . . . . . . . . . 26 136 9.1.1. Resource ID . . . . . . . . . . . . . . . . . . . . . 26 137 9.1.2. Media Type . . . . . . . . . . . . . . . . . . . . . . 27 138 9.1.3. Capabilities . . . . . . . . . . . . . . . . . . . . . 27 139 9.1.4. Accepts Input Parameters . . . . . . . . . . . . . . . 27 140 9.1.5. Dependent Resources . . . . . . . . . . . . . . . . . 27 141 9.2. Information Resource Directory (IRD) . . . . . . . . . . . 27 142 9.2.1. Media Type . . . . . . . . . . . . . . . . . . . . . . 28 143 9.2.2. Encoding . . . . . . . . . . . . . . . . . . . . . . . 28 144 9.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 30 145 9.2.4. Delegation using IRD . . . . . . . . . . . . . . . . . 33 146 9.2.5. Considerations of Using IRD . . . . . . . . . . . . . 35 147 10. Protocol Specification: Basic Data Types . . . . . . . . . . . 35 148 10.1. PID Name . . . . . . . . . . . . . . . . . . . . . . . . . 35 149 10.2. Resource ID . . . . . . . . . . . . . . . . . . . . . . . 36 150 10.3. Version Tag . . . . . . . . . . . . . . . . . . . . . . . 36 151 10.4. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 36 152 10.4.1. Address Type . . . . . . . . . . . . . . . . . . . . . 37 153 10.4.2. Endpoint Address . . . . . . . . . . . . . . . . . . . 37 154 10.4.3. Endpoint Prefixes . . . . . . . . . . . . . . . . . . 37 155 10.4.4. Endpoint Address Group . . . . . . . . . . . . . . . . 38 156 10.5. Cost Mode . . . . . . . . . . . . . . . . . . . . . . . . 39 157 10.6. Cost Metric . . . . . . . . . . . . . . . . . . . . . . . 39 158 10.7. Cost Type . . . . . . . . . . . . . . . . . . . . . . . . 39 159 10.8. Endpoint Property . . . . . . . . . . . . . . . . . . . . 40 160 10.8.1. Resource Specific Endpoint Properties . . . . . . . . 40 161 10.8.2. Global Endpoint Properties . . . . . . . . . . . . . . 40 162 11. Protocol Specification: Service Information Resources . . . . 40 163 11.1. Meta Information . . . . . . . . . . . . . . . . . . . . . 41 164 11.2. Map Service . . . . . . . . . . . . . . . . . . . . . . . 41 165 11.2.1. Network Map . . . . . . . . . . . . . . . . . . . . . 41 166 11.2.2. Cost Map . . . . . . . . . . . . . . . . . . . . . . . 43 167 11.3. Map Filtering Service . . . . . . . . . . . . . . . . . . 46 168 11.3.1. Filtered Network Map . . . . . . . . . . . . . . . . . 46 169 11.3.2. Filtered Cost Map . . . . . . . . . . . . . . . . . . 49 170 11.4. Endpoint Property Service . . . . . . . . . . . . . . . . 53 171 11.4.1. Endpoint Property . . . . . . . . . . . . . . . . . . 54 172 11.5. Endpoint Cost Service . . . . . . . . . . . . . . . . . . 57 173 11.5.1. Endpoint Cost . . . . . . . . . . . . . . . . . . . . 57 174 12. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 60 175 12.1. ALTO Client Embedded in P2P Tracker . . . . . . . . . . . 61 176 12.2. ALTO Client Embedded in P2P Client: Numerical Costs . . . 62 177 12.3. ALTO Client Embedded in P2P Client: Ranking . . . . . . . 63 178 13. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 64 179 13.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 64 180 13.2. Hosts with Multiple Endpoint Addresses . . . . . . . . . . 65 181 13.3. Network Address Translation Considerations . . . . . . . . 65 182 13.4. Endpoint and Path Properties . . . . . . . . . . . . . . . 66 183 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66 184 14.1. application/alto-* Media Types . . . . . . . . . . . . . . 66 185 14.2. ALTO Cost Metric Registry . . . . . . . . . . . . . . . . 67 186 14.3. ALTO Endpoint Property Type Registry . . . . . . . . . . . 69 187 14.4. ALTO Address Type Registry . . . . . . . . . . . . . . . . 69 188 14.5. ALTO Error Code Registry . . . . . . . . . . . . . . . . . 70 189 15. Security Considerations . . . . . . . . . . . . . . . . . . . 71 190 15.1. Authenticity and Integrity of ALTO Information . . . . . . 71 191 15.1.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 71 192 15.1.2. Protection Strategies . . . . . . . . . . . . . . . . 71 193 15.1.3. Limitations . . . . . . . . . . . . . . . . . . . . . 72 194 15.2. Potential Undesirable Guidance from Authenticated ALTO 195 Information . . . . . . . . . . . . . . . . . . . . . . . 72 196 15.2.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 72 197 15.2.2. Protection Strategies . . . . . . . . . . . . . . . . 72 198 15.3. Confidentiality of ALTO Information . . . . . . . . . . . 73 199 15.3.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 73 200 15.3.2. Protection Strategies . . . . . . . . . . . . . . . . 73 201 15.3.3. Limitations . . . . . . . . . . . . . . . . . . . . . 74 202 15.4. Privacy for ALTO Users . . . . . . . . . . . . . . . . . . 74 203 15.4.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 74 204 15.4.2. Protection Strategies . . . . . . . . . . . . . . . . 74 205 15.5. Availability of ALTO Service . . . . . . . . . . . . . . . 75 206 15.5.1. Risk Scenarios . . . . . . . . . . . . . . . . . . . . 75 207 15.5.2. Protection Strategies . . . . . . . . . . . . . . . . 75 208 16. Manageability Considerations . . . . . . . . . . . . . . . . . 75 209 16.1. Operations . . . . . . . . . . . . . . . . . . . . . . . . 75 210 16.1.1. Installation and Initial Setup . . . . . . . . . . . . 76 211 16.1.2. Migration Path . . . . . . . . . . . . . . . . . . . . 76 212 16.1.3. Requirements on Other Protocols and Functional 213 Components . . . . . . . . . . . . . . . . . . . . . . 76 214 16.1.4. Impact and Observation on Network Operation . . . . . 77 215 16.2. Management . . . . . . . . . . . . . . . . . . . . . . . . 77 216 16.2.1. Management Interoperability . . . . . . . . . . . . . 77 217 16.2.2. Management Information . . . . . . . . . . . . . . . . 78 218 16.2.3. Fault Management . . . . . . . . . . . . . . . . . . . 78 219 16.2.4. Configuration Management . . . . . . . . . . . . . . . 78 220 16.2.5. Performance Management . . . . . . . . . . . . . . . . 78 221 16.2.6. Security Management . . . . . . . . . . . . . . . . . 79 222 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 79 223 17.1. Normative References . . . . . . . . . . . . . . . . . . . 79 224 17.2. Informative References . . . . . . . . . . . . . . . . . . 80 225 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 82 226 Appendix B. Design History and Merged Proposals . . . . . . . . . 83 227 Appendix C. Authors . . . . . . . . . . . . . . . . . . . . . . . 84 228 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 84 230 1. Introduction 232 1.1. Problem Statement 234 This document defines the ALTO Protocol, which provides a solution 235 for the problem stated in [RFC5693]. Specifically, in today's 236 networks, network information such as network topologies, link 237 availability, routing policies, and path costs are hidden from the 238 application layer, and many applications benefited from such hiding 239 of network complexity. However, new applications, such as 240 application-layer overlays, can benefit from information about the 241 underlying network infrastructure. In particular, these modern 242 network applications can be adaptive, and hence become more network- 243 efficient (e.g., reduce network resource consumption) and achieve 244 better application performance (e.g., accelerated download rate), by 245 leveraging network-provided information. 247 At a high level, the ALTO Protocol specified in this document is a 248 unidirectional interface that allows a network to publish its network 249 information such as network locations, costs between them at 250 configurable granularities, and endhost properties to network 251 applications. The information published by the ALTO Protocol should 252 benefit both the network and the applications (i.e., the consumers of 253 the information). Either the operator of the network or a third- 254 party (e.g., an information aggregator) can retrieve or derive 255 related information of the network and publish it using the ALTO 256 Protocol. When a network provides information through the ALTO 257 Protocol, we say that the network provides the ALTO Service. 259 To better understand the goal of the ALTO Protocol, we provide a 260 short, non-normative overview of the benefits of ALTO to both 261 networks and applications: 263 o A network that provides an ALTO Service can achieve better 264 utilization of its networking infrastructure. For example, by 265 using ALTO as a tool to interact with applications, a network is 266 able to provide network information to applications so that the 267 applications can better manage traffic on more expensive or 268 difficult-to-provision links such as long distance, transit or 269 backup links. During the interaction, the network can choose to 270 protect its sensitive and confidential network state information, 271 by abstracting real metric values into non-real numerical scores 272 or ordinal ranking. 274 o An application that uses an ALTO Service can benefit from better 275 knowledge of the network to avoid network bottlenecks. For 276 example, an overlay application can use information provided by 277 the ALTO Service to avoid selecting peers connected via high-delay 278 links (e.g., some intercontinental links). Using ALTO to 279 initialize each node with promising ("better-than-random") peers, 280 an adaptive peer-to-peer overlay may achieve faster, better 281 convergence. 283 1.2. Design Overview 285 The ALTO Protocol specified in this document meets the ALTO 286 requirements specified in [RFC5693], and unifies multiple protocols 287 previously designed with similar intentions. See Appendix A for a 288 list of people and Appendix B for a list of proposals that have made 289 significant contributions to this effort. 291 The ALTO Protocol uses a REST-ful design [Fielding-Thesis], and 292 encodes its requests and responses using JSON [RFC4627]. These 293 designs are chosen because of their flexibility and extensibility. 294 In addition, these designs make it possible for ALTO to be deployed 295 at scale by leveraging existing HTTP [RFC2616] implementations, 296 infrastructures and deployment experience. 298 2. Terminology 300 We use the following terms defined in [RFC5693]: Application, Overlay 301 Network, Peer, Resource, Resource Identifier, Resource Provider, 302 Resource Consumer, Resource Directory, Transport Address, Host 303 Location Attribute, ALTO Service, ALTO Server, ALTO Client, ALTO 304 Query, ALTO Reply, ALTO Transaction, Local Traffic, Peering Traffic, 305 Transit Traffic. 307 We also use the following additional terms: Endpoint Address, Network 308 Location, ALTO Information, ALTO Information Base, and ALTO Service. 310 2.1. Endpoint 312 An Endpoint is an application or host that is capable of 313 communicating (sending and/or receiving messages) on a network. 315 An Endpoint is typically either a Resource Provider or Resource 316 Consumer. 318 2.2. Endpoint Address 320 An Endpoint Address represents the communication address of an 321 endpoint. Common forms of Endpoint Addresses include IP address, MAC 322 address, overlay ID, and phone number. An Endpoint Address can be 323 network-attachment based (e.g., IP address) or network-attachment 324 agnostic (e.g., MAC address). 326 Each Endpoint Address has an associated Address Type, which indicates 327 both its syntax and semantics. 329 2.3. Network Location 331 Network Location is a generic term denoting a single Endpoint or a 332 group of Endpoints. For instance, it can be a single IPv4 or IPv6 333 address, an IPv4 or IPv6 prefix, or a set of prefixes. 335 2.4. ALTO Information 337 ALTO Information is a generic term referring to the network 338 information sent by an ALTO Server. 340 2.5. ALTO Information Base 342 We use the term ALTO Information Base to refer to the internal 343 representation of ALTO Information maintained by an ALTO Server. 344 Note that the structure of this internal representation is not 345 defined by this document. 347 2.6. ALTO Service 349 A network that provides ALTO Information through the ALTO Protocol is 350 said to provide the ALTO Service. 352 3. Architecture 354 We now define the ALTO architecture and the ALTO Protocol's place in 355 the overall architecture. 357 3.1. ALTO Service and Protocol Scope 359 Each network region in the global Internet can provide its ALTO 360 Service, which conveys network information from the perspective of 361 that network region. A network region in this context can be an 362 Autonomous System (AS), an ISP, a region smaller than an AS or ISP, 363 or a set of ISPs. The specific network region that an ALTO Service 364 represents will depend on the ALTO deployment scenario and ALTO 365 service discovery mechanism. 367 The ALTO Service specified in this document defines network Endpoints 368 (and aggregations thereof) and generic costs amongst them from the 369 region's perspective. The network Endpoints may include all 370 Endpoints in the global Internet. Hence, we say that the network 371 information provided by the ALTO Service of a network region 372 represents the "my-Internet view" of the network region. One may 373 note that the "my-Internet view" defined in this document does not 374 specify the internal topology of a network, and hence, we say that it 375 provides a "single-switch" abstraction. Extensions to this document 376 may provide topology details in "my-Internet view". 378 To better understand the ALTO Service and the role of the ALTO 379 Protocol, we show in Figure 1 the overall ALTO system architecture. 380 In this architecture, an ALTO Server prepares ALTO Information; an 381 ALTO Client uses ALTO Service Discovery to identify an appropriate 382 ALTO Server; and the ALTO Client requests available ALTO Information 383 from the ALTO Server using the ALTO Protocol. 385 The ALTO Information provided by the ALTO Server can be updated 386 dynamically based on network conditions, or can be seen as a policy 387 which is updated at a larger time-scale. 389 +-------------------------------------------------------------------+ 390 | Network Region | 391 | | 392 | +-----------+ | 393 | | Routing | | 394 | +--------------+ | Protocols | | 395 | | Provisioning | +-----------+ | 396 | | Policy | | | 397 | +--------------+\ | | 398 | \ | | 399 | \ | | 400 | +-----------+ \+---------+ +--------+ | 401 | |Dynamic | | ALTO | ALTO Protocol | ALTO | | 402 | |Network |.......| Server | ==================== | Client | | 403 | |Information| +---------+ +--------+ | 404 | +-----------+ / / | 405 | / ALTO SD Query/Response / | 406 | / / | 407 | +----------+ +----------------+ | 408 | | External | | ALTO Service | | 409 | | Interface| | Discovery (SD) | | 410 | +----------+ +----------------+ | 411 | | | 412 +-------------------------------------------------------------------+ 413 | 414 +------------------+ 415 | Third Parties | 416 | | 417 | Content Providers| 418 +------------------+ 420 Figure 1: Basic ALTO Architecture. 422 Figure 1 illustrates that the ALTO Information provided by an ALTO 423 Server may be influenced (at the service provider's discretion) by 424 other systems. In particular, the ALTO Server can aggregate 425 information from multiple systems to provide an abstract and unified 426 view that can be more useful to applications. Examples of other 427 systems include (but are not limited to) static network configuration 428 databases, dynamic network information, routing protocols, 429 provisioning policies, and interfaces to outside parties. These 430 components are shown in the figure for completeness but are outside 431 the scope of this specification. Recall that while the ALTO Protocol 432 may convey dynamic network information, it is not intended to replace 433 near-real-time congestion control protocols. 435 It may also be possible for an ALTO Server to exchange network 436 information with other ALTO Servers (either within the same 437 administrative domain or another administrative domain with the 438 consent of both parties) in order to adjust exported ALTO 439 Information. Such a protocol is also outside the scope of this 440 specification. 442 3.2. ALTO Information Reuse and Redistribution 444 ALTO Information may be useful to a large number of applications and 445 users. At the same time, distributing ALTO Information must be 446 efficient and not become a bottleneck. 448 The design of the ALTO Protocol allows integration with the existing 449 HTTP caching infrastructure to redistribute ALTO Information. If 450 caching or redistribution is used, the response message to an ALTO 451 Client may be returned from a third-party. 453 Application-dependent mechanisms, such as P2P DHTs or P2P file- 454 sharing, may be used to cache and redistribute ALTO Information. 455 This document does not define particular mechanisms for such 456 redistribution. 458 Additional protocol mechanisms (e.g., expiration times and digital 459 signatures for returned ALTO information) are left for future 460 investigation. 462 4. ALTO Information Service Framework 464 The ALTO Protocol conveys network information through services, where 465 each service defines a set of related functionalities. An ALTO 466 Client can query each service individually. All of the services 467 defined in ALTO are said to form the ALTO service framework and are 468 provided through a common transport protocol, messaging structure and 469 encoding, and transaction model. Functionalities offered in 470 different services can overlap. 472 The goals of the services defined in this document are to convey (1) 473 Network Locations, which denote the locations of Endpoints at a 474 network, (2) provider-defined costs for paths between pairs of 475 Network Locations, and (3) network related properties of endhosts. 476 The aforementioned goals are achieved by defining the Map Service, 477 which provides the core ALTO information to clients, and three 478 additional services: the Map Filtering Service, Endpoint Property 479 Service, and Endpoint Cost Service. Additional services can be 480 defined in companion documents. Below we give an overview of the 481 services. Details of the services will be presented in the following 482 sections. 484 .-----------------------------------------. 485 | ALTO Information Services | 486 | .-----------. .----------. .----------. | 487 | | Map | | Endpoint | | Endpoint | | 488 | | Filtering | | Property | | Cost | | 489 | | Service | | Service | | Service | | 490 | `-----------' `----------' `----------' | 491 | .-------------------------------------. | 492 | | Map Service | | 493 | | .-------------. .--------------. | | 494 | | | Network Map | | Cost Map | | | 495 | | `-------------' `--------------' | | 496 | `-------------------------------------' | 497 `-----------------------------------------' 499 Figure 2: ALTO Service Framework. 