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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-10) exists of draft-ietf-cdni-use-cases-04 == Outdated reference: A later version (-03) exists of draft-jenkins-alto-cdn-use-cases-02 -- Obsolete informational reference (is this intentional?): RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) -- Obsolete informational reference (is this intentional?): RFC 3466 (Obsoleted by RFC 7336) -- Obsolete informational reference (is this intentional?): RFC 3570 (Obsoleted by RFC 6770) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Niven-Jenkins 3 Internet-Draft Velocix (Alcatel-Lucent) 4 Intended status: Informational F. Le Faucheur 5 Expires: November 21, 2012 Cisco 6 N. Bitar 7 Verizon 8 May 20, 2012 10 Content Distribution Network Interconnection (CDNI) Problem Statement 11 draft-ietf-cdni-problem-statement-06 13 Abstract 15 Content Delivery Networks (CDNs) provide numerous benefits: reduced 16 delivery cost for cacheable content, improved quality of experience 17 for End Users and increased robustness of delivery. For these 18 reasons they are frequently used for large-scale content delivery. 19 As a result, existing CDN Providers are scaling up their 20 infrastructure and many Network Service Providers (NSPs) are 21 deploying their own CDNs. It is generally desirable that a given 22 content item can be delivered to an End User regardless of that End 23 User's location or attachment network. This is the motivation for 24 interconnecting standalone CDNs so they can interoperate as an open 25 content delivery infrastructure for the end-to-end delivery of 26 content from Content Service Providers (CSPs) to End Users. However, 27 no standards or open specifications currently exist to facilitate 28 such CDN interconnection. 30 The goal of this document is to outline the problem area of CDN 31 interconnection for the IETF CDNI (CDN Interconnection) working 32 group. 34 Status of this Memo 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 39 Internet-Drafts are working documents of the Internet Engineering 40 Task Force (IETF). Note that other groups may also distribute 41 working documents as Internet-Drafts. The list of current Internet- 42 Drafts is at http://datatracker.ietf.org/drafts/current/. 44 Internet-Drafts are draft documents valid for a maximum of six months 45 and may be updated, replaced, or obsoleted by other documents at any 46 time. It is inappropriate to use Internet-Drafts as reference 47 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on November 21, 2012. 50 Copyright Notice 52 Copyright (c) 2012 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 69 1.2. CDN Background . . . . . . . . . . . . . . . . . . . . . . 10 70 2. CDN Interconnection Use Cases . . . . . . . . . . . . . . . . 10 71 3. CDN Interconnection Model & Problem Area for IETF . . . . . . 12 72 4. Scoping the CDNI Problem . . . . . . . . . . . . . . . . . . . 16 73 4.1. CDNI Request Routing Interface . . . . . . . . . . . . . . 17 74 4.2. CDNI Metadata Interface . . . . . . . . . . . . . . . . . 17 75 4.3. CDNI Logging Interface . . . . . . . . . . . . . . . . . . 18 76 4.4. CDNI Control Interface . . . . . . . . . . . . . . . . . . 18 77 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 78 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 79 6.1. Security of the CDNI Control interface . . . . . . . . . . 19 80 6.2. Security of the CDNI Request Routing Interface . . . . . . 19 81 6.3. Security of the CDNI Metadata interface . . . . . . . . . 19 82 6.4. Security of the CDNI Logging interface . . . . . . . . . . 20 83 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20 84 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 85 8.1. Normative References . . . . . . . . . . . . . . . . . . . 20 86 8.2. Informative References . . . . . . . . . . . . . . . . . . 20 87 Appendix A. Design considerations for realizing the CDNI 88 Interfaces . . . . . . . . . . . . . . . . . . . . . 23 89 A.1. CDNI Request Routing Interface . . . . . . . . . . . . . . 23 90 A.2. CDNI Metadata Interface . . . . . . . . . . . . . . . . . 25 91 A.3. CDNI Logging Interface . . . . . . . . . . . . . . . . . . 26 92 A.4. CDNI Control Interface . . . . . . . . . . . . . . . . . . 27 93 Appendix B. Additional Material . . . . . . . . . . . . . . . . . 27 94 B.1. Non-Goals for IETF . . . . . . . . . . . . . . . . . . . . 27 95 B.2. Related standardization activites . . . . . . . . . . . . 29 96 B.2.1. IETF CDI Working Group (Concluded) . . . . . . . . . . 30 97 B.2.2. 3GPP . . . . . . . . . . . . . . . . . . . . . . . . . 30 98 B.2.3. ISO MPEG . . . . . . . . . . . . . . . . . . . . . . . 31 99 B.2.4. ATIS IIF . . . . . . . . . . . . . . . . . . . . . . . 32 100 B.2.5. CableLabs . . . . . . . . . . . . . . . . . . . . . . 32 101 B.2.6. ETSI MCD . . . . . . . . . . . . . . . . . . . . . . . 32 102 B.2.7. ETSI TISPAN . . . . . . . . . . . . . . . . . . . . . 32 103 B.2.8. ITU-T . . . . . . . . . . . . . . . . . . . . . . . . 33 104 B.2.9. Open IPTV Forum (OIPF) . . . . . . . . . . . . . . . . 33 105 B.2.10. TV-Anytime Forum . . . . . . . . . . . . . . . . . . . 33 106 B.2.11. SNIA . . . . . . . . . . . . . . . . . . . . . . . . . 34 107 B.2.12. Summary of existing standardization work . . . . . . . 34 108 B.3. Related Research Projects . . . . . . . . . . . . . . . . 36 109 B.3.1. IRTF P2P Research Group . . . . . . . . . . . . . . . 36 110 B.3.2. OCEAN . . . . . . . . . . . . . . . . . . . . . . . . 36 111 B.3.3. Eurescom P1955 . . . . . . . . . . . . . . . . . . . . 36 112 B.4. Relationship to relevant IETF Working Groups . . . . . . . 37 113 B.4.1. ALTO . . . . . . . . . . . . . . . . . . . . . . . . . 37 114 B.4.2. DECADE . . . . . . . . . . . . . . . . . . . . . . . . 37 115 B.4.3. PPSP . . . . . . . . . . . . . . . . . . . . . . . . . 39 116 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39 118 1. Introduction 120 The volume of video and multimedia content delivered over the 121 Internet is rapidly increasing and expected to continue doing so in 122 the future. In the face of this growth, Content Delivery Networks 123 (CDNs) provide numerous benefits: reduced delivery cost for cacheable 124 content, improved quality of experience for End Users (EUs) and 125 increased robustness of delivery. For these reasons CDNs are 126 frequently used for large-scale content delivery. As a result, 127 existing CDN Providers are scaling up their infrastructure and many 128 Network Service Providers (NSPs) are deploying their own CDNs. 130 It is generally desirable that a given content item can be delivered 131 to an EU regardless of that EU's location or the network they are 132 attached to. However, a given CDN in charge of delivering a given 133 content may not have a footprint that expands close enough to the 134 EU's current location or attachment network, or may not have the 135 necessary resources, to realize the user experience and cost benefit 136 that a more distributed CDN infrastructure would allow. This is the 137 motivation for interconnecting standalone CDNs so that their 138 collective CDN footprint and resources can be leveraged for the end- 139 to-end delivery of content from Content Service Providers (CSPs) to 140 EUs. As an example, a CSP could contract with an "authoritative" CDN 141 Provider for the delivery of content and that authoritative CDN 142 Provider could contract with one or more downstream CDN Provider(s) 143 to distribute and deliver some or all of the content on behalf of the 144 authoritative CDN Provider. 146 A typical end to end content delivery scenario would then involve the 147 following business arrangements: 149 o A business arrangement between the EU and his CSP, authorizing 150 access by the EU to content items controlled by the CSP. 151 o A business arrangement between the CSP and an "authoritative" CDN 152 Provider where the CSP authorizes the CDN Provider to perform the 153 content delivery on behalf of the CSP. 154 o A business arrangement between the authoritative CDN Provider and 155 another (or other) CDN(s) where the authoritative CDN may delegate 156 the actual serving of some of the content delivery requests to the 157 other CDN(s). A particular case, is where this other CDN Provider 158 happens to also be the Network Service Provider providing network 159 access to the EU, in which case there is also a separate and 160 independent business relationship between the EU and the NSP for 161 the corresponding network access. 