501 4.1. ALTO Information Services 503 4.1.1. Map Service 505 The Map Service provides batch information to ALTO Clients in the 506 form of Network Map and Cost Map. A Network Map (See Section 5) 507 provides a full set of Network Location groupings defined by the ALTO 508 Server and the Endpoints contained within each grouping. A Cost Map 509 (see Section 6) provides costs between a defined groupings. 511 These two maps can be thought of (and implemented as) as simple files 512 with appropriate encoding provided by the ALTO Server. 514 4.1.2. Map Filtering Service 516 Resource constrained ALTO Clients may benefit from filtering of query 517 results at the ALTO Server. This avoids that an ALTO Client first 518 spends network bandwidth and CPU cycles to collect results and then 519 performs client-side filtering. The Map Filtering Service allows 520 ALTO Clients to query an ALTO Server on Network Map and Cost Map 521 based on additional parameters. 523 4.1.3. Endpoint Property Service 525 This service allows ALTO Clients to look up properties for individual 526 Endpoints. An example property of an Endpoint is its Network 527 Location (i.e., its grouping defined by the ALTO Server). Another 528 example property is its connectivity type such as ADSL (Asymmetric 529 Digital Subscriber Line), Cable, or FTTH (Fiber To The Home). 531 4.1.4. Endpoint Cost Service 533 Some ALTO Clients may also benefit from querying for costs and 534 rankings based on Endpoints. The Endpoint Cost Service allows an 535 ALTO Server to return either numerical costs or ordinal costs 536 (rankings) directly amongst Endpoints. 538 5. Network Map 540 An ALTO Network Map defines a grouping of network endpoints. In this 541 document, we use Network Map to refer to the syntax and semantics of 542 how an ALTO Server distributes the grouping. This document does not 543 discuss the internal representation of this data structure within the 544 ALTO Server. 546 The definition of Network Map is based on the observation that in 547 reality, many endpoints are close by to one another in terms of 548 network connectivity. By treating a group of close-by endpoints 549 together as a single entity, an ALTO Server indicates aggregation of 550 these endpoints due to their proximity. This aggregation can also 551 lead to greater scalability without losing critical information when 552 conveying other network information (e.g., when defining Cost Map). 554 5.1. Provider-defined Identifier (PID) 556 One issue is that proximity varies depending on the granularity of 557 the ALTO information configured by the provider. In one deployment, 558 endpoints on the same subnet may be considered close; while in 559 another deployment, endpoints connected to the same Point of Presence 560 (PoP) may be considered close. 562 ALTO introduces provider-defined Network Location identifiers called 563 Provider-defined Identifiers (PIDs) to provide an indirect and 564 network-agnostic way to specify an aggregation of network endpoints 565 that may be treated similarly, based on network topology, type, or 566 other properties. Specifically, a PID is a US-ASCII string of type 567 PIDName (see Section 10.1) and its associated set of Endpoint 568 Addresses. As we discussed above, there can be many different ways 569 of grouping the endpoints and assigning PIDs. For example, a PID may 570 denote a subnet, a set of subnets, a metropolitan area, a PoP, an 571 autonomous system, or a set of autonomous systems. Interpreting the 572 PIDs defined in a Network Map using the "single-switch" abstraction, 573 one can consider that each PID represents an abstract port (PoP) that 574 connects a set of endpoints. 576 A key use case of PIDs is to specify network preferences (costs) 577 between PIDs instead of individual endpoints. This allows cost 578 information to be more compactly represented and updated at a faster 579 time scale than the network aggregations themselves. For example, an 580 ISP may prefer that endpoints associated with the same PoP (Point-of- 581 Presence) in a P2P application communicate locally instead of 582 communicating with endpoints in other PoPs. The ISP may aggregate 583 endhosts within a PoP into a single PID in the Network Map. The cost 584 may be encoded to indicate that Network Locations within the same PID 585 are preferred; for example, cost(PID_i, PID_i) == c and cost(PID_i, 586 PID_j) > c for i != j. Section 6 provides further details on using 587 PIDs to represent costs in an ALTO Cost Map. 589 5.2. Endpoint Addresses 591 The endpoints aggregated into a PID are denoted by endpoint 592 addresses. There are many types of addresses, such as IP addresses, 593 MAC addresses, or overlay IDs. This specification only considers IP 594 addresses. 596 5.2.1. IP Addresses 598 When either an ALTO Client or an ALTO Server needs to determine which 599 PID in a Network Map contains a particular IP address, longest-prefix 600 matching MUST be used. 602 A Network Map MUST define a PID for each possible address in the IP 603 address space for all of the address types contained in the map. A 604 RECOMMENDED way to satisfy this property is to define a PID with the 605 shortest enclosing prefix of the addresses provided in the map. For 606 a map with full IPv4 reachability, this would mean including the 607 0.0.0.0/0 prefix in a PID; for full IPv6 reachability, this would be 608 the ::/0 prefix. 610 Each endpoint MUST map into exactly one PID. Since longest-prefix 611 matching is used to map an endpoint to a PID, this can be 612 accomplished by ensuring that no two PIDs contain an identical IP 613 prefix. 615 5.3. Example Network Map 617 Figure 3 illustrates an example Network Map. PIDs are used to 618 identify network-agnostic aggregations. 620 .-----------------------------------------------------------. 621 | An ALTO Network Map | 622 | | 623 | .-----------------------------------. .---------------. | 624 | | NetLoc: PID-1 | | NetLoc: PID-2 | | 625 | | .------------------------------. | | ... | | 626 | | | 192.0.2.0/24 | | `---------------` | 627 | | | .--------------------------. | | | 628 | | | | Endpoint: 192.0.2.34 | | | .---------------. | 629 | | | `--------------------------` | | | NetLoc: PID-3 | | 630 | | `------------------------------` | | ... | | 631 | | .------------------------------. | `---------------` | 632 | | | 198.51.100.0/25 | | | 633 | | | .--------------------------. | | .---------------. | 634 | | | | Endpoint: 198.51.100.100 | | | | NetLoc: PID-4 | | 635 | | | `--------------------------` | | | ... | | 636 | | `------------------------------` | `---------------` | 637 | `-----------------------------------` | 638 | | 639 `-----------------------------------------------------------` 641 Figure 3: Example Network Map. 643 6. Cost Map 645 An ALTO Server indicates preferences amongst network locations in the 646 form of Path Costs. Path Costs are generic costs and can be 647 internally computed by a network provider according to its own 648 policy. 650 For a given Network Map, an ALTO Cost Map defines Path Costs pairwise 651 amongst sets of source and destination Network Locations defined by 652 PIDs defined in the Network Map. Each Path Cost is the end-to-end 653 cost when a unit of traffic goes from the source to the destination. 655 Since cost is directional from the source to the destination, an 656 application, when using ALTO Information, may independently determine 657 how the Resource Consumer and Resource Provider are designated as the 658 source or destination in an ALTO query, and hence how to utilize the 659 Path Cost provided by ALTO Information. For example, if the cost is 660 expected to be correlated with throughput, a typical application 661 concerned with bulk data retrieval may use the Resource Provider as 662 the source, and Resource Consumer as the destination. 664 One advantage of separating ALTO information into a Network Map and a 665 Cost Map is that the two components can be updated at different time 666 scales. For example, Network Maps may be stable for a longer time 667 while Cost Maps may be updated to reflect dynamic network conditions. 669 As used in this document, a Cost Map refers to the syntax and 670 semantics of the information distributed by the ALTO Server. This 671 document does not discuss the internal representation of this data 672 structure within the ALTO Server. 674 6.1. Cost Types 676 Path Costs have attributes: 678 o Metric: identifies what the costs represent; 680 o Mode: identifies how the costs should be interpreted. 682 The combination of a metric and a mode defines a Cost Type. Certain 683 queries for Cost Maps allow the ALTO Client to indicate the desired 684 Cost Type. For a given ALTO Server, the combination of Cost Type and 685 Network Map defines a key. In other words, an ALTO Server MUST NOT 686 define two Cost Maps with the same Cost Type, Network Map pair. 688 6.1.1. Cost Metric 690 The Metric attribute indicates what the cost represents. For 691 example, an ALTO Server could define costs representing air-miles, 692 hop-counts, or generic routing costs. 694 Cost metrics are indicated in protocol messages as strings. 696 6.1.1.1. Cost Metric: routingcost 698 An ALTO Server MUST offer the 'routingcost' Cost Metric. 700 This Cost Metric conveys a generic measure for the cost of routing 701 traffic from a source to a destination. A lower value indicates a 702 higher preference for traffic to be sent from a source to a 703 destination. 705 Note that an ISP may internally compute routing cost using any method 706 that it chooses (e.g., air-miles or hop-count) as long as it conforms 707 to these semantics. 709 6.1.2. Cost Mode 711 The Mode attribute indicates how costs should be interpreted. 712 Specifically, the Mode attribute indicates whether returned costs 713 should be interpreted as numerical values or ordinal rankings. 715 It is important to communicate such information to ALTO Clients, as 716 certain operations may not be valid on certain costs returned by an 717 ALTO Server. For example, it is possible for an ALTO Server to 718 return a set of IP addresses with costs indicating a ranking of the 719 IP addresses. Arithmetic operations that would make sense for 720 numerical values, do not make sense for ordinal rankings. ALTO 721 Clients may handle such costs differently. 723 Cost Modes are indicated in protocol messages as strings. 725 An ALTO Server MUST support at least one of 'numerical' and 'ordinal' 726 modes. An ALTO Client SHOULD be cognizant of operations when a 727 desired Cost Mode is not supported. For example, an ALTO Client 728 desiring numerical costs may adjust its behaviors if only the ordinal 729 Cost Mode is available. Alternatively, an ALTO Client desiring 730 ordinal costs may construct ordinal costs from retrieved numerical 731 values, if only the numerical Cost Mode is available. 733 6.1.2.1. Cost Mode: numerical 735 This Cost Mode is indicated by the string 'numerical'. This mode 736 indicates that it is safe to perform numerical operations (e.g. 737 normalization or computing ratios for weighted load-balancing) on the 738 returned costs. The values are floating-point numbers. 740 6.1.2.2. Cost Mode: ordinal 742 This Cost Mode is indicated by the string 'ordinal'. This mode 743 indicates that the costs values in a Cost Map are a ranking (relative 744 to all other values in a Cost Map), with a lower value indicating a 745 higher preference. The values are non-negative integers. Ordinal 746 cost values in a Cost Map need not be unique nor contiguous. In 747 particular, it is possible that two entries in a map have an 748 identical rank (ordinal cost value). This document does not specify 749 any behavior by an ALTO Client in this case; an ALTO Client may 750 decide to break ties by random selection, other application 751 knowledge, or some other means. 753 It is important to note that the values in the Cost Map provided with 754 the ordinal Cost Mode are not necessarily the actual costs known to 755 the ALTO Server. 757 6.2. Cost Map Structure 759 A query for a Cost Map either explicitly or implicitly includes a 760 list of Source Network Locations and a list of Destination Network 761 Locations. (Recall that a Network Location can be an endpoint 762 address or a PID.) 764 Specifically, assume that a query has a list of multiple Source 765 Network Locations, say [Src_1, Src_2, ..., Src_m], and a list of 766 multiple Destination Network Locations, say [Dst_1, Dst_2, ..., 767 Dst_n]. 769 The ALTO Server will return the Path Cost for each of the m*n 770 communicating pairs (i.e., Src_1 -> Dst_1, ..., Src_1 -> Dst_n, ..., 771 Src_m -> Dst_1, ..., Src_m -> Dst_n). If the ALTO Server does not 772 define a Path Cost for a particular pair, it may be omitted. We 773 refer to this structure as a Cost Map. 775 If the Cost Mode is 'ordinal', the Path Cost of each communicating 776 pair is relative to the m*n entries. 778 6.3. Network Map and Cost Map Dependency 780 If a Cost Map contains PIDs in the list of Source Network Locations 781 or the list of Destination Network Locations, the Path Costs are 782 generated based on a particular Network Map (which defines the PIDs). 783 Version Tags are introduced to ensure that ALTO Clients are able to 784 use consistent information even though the information is provided in 785 two maps. 787 A Version Tag is a tuple of (1) an ID for the resource (e.g., a 788 Network Map), and (2) a tag (an opaque string) associated with the 789 version of that resource. A Network Map distributed by an ALTO 790 Server includes its Version Tag. A Cost Map referring to PIDs also 791 includes Version Tag for the Network Map on which it is based. 793 Two Network Maps are the same if they have the same Version Tag. 794 Whenever the content of the Network Map maintained by an ALTO Server 795 changes, tag MUST also be changed. Possibilities of setting the tag 796 component include the last-modified timestamp for the Network Map, or 797 a hash of its contents, where the collision probability is considered 798 zero in practical deployment scenarios. 800 6.4. Cost Map Update 802 An ALTO Server can update a Cost Map at any time. Hence, the same 803 Cost Map retrieved from the same ALTO Server but from different 804 requests can be inconsistent. 806 7. Endpoint Properties 808 An endpoint property defines a network-aware property of an endpoint. 810 7.1. Endpoint Property Type 812 For each endpoint and an endpoint property type, there can be a value 813 for the property. The type of an Endpoint property is indicated in 814 protocol messages as a string. The value depends on the specific 815 property. For example, for a property such as whether an endpoint is 816 metered, the value is a true or false value. 818 7.1.1. Endpoint Property Type: pid 820 An ALTO Server MUST define the 'pid' Endpoint Property Type for each 821 Network Map that it provides. 823 8. Protocol Specification: General Processing 825 This section first specifies general client and server processing. 826 The details of specific services will be covered in the following 827 sections. 829 8.1. Overall Design 831 The ALTO Protocol uses a REST-ful design. There are two primary 832 components to this design: 834 o Information Resources: An ALTO Server provides a set of network 835 information resources. Each information resource has a media type 836 [RFC2046]. An ALTO Client may construct an HTTP request for a 837 particular information resource (including any parameters, if 838 necessary), and the ALTO Server returns the requested information 839 resource in an HTTP response. 841 o Information Resource Directory (IRD): An ALTO Server provides to 842 ALTO Clients a list of available information resources and the URI 843 at which each is provided. This document refers to this list as 844 the Information Resource Directory. ALTO Clients consult the 845 directory to determine the services provided by an ALTO Server. 847 8.2. Notation 849 This document uses 'JSONString', 'JSONNumber', 'JSONBool' to indicate 850 the JSON string, number, and boolean types, respectively. The type 851 'JSONValue' indicates a JSON value, as specified in Section 2.1 of 852 [RFC4627]. 854 We use an adaptation of the C-style struct notation to define the 855 fields (names/values) of JSON objects. An optional field is enclosed 856 by [ ], and an array is indicated by two numbers in angle brackets, 857 , where m indicates the minimal number of values, and n is the 858 maximum. When we write * for n, it means no upper bound. In the 859 definitions, the JSON names of the fields are case sensitive. 861 For example, the definition below defines a new type Type4, with 862 three field members (or fields for short) named "name1", "name2", and 863 "name3" respectively. The field named "name3" is optional, and the 864 field named "name2" is an array of at least one value. 866 object { 867 Type1 name1; 868 Type2 name2<1..*>; 869 [Type3 name3;] 870 } Type4; 872 We also define dictionary maps (or maps for short) from strings to 873 JSON values. For example, the definition below defines a Type3 874 object as a map. Type1 must be defined as string, and Type2 can be 875 defined as any type. 877 object-map { 878 Type1 -> Type2; 879 } Type3; 881 We use subtyping to denote that one type is derived from another 882 type. The example below denotes that TypeDerived is derived from 883 TypeBase. TypeDerived includes all fields defined in TypeBase. If 884 TypeBase does not have a field named "name1", TypeDerived will have a 885 new field named "name1". If TypeBase already has a field named 886 "name1" but with a different type, TypeDerived will have a field 887 named "name1" with the type defined in TypeDerived (i.e., Type1 in 888 the example). 890 object { 891 Type1 name1; 892 } TypeDerived : TypeBase; 894 Note that despite the notation, no standard, machine-readable 895 interface definition or schema is provided in this document. 896 Extension documents may document these as necessary. 898 8.3. Basic Operations 900 The ALTO Protocol employs standard HTTP [RFC2616]. It is used for 901 discovering available Information Resources at an ALTO Server and 902 retrieving Information Resources. ALTO Clients and ALTO Servers use 903 HTTP requests and responses carrying ALTO-specific content with 904 encoding as specified in this document, and MUST be compliant with 905 [RFC2616]. 907 8.3.1. Client Discovering Information Resources 909 To discover available Information Resources, an ALTO Client requests 910 Information Resource Directories. Informally, an Information 911 Resource Directory enumerates URIs at which an ALTO Server offers 912 Information Resources. 