163 The formation and details of any business relationships between a CSP 164 and a CDN Provider as well as between one CDN Provider and another 165 CDN Provider are out of scope of this document. However, this 166 document concerns itself with the fact that no standards or open 167 specifications currently exist to facilitate such CDN interconnection 168 from a technical perspective. 170 The goal of this document is to outline the problem area of CDN 171 interconnection. Section 2 discusses the use cases for CDN 172 interconnection. Section 3 presents the CDNI model and problem area 173 being considered by the IETF. Section 4 describes each CDNI 174 interface individually and highlights example candidate protocols 175 that could be considered for reuse or leveraging to implement the 176 CDNI interfaces. Appendix B.2 discusses the relevant work of other 177 standards organizations. Appendix B.4 describes the relationships 178 between the CDNI problem space and other relevant IETF Working 179 Groups. 181 1.1. Terminology 183 This document uses the following terms: 185 Content: Any form of digital data. One important form of Content 186 with additional constraints on distribution and delivery is 187 continuous media (i.e. where there is a timing relationship between 188 source and sink). 190 Metadata: Metadata in general is data about data. 192 Content Metadata: This is metadata about Content. Content Metadata 193 comprises: 195 1. Metadata that is relevant to the distribution of the content (and 196 therefore relevant to a CDN involved in the delivery of that 197 content). We refer to this type of metadata as "Content 198 Distribution Metadata". See also the definition of Content 199 Distribution Metadata. 200 2. Metadata that is associated with the actual Content or content 201 representation, and not directly relevant to the distribution of 202 that Content. For example, such metadata may include information 203 pertaining to the Content's genre, cast, rating, etc as well as 204 information pertaining to the Content representation's 205 resolution, aspect ratio, etc. 207 Content Distribution Metadata: The subset of Content Metadata that is 208 relevant to the distribution of the content. This is the metadata 209 required by a CDN in order to enable and control content distribution 210 and delivery by the CDN. In a CDN Interconnection environment, some 211 of the Content Distribution Metadata may have an intra-CDN scope (and 212 therefore need not be communicated between CDNs), while some of the 213 Content Distribution Metadata may have an inter-CDN scope (and 214 therefore needs to be communicated between CDNs). 216 CDNI Metadata: Content Distribution Metadata with inter-CDN scope. 217 For example, CDNI Metadata may include geo-blocking information (i.e. 218 information defining geographical areas where the content is to be 219 made available or blocked), availability windows (i.e. information 220 defining time windows during which the content is to be made 221 available or blocked) and access control mechanisms to be enforced 222 (e.g. URI signature validation). CDNI Metadata may also include 223 information about desired distribution policy (e.g. prepositioned vs 224 dynamic acquisition) and about where/how a CDN can acquire the 225 content. CDNI Metadata may also include content management 226 information (e.g. request for deletion of Content from Surrogates) 227 across interconnected CDNs. 229 Dynamic content acquisition: Dynamic content acquisition is where a 230 CDN acquires content from the content source in response to an End 231 User requesting that content from the CDN. In the context of CDN 232 Interconnection, dynamic acquisition means that a downstream CDN 233 acquires the content from content sources (including upstream CDNs) 234 at some point in time after a request for that content is delegated 235 to the downstream CDN by an Upstream CDN (and that specific content 236 is not yet available in the downstream CDN). 238 Dynamic CDNI metadata acquisition: In the context of CDN 239 Interconnection, dynamic CDNI metadata acquisition means that a 240 downstream CDN acquires CDNI metadata for content from the upstream 241 CDN at some point in time after a request for that content is 242 delegated to the downstream CDN by an Upstream CDN (and that specific 243 CDNI metadata is not yet available in the downstream CDN). See also 244 the definitions for downstream CDN and upstream CDN. 246 Pre-positioned content acquisition: Content Pre-positioning is where 247 a CDN acquires content from the content source prior to, or 248 independently of, any End User requesting that content from the CDN. 249 In the context of CDN interconnection the Upstream CDN instructs the 250 Downstream CDN to acquire the content from content sources (including 251 upstream CDNs) in advance of or independent of any End User 252 requesting it. 254 Pre-positioned CDNI Metadata acquisition: In the context of CDN 255 Interconnection, CDNI Metadata pre-positioning is where the 256 Downstream CDN acquires CDNI metadata for content prior to or 257 independent of any End User requesting that content from the 258 Downstream CDN. 260 End User (EU): The 'real' user of the system, typically a human but 261 maybe some combination of hardware and/or software emulating a human 262 (e.g. for automated quality monitoring etc.) 264 User Agent (UA): Software (or a combination of hardware and software) 265 through which the End User interacts with a Content Service. The 266 User Agent will communicate with a Content Service for the selection 267 of content and one or more CDNs for the delivery of the Content. 268 Such communication is not restricted to HTTP and may be via a variety 269 of protocols. Examples of User Agents (non-exhaustive) are: 270 Browsers, Set Top Boxes (STBs), dedicated content applications (e.g. 271 media players), etc. 273 Network Service Provider (NSP): Provides network-based connectivity/ 274 services to End Users. 276 Content Service Provider (CSP): Provides a Content Service to End 277 Users (which they access via a User Agent). A CSP may own the 278 Content made available as part of the Content Service, or may license 279 content rights from another party. 281 Content Service: The service offered by a Content Service Provider. 282 The Content Service encompasses the complete service which may be 283 wider than just providing access to items of Content, e.g. the 284 Content Service also includes any middleware, key distribution, 285 program guide, etc. which may not require any direct interaction with 286 the CDN, or CDNs, involved in the distribution and delivery of the 287 content. 289 Content Distribution Network (CDN) / Content Delivery Network (CDN): 290 Network infrastructure in which the network elements cooperate at 291 layers 4 through layer 7 for more effective delivery of Content to 292 User Agents. Typically a CDN consists of a Request Routing system, a 293 Distribution System (that includes a set of Surrogates), a Logging 294 System and a CDN control system. 296 CDN Provider: The service provider who operates a CDN and offers a 297 service of content delivery, typically used by a Content Service 298 Provider or another CDN Provider. Note that a given entity may 299 operate in more than one role. For example, a company may 300 simultaneously operate as a Content Service Provider, a Network 301 Service Provider and a CDN Provider. 303 CDN Interconnection (CDNI): A relationship between a pair of CDNs 304 that enables one CDN to provide content delivery services on behalf 305 of another CDN. A CDN Interconnection may be wholly or partially 306 realized through a set of interfaces over which a pair of CDNs 307 communicate with each other in order to achieve the delivery of 308 content to User Agents by Surrogates in one CDN (the downstream CDN) 309 on behalf of another CDN (the upstream CDN). 311 Authoritative CDN: A CDN which has a direct relationship with a CSP 312 for the distribution & delivery of that CSP's content by the 313 authoritative CDN or by downstream CDNs of the authoritative CDN. 315 Upstream CDN: For a given End User request, the CDN (within a pair of 316 directly interconnected CDNs) that redirects the request to the other 317 CDN. 319 Downstream CDN: For a given End User request, the CDN (within a pair 320 of directly interconnected CDNs) to which the request is redirected 321 by the other CDN (the Upstream CDN). Note that in the case of 322 successive redirections (e.g. CDN1-->CDN2-->CDN3) a given CDN (e.g. 323 CDN2) may act as the Downstream CDN for a redirection (e.g. 324 CDN1-->CDN2) and as the Upstream CDN for the subsequent redirection 325 of the same request (e.g. CDN2-->CDN3). 327 Over-the-top (OTT): A service, e.g. content delivery using a CDN, 328 operated by a different operator than the NSP to which the users of 329 that service are attached. 331 Surrogate: A device/function (often called a cache) that interacts 332 with other elements of the CDN for the control and distribution of 333 Content within the CDN and interacts with User Agents for the 334 delivery of the Content. 336 Request Routing System: The function within a CDN responsible for 337 receiving a content request from a User Agent, obtaining and 338 maintaining necessary information about a set of candidate surrogates 339 or candidate CDNs, and for selecting and redirecting the user to the 340 appropriate surrogate or CDN. To enable CDN Interconnection, the 341 Request Routing System must also be capable of handling User Agent 342 content requests passed to it by another CDN. 344 Distribution System: The function within a CDN responsible for 345 distributing Content Distribution Metadata as well as the Content 346 itself inside the CDN (e.g. down to the surrogates). 348 Delivery: The function within CDN surrogates responsible for 349 delivering a piece of content to the User Agent. For example, 350 delivery may be based on HTTP progressive download or HTTP adaptive 351 streaming. 353 Logging System: The function within a CDN responsible for collecting 354 the measurement and recording of distribution and delivery 355 activities. The information recorded by the logging system may be 356 used for various purposes including charging (e.g. of the CSP), 357 analytics and monitoring. 359 Control System: The function within a CDN responsible for 360 bootstrapping and controlling the other components of the CDN as well 361 as for handling interactions with external systems (e.g. handling 362 delivery service creation/update/removal requests, or specific 363 service provisioning requests). 365 1.2. CDN Background 367 Readers are assumed to be familiar with the architecture, features 368 and operation of CDNs. For readers less familiar with the operation 369 of CDNs, the following resources may be useful: 371 o RFC 3040 [RFC3040] describes many of the component technologies 372 that are used in the construction of a CDN. 373 o Taxonomy [TAXONOMY] compares the architecture of a number of CDNs. 374 o RFC 3466 [RFC3466] and RFC 3570 [RFC3570] are the output of the 375 IETF Content Delivery Internetworking (CDI) working group which 376 was closed in 2003. 378 Note: Some of the terms used in this document are similar to terms 379 used the above referenced documents. When reading this document 380 terms should be interpreted as having the definitions provided in 381 Section 1.1. 383 2. CDN Interconnection Use Cases 385 An increasing number of NSPs are deploying CDNs in order to deal 386 cost-effectively with the growing usage of on-demand video services 387 and other content delivery applications. 389 CDNs allow caching of content closer to the edge of a network so that 390 a given item of content can be delivered by a CDN Surrogate (i.e. a 391 cache) to multiple User Agents (and their End Users) without 392 transiting multiple times through the network core (i.e from the 393 content origin to the surrogate). This contributes to bandwidth cost 394 reductions for the NSP and to improved quality of experience for the 395 End Users. CDNs also enable replication of popular content across 396 many surrogates, which enables content to be served to large numbers 397 of User Agents concurrently. This also helps dealing with situations 398 such as flash crowds and denial of service attacks. 400 The CDNs deployed by NSPs are not just restricted to the delivery of 401 content to support the Network Service Provider's own 'walled garden' 402 services, such as IP delivery of television services to Set Top 403 Boxes, but are also used for delivery of content to other devices 404 including PCs, tablets, mobile phones etc. 406 Some service providers operate over multiple geographies and federate 407 multiple affiliate NSPs. These NSPs typically operate independent 408 CDNs. As they evolve their services (e.g. for seamless support of 409 content services to nomadic users across affiliate NSPs) there is a 410 need for interconnection of these CDNs, that represents a first use 411 case for CDNI. However there are no open specifications, nor common 412 best practices, defining how to achieve such CDN interconnection. 414 CSPs have a desire to be able to get (some of) their content to very 415 large numbers of End Users, who are often distributed across a number 416 of geographies, while maintaining a high quality of experience, all 417 without having to maintain direct business relationships with many 418 different CDN Providers (or having to extend their own CDN to a large 419 number of locations). Some NSPs are considering interconnecting 420 their respective CDNs (as well as possibly over-the-top CDNs) so that 421 this collective infrastructure can address the requirements of CSPs 422 in a cost effective manner. This represents a second use case for 423 CDNI. In particular, this would enable the CSPs to benefit from on- 424 net delivery (i.e. within the Network Service Provider's own network/ 425 CDN footprint) whenever possible and off-net delivery otherwise, 426 without requiring the CSPs to maintain direct business relationships 427 with all the CDNs involved in the delivery. Again, CDN Providers 428 (NSPs or over-the-top CDN operators) are faced with a lack of open 429 specifications and best practices. 431 NSPs have often deployed CDNs as specialized cost-reduction projects 432 within the context of a particular service or environment. Some NSPs 433 operate separate CDNs for separate services. For example, there may 434 be a CDN for managed IPTV service delivery, a CDN for web-TV delivery 435 and a CDN for video delivery to Mobile terminals. As NSPs integrate 436 their service portfolio, there is a need for interconnecting these 437 CDNs, representing a third use case for CDNI. Again, NSPs face the 438 problem of lack of open interfaces for CDN interconnection. 440 For operational reasons (e.g. disaster, flash crowd) or commercial 441 reasons, an over-the-top CDN may elect to make use of another CDN 442 (e.g. an NSP CDN with on-net Surrogates for a given footprint) for 443 serving a subset of the user requests (e.g. requests from users 444 attached to that NSP), which results in a fourth use case for CDNI 445 because CDN Providers (over-the-top CDN Providers or NSPs) are faced 446 with a lack of open specifications and best practices. 448 Use cases for CDN Interconnection are further discussed in 449 [I-D.ietf-cdni-use-cases]. 451 3. CDN Interconnection Model & Problem Area for IETF 453 This section discusses the problem area for the IETF work on CDN 454 Interconnection. 456 Interconnecting CDNs involves interactions among multiple different 457 functions and components that form each CDN. Only some of those 458 require standardization. 