914 Specifically, using the ALTO Discovery protocol, an ALTO Client 915 obtains a URI through which it can request an Information Resource 916 Directory (IRD). We refer to this IRD as the Root IRD of the ALTO 917 Client. Each entry in an IRD indicates a URI at which an ALTO Server 918 accepts requests, and returns either an Information Resource or an 919 Information Resource Directory that references additional Information 920 Resources. Beginning with its Root IRD and following links to IRDs 921 recursively, an ALTO Client can discover all Information Resources 922 available to it. We refer to this set of Information Resources as 923 the Information Resource Closure of the ALTO Client. By inspecting 924 its Information Resource Closure, an ALTO Client can determine 925 whether an ALTO Server supports the desired Information Resource, and 926 if it is supported, the URI at which it is available. 928 See Section 9.2 for a detailed specification on IRDs. 930 8.3.2. Client Requesting Information Resources 932 Where possible, the ALTO Protocol uses the HTTP GET method to request 933 resources. However, some ALTO services provide Information Resources 934 that are the function of one or more input parameters. Input 935 parameters are encoded in the HTTP request's entity body, and the 936 ALTO Client MUST use the HTTP POST method to send the parameters. 938 When requesting an ALTO Information Resource that requires input 939 parameters specified in a HTTP POST request, an ALTO Client MUST set 940 the Content-Type HTTP header to the media type corresponding to the 941 format of the supplied input parameters. 943 8.3.3. Server Responding to IR Request 945 Upon receiving a request for an Information Resource that the ALTO 946 Server can provide, the ALTO Server MUST return the requested 947 Information Resource. In other cases, to be more informative 948 ([I-D.ietf-httpbis-p2-semantics]), the ALTO Server MAY provide the 949 ALTO Client with an Information Resource Directory indicating how to 950 reach the desired information resource, or return an ALTO error 951 object; see Section 8.5 for more details on ALTO error handling. 953 It is possible for an ALTO Server to leverage caching HTTP 954 intermediaries to respond to both GET and POST requests by including 955 explicit freshness information (see Section 14 of [RFC2616]). 956 Caching of POST requests is not widely implemented by HTTP 957 intermediaries, however an alternative approach is for an ALTO 958 Server, in response to POST requests, to return an HTTP 303 status 959 code ("See Other") indicating to the ALTO Client that the resulting 960 Information Resource is available via a GET request to an alternate 961 URL. HTTP intermediaries that do not support caching of POST 962 requests could then cache the response to the GET request from the 963 ALTO Client following the alternate URL in the 303 response if the 964 response to the subsequent GET request contains explicit freshness 965 information. 967 The ALTO Server MUST indicate the type of its response using a media 968 type (i.e., the Content-Type HTTP header of the response). 970 8.3.4. Client Handling Server Response 972 8.3.4.1. Using Information Resources 974 This specification does not indicate any required actions taken by 975 ALTO Clients upon successfully receiving an Information Resource from 976 an ALTO Server. Although ALTO Clients are suggested to interpret the 977 received ALTO Information and adapt application behavior, ALTO 978 Clients are not required to do so. 980 8.3.4.2. Handling Server Response and IRD 982 After receiving an Information Resource Directory, the Client can 983 consult it to determine if any of the offered URIs contain the 984 desired Information Resource. However, an ALTO Client MUST NOT 985 assume that the media type returned by the ALTO Server for a request 986 to a URI is the media type advertised in the IRD or specified in its 987 request (i.e., the client must still check the Content-Type header). 988 The expectation is that the media type returned should normally be 989 the media type advertised and requested, but in some cases it may 990 legitimately not be so. 992 In particular, it is possible for an ALTO Client to receive an 993 Information Resource Directory from an ALTO Server as a response to 994 its request for a specific Information Resource. In this case, the 995 ALTO Client may ignore the response or still parse the response. To 996 indicate that an ALTO Client will always check if a response is an 997 Information Resource Directory, the ALTO Client can indicate in the 998 "Accept" header of a HTTP request that it can accept Information 999 Resource Directory; see Section 9.2 for the media type. 1001 8.3.4.3. Handling Error Conditions 1003 If an ALTO Client does not successfully receive a desired Information 1004 Resource from a particular ALTO Server (i.e., server response 1005 indicates error or there is no response), the Client can either 1006 choose another server (if one is available) or fall back to a default 1007 behavior (e.g., perform peer selection without the use of ALTO 1008 information, when used in a peer-to-peer system). 1010 8.3.5. Authentication and Encryption 1012 When server and/or client authentication, encryption, and/or 1013 integrity protection are required, an ALTO Server MUST support SSL/ 1014 TLS [RFC5246] as a mechanism. For cases such as a public ALTO 1015 service or deployment scenarios where there is an implicit trust 1016 relationship between the client and the server and the network 1017 infrastructure connecting them is secure, SSL/TLS may not be 1018 necessary. See [RFC6125] for considerations regarding verification 1019 of server identity. 1021 8.3.6. Information Refreshing 1023 An ALTO Client MAY determine the frequency at which ALTO Information 1024 is refreshed based on information made available via HTTP. 1026 8.3.7. HTTP Cookies 1028 If cookies are included in an HTTP request received by an ALTO 1029 Server, they MUST be ignored. 1031 8.3.8. Parsing of Unknown Fields 1033 This document only details object fields used by this specification. 1034 Extensions may include additional fields within JSON objects defined 1035 in this document. ALTO implementations MUST ignore unknown fields 1036 when processing ALTO messages. 1038 8.4. Server Response Encoding 1040 Though each type of ALTO Server response (i.e., an Information 1041 Resource Directory, an individual Information Resource, or an error 1042 message) has its distinct syntax and hence its unique Media Type, 1043 they are designed to have a similar structure: a meta field providing 1044 meta definitions, and another field containing the data, if needed. 1046 Specifically, we define the base type of each ALTO Server response as 1047 ResponseEntityBase: 1049 object { 1050 ResponseMeta meta; 1051 } ResponseEntityBase; 1053 with field: 1055 meta meta-information pertaining to the response. 1057 8.4.1. Meta Information 1059 Meta information is encoded as a map object for flexibility. 1060 Specifically, ResponseMeta is defined as: 1062 object-map { 1063 JSONString -> JSONValue 1064 } ResponseMeta; 1066 8.4.2. Data Information 1068 The data component of the response encodes the response-specific 1069 data. In this document, we derive five types from ResponseEntityBase 1070 to add different types of data component: InforResourceDirectory 1071 (Section 9.2.2), InfoResourceNetworkMap (Section 11.2.1.6), 1072 InfoResourceCostMap (Section 11.2.2.6), 1073 InfoResourceEndpointProperties (Section 11.4.1.6), and 1074 InfoResourceEndpointCostMap (Section 11.5.1.6). 1076 8.5. Protocol Errors 1078 If there is an error processing a request, an ALTO Server SHOULD 1079 return additional ALTO-layer information, if it is available, in the 1080 form of an ALTO Error Resource encoded in the HTTP response' entity 1081 body. If no ALTO-layer information is available, an ALTO Server may 1082 omit an ALTO Error resource from the response. 1084 With or without additional ALTO-layer error information, an ALTO 1085 Server MUST set an appropriate HTTP status code. It is important to 1086 note that the HTTP Status Code and ALTO Error Resource have distinct 1087 roles. An ALTO Error Resource provides detailed information about 1088 why a particular request for an ALTO Resource was not successful. 1089 The HTTP status code indicates to HTTP processing elements (e.g., 1090 intermediaries and clients) how the response should be treated. 1092 8.5.1. Media Type 1094 The media type for an ALTO Error Response is "application/ 1095 alto-error+json". 1097 8.5.2. Response Format and Error Codes 1099 An ALTO Error Response MUST include the "code" key in the "meta" 1100 field of the response. 1102 The value of "code" MUST be an ALTO Error Code defined in Table 1. 1103 Note that the ALTO Error Codes defined in Table 1 are limited to 1104 support the error conditions needed for purposes of this document. 1105 Additional status codes may be defined in companion or extension 1106 documents. 1108 +-------------------------+-----------------------------------------+ 1109 | ALTO Error Code | Description | 1110 +-------------------------+-----------------------------------------+ 1111 | E_SYNTAX | Parsing error in request (including | 1112 | | identifiers) | 1113 | E_JSON_FIELD_MISSING | Required field missing | 1114 | E_JSON_VALUE_TYPE | JSON Value of unexpected type | 1115 | E_INVALID_COST_MODE | Invalid cost mode | 1116 | E_INVALID_COST_METRIC | Invalid cost metric | 1117 | E_INVALID_PROPERTY_TYPE | Invalid property type | 1118 +-------------------------+-----------------------------------------+ 1120 Table 1: Defined ALTO Error Codes. 1122 If multiple errors are present in a single request (e.g., a request 1123 uses a JSONString when a JSONNumber is expected and a required field 1124 is missing), then the ALTO Server MUST return exactly one of the 1125 detected errors. However, the reported error is implementation 1126 defined, since specifying a particular order for message processing 1127 encroaches needlessly on implementation technique. 1129 8.5.3. Overload Conditions and Server Unavailability 1131 If an ALTO Server detects that it cannot handle a request from an 1132 ALTO Client due to excessive load, technical problems, or system 1133 maintenance, it SHOULD do one of the following: 1135 o Return an HTTP 503 ("Service Unavailable") status code to the ALTO 1136 Client. As indicated by [RFC2616], a the Retry-After HTTP header 1137 may be used to indicate when the ALTO Client should retry the 1138 request. 1140 o Return an HTTP 307 ("Temporary Redirect") status code indicating 1141 an alternate ALTO Server that may be able to satisfy the request. 1143 The ALTO Server MAY also terminate the connection with the ALTO 1144 Client. 1146 The particular policy applied by an ALTO Server to determine that it 1147 cannot service a request is outside of the scope of this document. 1149 9. Protocol Specification: Information Resource Directory 1151 As we discussed, an ALTO Client starts by retrieving an Information 1152 Resource Directory, which specifies the attributes of individual 1153 Information Resources that an ALTO Server provides. 1155 9.1. Information Resource Attributes 1157 In this document, each Information Resource has five attributes 1158 associated with it, including its assigned ID, its response format, 1159 its capabilities, its accepted input parameters, and other resources 1160 that it may depend on. The function of an Information Resource 1161 Directory is to publishes these attributes. 1163 9.1.1. Resource ID 1165 Each Information Resource that an ALTO Client can request MUST be 1166 assigned an ID that is unique amongst all Information Resources in 1167 the Information Resource Closure of the client. The ID SHOULD remain 1168 stable even when the data provided by that resource changes. For 1169 example, even though the number of PIDs in a Network Map may be 1170 adjusted, its Resource ID should remain the same. Similarly, if the 1171 entries in a Cost Map are updated, its Resource ID should remain the 1172 same. IDs SHOULD NOT be re-used for different resources over time. 1174 9.1.2. Media Type 1176 ALTO uses Media Type [RFC2046] to uniquely indicate the data format 1177 used to encode the content to be transmitted between an ALTO Server 1178 and an ALTO Client in the HTTP entity body. 1180 9.1.3. Capabilities 1182 The Capabilities attribute of an Information Resource indicates 1183 specific capabilities that the server can provide. For example, if 1184 an ALTO Server allows an ALTO Client to specify cost constraints when 1185 the Client requests a Cost Map Information Resource, then the Server 1186 advertises the cost-constraints capability of the Cost Map 1187 Information Resource. 1189 9.1.4. Accepts Input Parameters 1191 An ALTO Server may allow an ALTO Client to supply input parameters 1192 when requesting certain Information Resources. The associated 1193 accepts attribute of an Information Resource is a Media Type, which 1194 indicates how the Client specifies the input parameters as contained 1195 in the entity body of the HTTP POST request. 1197 9.1.5. Dependent Resources 1199 The information provided in an Information Resource may use 1200 information provided in some other resources (e.g., a Cost Map uses 1201 the PIDs defined in a Network Map). The uses attribute conveys such 1202 information. 1204 9.2. Information Resource Directory (IRD) 1206 An ALTO Server uses Information Resource Directory to publish 1207 available Information Resources and their aforementioned attributes. 1208 Since resource selection happens after consumption of the Information 1209 Resource Directory, the format of the Information Resource Directory 1210 is designed to be simple with the intention of future ALTO Protocol 1211 versions maintaining backwards compatibility. Future extensions or 1212 versions of the ALTO Protocol SHOULD be accomplished by extending 1213 existing media types or adding new media types, but retaining the 1214 same format for the Information Resource Directory. 1216 An ALTO Server MUST make an Information Resource Directory available 1217 via the HTTP GET method to a URI discoverable by an ALTO Client. 1218 Discovery of this URI is out of scope of this document, but could be 1219 accomplished by manual configuration or by returning the URI of an 1220 Information Resource Directory from the ALTO Discovery Protocol 1221 [I-D.ietf-alto-server-discovery]. For recommendations on how the URI 1222 may look like, see [I-D.ietf-alto-server-discovery]. 1224 9.2.1. Media Type 1226 The media type to indicate an information directory is "application/ 1227 alto-directory+json". 1229 9.2.2. Encoding 1231 An Information Resource Directory response may include in "meta" the 1232 "cost-types" key, whose value is of type IRDMetaCostTypes defined 1233 below, where CostType is defined in Section 10.7: 1235 object-map { 1236 JSONString -> CostType; 1237 } IRDMetaCostTypes; 1239 The function of "cost-types" is to assign names to a set of CostTypes 1240 that can be used in one or more "resources" entries in the IRD to 1241 simplify specification. The names defined in "cost-types" in an IRD 1242 are local to the IRD. 1244 For a Root IRD, "meta" MUST include the "default-alto-network-map" 1245 key, which specifies the Resource ID of a Network Map. When there are 1246 multiple Network Maps defined in an IRD (e.g., with different levels 1247 of granularity), the "default-alto-network-map" key provides a 1248 guideline to simple clients that use only one Network Map. 1250 The data component of an Information Resource Directory response is 1251 named "resources", which is a JSON object of type IRDResourceEntries: 1253 object { 1254 IRDResourceEntries resources; 1255 } InfoResourceDirectory : ResponseEntityBase; 1257 object-map { 1258 ResourceID -> IRDResourceEntry; 1259 } IRDResourceEntries; 1261 object { 1262 JSONString uri; 1263 JSONString media-type; 1264 [JSONString accepts;] 1265 [Capabilities capabilities;] 1266 [ResourceID uses<0..*>;] 1267 } IRDResourceEntry; 1269 object { 1270 ... 1271 } Capabilities; 1273 An IRDResourceEntries object is a dictionary map keyed by 1274 ResourceIDs, where ResourceID is defined in Section 10.2. The value 1275 of each entry specifies: 1277 uri A URI at which the ALTO Server provides one or more Information 1278 Resources, or an Information Resource Directory indicating 1279 additional Information Resources. URIs can be relative to the URI 1280 of the IRD and MUST be resolved according to Section 5 of 1281 [RFC3986]. 1283 media-type The media type of Information Resource (see 1284 Section 9.1.2) available via GET or POST requests to the 1285 corresponding URI or "application/alto-directory+json", which 1286 indicates that the response for a request to the URI will be an 1287 Information Resource Directory for URIs discoverable via the URI. 1289 accepts The media type of input parameters (see Section 9.1.4) 1290 accepted by POST requests to the corresponding URI. If this field 1291 is not present, it MUST be assumed to be empty. 1293 capabilities A JSON Object enumerating capabilities of an ALTO 1294 Server in providing the Information Resource at the corresponding 1295 URI and Information Resources discoverable via the URI. If this 1296 field is not present, it MUST be assumed to be an empty object. 1298 If a capability for one of the offered Information Resources is 1299 not explicitly listed here, an ALTO Client may either issue an 1300 OPTIONS HTTP request to the corresponding URI to determine if the 1301 capability is supported, or assume its default value documented in 1302 this specification or an extension document describing the 1303 capability. 1305 uses A list of Resource IDs, defined in the same IRD, that define 1306 the resources on which this resource directly depends. An ALTO 1307 Server SHOULD include in this list any resources that the ALTO 1308 Client would need to retrieve in order to interpret the contents 1309 of this resource. For example, a Cost Map resource should include 1310 in this list the Network Map on which it depends. ALTO Clients 1311 may wish to consult this list in order to pre-fetch necessary 1312 resources. 1314 If an entry has an empty list for "accepts", then the corresponding 1315 URI MUST support GET requests. If an entry has a non-empty 1316 "accepts", then the corresponding URI MUST support POST requests. If 1317 an ALTO Server wishes to support both GET and POST on a single URI, 1318 it MUST specify two entries in the Information Resource Directory. 1320 9.2.3. Example 1322 The following is an example Information Resource Directory returned 1323 by an ALTO Server to an ALTO Client. Assume it is the Root IRD of 1324 the Client. 1326 GET /directory HTTP/1.1 1327 Host: alto.example.com 1328 Accept: application/alto-directory+json,application/alto-error+json 1330 HTTP/1.1 200 OK 1331 Content-Length: TBA 1332 Content-Type: application/alto-directory+json 1334 { 1335 "meta" : { 1336 "cost-types": { 1337 "num-routing": { 1338 "cost-mode" : "numerical", 1339 "cost-metric": "routingcost", 1340 "description": "My default" 1341 }, 1342 "num-hop": { 1343 "cost-mode" : "numerical", 1344 "cost-metric": "hopcount" 1345 }, 1346 "ord-routing": { 1347 "cost-mode" : "ordinal", 1348 "cost-metric": "routingcost" 1349 }, 1350 "ord-hop": { 1351 "cost-mode" : "ordinal", 1352 "cost-metric": "hopcount" 1353 } 1354 }, 1355 "default-alto-network-map" : "my-default-network-map" 1356 }, 1357 "resources" : { 1358 "my-default-network-map" : { 1359 "uri" : "http://alto.example.com/networkmap", 1360 "media-type" : "application/alto-networkmap+json" 1361 }, 1362 "numerical-routing-cost-map" : { 1363 "uri" : "http://alto.example.com/costmap/num/routingcost", 1364 "media-type" : "application/alto-costmap+json", 1365 "capabilities" : { 1366 "cost-type-names" : [ "num-routing" ] 1367 }, 1368 "uses": [ "my-default-network-map" ] 1369 }, 1370 "numerical-hopcount-cost-map" : { 1371 "uri" : "http://alto.example.com/costmap/num/hopcount", 1372 "media-type" : "application/alto-costmap+json", 1373 "capabilities" : { 1374 "cost-type-names" : [ "num-hop" ] 1375 }, 1376 "uses": [ "my-default-network-map" ] 1377 }, 1378 "custom-maps-resources" : { 1379 "uri" : "http://custom.alto.example.com/maps", 1380 "media-type" : "application/alto-directory+json" 1381 }, 1382 "endpoint-property" : { 1383 "uri" : "http://alto.example.com/endpointprop/lookup", 1384 "media-type" : "application/alto-endpointprop+json", 1385 "accepts" : "application/alto-endpointpropparams+json", 1386 "capabilities" : { 1387 "prop-types" : [ "my-default-network-map.pid", 1388 "priv:ietf-example-prop" ] 1389 }, 1391 }, 1392 "endpoint-cost" : { 1393 "uri" : "http://alto.example.com/endpointcost/lookup", 1394 "media-type" : "application/alto-endpointcost+json", 1395 "accepts" : "application/alto-endpointcostparams+json", 1396 "capabilities" : { 1397 "cost-constraints" : true, 1398 "cost-type-names" : [ "num-routing", "num-hop", 1399 "ord-routing", "ord-hop"] 1400 } 1401 } 1402 } 1403 } 1405 Specifically, the "cost-types" key of "meta" of the example IRD 1406 defines names for four cost types in this IRD. For example, "num- 1407 routing" in the example is the name that refers to a Cost Type with 1408 Cost Mode being "numerical" and Cost Metric being "routingcost". 1409 This name is used in the second entry of "resources", which defines a 1410 Cost Map. In particular, the "cost-type-names" of its "capabilities" 1411 specifies that this resource supports a Cost Type named as "num- 1412 routing". The ALTO Client looks up the name "num-routing" in "cost- 1413 types" of the IRD to obtain the Cost Type named as "num-routing". 1414 The last entry of "resources" uses all four names defined in "cost- 1415 types". 1417 Another key defined in "meta" of the example IRD is "default-alto- 1418 network-map", which has value "my-default-network-map", which is the 1419 Resource ID of a Network Map that will be defined in "resources". 1421 The "resources" field of the example IRD defines six Information 1422 Resources. For example, the second entry, which is assigned a 1423 Resource ID "numerical-routing-cost-map", provides a Cost Map, as 1424 indicated by the media-type "application/alto-costmap+json". The 1425 Cost Map is based on the Network Map defined with Resource ID "my- 1426 default-network-map". As another example, the last entry, which is 1427 assigned Resource ID "endpoint-cost", provides the Endpoint Cost 1428 Service, which is indicated by the media-type "application/ 1429 alto-endpointcost+json". An ALTO Client should use uri 1430 "http://alto.example.com/endpointcost/lookup" to access the service. 1431 The ALTO Client should format its request body to be the 1432 "application/alto-endpointcostparams+json" media type, as specified 1433 by the "accepts" attribute of the Information Resource. The "cost- 1434 type-names" field of the "capabilities" attribute of the Information 1435 Resource includes four defined cost types specified in the "cost- 1436 types" key of "meta" of the IRD. Hence, one can verify that the 1437 Endpoint Cost Information Resource supports both Cost Metrics 1438 'routingcost' and 'hopcount', each available for both 'numerical' and 1439 'ordinal'. When requesting the Information Resource, an ALTO Client 1440 can specify cost constraints, as indicated by the "cost-constraints" 1441 field of the "capabilities" attribute. 1443 9.2.4. Delegation using IRD 1445 ALTO Information Resource Directory provides flexibility to provide 1446 ALTO Service (e.g., delegation to another domain). Consider the 1447 preceding example. Assume that the ALTO Server running at 1448 alto.example.com wants to delegate some Information Resources to a 1449 separate subdomain: "custom.alto.example.com". In particular, assume 1450 that the maps available via this subdomain are filtered Network Maps, 1451 filtered Cost Maps, and some pre-generated maps for the "hopcount" 1452 and "routingcost" Cost Metrics in the "ordinal" Cost Mode. The 1453 fourth entry of "resources" in the preceding example IRD implements 1454 the delegation. The entry has a media-type of "application/ 1455 alto-directory+json", and an ALTO Client can discover the Information 1456 Resources available at "custom.alto.example.com" if its request to 1457 "http://custom.alto.example.com/maps" is successful: 1459 GET /maps HTTP/1.1 1460 Host: custom.alto.example.com 1461 Accept: application/alto-directory+json,application/alto-error+json 1463 HTTP/1.1 200 OK 1464 Content-Length: TBA 1465 Content-Type: application/alto-directory+json 1467 { 1468 "meta" : { 1469 "cost-types": { 1470 "num-routing": { 1471 "cost-mode" : "numerical", 1472 "cost-metric": "routingcost", 1473 "description": "My default" 1474 }, 1475 "num-hop": { 1476 "cost-mode" : "numerical", 1477 "cost-metric": "hopcount" 1478 }, 1479 "ord-routing": { 1480 "cost-mode" : "ordinal", 1481 "cost-metric": "routingcost" 1483 }, 1484 "ord-hop": { 1485 "cost-mode" : "ordinal", 1486 "cost-metric": "hopcount" 1487 } 1488 } 1489 }, 1490 "resources" : { 1491 "filtered-network-map" : { 1492 "uri" : "http://custom.alto.example.com/networkmap/filtered", 1493 "media-type" : "application/alto-networkmap+json", 1494 "accepts" : "application/alto-networkmapfilter+json", 1495 "uses": [ "my-default-network-map" ] 1496 }, 1497 "filtered-cost-map" : { 1498 "uri" : "http://custom.alto.example.com/costmap/filtered", 1499 "media-type" : "application/alto-costmap+json", 1500 "accepts" : "application/alto-costmapfilter+json", 1501 "capabilities" : { 1502 "cost-constraints" : true, 1503 "cost-type-names" : [ "num-routing", "num-hop", 1504 "ord-routing", "ord-hop" ] 1505 }, 1506 "uses": [ "my-default-network-map" ] 1507 }, 1508 "ordinal-routing-cost-map" : { 1509 "uri" : "http://custom.alto.example.com/ord/routingcost", 1510 "media-type" : "application/alto-costmap+json", 1511 "capabilities" : { 1512 "cost-type-names" : [ "ord-routing" ] 1513 }, 1514 "uses": [ "my-default-network-map" ] 1515 }, 1516 "ordinal-hopcount-cost-map" : { 1517 "uri" : "http://custom.alto.example.com/ord/hopcount", 1518 "media-type" : "application/alto-costmap+json", 1519 "capabilities" : { 1520 "cost-type-names" : [ "ord-hop" ], 1521 }, 1522 "uses": [ "my-default-network-map" ] 1523 } 1524 } 1525 } 1527 Note that the subdomain does not define Network Map, and uses the 1528 Network Map with Resource ID "my-default-network-map" defined in the 1529 Root IRD. 1531 9.2.5. Considerations of Using IRD 1533 9.2.5.1. ALTO Client 1535 This document specifies no requirements or constraints on ALTO 1536 Clients with regards to how they process an Information Resource 1537 Directory to identify the URI corresponding to a desired Information 1538 Resource. However, some advice is provided for implementors. 1540 It is possible that multiple entries in the directory match a desired 1541 Information Resource. For instance, in the example in Section 9.2.3, 1542 a full Cost Map with "numerical" Cost Mode and "routingcost" Cost 1543 Metric could be retrieved via a GET request to 1544 "http://alto.example.com/costmap/num/routingcost", or via a POST 1545 request to "http://custom.alto.example.com/costmap/filtered". 1547 In general, it is preferred for ALTO Clients to use GET requests 1548 where appropriate, since it is more likely for responses to be 1549 cachable. However, an ALTO Client may need to use POST, for example, 1550 to get ALTO costs or properties that are for a restricted set of PIDs 1551 or Endpoints, or to update cached information previously acquired via 1552 GET requests." 1554 9.2.5.2. ALTO Server 1556 This document indicates that an ALTO Server may or may not provide 1557 the Information Resources specified in the Map Filtering Service. If 1558 these resources are not provided, it is indicated to an ALTO Client 1559 by the absence of a Network Map or Cost Map with any media types 1560 listed under "accepts". 1562 10. Protocol Specification: Basic Data Types 1564 This section details the format of basic data types. 1566 10.1. PID Name 1568 A PID Name is encoded as a US-ASCII string. The string MUST be no 1569 more than 64 characters, and MUST NOT contain characters other than 1570 alphanumeric characters (code points 0x30-0x39, 0x41-0x5A, and 0x61- 1571 0x7A), the hyphen ('-', code point 0x2D), the colon (':', code point 1572 0x3A), the at ('@', code point 0x40), the underline ('_', code point 1573 0x5F), or the '.' separator (code point 0x2E). The '.' separator is 1574 reserved for future use and MUST NOT be used unless specifically 1575 indicated in this document, or an extension document. 1577 The type 'PIDName' is used in this document to indicate a string of 1578 this format. 1580 10.2. Resource ID 1582 A Resource ID uniquely identifies an particular resource (e.g., a 1583 Network Map) within an ALTO Server (see Section 9.2). 1585 A Resource ID is encoded as a US-ASCII string with the same format as 1586 that of PIDName. 1588 The type 'ResourceID' is used in this document to indicate a string 1589 of this format. 1591 10.3. Version Tag 1593 A Version Tag is defined as: 1595 object { 1596 ResourceID resource-id; 1597 JSONString tag; 1598 } VersionTag; 1600 The 'resource-id' attribute is the Resource ID of a resource (e.g., a 1601 Network Map) defined in the Information Resource Directory, and 'tag' 1602 is a case-sensitive US-ASCII string. The 'tag' string MUST be no 1603 more than 64 characters, and MUST NOT contain any ASCII character 1604 below 0x21 or above 0x7E. 1606 Two values of the VersionTag are equal if and only if both the the 1607 'resource-id' attributes are byte-for-byte equal and the 'tag' 1608 attributes are byte-for-byte equal. 1610 10.4. Endpoints 1612 This section defines formats used to encode addresses for Endpoints. 1613 In a case that multiple textual representations encode the same 1614 Endpoint address or prefix (within the guidelines outlined in this 1615 document), the ALTO Protocol does not require ALTO Clients or ALTO 1616 Servers to use a particular textual representation, nor does it 1617 require that ALTO Servers reply to requests using the same textual 1618 representation used by requesting ALTO Clients. ALTO Clients must be 1619 cognizant of this. 1621 10.4.1. Address Type 1623 Address Types are encoded as US-ASCII strings consisting of only 1624 alphanumeric characters (code points 0x30-0x39, 0x41-0x5A, and 0x61- 1625 0x7A). This document defines the address type 'ipv4' to refer to 1626 IPv4 addresses, and 'ipv6' to refer to IPv6 addresses. All Address 1627 Type identifiers appearing in an HTTP request or response with an 1628 'application/alto-*' media type MUST be registered in the ALTO 1629 Address Type registry (see Section 14.4). 1631 The type 'AddressType' is used in this document to indicate a string 1632 of this format. 1634 10.4.2. Endpoint Address 1636 Endpoint Addresses are encoded as US-ASCII strings. The exact 1637 characters and format depend on the type of endpoint address. 1639 The type 'EndpointAddr' is used in this document to indicate a string 1640 of this format. 1642 10.4.2.1. IPv4 1644 IPv4 Endpoint Addresses are encoded as specified by the 'IPv4address' 1645 rule in Section 3.2.2 of [RFC3986]. 1647 10.4.2.2. IPv6 1649 IPv6 Endpoint Addresses are encoded as specified in Section 4 of 1650 [RFC5952]. 1652 10.4.2.3. Typed Endpoint Addresses 1654 When an Endpoint Address is used, an ALTO implementation must be able 1655 to determine its type. For this purpose, the ALTO Protocol allows 1656 endpoint addresses to also explicitly indicate their type. 1658 Typed Endpoint Addresses are encoded as US-ASCII strings of the 1659 format 'AddressType:EndpointAddr' (with the ':' character as a 1660 separator). The type 'TypedEndpointAddr' is used to indicate a 1661 string of this format. 1663 10.4.3. Endpoint Prefixes 1665 For efficiency, it is useful to denote a set of Endpoint Addresses 1666 using a special notation (if one exists). This specification makes 1667 use of the prefix notations for both IPv4 and IPv6 for this purpose. 1669 Endpoint Prefixes are encoded as US-ASCII strings. The exact 1670 characters and format depend on the type of endpoint address. 1672 The type 'EndpointPrefix' is used in this document to indicate a 1673 string of this format. 1675 10.4.3.1. IPv4 1677 IPv4 Endpoint Prefixes are encoded as specified in Section 3.1 of 1678 [RFC4632]. 1680 10.4.3.2. IPv6 1682 IPv6 Endpoint Prefixes are encoded as specified in Section 7 of 1683 [RFC5952]. 1685 10.4.4. Endpoint Address Group 1687 The ALTO Protocol includes messages that specify potentially large 1688 sets of endpoint addresses. Endpoint Address Groups provide a more 1689 efficient way to encode such sets, even when the set contains 1690 endpoint addresses of different types. 1692 An Endpoint Address Group is defined as: 1694 object-map { 1695 AddressType -> EndpointPrefix<0..*>; 1696 } EndpointAddrGroup; 1698 In particular, an Endpoint Address Group is a JSON object 1699 representing a map, where each key is the string corresponding to an 1700 address type, and the corresponding value is an array listing 1701 prefixes of addresses of that type. 1703 The following is an example with both IPv4 and IPv6 endpoint 1704 addresses: 1706 { 1707 "ipv4": [ 1708 "192.0.2.0/24", 1709 "198.51.100.0/25" 1710 ], 1711 "ipv6": [ 1712 "2001:db8:0:1::/64", 1713 "2001:db8:0:2::/64" 1715 ] 1716 } 1718 10.5. Cost Mode 1720 A Cost Mode is encoded as a US-ASCII string. The string MUST either 1721 have the value 'numerical' or 'ordinal'. 1723 The type 'CostMode' is used in this document to indicate a string of 1724 this format. 1726 10.6. Cost Metric 1728 A Cost Metric is encoded as a US-ASCII string. The string MUST be no 1729 more than 32 characters, and MUST NOT contain characters other than 1730 alphanumeric characters (code points 0x30-0x39, 0x41-0x5A, and 0x61- 1731 0x7A), the hyphen ('-', code point 0x2D), the colon (':', code point 1732 0x3A), the underline ('_', code point 0x5F), or the '.' separator 1733 (0x2E). The '.' separator is reserved for future use and MUST NOT be 1734 used unless specifically indicated by a companion or extension 1735 document. 1737 Identifiers prefixed with 'priv:' are reserved for Private Use 1738 [RFC5226]. Identifiers prefixed with 'exp:' are reserved for 1739 Experimental use. For an identifier with the 'priv:' or 'exp:' 1740 prefix, an additional string (e.g., company identifier or random 1741 string) MUST follow to reduce potential collisions. For example, a 1742 short string after 'exp:' to indicate the starting time of a specific 1743 experiment is recommended. All other identifiers that appear in an 1744 HTTP request or response with an 'application/alto-*' media type and 1745 indicate Cost Metrics MUST be registered in the ALTO Cost Metrics 1746 registry Section 14.2. 1748 The type 'CostMetric' is used in this document to indicate a string 1749 of this format. 1751 10.7. Cost Type 1753 The combination of a CostMetric and a CostMode defines a CostType: 1755 object { 1756 CostMetric cost-metric; 1757 CostMode cost-mode; 1758 [JSONString description;] 1759 } CostType; 1760 'description', if present, MUST contain a US-ASCII string with a 1761 human-readable description of the cost-metric and cost-mode. An ALTO 1762 Client MAY present this string to a developer, as part of a discovery 1763 process. But the field SHOULD NOT be interpreted by an ALTO Client. 1765 10.8. Endpoint Property 1767 We distinguish two types of Endpoint Properties: Resource Specific 1768 Endpoint Properties and Global Endpoint Properties. The type 1769 'EndpointPropertyType' is used in this document to indicate a US- 1770 ASCII string denoting either a Resource Specific Endpoint Property or 1771 a Global Endpoint Property. 1773 10.8.1. Resource Specific Endpoint Properties 1775 We define only one Resource Specific Endpoint Property in this 1776 document: pid. It has the following format: a Resource ID, followed 1777 by the '.' separator (0x2E), followed by "pid". An example is "my- 1778 default-networkmap.pid". 1780 10.8.2. Global Endpoint Properties 1782 An Global Endpoint Property is encoded as a US-ASCII string. The 1783 string MUST be no more than 32 characters, and MUST NOT contain 1784 characters other than alphanumeric characters (code points 0x30-0x39, 1785 0x41-0x5A, and 0x61-0x7A), the hyphen ('-', code point 0x2D), the 1786 colon (':', code point 0x3A), or the underline ('_', code point 1787 0x5F). Note that the '.' separator is not allowed so that there is 1788 no ambiguity on whether an endpoint property is global or resource 1789 specific. 1791 Identifiers prefixed with 'priv:' are reserved for Private Use 1792 [RFC5226]. Identifiers prefixed with 'exp:' are reserved for 1793 Experimental use. For an identifier with the 'priv:' or 'exp:' 1794 prefix, an additional string (e.g., company identifier or random 1795 string) MUST follow to reduce potential collisions. For example, a 1796 short string after 'exp:' to indicate the starting time of a specific 1797 experiment is recommended. All other identifiers for Endpoint 1798 Properties appearing in an HTTP request or response with an 1799 'application/alto-*' media type MUST be registered in the ALTO 1800 Endpoint Property registry Section 14.3. 1802 11. Protocol Specification: Service Information Resources 1804 This section documents the individual Information Resources defined 1805 to provide the services defined in this document. 