460 Some NSPs have started to perform experiments to explore whether 461 their CDN use cases can already be addressed with existing CDN 462 implementations. One set of such experiments is documented in 463 [I-D.bertrand-cdni-experiments]. The conclusions of those 464 experiments are that while some basic limited CDN Interconnection 465 functionality can be achieved with existing CDN technology, the 466 current lack of any standardized CDNI interfaces with the necessary 467 level of functionality such as those discussed in this document is 468 preventing the deployment of CDN Interconnection. 470 Listed below are the four interfaces required to interconnect a pair 471 of CDNs and that constitute the problem space of CDN Interconnection 472 along with the required functionality of each interface for which 473 standards do not currently exist. As part of the development of the 474 CDNI interfaces it will also be necessary to agree on common 475 mechanisms for how to identify and name the data objects that are to 476 be interchanged between interconnected CDNs. 478 The use of the term "interface" is meant to encompass the protocol 479 over which CDNI data representations (e.g. CDNI Metadata objects) 480 are exchanged as well as the specification of the data 481 representations themselves (i.e. what properties/fields each object 482 contains, its structure, etc.). 484 o CDNI Control interface: This interface allows the "CDNI Control" 485 system in interconnected CDNs to communicate. This interface may 486 support the following: 487 * Allow bootstrapping of the other CDNI interfaces (e.g. 488 interface address/URL discovery and establishment of security 489 associations). 490 * Allow configuration of the other CDNI interfaces (e.g. 491 Upstream CDN specifies information to be reported through the 492 CDNI Logging interface). 493 * Allow the downstream CDN to communicate static (or fairly 494 static) information about its delivery capabilities and 495 policies. 496 * Allow bootstrapping of the interface between CDNs for content 497 acquisition (even if that interface itself is outside the scope 498 of the CDNI work). 500 * Allow an upstream CDN to initiate or request specific actions 501 to be undertaken in the downstream CDN. For example, to allow 502 an upstream CDN to initiate content or CDNI Metadata 503 acquisition (pre-positioning) or to request the invalidation or 504 purging of content files and/or CDNI Metadata in a downstream 505 CDN. 506 o CDNI Request Routing interface: This interface allows the Request 507 Routing systems in interconnected CDNs to communicate to ensure 508 that an End User request can be (re)directed from an upstream CDN 509 to a surrogate in the downstream CDN, in particular where 510 selection responsibilities may be split across CDNs (for example 511 the upstream CDN may be responsible for selecting the downstream 512 CDN while the downstream CDN may be responsible for selecting the 513 actual surrogate within that downstream CDN). In particular, the 514 functions of the CDN Request Routing interface may be divided as 515 follows: 516 * A CDNI Request Routing Redirection interface which allows the 517 upstream CDN to query the downstream CDN at request routing 518 time before redirecting the request to the downstream CDN. 519 * A CDNI Footprint & Capabilities advertisement interface which 520 allows the downstream CDN to provide to the upstream CDN 521 (static or dynamic) information (e.g. resources, footprint, 522 load) to facilitate selection of the downstream CDN by the 523 upstream CDN request routing system when processing subsequent 524 content requests from User Agents. 525 o CDNI Metadata distribution interface: This interface allows the 526 Distribution system in interconnected CDNs to communicate to 527 ensure CDNI Metadata can be exchanged across CDNs. See 528 Section 1.1 for definition and examples of CDNI Metadata. 529 o CDNI Logging interface: This interface allows the Logging system 530 in interconnected CDNs to communicate the relevant activity logs 531 in order to allow log consuming applications to operate in a 532 multi-CDN environments. For example, an upstream CDN may collect 533 delivery logs from a downstream CDN in order to perform 534 consolidated charging of the CSP or for settlement purposes across 535 CDNs. Similarly, an upstream CDN may collect delivery logs from a 536 downstream CDN in order to provide consolidated reporting and 537 monitoring to the CSP. 539 Note that the actual grouping of functionalities under these four 540 interfaces is considered tentative at this stage and may be changed 541 after further study (e.g. some subset of functionality be moved from 542 one interface into another). 544 The above list covers a significant potential problem space, in part 545 because in order to interconnect two CDNs there are several 'touch 546 points' that require standardization. However, it is expected that 547 the CDNI interfaces need not be defined from scratch and instead can 548 very significantly reuse or leverage existing protocols; this is 549 discussed further in Section 4. 551 The interfaces that form the CDNI problem area are illustrated in 552 Figure 1. 554 -------- 555 / \ 556 | CSP | 557 \ / 558 -------- 559 * 560 * 561 * /\ 562 * / \ 563 ---------------------- |CDNI| ---------------------- 564 / Upstream CDN \ | | / Downstream CDN \ 565 | +-------------+ | Control Interface| +-------------+ | 566 |******* Control |<======|====|========>| Control *******| 567 |* +------*----*-+ | | | | +-*----*------+ *| 568 |* * * | | | | * * *| 569 |* +------*------+ | Logging Interface| +------*------+ *| 570 |* ***** Logging |<======|====|========>| Logging ***** *| 571 |* * +-*-----------+ | | | | +-----------*-+ * *| 572 |* * * * | Request Routing | * * * *| 573 .....*...+-*---------*-+ | Interface | +-*---------*-+...*.*... 574 . |* * *** Req-Routing |<======|====|========>| Req-Routing *** * *| . 575 . |* * * +-------------+.| | | | +-------------+ * * *| . 576 . |* * * . CDNI Metadata | * * *| . 577 . |* * * +-------------+ |. Interface | +-------------+ * * *| . 578 . |* * * | Distribution|<==.===|====|========>| Distribution| * * *| . 579 . |* * * | | | . \ / | | | * * *| . 580 . |* * * |+---------+ | | . \/ | | +---------+| * * *| . 581 . |* * ***| +---------+| | ....Request......+---------+ |*** * *| . 582 . |* *****+-|Surrogate|************************|Surrogate|-+***** *| . 583 . |******* +---------+| | Acquisition | |+----------+ *******| . 584 . | +-------------+ | | +-------*-----+ | . 585 . \ / \ * / . 586 . ---------------------- ---------*------------ . 587 . * . 588 . * Delivery . 589 . * . 590 . +--*---+ . 591 ...............Request.............................| User |..Request.. 592 | Agent| 593 +------+ 595 <==> interfaces inside the scope of CDNI 596 **** interfaces outside the scope of CDNI 597 .... interfaces outside the scope of CDNI 599 Figure 1: A Model for the CDNI Problem Area 601 As illustrated in Figure 1, the acquisition of content between 602 interconnected CDNs is out of scope for CDNI, which deserves some 603 additional explanation. The consequence of such a decision is that 604 the CDNI problem space described in this document is focussed on only 605 defining the control plane for CDNI; and the CDNI data plane (i.e. 606 the acquisition & distribution of the actual content objects) is out 607 of scope. The rationale for such a decision is that CDNs today 608 typically already use standardized protocols such as HTTP, FTP, 609 rsync, etc. to acquire content from their CSP customers and it is 610 expected that the same protocols could be used for acquisition 611 between interconnected CDNs. Therefore the problem of content 612 acquisition is considered already solved and all that is required 613 from specifications developed by the CDNI working group is to 614 describe within the CDNI Metadata the parameters to use to retrieve 615 the content for example the IP address/hostname to connect to, what 616 protocol to use to retrieve the content, etc. 618 4. Scoping the CDNI Problem 620 This section outlines how the scope of work addressing the CDNI 621 problem space can be constrained through reuse or leveraging of 622 existing protocols to implement the CDNI interfaces. This discussion 623 is not intended to pre-empt any working group decision as to the most 624 appropriate protocols, technologies and solutions to select to 625 realize the CDNI interfaces but is intended as an illustration of the 626 fact that the CDNI interfaces need not be created in a vacuum and 627 that reuse or leverage of existing protocols is likely possible. 