1807 11.1. Meta Information 1809 For the "meta" field of the response to an individual Information 1810 Resource, we define two generic keys: "vtag", which is the Version 1811 Tag of the current Information Resource; and "dependent-vtags", which 1812 is an array of Version Tags, to indicate the Version Tags of the 1813 resources that this resource depends on. 1815 11.2. Map Service 1817 The Map Service provides batch information to ALTO Clients in the 1818 form of two types of maps: a Network Map and Cost Map. 1820 11.2.1. Network Map 1822 A Network Map Information Resource defines a set of PIDs, and for 1823 each PID, lists the network locations (endpoints) within the PID. An 1824 ALTO Server MUST provide at least one Network Map. 1826 11.2.1.1. Media Type 1828 The media type of Network Map is "application/alto-networkmap+json". 1830 11.2.1.2. HTTP Method 1832 A Network Map resource is requested using the HTTP GET method. 1834 11.2.1.3. Accept Input Parameters 1836 None. 1838 11.2.1.4. Capabilities 1840 None. 1842 11.2.1.5. Uses 1844 None. 1846 11.2.1.6. Response 1848 The "meta" field of a Network Map response MUST include "vtag", which 1849 is the Version Tag of the retrieved Network Map. 1851 The data component of a Network Map response is named "network-map", 1852 which is a JSON object of type NetworkMapData: 1854 object { 1855 NetworkMapData network-map; 1856 } InfoResourceNetworkMap : ResponseEntityBase; 1858 object-map { 1859 PIDName -> EndpointAddrGroup; 1860 } NetworkMapData; 1862 Specifically, a NetworkMapData object is a dictionary map keyed by 1863 PIDs, and each value representing the associated set of endpoint 1864 addresses of a PID. 1866 The returned Network Map MUST include all PIDs known to the ALTO 1867 Server. 1869 11.2.1.7. Example 1871 GET /networkmap HTTP/1.1 1872 Host: alto.example.com 1873 Accept: application/alto-networkmap+json,application/alto-error+json 1874 HTTP/1.1 200 OK 1875 Content-Length: TBA 1876 Content-Type: application/alto-networkmap+json 1878 { 1879 "meta" : { 1880 "vtag": [ 1881 {"resource-id": "my-default-network-map", 1882 "tag": "1266506139" 1883 } 1884 ] 1885 }, 1886 "network-map" : { 1887 "PID1" : { 1888 "ipv4" : [ 1889 "192.0.2.0/24", 1890 "198.51.100.0/25" 1891 ] 1892 }, 1893 "PID2" : { 1894 "ipv4" : [ 1895 "198.51.100.128/25" 1896 ] 1897 }, 1898 "PID3" : { 1899 "ipv4" : [ 1900 "0.0.0.0/0" 1901 ], 1902 "ipv6" : [ 1903 "::/0" 1904 ] 1905 } 1906 } 1907 } 1909 Note that the encoding of a Network Map response was chosen for 1910 readability and compactness. If lookup efficiency at runtime is 1911 crucial, then the returned Network Map can be transformed into data 1912 structures offering more efficient lookup. For example, one may 1913 store the Network Map as a trie-based data structure, which may allow 1914 efficient longest-prefix matching of IP addresses. 1916 11.2.2. Cost Map 1918 A Cost Map resource lists the Path Cost for each pair of source/ 1919 destination PID defined by the ALTO Server for a given Cost Metric 1920 and Cost Mode. This resource MUST be provided for at least the 1921 'routingcost' Cost Metric. 1923 11.2.2.1. Media Type 1925 The media type of Cost Map is "application/alto-costmap+json". 1927 11.2.2.2. HTTP Method 1929 A Cost Map resource is requested using the HTTP GET method. 1931 11.2.2.3. Accept Input Parameters 1933 None. 1935 11.2.2.4. Capabilities 1937 The capabilities of an ALTO Server URI providing an unfiltered cost 1938 map is a JSON Object of type CostMapCapabilities: 1940 object { 1941 JSONString cost-type-names<1..1>; 1942 } CostMapCapabilities; 1944 with field: 1946 cost-type-names Note that the array MUST include a single CostType 1947 name defined by key "cost-types" in "meta" of the IRD. This is 1948 because an unfiltered Cost Map (accept == "") is requested via an 1949 HTTP GET that accepts no input parameters. As a contrast, for 1950 filtered cost maps (see Section 11.3.2), the array can have 1951 multiple elements. 1953 11.2.2.5. Uses 1955 The Resource ID of the Network Map based on which the Cost Map will 1956 be defined. Recall (Section 6) that the combination of a Network Map 1957 and a CostType defines a key. In other words, an ALTO Server MUST 1958 NOT define two Cost Maps with the same Cost Type, Network Map pair. 1960 11.2.2.6. Response 1962 The "meta" field of a Cost Map response MUST include the "dependent- 1963 vtags" key, whose value is a single-element array to indicate the 1964 Version Tag of the Network Map used, where the Network Map is 1965 specified in "uses" of the IRD. The "meta" MUST also include "cost- 1966 type", to indicate the Cost Type (Section 10.7) of the Cost Map. 1968 The data component of a Cost Map response is named "cost-map", which 1969 is a JSON object of type CostMapData: 1971 object { 1972 CostMapData cost-map; 1973 } InfoResourceCostMap : ResponseEntityBase; 1975 object-map { 1976 PIDName -> DstCosts; 1977 } CostMapData; 1979 object-map { 1980 PIDName -> JSONValue; 1981 } DstCosts; 1983 Specifically, a CostMapData object is a dictionary map object, with 1984 each key being the PIDName string identifying the corresponding 1985 Source PID, and value being a type of DstCosts, which denotes the 1986 associated costs from the Source PID to a set of destination PIDs ( 1987 Section 6.2). An implementation of the protocol in this document 1988 SHOULD assume that the cost is a JSONNumber and fail to parse if it 1989 is not, unless the implementation is using an extension to this 1990 document that indicates when and how costs of other data types are 1991 signaled. 1993 The returned Cost Map MUST include the Path Cost for each (Source 1994 PID, Destination PID) pair for which a Path Cost is defined. An ALTO 1995 Server MAY omit entries for which a Path Cost is not defined (e.g., 1996 both the Source and Destination PIDs contain addresses outside of the 1997 Network Provider's administrative domain). 1999 Similar to Network Map, the encoding of Cost Map was chosen for 2000 readability and compactness. If lookup efficiency at runtime is 2001 crucial, then the returned Cost Map can be transformed into data 2002 structures offering more efficient lookup. For example, one may 2003 store a Cost Map as a matrix. 2005 11.2.2.7. Example 2007 GET /costmap/num/routingcost HTTP/1.1 2008 Host: alto.example.com 2009 Accept: application/alto-costmap+json,application/alto-error+json 2010 HTTP/1.1 200 OK 2011 Content-Length: TBA 2012 Content-Type: application/alto-costmap+json 2014 { 2015 "meta" : { 2016 "dependent-vtags" : [ 2017 {"resource-id": "my-default-network-map", 2018 "tag": "1266506139" 2019 } 2020 ], 2021 "cost-type" : {"cost-mode" : "numerical", 2022 "cost-metric": "routingcost" 2023 } 2024 }, 2025 "cost-map" : { 2026 "PID1": { "PID1": 1, "PID2": 5, "PID3": 10 }, 2027 "PID2": { "PID1": 5, "PID2": 1, "PID3": 15 }, 2028 "PID3": { "PID1": 20, "PID2": 15 } 2029 } 2030 } 2032 Similar to the Network Map case, we considered array-based encoding 2033 for "map", but chose the current encoding for clarity. 2035 11.3. Map Filtering Service 2037 The Map Filtering Service allows ALTO Clients to specify filtering 2038 criteria to return a subset of the full maps available in the Map 2039 Service. 2041 11.3.1. Filtered Network Map 2043 A Filtered Network Map is a Network Map Information Resource 2044 (Section 11.2.1) for which an ALTO Client may supply a list of PIDs 2045 to be included. A Filtered Network Map MAY be provided by an ALTO 2046 Server. 2048 11.3.1.1. Media Type 2050 Since a Filtered Network Map is still a Network Map, it uses the 2051 media type defined for Network Map at Section 11.2.1.1. 2053 11.3.1.2. HTTP Method 2055 A Filtered Network Map is requested using the HTTP POST method. 2057 11.3.1.3. Accept Input Parameters 2059 An ALTO Client supplies filtering parameters by specifying media type 2060 "application/alto-networkmapfilter+json" with HTTP POST body 2061 containing a JSON Object of type ReqFilteredNetworkMap, where: 2063 object { 2064 PIDName pids<0..*>; 2065 [AddressType address-types<0..*>;] 2066 } ReqFilteredNetworkMap; 2068 with fields: 2070 pids Specifies list of PIDs to be included in the returned Filtered 2071 Network Map. If the list of PIDs is empty, the ALTO Server MUST 2072 interpret the list as if it contained a list of all currently- 2073 defined PIDs. The ALTO Server MUST interpret entries appearing 2074 multiple times as if they appeared only once. 2076 address-types Specifies list of address types to be included in the 2077 returned Filtered Network Map. If the "address-types" field is not 2078 specified, or the list of address types is empty, the ALTO Server 2079 MUST interpret the list as if it contained a list of all address 2080 types known to the ALTO Server. The ALTO Server MUST interpret 2081 entries appearing multiple times as if they appeared only once. 2083 11.3.1.4. Capabilities 2085 None. 2087 11.3.1.5. Uses 2089 The Resource ID of the Network Map based on which the filtering is 2090 performed. 2092 11.3.1.6. Response 2094 The format is the same as unfiltered Network Map. See 2095 Section 11.2.1.6 for the format. 2097 The ALTO Server MUST only include PIDs in the response that were 2098 specified (implicitly or explicitly) in the request. If the input 2099 parameters contain a PID name that is not currently defined by the 2100 ALTO Server, the ALTO Server MUST behave as if the PID did not appear 2101 in the input parameters. Similarly, the ALTO Server MUST only 2102 enumerate addresses within each PID that have types which were 2103 specified (implicitly or explicitly) in the request. If the input 2104 parameters contain an address type that is not currently known to the 2105 ALTO Server, the ALTO Server MUST behave as if the address type did 2106 not appear in the input parameters. 2108 The Version Tag included in the "vtag" of the response MUST 2109 correspond to the full (unfiltered) Network Map Information Resource 2110 from which the filtered information is provided. This ensures that a 2111 single, canonical Version Tag is used independent of any filtering 2112 that is requested by an ALTO Client. 2114 11.3.1.7. Example 2116 POST /networkmap/filtered HTTP/1.1 2117 Host: custom.alto.example.com 2118 Content-Length: TBA 2119 Content-Type: application/alto-networkmapfilter+json 2120 Accept: application/alto-networkmap+json,application/alto-error+json 2122 { 2123 "pids": [ "PID1", "PID2" ] 2124 } 2126 HTTP/1.1 200 OK 2127 Content-Length: TBA 2128 Content-Type: application/alto-networkmap+json 2130 { 2131 "meta" : { 2132 "vtag" : [ 2133 {"resource-id": "my-default-network-map", 2134 "tag": "1266506139" 2135 } 2136 ] 2137 }, 2138 "network-map" : { 2139 "PID1" : { 2140 "ipv4" : [ 2141 "192.0.2.0/24", 2142 "198.51.100.0/24" 2143 ] 2144 }, 2145 "PID2" : { 2146 "ipv4": [ 2147 "198.51.100.128/24" 2148 ] 2149 } 2150 } 2151 } 2153 11.3.2. Filtered Cost Map 2155 A Filtered Cost Map is a Cost Map Information Resource 2156 (Section 11.2.2) for which an ALTO Client may supply additional 2157 parameters limiting the scope of the resulting Cost Map. A Filtered 2158 Cost Map MAY be provided by an ALTO Server. 2160 11.3.2.1. Media Type 2162 Since a Filtered Cost Map is still a Cost Map, it uses the media type 2163 defined for Cost Map at Section 11.2.2.1. 2165 11.3.2.2. HTTP Method 2167 A Filtered Cost Map is requested using the HTTP POST method. 2169 11.3.2.3. Accept Input Parameters 2171 The input parameters for a Filtered Map are supplied in the entity 2172 body of the POST request. This document specifies the input 2173 parameters with a data format indicated by the media type 2174 "application/alto-costmapfilter+json", which is a JSON Object of type 2175 ReqFilteredCostMap, where: 2177 object { 2178 CostType cost-type; 2179 [JSONString constraints<0..*>;] 2180 [PIDFilter pids;] 2181 } ReqFilteredCostMap; 2183 object { 2184 PIDName srcs<0..*>; 2185 PIDName dsts<0..*>; 2186 } PIDFilter; 2188 with fields: 2190 cost-type The CostType (Section 10.7) for the returned costs. The 2191 cost-metric and cost-mode fields MUST match one of the supported 2192 Cost Types indicated in this resource's capabilities 2193 (Section 11.3.2.4). The ALTO Client SHOULD omit the description 2194 field, and if present, the ALTO Server MUST ignore the description 2195 field. 2197 constraints Defines a list of additional constraints on which 2198 elements of the Cost Map are returned. This parameter MUST NOT be 2199 specified if this resource's capabilities ( Section 11.3.2.4) 2200 indicate that constraint support is not available. A constraint 2201 contains two entities separated by whitespace: (1) an operator, 2202 'gt' for greater than, 'lt' for less than, 'ge' for greater than 2203 or equal to, 'le' for less than or equal to, or 'eq' for equal to; 2204 (2) a target cost value. The cost value is a number that MUST be 2205 defined in the same units as the Cost Metric indicated by the 2206 cost-metric parameter. ALTO Servers SHOULD use at least IEEE 754 2207 double-precision floating point [IEEE.754.2008] to store the cost 2208 value, and SHOULD perform internal computations using double- 2209 precision floating-point arithmetic. If multiple 'constraint' 2210 parameters are specified, they are interpreted as being related to 2211 each other with a logical AND. 2213 pids A list of Source PIDs and a list of Destination PIDs for which 2214 Path Costs are to be returned. If a list is empty, the ALTO 2215 Server MUST interpret it as the full set of currently-defined 2216 PIDs. The ALTO Server MUST interpret entries appearing in a list 2217 multiple times as if they appeared only once. If the "pids" field 2218 is not present, both lists MUST be interpreted by the ALTO Server 2219 as containing the full set of currently-defined PIDs. 2221 11.3.2.4. Capabilities 2223 The URI providing this resource supports all capabilities documented 2224 in Section 11.2.2.4 (with identical semantics), plus additional 2225 capabilities. In particular, the capabilities are defined by a JSON 2226 object of type FilteredCostMapCapabilities: 2228 object { 2229 JSONString cost-type-names<1..*>; 2230 JSONBool cost-constraints; 2231 } FilteredCostMapCapabilities; 2233 with fields: 2235 cost-type-names See Section 11.2.2.4 and note that the array can 2236 have 1 to many cost types. 2238 cost-constraints If true, then the ALTO Server allows cost 2239 constraints to be included in requests to the corresponding URI. 2240 If not present, this field MUST be interpreted as if it specified 2241 false. ALTO Clients should be aware that constraints may not have 2242 the intended effect for cost maps with the 'ordinal' Cost Mode 2243 since ordinal costs are not restricted to being sequential 2244 integers. 2246 11.3.2.5. Uses 2248 The Resource ID of the Network Map based on which the Cost Map will 2249 be filtered. 2251 11.3.2.6. Response 2253 The format is the same as an unfiltered Cost Map. See 2254 Section 11.2.2.6 for the format. 2256 The "dependent-vtags" key in the "meta" field specifies a single 2257 element, which is the Version Tag of the Network Map used in 2258 filtering. ALTO Clients should verify that the Version Tag included 2259 in the response is consistent with the Version Tag of the Network Map 2260 used to generate the request (if applicable). If it is not, the ALTO 2261 Client may wish to request an updated Network Map, identify changes, 2262 and consider requesting a new Filtered Cost Map. 2264 The returned Cost Map MUST contain only source/destination pairs that 2265 have been indicated (implicitly or explicitly) in the input 2266 parameters. If the input parameters contain a PID name that is not 2267 currently defined by the ALTO Server, the ALTO Server MUST behave as 2268 if the PID did not appear in the input parameters. 2270 If any constraints are specified, Source/Destination pairs for which 2271 the Path Costs do not meet the constraints MUST NOT be included in 2272 the returned Cost Map. If no constraints were specified, then all 2273 Path Costs are assumed to meet the constraints. 2275 11.3.2.7. Example 2277 POST /costmap/filtered HTTP/1.1 2278 Host: custom.alto.example.com 2279 Content-Type: application/alto-costmapfilter+json 2280 Accept: application/alto-costmap+json,application/alto-error+json 2282 { 2283 "cost-type" : {"cost-mode": "numerical", 2284 "cost-metric": "routingcost" 2285 }, 2286 "pids" : { 2287 "srcs" : [ "PID1" ], 2288 "dsts" : [ "PID1", "PID2", "PID3" ] 2289 } 2290 } 2292 HTTP/1.1 200 OK 2293 Content-Length: TBA 2294 Content-Type: application/alto-costmap+json 2296 { 2297 "meta" : { 2298 "dependent-vtags" : [ 2299 {"resource-id": "my-default-network-map", 2300 "tag": "1266506139" 2301 } 2302 ], 2303 "cost-type": {"cost-mode" : "numerical", 2304 "cost-metric" : "routingcost" 2305 } 2306 }, 2307 "cost-map" : { 2308 "PID1": { "PID1": 0, "PID2": 1, "PID3": 2 } 2309 } 2310 } 2312 11.4. Endpoint Property Service 2314 The Endpoint Property Service provides information about Endpoint 2315 properties to ALTO Clients. 2317 11.4.1. Endpoint Property 2319 An Endpoint Property resource provides information about properties 2320 for individual endpoints. It MAY be provided by an ALTO Server. 2322 11.4.1.1. Media Type 2324 The media type of Endpoint Property is "application/ 2325 alto-endpointprop+json". 2327 11.4.1.2. HTTP Method 2329 The Endpoint Property resource is requested using the HTTP POST 2330 method. 2332 11.4.1.3. Accept Input Parameters 2334 An ALTO Client supplies the endpoint properties to be queried through 2335 a media type "application/alto-endpointpropparams+json", and 2336 specifies in the HTTP POST entity body a JSON Object of type 2337 ReqEndpointProp: 2339 object { 2340 EndpointPropertyType properties<1..*>; 2341 TypedEndpointAddr endpoints<1..*>; 2342 } ReqEndpointProp; 2344 with fields: 2346 properties List of endpoint properties to be returned for each 2347 endpoint. Each specified property MUST be included in the list of 2348 supported properties indicated by this resource's capabilities 2349 (Section 11.4.1.4). The ALTO Server MUST interpret entries 2350 appearing multiple times as if they appeared only once. 2352 endpoints List of endpoint addresses for which the specified 2353 properties are to be returned. The ALTO Server MUST interpret 2354 entries appearing multiple times as if they appeared only once. 2356 11.4.1.4. Capabilities 2358 This resource may be defined across multiple types of endpoint 2359 properties. The capabilities of an ALTO Server URI providing 2360 Endpoint Properties are defined by a JSON Object of type 2361 EndpointPropertyCapabilities: 2363 object { 2364 EndpointPropertyType prop-types<1..*>; 2365 } EndpointPropertyCapabilities; 2367 with field: 2369 prop-types The Endpoint Properties (see Section 10.8) supported by 2370 the corresponding URI. 2372 In particular, the Information Resource Closure MUST provide the look 2373 up of pid for every Network Map defined. 