629 The four CDNI interfaces (CDNI Control interface, CDNI Request 630 Routing interface, CDNI Metadata interface, CDNI Logging interface) 631 described in Section 3 within the CDNI problem area are all control 632 plane interfaces operating at the application layer (Layer 7 in the 633 OSI network model). Firstly, since it is not expected that these 634 interfaces would exhibit unique session, transport or network 635 requirements as compared to the many other existing applications in 636 the Internet, it is expected that the CDNI interfaces will be defined 637 on top of existing session, transport and network protocols. 639 Secondly, although a new application protocol could be designed 640 specifically for CDNI our analysis below shows that this is 641 unnecessary and it is recommended that existing application protocols 642 be reused or leveraged (HTTP [RFC2616], Atom Publishing Protocol 643 [RFC5023], XMPP [RFC6120], for example) to realize the CDNI 644 interfaces. 646 4.1. CDNI Request Routing Interface 648 The CDNI Request Routing interface enables a Request Routing function 649 in an upstream CDN to query a Request Routing function in a 650 downstream CDN to determine if the downstream CDN is able (and 651 willing) to accept the delegated content request. It also allows the 652 downstream CDN to control what should be returned to the User Agent 653 in the redirection message by the upstream Request Routing function . 655 The CDNI Request Routing interface is therefore a fairly 656 straightforward request/response interface and could be implemented 657 over any number of request/response protocols. For example, it may 658 be implemented as a WebService using one of the common WebServices 659 methodologies (XML-RPC, HTTP query to a known URI, etc.). This 660 removes the need for the CDNI working group to define a new protocol 661 for the request/response element of the CDNI Request Routing 662 interface. 664 Additionally, as discussed in Section 3, the CDNI Request Routing 665 interface is also expected to enable a downstream CDN to provide to 666 the upstream CDN (static or dynamic) information (e.g. resources, 667 footprint, load) to facilitate selection of the downstream CDN by the 668 upstream CDN request routing system when processing subsequent 669 content requests from User Agents. It is expected that such 670 functionality of the CDNI request Routing could be specified by the 671 CDNI working group with significant leveraging of existing IETF 672 protocols supporting the dynamic distribution of reachability 673 information (for example by leveraging existing routing protocols) or 674 supporting application level queries for topological information (for 675 example by leveraging ALTO [RFC5693]). 677 4.2. CDNI Metadata Interface 679 The CDNI Metadata interface enables the Distribution System in a 680 downstream CDN to request CDNI Metadata from an upstream CDN so that 681 the downstream CDN can properly process and respond to redirection 682 requests received over the CDNI Request Routing interface and Content 683 Requests received directly from User Agents. 685 The CDNI Metadata interface is therefore similar to the CDNI Request 686 Routing interface because it is a request/response interface with the 687 potential addition that CDNI Metadata search may have more complex 688 semantics than a straightforward Request Routing redirection request. 689 Therefore, like the CDNI Request Routing interface, the CDNI Metadata 690 interface may be implemented as a WebService using one of the common 691 WebServices methodologies (XML-RPC, HTTP query to a known URI, etc.) 692 or possibly using other existing protocols such as XMPP [RFC6120]. 693 This removes the need for the CDNI working group to define a new 694 protocol for the request/response element of the CDNI Metadata 695 interface. 697 4.3. CDNI Logging Interface 699 The CDNI Logging interface enables details of logs or events to be 700 exchanged between interconnected CDNs, where events could be for 701 example log records related to the delivery of content (similar to 702 the log records recorded in a web server's access log) as well as 703 real-time or near-real time events before, during or after content 704 delivery and operations and diagnostic messages. 706 Several protocols already exist that could potentially be used to 707 exchange CDNI logs between interconnected CDNs including SNMP, 708 syslog, ftp (and secure variants), HTTP POST, etc. 710 4.4. CDNI Control Interface 712 The CDNI Control interface allows the Control System in 713 interconnected CDNs to communicate. The exact inter-CDN control 714 functionality required to be supported by the CDNI Control interface 715 is less well defined than the other three CDNI interfaces at this 716 time. 718 It is expected that for the Control interface, as for the other CDNI 719 Interfaces, existing protocols can be reused or leveraged. 721 5. IANA Considerations 723 This document makes no request of IANA. 725 Note to RFC Editor: this section may be removed on publication as an 726 RFC. 728 6. Security Considerations 730 Distribution of content by a CDN comes with a range of security 731 considerations such as how to enforce control of access to the 732 content by end users in line with the CSP policy, or how to trust the 733 logging information generated by the CDN for the purposes of charging 734 the CSP. These security aspects are already dealt with by CDN 735 Providers and CSPs today in the context of standalone CDNs. However, 736 interconnection of CDNs introduces a new set of security 737 considerations by extending the trust model to a chain of trust (i.e. 738 the CSP "trusts" a CDN that "trusts" another CDN). The mechanisms 739 used to mitigate these risks in multi-CDN environments may be similar 740 to those used in the single CDN case, but their suitability in this 741 more complex environment must be validated. 743 Maintaining the security of the content itself, its associated 744 metadata (including delivery policies) and the CDNs distributing and 745 delivering it, are critical requirements for both CDN Providers and 746 CSPs and the CDN Interconnection interfaces must provide sufficient 747 mechanisms to maintain the security of the overall system of 748 interconnected CDNs as well as the information (content, metadata, 749 logs, etc) distributed and delivered through any set of 750 interconnected CDNs. 752 6.1. Security of the CDNI Control interface 754 Information on this interface is of a very private nature between 755 interconnected CDNs. A pair of CDNs use this interface to allow 756 bootstrapping of all the other CDNI interfaces possibly including 757 establishment of the mechanisms for securing these interfaces. 758 Therefore, corruption of that interface may result in corruption of 759 all other interfaces. Using this interface, an upstream CDN may pre- 760 position or delete content or metadata in a downstream CDN and a 761 downstream CDN may provide administrative information to an upstream 762 CDN, etc. All of these operations require that the peer CDNs are 763 appropriately authenticated and that the confidentiality and 764 integrity of information flowing between them can be ensured. 766 6.2. Security of the CDNI Request Routing Interface 768 Appropriate levels of authentication and confidentiality must be used 769 in this interface because it allows an upstream CDN to query the 770 downstream CDN in order to redirect requests, and conversely, allows 771 the downstream CDN to influence the upstream CDN's Request Routing 772 function. 774 In the absence of appropriate security on this interface, a rogue 775 upstream CDN could inundate downstream CDNs with bogus requests, or 776 have the downstream CDN send the rogue upstream CDN private 777 information. Also, a rogue downstream CDN could influence the 778 upstream CDN so the upstream CDN redirects requests to the rogue dCDN 779 or another dCDN in order to, for example, attract additional delivery 780 revenue. 782 6.3. Security of the CDNI Metadata interface 784 This interface allows a downstream CDN to request CDNI metadata from 785 an upstream CDN, and therefore the upstream CDN must ensure that the 786 former is appropriately authenticated before sending the data. 787 Conversely, a downstream CDN must authenticate an upstream CDN before 788 requesting metadata to insulate itself from poisoning by rogue 789 upstream CDNs. The confidentiality and integrity of the information 790 exchanged between the peers must be protected. 792 6.4. Security of the CDNI Logging interface 794 Logging data consists of potentially sensitive information (which end 795 user accessed which media resource, IP addresses of end users, 796 potential names and subscriber account information, etc.). 797 Confidentiality of this information must be protected as log records 798 are moved between CDNs. This information may also be sensitive from 799 the viewpoint that it can be the basis for charging across CDNs. 800 Therefore, appropriate levels of protection are needed against 801 corruption, duplication and loss of this information. 803 7. Acknowledgements 805 The authors would like to thank Andre Beck, Gilles Bertrand, Mark 806 Carlson, Bruce Davie, David Ferguson, Yiu Lee, Kent Leung, Will Li, 807 Kevin Ma, Julien Maisonneuve, Guy Meador, Larry Peterson, Emile 808 Stephan, Oskar van Deventer, Mahesh Viveganandhan and Richard Woundy 809 for their review comments and contributions to the text. 811 8. References 813 8.1. Normative References 815 8.2. Informative References 817 [3GP-DASH] 818 "Transparent end-to-end Packet-switched Streaming Service 819 (PSS); Progressive Download and Dynamic Adaptive Streaming 820 over HTTP (3GP-DASH) 821 http://www.3gpp.org/ftp/Specs/html-info/26247.htm". 823 [ALTO-Charter] 824 "IETF ALTO WG Charter 825 (http://datatracker.ietf.org/wg/alto/charter/)". 827 [ATIS] "ATIS (http://www.atis.org/)". 829 [ATIS-COD] 830 "ATIS IIF: IPTV Content on Demand Service, January 2011 (h 831 ttp://www.atis.org/iif/_Com/Docs/Task_Forces/ARCH/ 832 ATIS-0800042.pdf)". 834 [CDI-Charter] 835 "IETF CDI WG Charter 836 (http://www.ietf.org/wg/concluded/cdi)". 838 [CableLabs] 839 "CableLabs (http://www.cablelabs.com/about/)". 841 [CableLabs-Metadata] 842 "CableLabs VoD Metadata Project Primer 843 (http://www.cablelabs.com/projects/metadata/primer/)". 845 [DECADE-Charter] 846 "IETF DECADE WG Charter 847 (http://datatracker.ietf.org/wg/decade/charter/)". 849 [I-D.bertrand-cdni-experiments] 850 Faucheur, F. and L. Peterson, "Content Distribution 851 Network Interconnection (CDNI) Experiments", 852 draft-bertrand-cdni-experiments-02 (work in progress), 853 February 2012. 855 [I-D.ietf-cdni-use-cases] 856 Bertrand, G., Emile, S., Watson, G., Burbridge, T., 857 Eardley, P., and K. Ma, "Use Cases for Content Delivery 858 Network Interconnection", draft-ietf-cdni-use-cases-04 859 (work in progress), March 2012. 861 [I-D.jenkins-alto-cdn-use-cases] 862 Previdi, S., Watson, G., Medved, J., Bitar, N., and B. 863 Niven-Jenkins, "Use Cases for ALTO within CDNs", 864 draft-jenkins-alto-cdn-use-cases-02 (work in progress), 865 December 2011. 867 [MPEG-DASH] 868 "Information technology - MPEG systems technologies - Part 869 6: Dynamic adaptive streaming over HTTP (DASH), (DIS 870 version), February 2011 871 http://mpeg.chiariglione.org/ 872 working_documents.htm#MPEG-B". 874 [OIPF-Overview] 875 "OIPF Release 2 Specification Volume 1 - Overview", 876 September 2010. 878 [P2PRG-CDNI] 879 Davie, B. and F. Le Faucheur, "Interconnecting CDNs aka 880 "Peering Peer-to-Peer" 881 (http://www.ietf.org/proceedings/77/slides/P2PRG-2.pdf)", 882 March 2010. 884 [PPSP-Charter] 885 "IETF PPSP WG Charter 886 (http://datatracker.ietf.org/wg/ppsp/charter/)". 888 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 889 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 890 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 892 [RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web 893 Replication and Caching Taxonomy", RFC 3040, January 2001. 895 [RFC3466] Day, M., Cain, B., Tomlinson, G., and P. Rzewski, "A Model 896 for Content Internetworking (CDI)", RFC 3466, 897 February 2003. 899 [RFC3568] Barbir, A., Cain, B., Nair, R., and O. Spatscheck, "Known 900 Content Network (CN) Request-Routing Mechanisms", 901 RFC 3568, July 2003. 903 [RFC3570] Rzewski, P., Day, M., and D. Gilletti, "Content 904 Internetworking (CDI) Scenarios", RFC 3570, July 2003. 906 [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing 907 Protocol", RFC 5023, October 2007. 909 [RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic 910 Optimization (ALTO) Problem Statement", RFC 5693, 911 October 2009. 913 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 914 Protocol (XMPP): Core", RFC 6120, March 2011. 916 [SNIA-CDMI] 917 "SNIA CDMI (http://www.snia.org/tech_activities/standards/ 918 curr_standards/cdmi)". 920 [TAXONOMY] 921 Pathan, A., "A Taxonomy and Survey of Content Delivery 922 Networks 923 (http://www.gridbus.org/reports/CDN-Taxonomy.pdf)", 2007. 925 [Y.1910] "ITU-T Recomendation Y.1910 "IPTV functional 926 architecture"", September 2008. 928 [Y.2019] "ITU-T Recomendation Y.2019 "Content delivery functional 929 architecture in NGN"", September 2010. 931 Appendix A. Design considerations for realizing the CDNI Interfaces 933 This section expands on how CDNI interfaces can reuse and leverage 934 existing protocols before describing each CDNI interface individually 935 and highlighting example candidate protocols that could be considered 936 for reuse or leveraging to implement the CDNI interfaces. 938 A.1. CDNI Request Routing Interface 940 The CDNI Request Routing interface enables a Request Routing function 941 in an upstream CDN to query a Request Routing function in a 942 downstream CDN to determine if the downstream CDN is able (and 943 willing) to accept the delegated content request and to allow the 944 downstream CDN to control what the upstream Request Routing function 945 should return to the User Agent in the redirection message. 947 Therefore, the CDNI Request Routing interface needs to offer a 948 mechanism for an upstream CDN to issue a "Redirection Request" to a 949 downstream CDN. The Request Routing interface needs to be able to 950 support scenarios where the initial User Agent request to the 951 upstream CDN is received over DNS as well as over a content specific 952 application protocol (e.g. HTTP, RTSP, RTMP, etc.). 954 Therefore a Redirection Request is expected to contain information 955 such as: 957 o The protocol (e.g. DNS, HTTP) over which the upstream CDN 958 received the initial User Agent request. 959 o Additional details of the User Agent request that are required to 960 perform effective Request Routing by the Downstream CDN. For DNS 961 this would typically be the IP address of the DNS resolver making 962 the request on behalf of the User Agent. For requests received 963 over content specific application protocols the Redirection 964 Request could contain significantly more information related to 965 the original User Agent request but at a minimum is expected to 966 include the User Agent's IP address, the equivalent of the HTTP 967 Host header and the equivalent of the HTTP abs_path defined in 968 [RFC2616]. 970 It should be noted that, the CDNI architecture needs to consider that 971 a downstream CDN may receive requests from User Agents without first 972 receiving a Redirection Request from an upstream CDN for the 973 corresponding User Agent request, for example because: 975 o User Agents (or DNS resolvers) may cache DNS or application 976 responses from Request Routers. 