2375 11.4.1.5. Uses 2377 None. 2379 11.4.1.6. Response 2381 The "dependent-vtags" key in the "meta" field of the response MUST 2382 include the Version Tags of all Network Maps whose 'pid' is queried. 2384 The data component of an Endpoint Properties response is named 2385 "endpoint-properties", which is a JSON object of type 2386 EndpointPropertyMapData, where: 2388 object { 2389 EndpointPropertyMapData endpoint-properties; 2390 } InfoResourceEndpointProperties : ResponseEntityBase; 2392 object-map { 2393 TypedEndpointAddr -> EndpointProps; 2394 } EndpointPropertyMapData; 2396 object { 2397 EndpointPropertyType -> JSONValue; 2398 } EndpointProps; 2400 Specifically, an EndpointPropertyMapData object has one member for 2401 each endpoint indicated in the input parameters (with the name being 2402 the endpoint encoded as a TypedEndpointAddr). The requested 2403 properties for each endpoint are encoded in a corresponding 2404 EndpointProps object, which encodes one name/value pair for each 2405 requested property, where the property names are encoded as strings 2406 of type EndpointPropertyType. An implementation of the protocol in 2407 this document SHOULD assume that the property value is a JSONString 2408 and fail to parse if it is not, unless the implementation is using an 2409 extension to this document that indicates when and how property 2410 values of other data types are signaled. 2412 The ALTO Server returns the value for each of the requested endpoint 2413 properties for each of the endpoints listed in the input parameters. 2415 If the ALTO Server does not define a requested property's value for a 2416 particular endpoint, then it MUST omit that property from the 2417 response for only that endpoint. 2419 11.4.1.7. Example 2421 POST /endpointprop/lookup HTTP/1.1 2422 Host: alto.example.com 2423 Content-Length: TBA 2424 Content-Type: application/alto-endpointpropparams+json 2425 Accept: application/alto-endpointprop+json,application/alto-error+json 2427 { 2428 "properties" : [ "my-default-networkmap.pid", 2429 "priv:ietf-example-prop" ], 2430 "endpoints" : [ "ipv4:192.0.2.34", 2431 "ipv4:203.0.113.129" ] 2432 } 2434 HTTP/1.1 200 OK 2435 Content-Length: TBA 2436 Content-Type: application/alto-endpointprop+json 2438 { 2439 "meta" : { 2440 "dependent-vtags" : [ 2441 {"resource-id": "my-default-network-map", 2442 "tag": "1266506139" 2443 } 2444 ] 2445 }, 2446 "endpoint-properties": { 2447 "ipv4:192.0.2.34" : { "my-default-network-map.pid": "PID1", 2448 "priv:ietf-example-prop": "1" }, 2449 "ipv4:203.0.113.129" : { "my-default-network-map.pid": "PID3" } 2450 } 2451 } 2453 11.5. Endpoint Cost Service 2455 The Endpoint Cost Service provides information about costs between 2456 individual endpoints. 2458 In particular, this service allows lists of Endpoint prefixes (and 2459 addresses, as a special case) to be ranked (ordered) by an ALTO 2460 Server. 2462 11.5.1. Endpoint Cost 2464 An Endpoint Cost resource provides information about costs between 2465 individual endpoints. It MAY be provided by an ALTO Server. 2467 It is important to note that although this resource allows an ALTO 2468 Server to reveal costs between individual endpoints, an ALTO Server 2469 is not required to do so. A simple alternative would be to compute 2470 the cost between two endpoints as the cost between the PIDs 2471 corresponding to the endpoints. See Section 15.3 for additional 2472 details. 2474 11.5.1.1. Media Type 2476 The media type of Endpoint Cost is "application/ 2477 alto-endpointcost+json". 2479 11.5.1.2. HTTP Method 2481 The Endpoint Cost resource is requested using the HTTP POST method. 2483 11.5.1.3. Accept Input Parameters 2485 An ALTO Client supplies the endpoint cost parameters through a media 2486 type "application/alto-endpointcostparams+json", with an HTTP POST 2487 entity body of a JSON Object of type ReqEndpointCostMap: 2489 object { 2490 CostType cost-type; 2491 [JSONString constraints<0..*>;] 2492 EndpointFilter endpoints; 2493 } ReqEndpointCostMap; 2495 object { 2496 [TypedEndpointAddr srcs<0..*>;] 2497 [TypedEndpointAddr dsts<0..*>;] 2498 } EndpointFilter; 2499 with fields: 2501 cost-type The Cost Type (Section 10.7) to use for returned costs. 2502 The cost-metric and cost-mode fields MUST match one of the 2503 supported Cost Types indicated in this resource's capabilities ( 2504 Section 11.5.1.4). The ALTO Client SHOULD omit the description 2505 field, and if present, the ALTO Server MUST ignore the description 2506 field. 2508 constraints Defined equivalently to the "constraints" input 2509 parameter of a Filtered Cost Map (see Section 11.3.2). 2511 endpoints A list of Source Endpoints and Destination Endpoints for 2512 which Path Costs are to be returned. If the list of Source or 2513 Destination Endpoints is empty (or not included), the ALTO Server 2514 MUST interpret it as if it contained the Endpoint Address 2515 corresponding to the client IP address from the incoming 2516 connection (see Section 13.3 for discussion and considerations 2517 regarding this mode). The Source and Destination Endpoint lists 2518 MUST NOT be both empty. The ALTO Server MUST interpret entries 2519 appearing multiple times in a list as if they appeared only once. 2521 11.5.1.4. Capabilities 2523 In this document, we define EndpointCostCapabilities the same as 2524 FilteredCostMapCapabilities. See Section 11.3.2.4. 2526 11.5.1.5. Uses 2528 It is important to note that although this resource allows an ALTO 2529 Server to reveal costs between individual endpoints, an ALTO Server 2530 is not required to do so. A simple implementation of an ECS resource 2531 may compute the cost between two endpoints as the cost between the 2532 PIDs corresponding to the endpoints, using one of the exposed network 2533 and cost maps defined by the server. However, to preserve 2534 flexibility, the ECS resource MAY omit declaring in the "uses" 2535 attribute the network map and/or cost map on which it depends. 2537 11.5.1.6. Response 2539 The "meta" field of an Endpoint Cost response MUST include the "cost- 2540 type" key, to indicate the Cost Type used. 2542 The data component of an Endpoint Cost response is named "endpoint- 2543 cost-map", which is a JSON object of type EndpointCostMapData: 2545 object { 2546 EndpointCostMapData endpoint-cost-map; 2547 } InfoResourceEndpointCostMap : ResponseEntityBase; 2549 object-map { 2550 TypedEndpointAddr -> EndpointDstCosts; 2551 } EndpointCostMapData; 2553 object-map { 2554 TypedEndpointAddr -> JSONValue; 2555 } EndpointDstCosts; 2557 Specifically, an EndpointCostMapData object is a dictionary map with 2558 each key representing a TypedEndpointAddr string identifying the 2559 Source Endpoint specified in the input parameters. For each Source 2560 Endpoint, a EndpointDstCosts dictionary map object denotes the 2561 associated cost to each Destination Endpoint specified in input 2562 parameters. An implementation of the protocol in this document 2563 SHOULD assume that the cost value is a JSONNumber and fail to parse 2564 if it is not, unless the implementation is using an extension to this 2565 document that indicates when and how costs of other data types are 2566 signaled. If the ALTO Server does not define a cost value from a 2567 Source Endpoint to a particular Destination Endpoint, it MAY be 2568 omitted from the response. 2570 11.5.1.7. Example 2572 POST /endpointcost/lookup HTTP/1.1 2573 Host: alto.example.com 2574 Content-Length: TBA 2575 Content-Type: application/alto-endpointcostparams+json 2576 Accept: application/alto-endpointcost+json,application/alto-error+json 2578 { 2579 "cost-type": {"cost-mode" : "ordinal", 2580 "cost-metric" : "routingcost"}, 2581 "endpoints" : { 2582 "srcs": [ "ipv4:192.0.2.2" ], 2583 "dsts": [ 2584 "ipv4:192.0.2.89", 2585 "ipv4:198.51.100.34", 2586 "ipv4:203.0.113.45" 2587 ] 2588 } 2589 } 2591 HTTP/1.1 200 OK 2592 Content-Length: TBA 2593 Content-Type: application/alto-endpointcost+json 2595 { 2596 "meta" : { 2597 "cost-type": {"cost-mode" : "ordinal", 2598 "cost-metric" : "routingcost" 2599 } 2600 }, 2601 "endpoint-cost-map" : { 2602 "ipv4:192.0.2.2": { 2603 "ipv4:192.0.2.89" : 1, 2604 "ipv4:198.51.100.34" : 2, 2605 "ipv4:203.0.113.45" : 3 2606 } 2607 } 2608 } 2610 12. Use Cases 2612 The sections below depict typical use cases. While these use cases 2613 focus on peer-to-peer applications, ALTO can be applied to other 2614 environments such as CDNs [I-D.jenkins-alto-cdn-use-cases]. 2616 12.1. ALTO Client Embedded in P2P Tracker 2618 Many currently-deployed P2P systems use a Tracker to manage swarms 2619 and perform peer selection. Such a P2P Tracker can already use a 2620 variety of information to perform peer selection to meet application- 2621 specific goals. By acting as an ALTO Client, the P2P Tracker can use 2622 ALTO information as an additional information source to enable more 2623 network-efficient traffic patterns and improve application 2624 performance. 2626 A particular requirement of many P2P trackers is that they must 2627 handle a large number of P2P clients. A P2P tracker can obtain and 2628 locally store ALTO information (the Network Map and Cost Map) from 2629 the ISPs containing the P2P clients, and benefit from the same 2630 aggregation of network locations done by ALTO Servers. 2632 .---------. (1) Get Network Map .---------------. 2633 | | <----------------------> | | 2634 | ALTO | | P2P Tracker | 2635 | Server | (2) Get Cost Map | (ALTO Client) | 2636 | | <----------------------> | | 2637 `---------' `---------------' 2638 ^ | 2639 (3) Get Peers | | (4) Selected Peer 2640 | v List 2641 .---------. .-----------. 2642 | Peer 1 | <-------------- | P2P | 2643 `---------' | Client | 2644 . (5) Connect to `-----------' 2645 . Selected Peers / 2646 .---------. / 2647 | Peer 50 | <------------------ 2648 `---------' 2650 Figure 4: ALTO Client Embedded in P2P Tracker 2652 Figure 4 shows an example use case where a P2P tracker is an ALTO 2653 Client and applies ALTO information when selecting peers for its P2P 2654 clients. The example proceeds as follows: 2656 1. The P2P Tracker requests from the ALTO Server using the Network 2657 Map query the Network Map covering all PIDs. The Network Map 2658 includes the IP prefixes contained in each PID, allowing the P2P 2659 tracker to locally map P2P clients into PIDs. 2661 2. The P2P Tracker requests from the ALTO Server the Cost Map 2662 amongst all PIDs identified in the preceding step. 2664 3. A P2P Client joins the swarm, and requests a peer list from the 2665 P2P Tracker. 2667 4. The P2P Tracker returns a peer list to the P2P client. The 2668 returned peer list is computed based on the Network Map and Cost 2669 Map returned by the ALTO Server, and possibly other information 2670 sources. Note that it is possible that a tracker may use only 2671 the Network Map to implement hierarchical peer selection by 2672 preferring peers within the same PID and ISP. 2674 5. The P2P Client connects to the selected peers. 2676 Note that the P2P tracker may provide peer lists to P2P clients 2677 distributed across multiple ISPs. In such a case, the P2P tracker 2678 may communicate with multiple ALTO Servers. 2680 12.2. ALTO Client Embedded in P2P Client: Numerical Costs 2682 P2P clients may also utilize ALTO information themselves when 2683 selecting from available peers. It is important to note that not all 2684 P2P systems use a P2P tracker for peer discovery and selection. 2685 Furthermore, even when a P2P tracker is used, the P2P clients may 2686 rely on other sources, such as peer exchange and DHTs, to discover 2687 peers. 2689 When an P2P Client uses ALTO information, it typically queries only 2690 the ALTO Server servicing its own ISP. The my-Internet view provided 2691 by its ISP's ALTO Server can include preferences to all potential 2692 peers. 2694 .---------. (1) Get Network Map .---------------. 2695 | | <----------------------> | | 2696 | ALTO | | P2P Client | 2697 | Server | (2) Get Cost Map | (ALTO Client) | 2698 | | <----------------------> | | .---------. 2699 `---------' `---------------' <- | P2P | 2700 .---------. / | ^ ^ | Tracker | 2701 | Peer 1 | <-------------- | | \ `---------' 2702 `---------' | (3) Gather Peers 2703 . (4) Select Peers | | \ 2704 . and Connect / .--------. .--------. 2705 .---------. / | P2P | | DHT | 2706 | Peer 50 | <---------------- | Client | `--------' 2707 `---------' | (PEX) | 2708 `--------' 2710 Figure 5: ALTO Client Embedded in P2P Client 2712 Figure 5 shows an example use case where a P2P Client locally applies 2713 ALTO information to select peers. The use case proceeds as follows: 2715 1. The P2P Client requests the Network Map covering all PIDs from 2716 the ALTO Server servicing its own ISP. 2718 2. The P2P Client requests the Cost Map amongst all PIDs from the 2719 ALTO Server. The Cost Map by default specifies numerical costs. 2721 3. The P2P Client discovers peers from sources such as Peer Exchange 2722 (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and 2723 P2P Trackers. 2725 4. The P2P Client uses ALTO information as part of the algorithm for 2726 selecting new peers, and connects to the selected peers. 2728 12.3. ALTO Client Embedded in P2P Client: Ranking 2730 It is also possible for a P2P Client to offload the selection and 2731 ranking process to an ALTO Server. In this use case, the ALTO Client 2732 gathers a list of known peers in the swarm, and asks the ALTO Server 2733 to rank them. 2735 As in the use case using numerical costs, the P2P Client typically 2736 only queries the ALTO Server servicing its own ISP. 2738 .---------. .---------------. 2739 | | | | 2740 | ALTO | (2) Get Endpoint Ranking | P2P Client | 2741 | Server | <----------------------> | (ALTO Client) | 2742 | | | | .---------. 2743 `---------' `---------------' <- | P2P | 2744 .---------. / | ^ ^ | Tracker | 2745 | Peer 1 | <-------------- | | \ `---------' 2746 `---------' | (1) Gather Peers 2747 . (3) Connect to | | \ 2748 . Selected Peers / .--------. .--------. 2749 .---------. / | P2P | | DHT | 2750 | Peer 50 | <---------------- | Client | `--------' 2751 `---------' | (PEX) | 2752 `--------' 2754 Figure 6: ALTO Client Embedded in P2P Client: Ranking 2756 Figure 6 shows an example of this scenario. The use case proceeds as 2757 follows: 2759 1. The P2P Client discovers peers from sources such as Peer Exchange 2760 (PEX) from other P2P Clients, Distributed Hash Tables (DHT), and 2761 P2P Trackers. 2763 2. The P2P Client queries the ALTO Server's Ranking Service, 2764 including discovered peers as the set of Destination Endpoints, 2765 and indicates the 'ordinal' Cost Mode. The response indicates 2766 the ranking of the candidate peers. 2768 3. The P2P Client connects to the peers in the order specified in 2769 the ranking. 2771 13. Discussions 2773 13.1. Discovery 2775 The discovery mechanism by which an ALTO Client locates an 2776 appropriate ALTO Server is out of scope for this document. This 2777 document assumes that an ALTO Client can discover an appropriate ALTO 2778 Server. Once it has done so, the ALTO Client may use the Information 2779 Resource Directory (see Section 9.2) to locate an Information 2780 Resource with the desired ALTO Information. 2782 13.2. Hosts with Multiple Endpoint Addresses 2784 In practical deployments, a particular host can be reachable using 2785 multiple addresses (e.g., a wireless IPv4 connection, a wireline IPv4 2786 connection, and a wireline IPv6 connection). In general, the 2787 particular network path followed when sending packets to the host 2788 will depend on the address that is used. Network providers may 2789 prefer one path over another. An additional consideration may be how 2790 to handle private address spaces (e.g., behind carrier-grade NATs). 2792 To support such behavior, this document allows multiple endpoint 2793 addresses and address types. With this support, the ALTO Protocol 2794 allows an ALTO Service Provider the flexibility to indicate 2795 preferences for paths from an endpoint address of one type to an 2796 endpoint address of a different type. 2798 13.3. Network Address Translation Considerations 2800 At this day and age of NAT v4<->v4, v4<->v6 [RFC6144], and possibly 2801 v6<->v6[I-D.mrw-nat66], a protocol should strive to be NAT friendly 2802 and minimize carrying IP addresses in the payload, or provide a mode 2803 of operation where the source IP address provide the information 2804 necessary to the server. 2806 The protocol specified in this document provides a mode of operation 2807 where the source network location is computed by the ALTO Server 2808 (i.e., the the Endpoint Cost Service) from the source IP address 2809 found in the ALTO Client query packets. This is similar to how some 2810 P2P Trackers (e.g., BitTorrent Trackers - see "Tracker HTTP/HTTPS 2811 Protocol" in [BitTorrent]) operate. 2813 There may be cases where an ALTO Client needs to determine its own IP 2814 address, such as when specifying a source Endpoint Address in the 2815 Endpoint Cost Service. It is possible that an ALTO Client has 2816 multiple network interface addresses, and that some or all of them 2817 may require NAT for connectivity to the public Internet. 2819 If a public IP address is required for a network interface, the ALTO 2820 Client SHOULD use the Session Traversal Utilities for NAT (STUN) 2821 [RFC5389]. If using this method, the host MUST use the "Binding 2822 Request" message and the resulting "XOR-MAPPED-ADDRESS" parameter 2823 that is returned in the response. Using STUN requires cooperation 2824 from a publicly accessible STUN server. Thus, the ALTO Client also 2825 requires configuration information that identifies the STUN server, 2826 or a domain name that can be used for STUN server discovery. To be 2827 selected for this purpose, the STUN server needs to provide the 2828 public reflexive transport address of the host. 2830 ALTO Clients should be cognizant that the network path between 2831 Endpoints can depend on multiple factors, e.g., source address, and 2832 destination address used for communication. An ALTO Server provides 2833 information based on Endpoint Addresses (more generally, Network 2834 Locations), but the mechanisms used for determining existence of 2835 connectivity or usage of NAT between Endpoints are out of scope of 2836 this document. 2838 13.4. Endpoint and Path Properties 2840 An ALTO Server could make available many properties about Endpoints 2841 beyond their network location or grouping. For example, connection 2842 type, geographical location, and others may be useful to 2843 applications. This specification focuses on network location and 2844 grouping, but the protocol may be extended to handle other Endpoint 2845 properties. 