978 o Responses to Redirection Requests over the Request Routing 979 interface may be cacheable. 980 o Some CDNs may rely on simple coarse policies, e.g. CDN B agrees 981 to always serve CDN A's delegated redirection requests, in which 982 case the necessary redirection details are exchanged out of band 983 (of the CDNI interfaces), e.g. configured. 985 On receiving a Redirection Request, the downstream CDN will use the 986 information provided in the request to determine if it is able (and 987 willing) to accept the delegated content request and needs to return 988 the result of its decision to the upstream CDN. 990 Thus, a Redirection Response from the downstream CDN is expected to 991 contain information such as: 993 o Status code indicating acceptance or rejection (possibly with 994 accompanying reasons). 995 o Information to allow redirection by the Upstream CDN. In the case 996 of DNS-based request routing, this is expected to include the 997 equivalent of a DNS record(s) (e.g. a CNAME) that the upstream CDN 998 should return to the requesting DNS resolver. In the case of 999 application based request routing, this is expected to include the 1000 information necessary to construct the application specific 1001 redirection response(s) to return to the requesting User Agent. 1002 For HTTP requests from User Agents this could include a URI that 1003 the upstream CDN could return in a HTTP 3xx response. 1005 The CDNI Request Routing interface is therefore a fairly 1006 straightforward request/response interface and could be implemented 1007 over any number of request/response protocols. For example, it may 1008 be implemented as a WebService using one of the common WebServices 1009 methodologies (XML-RPC, HTTP query to a known URI, etc.). This 1010 removes the need for the CDNI working group to define a new protocol 1011 for the request/response element of the CDNI Request Routing 1012 interface. Thus, the CDNI working group would be left only with the 1013 task of specifying: 1015 o The recommended request/response protocol to use along with any 1016 additional semantics and procedures that are specific to the CDNI 1017 Request Routing interface (e.g. handling of malformed requests/ 1018 responses). 1019 o The syntax (i.e representation/encoding) of the redirection 1020 requests and responses. 1021 o The semantics (i.e. meaning and expected contents) of the 1022 redirection requests and responses. 1024 Additionally, as discussed in Section 3, the CDNI Request Routing 1025 interface is also expected to enable a downstream CDN to provide to 1026 the upstream CDN (static or dynamic) information (e.g. resources, 1027 footprint, load) to facilitate selection of the downstream CDN by the 1028 upstream CDN request routing system when processing subsequent 1029 content requests from User Agents. It is expected that such 1030 functionality of the CDNI request Routing could be specified by the 1031 CDNI working group with significant leveraging of existing IETF 1032 protocols supporting the dynamic distribution of reachability 1033 information (for example by leveraging existing routing protocols) or 1034 supporting application level queries for topological information (for 1035 example by leveraging ALTO). 1037 A.2. CDNI Metadata Interface 1039 The CDNI Metadata interface enables the Distribution System in a 1040 downstream CDN to obtain CDNI Metadata from an upstream CDN so that 1041 the downstream CDN can properly process and respond to: 1043 o Redirection Requests received over the CDNI Request Routing 1044 interface. 1045 o Content Requests received directly from User Agents. 1047 The CDNI Metadata interface needs to offer a mechanism for an 1048 Upstream CDN to: 1050 o Distribute/update/remove CDNI Metadata to a Downstream CDN. 1052 and/or to allow a downstream CDN to: 1054 o Make direct requests for CDNI Metadata objects 1055 o Make recursive requests for CDNI metadata, for example to enable a 1056 downstream CDN to walk down a tree of objects with inter-object 1057 relationships. 1059 The CDNI Metadata interface is therefore similar to the CDNI Request 1060 Routing interface because it is a request/response interface with the 1061 potential addition that CDNI Metadata search may have more complex 1062 semantics than a straightforward Request Routing redirection request. 1063 Therefore, like the CDNI Request Routing interface, the CDNI Metadata 1064 interface may be implemented as a WebService using one of the common 1065 WebServices methodologies (XML-RPC, HTTP query to a known URI, etc.) 1066 or possibly using other existing protocols such as XMPP [RFC6120]. 1067 This removes the need for the CDNI working group to define a new 1068 protocol for the request/response element of the CDNI Metadata 1069 interface. 1071 Thus, the CDNI working group would be left only with the task of 1072 specifying: 1074 o The recommended request/response protocol to use along with any 1075 additional semantics that are specific to the CDNI Metadata 1076 interface (e.g. handling of malformed requests/responses). 1077 o The syntax (i.e representation/encoding) of the CDNI Metadata 1078 objects that will be exchanged over the interface. 1079 o The semantics (i.e. meaning and expected contents) of the 1080 individual properties of a Metadata object. 1081 o How the relationships between different CDNI Metadata objects are 1082 represented. 1084 A.3. CDNI Logging Interface 1086 The CDNI Logging interface enables details of logs or events to be 1087 exchanged between interconnected CDNs, where events could be: 1089 o Log records related to the delivery of content (similar to the log 1090 records recorded in a web server's access log). 1091 o Real-time or near-real time events before, during or after content 1092 delivery, e.g. content delivery interruption 1093 o Operations and diagnostic messages. 1095 Within CDNs today, logs and events are used for a variety of purposes 1096 in addition to real-time and non real-time diagnostics and auditing 1097 by the CDN Provider and its customers. Specifically CDNs use logs to 1098 generate Call Data Records (CDRs) for passing to billing and payment 1099 systems and to real-time (and near real-time) analytics systems. 1100 Such applications place requirements on the CDNI Logging interface to 1101 support guaranteed and timely delivery of log messages between 1102 interconnected CDNs. It may also be necessary to be able to prove 1103 the integrity of received log messages. 1105 Several protocols already exist that could potentially be used to 1106 exchange CDNI logs between interconnected CDNs including SNMP Traps, 1107 syslog, ftp, HTTP POST, etc. although it is likely that some of the 1108 candidate protocols may not be well suited to meet all the 1109 requirements of CDNI. For example SNMP traps pose scalability 1110 concerns and SNMP does not support guaranteed delivery of Traps and 1111 therefore could result in log records being lost and the consequent 1112 CDRs and billing records for that content delivery not being produced 1113 as well as that content delivery being invisible to any analytics 1114 platforms. 1116 Although it is not necessary to define a new protocol for exchanging 1117 logs across the CDNI Logging interface, the CDNI working group would 1118 still need to specify: 1120 o The recommended protocol to use. 1121 o A default set of log fields and their syntax & semantics. Today 1122 there is no standard set of common log fields across different 1123 content delivery protocols and in some cases there is not even a 1124 standard set of log field names and values for different 1125 implementations of the same delivery protocol. 1126 o A default set of events that trigger logs to be generated. 