2847 14. IANA Considerations 2849 14.1. application/alto-* Media Types 2851 This document requests the registration of multiple media types, 2852 listed in Table 2. 2854 +-------------+------------------------------+----------------+ 2855 | Type | Subtype | Specification | 2856 +-------------+------------------------------+----------------+ 2857 | application | alto-directory+json | Section 9.2 | 2858 | application | alto-networkmap+json | Section 11.2.1 | 2859 | application | alto-networkmapfilter+json | Section 11.3.1 | 2860 | application | alto-costmap+json | Section 11.2.2 | 2861 | application | alto-costmapfilter+json | Section 11.3.2 | 2862 | application | alto-endpointprop+json | Section 11.4.1 | 2863 | application | alto-endpointpropparams+json | Section 11.4.1 | 2864 | application | alto-endpointcost+json | Section 11.5.1 | 2865 | application | alto-endpointcostparams+json | Section 11.5.1 | 2866 | application | alto-error+json | Section 8.5 | 2867 +-------------+------------------------------+----------------+ 2869 Table 2: ALTO Protocol Media Types. 2871 Type name: application 2873 Subtype name: This documents requests the registration of multiple 2874 subtypes, as listed in Table 2. 2876 Required parameters: n/a 2878 Optional parameters: n/a 2880 Encoding considerations: Encoding considerations are identical to 2881 those specified for the 'application/json' media type. See 2882 [RFC4627]. 2884 Security considerations: Security considerations relating to the 2885 generation and consumption of ALTO Protocol messages are discussed 2886 in Section 15. 2888 Interoperability considerations: This document specifies format of 2889 conforming messages and the interpretation thereof. 2891 Published specification: This document is the specification for 2892 these media types; see Table 2 for the section documenting each 2893 media type. 2895 Applications that use this media type: ALTO Servers and ALTO Clients 2896 either standalone or embedded within other applications. 2898 Additional information: 2900 Magic number(s): n/a 2902 File extension(s): This document uses the mime type to refer to 2903 protocol messages and thus does not require a file extension. 2905 Macintosh file type code(s): n/a 2907 Person & email address to contact for further information: See 2908 "Authors' Addresses" section. 2910 Intended usage: COMMON 2912 Restrictions on usage: n/a 2914 Author: See "Authors' Addresses" section. 2916 Change controller: Internet Engineering Task Force 2917 (mailto:iesg@ietf.org). 2919 14.2. ALTO Cost Metric Registry 2921 This document requests the creation of an ALTO Cost Metric registry, 2922 listed in Table 3, to be maintained by IANA. 2924 +-------------+---------------------+ 2925 | Identifier | Intended Semantics | 2926 +-------------+---------------------+ 2927 | routingcost | See Section 6.1.1.1 | 2928 | priv: | Private use | 2929 | exp: | Experimental use | 2930 +-------------+---------------------+ 2932 Table 3: ALTO Cost Metrics. 2934 This registry serves two purposes. First, it ensures uniqueness of 2935 identifiers referring to ALTO Cost Metrics. Second, it provides 2936 references to particular semantics of allocated Cost Metrics to be 2937 applied by both ALTO Servers and applications utilizing ALTO Clients. 2939 New ALTO Cost Metrics are assigned after Expert Review [RFC5226]. 2940 The Expert Reviewer will generally consult the ALTO Working Group or 2941 its successor. Expert Review is used to ensure that proper 2942 documentation regarding ALTO Cost Metric semantics and security 2943 considerations has been provided. The provided documentation should 2944 be detailed enough to provide guidance to both ALTO Service Providers 2945 and applications utilizing ALTO Clients as to how values of the 2946 registered ALTO Cost Metric should be interpreted. Updates and 2947 deletions of ALTO Cost Metrics follow the same procedure. 2949 Registered ALTO Cost Metric identifiers MUST conform to the 2950 syntactical requirements specified in Section 10.6. Identifiers are 2951 to be recorded and displayed as ASCII strings. 2953 Identifiers prefixed with 'priv:' are reserved for Private Use. 2954 Identifiers prefixed with 'exp:' are reserved for Experimental use. 2956 Requests to add a new value to the registry MUST include the 2957 following information: 2959 o Identifier: The name of the desired ALTO Cost Metric. 2961 o Intended Semantics: ALTO Costs carry with them semantics to guide 2962 their usage by ALTO Clients. For example, if a value refers to a 2963 measurement, the measurement units must be documented. For proper 2964 implementation of the ordinal Cost Mode (e.g., by a third-party 2965 service), it should be documented whether higher or lower values 2966 of the cost are more preferred. 2968 o Security Considerations: ALTO Costs expose information to ALTO 2969 Clients. As such, proper usage of a particular Cost Metric may 2970 require certain information to be exposed by an ALTO Service 2971 Provider. Since network information is frequently regarded as 2972 proprietary or confidential, ALTO Service Providers should be made 2973 aware of the security ramifications related to usage of a Cost 2974 Metric. 2976 This specification requests registration of the identifier 2977 'routingcost'. Semantics for the this Cost Metric are documented in 2978 Section 6.1.1.1, and security considerations are documented in 2979 Section 15.3. 2981 14.3. ALTO Endpoint Property Type Registry 2983 This document requests the creation of an ALTO Endpoint Property 2984 Types registry, listed in Table 4, to be maintained by IANA. 2986 +------------+--------------------+ 2987 | Identifier | Intended Semantics | 2988 +------------+--------------------+ 2989 | pid | See Section 7.1.1 | 2990 | priv: | Private use | 2991 | exp: | Experimental use | 2992 +------------+--------------------+ 2994 Table 4: ALTO Endpoint Property Types. 2996 The maintenance of this registry is similar to that of the preceding 2997 ALTO Cost Metrics. 2999 14.4. ALTO Address Type Registry 3001 This document requests the creation of an ALTO Address Type registry, 3002 listed in Table 5, to be maintained by IANA. 3004 +------------+-----------------+-----------------+------------------+ 3005 | Identifier | Address | Prefix Encoding | Mapping to/from | 3006 | | Encoding | | IPv4/v6 | 3007 +------------+-----------------+-----------------+------------------+ 3008 | ipv4 | See | See | Direct mapping | 3009 | | Section 10.4.2 | Section 10.4.3 | to IPv4 | 3010 | ipv6 | See | See | Direct mapping | 3011 | | Section 10.4.2 | Section 10.4.3 | to IPv6 | 3012 +------------+-----------------+-----------------+------------------+ 3014 Table 5: ALTO Address Types. 3016 This registry serves two purposes. First, it ensures uniqueness of 3017 identifiers referring to ALTO Address Types. Second, it states the 3018 requirements for allocated Address Type identifiers. 3020 New ALTO Address Types are assigned after Expert Review [RFC5226]. 3021 The Expert Reviewer will generally consult the ALTO Working Group or 3022 its successor. Expert Review is used to ensure that proper 3023 documentation regarding the new ALTO Address Types and their security 3024 considerations has been provided. The provided documentation should 3025 indicate how an address of a registered type is encoded as an 3026 EndpointAddr and, if possible, a compact method (e.g., IPv4 and IPv6 3027 prefixes) for encoding a set of addresses as an EndpointPrefix. 3028 Updates and deletions of ALTO Address Types follow the same 3029 procedure. 3031 Registered ALTO Address Type identifiers MUST conform to the 3032 syntactical requirements specified in Section 10.4.1. Identifiers 3033 are to be recorded and displayed as ASCII strings. 3035 Requests to add a new value to the registry MUST include the 3036 following information: 3038 o Identifier: The name of the desired ALTO Address Type. 3040 o Endpoint Address Encoding: The procedure for encoding an address 3041 of the registered type as an EndpointAddr (see Section 10.4.2). 3043 o Endpoint Prefix Encoding: The procedure for encoding a set of 3044 addresses of the registered type as an EndpointPrefix (see 3045 Section 10.4.3). If no such compact encoding is available, the 3046 same encoding used for a singular address may be used. In such a 3047 case, it must be documented that sets of addresses of this type 3048 always have exactly one element. 3050 o Mapping to/from IPv4/IPv6 Addresses: If possible, a mechanism to 3051 map addresses of the registered type to and from IPv4 or IPv6 3052 addresses should be specified. 3054 o Security Considerations: In some usage scenarios, Endpoint 3055 Addresses carried in ALTO Protocol messages may reveal information 3056 about an ALTO Client or an ALTO Service Provider. Applications 3057 and ALTO Service Providers using addresses of the registered type 3058 should be made aware of how (or if) the addressing scheme relates 3059 to private information and network proximity. 3061 This specification requests registration of the identifiers 'ipv4' 3062 and 'ipv6', as shown in Table 5. 3064 14.5. ALTO Error Code Registry 3066 This document requests the creation of an ALTO Error Code registry, 3067 listed in Table 1, to be maintained by IANA. 3069 15. Security Considerations 3071 Some environments and use cases of ALTO require consideration of 3072 security attacks on ALTO Servers and Clients. In order to support 3073 those environments interoperably, the ALTO requirements document 3074 [RFC6708] outlines minimum-to-implement authentication and other 3075 security requirements. Below we consider the threats and protection 3076 strategies. 3078 15.1. Authenticity and Integrity of ALTO Information 3080 15.1.1. Risk Scenarios 3082 An attacker may want to provide false or modified ALTO Information 3083 Resources or Information Resource Directory to ALTO Clients to 3084 achieve certain malicious goals. As an example, an attacker may 3085 provide false endpoint properties. For example, suppose that a 3086 network supports an endpoint property named "hasQuota" which reports 3087 if the endpoint has usage quota. An attacker may want to generate a 3088 false reply to lead to unexpected charges to the endpoint. An attack 3089 may also want to provide false Cost Map. For example, by faking a 3090 Cost Map that highly prefers a small address range or a single 3091 address, the attacker may be able to turn a distributed application 3092 into a Distributed Denial of Service (DDoS) tool. 3094 Depending on the network scenario, an attacker can attack 3095 authenticity and integrity of ALTO Information Resources using 3096 various techniques, including, but not limited to, sending forged 3097 DHCP replies in an Ethernet, DNS poisoning, and installing a 3098 transparent HTTP proxy that does some modifications. 3100 15.1.2. Protection Strategies 3102 ALTO protects the authenticity and integrity of ALTO Information 3103 (both Information Directory and individual Information Resources) by 3104 leveraging the authenticity and integrity mechanisms in TLS. In 3105 particular, the ALTO Protocol requires that HTTP over TLS [RFC2818] 3106 MUST be supported, when protecting the authenticity and integrity of 3107 ALTO Information is required. The rules in [RFC2818] for a client to 3108 verify server identity using server certificates MUST be supported. 3109 ALTO Providers who request server certificates and certification 3110 authorities who issue ALTO-specific certificates SHOULD consider the 3111 recommendations and guidelines defined in [RFC6125] 3113 Software engineers developing and service providers deploying ALTO 3114 should make themselves familiar with up-to-date Best Current 3115 Practices on configuring HTTP over TLS. 3117 15.1.3. Limitations 3119 The protection of HTTP over TLS for ALTO depends on that the domain 3120 name in the URI for the Information Resources is not comprised. This 3121 will depend on the protection implemented by service discovery. 3123 A deployment scenario may require redistribution of ALTO information 3124 to improve scalability. When authenticity and integrity of ALTO 3125 information are still required, then ALTO Clients obtaining ALTO 3126 information through redistribution must be able to validate the 3127 received ALTO information. Support for this validation is not 3128 provided in this document, but may be provided by extension 3129 documents. 3131 15.2. Potential Undesirable Guidance from Authenticated ALTO 3132 Information 3134 15.2.1. Risk Scenarios 3136 The ALTO Service makes it possible for an ALTO Provider to influence 3137 the behavior of network applications. An ALTO Provider may be 3138 hostile to some applications and hence try to use ALTO Information 3139 Resources to achieve certain goals [RFC5693]: "redirecting 3140 applications to corrupted mediators providing malicious content, or 3141 applying policies in computing Cost Map based on criteria other than 3142 network efficiency." See [I-D.ietf-alto-deployments] for additional 3143 discussions on faked ALTO Guidance. 3145 A related scenario is that an ALTO Server could unintentionally give 3146 "bad" guidance. For example, if many ALTO Clients follow the Cost 3147 Map or Endpoint Cost guidance without doing additional sanity checks 3148 or adaptation, more preferable hosts and/or links could get 3149 overloaded while less preferable ones remain idle; see AR-14 of 3150 [RFC6708] for related application considerations. 3152 15.2.2. Protection Strategies 3154 To protect applications from undesirable ALTO Information Resources, 3155 it is important to note that there is no protocol mechanism to 3156 require conforming behaviors on how applications use ALTO Information 3157 Resources. An application using ALTO may consider including a 3158 mechanism to detect misleading or undesirable results from using ALTO 3159 Information Resources. For example, if throughput measurements do 3160 not show "better-than-random" results when using the Cost Map to 3161 select resource providers, the application may want to disable ALTO 3162 usage or switch to an external ALTO Server provided by an 3163 "independent organization" (see AR-20 and AR-21 in [RFC 6708]). If 3164 the first ALTO Server is provided by the access network service 3165 provider and the access network service provider tries to redirect 3166 access to the external ALTO Server back to the provider's ALTO Server 3167 or try to tamper with the responses, the preceding authentication and 3168 integrity protection can detect such a behavior. 3170 15.3. Confidentiality of ALTO Information 3172 15.3.1. Risk Scenarios 3174 Although in many cases ALTO Information Resources may be regarded as 3175 non-confidential information, there are deployment cases where ALTO 3176 Information Resources can be sensitive information that can pose 3177 risks if exposed to unauthorized parties. We discuss the risks and 3178 protection strategies for such deployment scenarios. 3180 For example, an attacker may infer details regarding the topology, 3181 status, and operational policies of a network through the Network and 3182 Cost Maps. As a result, a sophisticated attacker may be able to 3183 infer more fine-graind topology information than an ISP hosting an 3184 ALTO Server intends to disclose. The attacker can leverage the 3185 information to mount effective attacks such as focusing on high-cost 3186 links. 3188 Revealing some endpoint properties may also reveal additional 3189 information than the Provider intended. For example, when adding the 3190 line bitrate as one endpoint property, such information may be 3191 potentially linked to the income of the habitants at the network 3192 location of an endpoint. 3194 In [RFC6708] Section 5.2.1, three types of risks associated with the 3195 confidentiality of ALTO Information Resources are identified: risk 3196 type (1) Excess disclosure of the ALTO service provider's data to an 3197 authorized ALTO Client; risk type (2) Disclosure of the ALTO service 3198 provider's data (e.g., network topology information) to an 3199 unauthorized third party; and risk type (3) Excess retrieval of the 3200 ALTO service provider's data by collaborating ALTO Clients. Section 3201 10 of [I-D.ietf-alto-deployments] also discusses information leakage 3202 from ALTO. 3204 15.3.2. Protection Strategies 3206 To address risk types (1) and (3), the Provider of an ALTO Server 3207 must be cognizant that the network topology and provisioning 3208 information provided through ALTO may lead to attacks. ALTO does not 3209 require any particular level of details of information disclosure, 3210 and hence the Provider should evaluate how much information is 3211 revealed and the associated risks. 3213 To address risk type (2), the ALTO Protocol need confidentiality. 3214 Since ALTO requires that HTTP over TLS MUST be supported, the 3215 confidentiality mechanism is provided by HTTP over TLS. 3217 For deployment scenarios where client authentication is desired to 3218 address risk type (2), ALTO requires that HTTP Digestion 3219 Authentication MUST be supported to achieve ALTO Client 3220 Authentication to limit the number of parties with whom ALTO 3221 information is directly shared. Depending on the use-case and 3222 scenario, an ALTO Server may apply other access control techniques to 3223 restrict access to its services. Access control can also help to 3224 prevent Denial-of-Service attacks by arbitrary hosts from the 3225 Internet. See [I-D.ietf-alto-deployments] for a more detailed 3226 discussion on this issue. 3228 15.3.3. Limitations 3230 ALTO Information Providers should be cognizant that encryption only 3231 protects ALTO information until it is decrypted by the intended ALTO 3232 Client. Digital Rights Management (DRM) techniques and legal 3233 agreements protecting ALTO information are outside of the scope of 3234 this document. 3236 15.4. Privacy for ALTO Users 3238 15.4.1. Risk Scenarios 3240 The ALTO Protocol provides mechanisms in which the ALTO Client 3241 serving a user can send messages containing Network Location 3242 Identifiers (IP addresses or fine-grained PIDs) to the ALTO Server. 3243 This is particularly true for the Endpoint Property, Endpoint Cost, 3244 and fine-grained Filtered Map services. The ALTO Server or a third- 3245 party who is able to intercept such messages can store and process 3246 obtained information in order to analyze user behaviors and 3247 communication patterns. The analysis may correlate information 3248 collected from multiple clients to deduce additional application/ 3249 content information. Such analysis can lead to privacy risks. For a 3250 more comprehensive classification of related risk scenarios, see 3251 cases 4, 5, and 6 in [RFC 6708], Section 5.2. 3253 15.4.2. Protection Strategies 3255 To protect user privacy, an ALTO Client should be cognizant about 3256 potential ALTO Server tracking through client queries. An ALTO 3257 Client may consider the possibility of relying only on Network Map 3258 for PIDs and Cost Map amongst PIDs to avoid passing IP addresses of 3259 other endpoints (e.g., peers) to the ALTO Server. When specific IP 3260 addresses are needed (e.g., when using the Endpoint Cost Service), an 3261 ALTO Client may consider obfuscation techniques such as specifying a 3262 broader address range (i.e., a shorter prefix length) or by zeroing 3263 out or randomizing the last few bits of IP addresses. Note that 3264 obfuscation may yield less accurate results. 3266 15.5. Availability of ALTO Service 3268 15.5.1. Risk Scenarios 3270 An attacker may want to disable ALTO Service as a way to disable 3271 network guidance to large scale applications.In particular, queries 3272 which can be generated with low effort but result in expensive 3273 workloads at the ALTO Server could be exploited for Denial-of-Service 3274 attacks. For instance, a simple ALTO query with n Source Network 3275 Locations and m Destination Network Locations can be generated fairly 3276 easily but results in the computation of n*m Path Costs between pairs 3277 by the ALTO Server (see Section 5.2). 3279 15.5.2. Protection Strategies 3281 ALTO Provider should be cognizant of the workload at the ALTO Server 3282 generated by certain ALTO Queries, such as certain queries to the Map 3283 Service, the Map Filtering Service and the Endpoint Cost (Ranking) 3284 Service. One way to limit Denial-of-Service attacks is to employ 3285 access control to the ALTO Server. The ALTO Server can also indicate 3286 overload and reject repeated requests that can cause availability 3287 problems. More advanced protection schemes such as computational 3288 puzzles [I-D.jennings-sip-hashcash] may be considered in an extension 3289 document. 3291 An ALTO Provider should also leverage the fact that the Map Service 3292 allows ALTO Servers to pre-generate maps that can be distributed to 3293 many ALTO Clients. 3295 16. Manageability Considerations 3297 This section details operations and management considerations based 3298 on existing deployments and discussions during protocol development. 3299 It also indicates where extension documents are expected to provide 3300 appropriate functionality discussed in [RFC5706] as additional 3301 deployment experience becomes available. 3303 16.1. Operations 3304 16.1.1. Installation and Initial Setup 3306 The ALTO Protocol is based on HTTP. Thus, configuring an ALTO Server 3307 may require configuring the underlying HTTP server implementation to 3308 define appropriate security policies, caching policies, performance 3309 settings, etc. 3311 Additionally, an ALTO Service Provider will need to configure the 3312 ALTO information to be provided by the ALTO Server. The granularity 3313 of the topological map and the cost map is left to the specific 3314 policies of the ALTO Service Provider. However, a reasonable default 3315 may include two PIDs, one to hold the endpoints in the provider's 3316 network and the second PID to represent full IPv4 and IPv6 3317 reachability (see Section 5.2.1), with the cost between each source/ 3318 destination PID set to 1. Another operational issue that the ALTO 3319 Service Provider needs to consider is that the filtering service can 3320 degenerate into a full map service when the filtering input is empty. 3321 Although this choice as the degeneration behavior provides 3322 continuity, the operational impact should be considered. 3324 Implementers employing an ALTO Client should attempt to automatically 3325 discover an appropriate ALTO Server. Manual configuration of the 3326 ALTO Server location may be used where automatic discovery is not 3327 appropriate. Methods for automatic discovery and manual 3328 configuration are discussed in [I-D.ietf-alto-server-discovery]. 3330 Specifications for underlying protocols (e.g., TCP, HTTP, SSL/TLS) 3331 should be consulted for their available settings and proposed default 3332 configurations. 3334 16.1.2. Migration Path 3336 This document does not detail a migration path for ALTO Servers since 3337 there is no previous standard protocol providing the similar 3338 functionality. 3340 There are existing applications making use of network information 3341 discovered from other entities such as whois, geo-location databases, 3342 or round-trip time measurements, etc. Such applications should 3343 consider using ALTO as an additional source of information; ALTO need 3344 not be the sole source of network information. 3346 16.1.3. Requirements on Other Protocols and Functional Components 3348 The ALTO Protocol assumes that HTTP client and server implementations 3349 exist. It also assumes that JSON encoder and decoder implementations 3350 exist. 3352 An ALTO Server assumes that it can gather sufficient information to 3353 populate Network and Cost maps. "Sufficient information" is 3354 dependent on the information being exposed, but likely includes 3355 information gathered from protocols such as IGP and EGP Routing 3356 Information Bases (see Figure 1). Specific mechanisms have been 3357 proposed (e.g., [I-D.medved-alto-svr-apis]) and are expected to be 3358 provided in extension documents. 3360 16.1.4. Impact and Observation on Network Operation 3362 ALTO presents a new opportunity for managing network traffic by 3363 providing additional information to clients. The potential impact to 3364 network operation is large. 3366 Deployment of an ALTO Server may shift network traffic patterns. 3367 Thus, an ALTO Service Provider should consider impacts on (or 3368 integration with) traffic engineering and the deployment of a 3369 monitoring service to observe the effects of ALTO operations. Note 3370 that ALTO-specific monitoring and metrics are discussed in 6.3 of 3371 [I-D.ietf-alto-deployments] and future versions of that document. In 3372 particular, an ALTO Service Provider may observe that ALTO Clients 3373 are not bound to ALTO Server guidance as ALTO is only one source of 3374 information. 3376 An ALTO Service Provider should ensure that appropriate information 3377 is being exposed. Privacy implications for ISPs are discussed in 3378 Section 15.3. Both ALTO Service Providers and those using ALTO 3379 Clients should be aware of the impact of incorrect or faked guidance 3380 (see Section 10.3 of [I-D.ietf-alto-deployments] and future versions 3381 of that document). 3383 16.2. Management 3385 16.2.1. Management Interoperability 3387 A common management API would be desirable given that ALTO Servers 3388 may typically be configured with dynamic data from various sources, 3389 and ALTO Servers are intended to scale horizontally for fault- 3390 tolerance and reliability. A specific API or protocol is outside the 3391 scope of this document, but may be provided by an extension document. 3393 Logging is an important functionality for ALTO Servers and, depending 3394 on the deployment, ALTO Clients. Logging should be done via syslog 3395 [RFC5424]. 3397 16.2.2. Management Information 3399 A Management Information Model (see Section 3.2 of [RFC5706] is not 3400 provided by this document, but should be included or referenced by 3401 any extension documenting an ALTO-related management API or protocol. 3403 16.2.3. Fault Management 3405 Monitoring ALTO Servers and Clients is described in Section 6.3 of 3406 [I-D.ietf-alto-deployments] and future versions of that document. 3408 16.2.4. Configuration Management 3410 Standardized approaches and protocols to configuration management for 3411 ALTO are outside the scope of this document, but this document does 3412 outline high-level principles suggested for future standardization 3413 efforts. 3415 An ALTO Server requires at least the following logical inputs: 3417 o Data sources from which ALTO Information is derived. This can 3418 either be raw network information (e.g., from routing elements) or 3419 pre-processed ALTO-level information in the form of a Network Map, 3420 Cost Map, etc. 3422 o Algorithms for computing the ALTO information returned to clients. 3423 These could either return information from a database, or 3424 information customized for each client. 3426 o Security policies mapping potential clients to the information 3427 that they have privilege to access. 3429 Multiple ALTO Servers can be deployed for scalability. A centralized 3430 configuration database may be used to ensure they are providing the 3431 desired ALTO information with appropriate security controls. The 3432 ALTO information (e.g., Network Maps and Cost Maps) being served by 3433 each ALTO Server, as well as security policies (HTTP authentication, 3434 SSL/TLS client and server authentication, SSL/TLS encryption 3435 parameters) intended to serve the same information should be 3436 monitored for consistency. 3438 16.2.5. Performance Management 3440 An exhaustive list of desirable performance information from a ALTO 3441 Servers and ALTO Clients are outside of the scope of this document. 3442 The following is a list of suggested ALTO-specific to be monitored 3443 based on the existing deployment and protocol development experience: 3445 o Requests and responses for each service listed in a Information 3446 Directory (total counts and size in bytes). 3448 o CPU and memory utilization 3450 o ALTO map updates 3452 o Number of PIDs 3454 o ALTO map sizes (in-memory size, encoded size, number of entries) 3456 16.2.6. Security Management 3458 Section 15 documents ALTO-specific security considerations. 3459 Operators should configure security policies with those in mind. 3460 Readers should refer to HTTP [RFC2616] and SSL/TLS [RFC5246] and 3461 related documents for mechanisms available for configuring security 3462 policies. Other appropriate security mechanisms (e.g., physical 3463 security, firewalls, etc) should also be considered. 3465 17. References 3467 17.1. Normative References 3469 [IEEE.754.2008] 3470 Institute of Electrical and Electronics Engineers, 3471 "Standard for Binary Floating-Point Arithmetic", IEEE 3472 Standard 754, August 2008. 3474 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 3475 Extensions (MIME) Part Two: Media Types", RFC 2046, 3476 November 1996. 3478 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3479 Requirement Levels", BCP 14, RFC 2119, March 1997. 3481 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 3482 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 3483 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 3485 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 3487 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 3488 Resource Identifier (URI): Generic Syntax", STD 66, 3489 RFC 3986, January 2005. 3491 [RFC4627] Crockford, D., "The application/json Media Type for 3492 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 3494 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 3495 (CIDR): The Internet Address Assignment and Aggregation 3496 Plan", BCP 122, RFC 4632, August 2006. 3498 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 3499 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 3500 May 2008. 3502 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 3503 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 3505 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 3506 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 3507 October 2008. 3509 [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009. 3511 [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic 3512 Optimization (ALTO) Problem Statement", RFC 5693, 3513 October 2009. 3515 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 3516 Address Text Representation", RFC 5952, August 2010. 3518 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 3519 Verification of Domain-Based Application Service Identity 3520 within Internet Public Key Infrastructure Using X.509 3521 (PKIX) Certificates in the Context of Transport Layer 3522 Security (TLS)", RFC 6125, March 2011. 3524 [RFC6708] Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and 3525 Y. Yang, "Application-Layer Traffic Optimization (ALTO) 3526 Requirements", RFC 6708, September 2012. 3528 17.2. Informative References 3530 [BitTorrent] 3531 "Bittorrent Protocol Specification v1.0", 3532 . 3534 [Fielding-Thesis] 3535 Fielding, R., "Architectural Styles and the Design of 3536 Network-based Software Architectures", University of 3537 California, Irvine, Dissertation 2000, 2000. 3539 [I-D.akonjang-alto-proxidor] 3540 Akonjang, O., Feldmann, A., Previdi, S., Davie, B., and D. 3541 Saucez, "The PROXIDOR Service", 3542 draft-akonjang-alto-proxidor-00 (work in progress), 3543 March 2009. 3545 [I-D.ietf-alto-deployments] 3546 Stiemerling, M., Kiesel, S., Previdi, S., and M. Scharf, 3547 "ALTO Deployment Considerations", 3548 draft-ietf-alto-deployments-07 (work in progress), 3549 July 2013. 3551 [I-D.ietf-alto-server-discovery] 3552 Kiesel, S., Stiemerling, M., Schwan, N., Scharf, M., and 3553 S. Yongchao, "ALTO Server Discovery", 3554 draft-ietf-alto-server-discovery-10 (work in progress), 3555 September 2013. 3557 [I-D.ietf-httpbis-p2-semantics] 3558 Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 3559 (HTTP/1.1): Semantics and Content", 3560 draft-ietf-httpbis-p2-semantics-23 (work in progress), 3561 July 2013. 3563 [I-D.jenkins-alto-cdn-use-cases] 3564 Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and 3565 S. Previdi, "Use Cases for ALTO within CDNs", 3566 draft-jenkins-alto-cdn-use-cases-03 (work in progress), 3567 June 2012. 3569 [I-D.medved-alto-svr-apis] 3570 Medved, J., Ward, D., Peterson, J., Woundy, R., and D. 3571 McDysan, "ALTO Network-Server and Server-Server APIs", 3572 draft-medved-alto-svr-apis-00 (work in progress), 3573 March 2011. 3575 [I-D.mrw-nat66] 3576 Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix 3577 Translation", draft-mrw-nat66-16 (work in progress), 3578 April 2011. 3580 [I-D.p4p-framework] 3581 Alimi, R., Pasko, D., Popkin, L., Wang, Y., and Y. Yang, 3582 "P4P: Provider Portal for P2P Applications", 3583 draft-p4p-framework-00 (work in progress), November 2008. 3585 [I-D.saumitra-alto-multi-ps] 3586 Das, S., Narayanan, V., and L. Dondeti, "ALTO: A Multi 3587 Dimensional Peer Selection Problem", 3588 draft-saumitra-alto-multi-ps-00 (work in progress), 3589 October 2008. 3591 [I-D.saumitra-alto-queryresponse] 3592 Das, S. and V. Narayanan, "A Client to Service Query 3593 Response Protocol for ALTO", 3594 draft-saumitra-alto-queryresponse-00 (work in progress), 3595 March 2009. 3597 [I-D.shalunov-alto-infoexport] 3598 Shalunov, S., Penno, R., and R. Woundy, "ALTO Information 3599 Export Service", draft-shalunov-alto-infoexport-00 (work 3600 in progress), October 2008. 3602 [I-D.wang-alto-p4p-specification] 3603 Wang, Y., Alimi, R., Pasko, D., Popkin, L., and Y. Yang, 3604 "P4P Protocol Specification", 3605 draft-wang-alto-p4p-specification-00 (work in progress), 3606 March 2009. 3608 [P4P-SIGCOMM08] 3609 Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A. 3610 Silberschatz, "P4P: Provider Portal for (P2P) 3611 Applications", SIGCOMM 2008, August 2008. 3613 [RFC5706] Harrington, D., "Guidelines for Considering Operations and 3614 Management of New Protocols and Protocol Extensions", 3615 RFC 5706, November 2009. 3617 [RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for 3618 IPv4/IPv6 Translation", RFC 6144, April 2011. 3620 Appendix A. Acknowledgments 3622 Thank you to Sebastian Kiesel (University of Stuttgart) and Jan 3623 Seedorf (NEC) for substantial contributions to the Security 3624 Considerations section. Ben Niven-Jenkins (Velocix), Michael Scharf 3625 and Sabine Randriamasy (Alcatel-Lucent) gave substantial feedback and 3626 suggestions on the protocol design. We are particularly grateful to 3627 the substantial contributions of Wendy Roome (Alcatel-Lucent). 3629 We would like to thank the following people whose input and 3630 involvement was indispensable in achieving this merged proposal: 3632 Obi Akonjang (DT Labs/TU Berlin), 3633 Saumitra M. Das (Qualcomm Inc.), 3635 Syon Ding (China Telecom), 3637 Doug Pasko (Verizon), 3639 Laird Popkin (Pando Networks), 3641 Satish Raghunath (Juniper Networks), 3643 Albert Tian (Ericsson/Redback), 3645 Yu-Shun Wang (Microsoft), 3647 David Zhang (PPLive), 3649 Yunfei Zhang (China Mobile). 3651 We would also like to thank the following additional people who were 3652 involved in the projects that contributed to this merged document: 3653 Alex Gerber (ATT), Chris Griffiths (Comcast), Ramit Hora (Pando 3654 Networks), Arvind Krishnamurthy (University of Washington), Marty 3655 Lafferty (DCIA), Erran Li (Bell Labs), Jin Li (Microsoft), Y. Grace 3656 Liu (IBM Watson), Jason Livingood (Comcast), Michael Merritt (ATT), 3657 Ingmar Poese (DT Labs/TU Berlin), James Royalty (Pando Networks), 3658 Damien Saucez (UCL) Thomas Scholl (ATT), Emilio Sepulveda 3659 (Telefonica), Avi Silberschatz (Yale University), Hassan Sipra (Bell 3660 Canada), Georgios Smaragdakis (DT Labs/TU Berlin), Haibin Song 3661 (Huawei), Oliver Spatscheck (ATT), See-Mong Tang (Microsoft), Jia 3662 Wang (ATT), Hao Wang (Yale University), Ye Wang (Yale University), 3663 Haiyong Xie (Yale University). 3665 Appendix B. Design History and Merged Proposals 3667 The ALTO Protocol specified in this document consists of 3668 contributions from 3670 o P4P [I-D.p4p-framework], [P4P-SIGCOMM08], 3671 [I-D.wang-alto-p4p-specification]; 3673 o ALTO Info-Export [I-D.shalunov-alto-infoexport]; 3675 o Query/Response [I-D.saumitra-alto-queryresponse], 3676 [I-D.saumitra-alto-multi-ps]; 3678 o ATTP [ATTP]; and 3679 o Proxidor [I-D.akonjang-alto-proxidor]. 3681 Appendix C. Authors 3683 [[CmtAuthors: RFC Editor: Please move information in this section to 3684 the Authors' Addresses section at publication time.]] 3686 Stefano Previdi 3687 Cisco 3689 Email: sprevidi@cisco.com 3691 Stanislav Shalunov 3692 BitTorrent 3694 Email: shalunov@bittorrent.com 3696 Richard Woundy 3697 Comcast 3699 Richard_Woundy@cable.comcast.com 3701 Authors' Addresses 3703 Richard Alimi (editor) 3704 Google 3705 1600 Amphitheatre Parkway 3706 Mountain View CA 3707 USA 3709 Email: ralimi@google.com 3711 Reinaldo Penno (editor) 3712 Cisco Systems 3713 170 West Tasman Dr 3714 San Jose CA 3715 USA 3717 Email: repenno@cisco.com 3718 Y. Richard Yang (editor) 3719 Yale University 3720 51 Prospect St 3721 New Haven CT 3722 USA 3724 Email: yry@cs.yale.edu