1128 A.4. CDNI Control Interface 1130 The CDNI Control interface allows the Control System in 1131 interconnected CDNs to communicate. The exact inter-CDN control 1132 functionality required to be supported by the CDNI Control interface 1133 is less well defined than the other three CDNI interfaces at this 1134 time. 1136 However, as discussed in Section 3, the CDNI Control interface may be 1137 required to support functionality similar to the following: 1138 o Allow an upstream CDN and downstream CDN to establish, update or 1139 terminate their CDNI interconnection. 1140 o Allow bootstrapping of the other CDNI interfaces (e.g. protocol 1141 address discovery and establishment of security associations). 1142 o Allow configuration of the other CDNI interfaces (e.g. Upstream 1143 CDN specifies information to be reported through the CDNI Logging 1144 interface). 1145 o Allow the downstream CDN to communicate static information about 1146 its delivery capabilities, resources and policies. 1147 o Allow bootstrapping of the interface between CDNs for content 1148 acquisition (even if that interface itself is outside the scope of 1149 the CDNI work). 1150 It is expected that for the Control interface also, existing 1151 protocols can be reused or leveraged. Those will be considered once 1152 the requirements for the Control interface have been refined. 1154 Appendix B. Additional Material 1156 Note to RFC Editor: This appendix is to be removed on publication as 1157 an RFC. 1159 B.1. Non-Goals for IETF 1161 Listed below are aspects of content delivery that the authors propose 1162 be kept outside of the scope of a potential CDNI working group: 1163 o The interface between Content Service Provider and the 1164 Authoritative CDN (i.e. the upstream CDN contracted by the CSP for 1165 delivery by this CDN or by its downstream CDNs). 1167 o The delivery interface between the delivering CDN surrogate and 1168 the User Agent, such as streaming protocols. 1169 o The request interface between the User Agent and the request- 1170 routing system of a given CDN. Existing IETF protocols (e.g. 1171 HTTP, RTSP, DNS) are commonly used by User Agents to request 1172 content from a CDN and by CDN request routing systems to redirect 1173 the User Agent requests. The CDNI working group need not define 1174 new protocols for this purpose. Note however, that the CDNI 1175 control plane interface may indirectly affect some of the 1176 information exchanged through the request interface (e.g. URI). 1177 o The content acquisition interface between CDNs (i.e. the data 1178 plane interface for actual delivery of a piece of content from one 1179 CDN to the other). This is expected to use existing protocols 1180 such as HTTP or protocols defined in other forums for content 1181 acquisition between an origin server and a CDN (e.g. HTTP-based 1182 C2 reference point of ATIS IIF CoD). The CDN Interconnection 1183 problem space described in this document may therefore only 1184 concern itself with the agreement/negotiation aspects of which 1185 content acquisition protocol is to be used between two 1186 interconnected CDNs in view of facilitating interoperability. 1187 o End User/User Agent Authentication. End User/User Agent 1188 authentication and authorization are the responsibility of the 1189 Content Service Provider. 1190 o Content preparation, including encoding and transcoding. The CDNI 1191 architecture aims at allowing distribution across interconnected 1192 CDNs of content treated as opaque objects. Interpretation and 1193 processing of the objects, as well as optimized delivery of these 1194 objects by the surrogate to the End User are outside the scope of 1195 CDNI. 1196 o Digital Rights Management (DRM). DRM is an end-to-end issue 1197 between a content protection system and the User Agent. 1198 o Applications consuming CDNI logs (e.g. charging, analytics, 1199 reporting,...). 1200 o Internal CDN interfaces & protocols (i.e. interfaces & protocols 1201 within one CDN). 1202 o Scalability of individual CDNs. While scalability of the CDNI 1203 interfaces/approach is in scope, how an individual CDN scales is 1204 out of scope. 1205 o Actual algorithms for selection of CDNs or Surrogates by Request 1206 Routing systems (however, some specific parameters required as 1207 input to these algorithms may be in scope when they need to be 1208 communicated across CDNs). 1209 o Surrogate algorithms. For example caching algorithms and content 1210 acquisition methods are outside the scope of the CDNI work. 1211 Content management (e.g. Content Deletion) as it relates to CDNI 1212 content management policies, is in scope but the internal 1213 algorithms used by a cache to determine when to no longer cache an 1214 item of Content (in the absence of any specific metadata to the 1215 contrary) is out of scope. 1216 o Element management interfaces. 1217 o Commercial, business and legal aspects related to the 1218 interconnections of CDNs. 1220 B.2. Related standardization activites 1222 There are a number of other standards bodies and industry forums that 1223 are working in areas related to CDNs, and in some cases related to 1224 CDNI. This section outlines any potential overlap with the work of 1225 the CDNI working group and any component that could potentially be 1226 reused to realize the CDNI interfaces. 1228 A number of standards bodies have produced specifications related to 1229 CDNs, for example: 1231 o ETSI TISPAN (Telecommunications and Internet converged Services 1232 and Protocols for Advanced Networking) has a series of 1233 specifications focusing on CDNs. 1234 o The Open IPTV Forum (OIPF) and ATIS IPTV Interoperability Forum 1235 (IIF) specify the architecture and the protocols of an IPTV 1236 solution. Although OIPF and ATIS specifications include the 1237 interaction with a CDN, the CDN specifications are coupled with 1238 their IPTV specifications and do not cover interconnection of 1239 CDNs. 1240 o ATIS Cloud Services Forum (CSF) has started investigating 1241 interconnection of CDNs. The ATIS CSF focuses on defining use 1242 cases and requirements for such CDN interconnection, which are 1243 expected to be considered as input into the work of the CDNI 1244 working group. At the time of writing this document, ATIS CSF is 1245 not specifying the corresponding protocols or interfaces and is 1246 expected to leverage the work of the IETF CDNI working group for 1247 those. 1248 o CableLabs, SNIA and ITU have developed (or are working on) 1249 definitions for content related metadata and specifications for 1250 its distribution. However, they do not include metadata specific 1251 to the distribution of content within a CDN or between 1252 interconnected CDNs. 1253 o IETF CDI working group (now concluded) touched on the same problem 1254 space as the present document. However, in accordance with its 1255 initial charter, the CDI working group did not define any 1256 protocols or interfaces to actually enable CDN Interconnection and 1257 at that time (2003) there was not enough industry interest and 1258 real life requirements to justify rechartering the working group 1259 to conduct the corresponding protocol work. 1261 Although some of the specifications describe multi-CDN cooperation or 1262 include reference points for interconnecting CDNs, none of them 1263 specify in sufficient detail all the CDNI interfaces and CDNI 1264 Metadata representations required to enable even a base level of CDN 1265 Interconnection functionality to be implemented. 1267 B.2.1. IETF CDI Working Group (Concluded) 1269 The Content Distribution Internetworking (CDI) Working Group was 1270 formed in the IETF following a BoF in December 2000 and closed in mid 1271 2003. 1273 For convenience, here is an extract from the CDI working group 1274 charter [CDI-Charter]: 1276 " 1278 o The goal of this working group is to define protocols to allow the 1279 interoperation of separately-administered content networks. 1280 o A content network is an architecture of network elements, arranged 1281 for efficient delivery of digital content. Such content includes, 1282 but is not limited to, web pages and images delivered via HTTP, 1283 and streaming or continuous media which are controlled by RTSP. 1284 o The working group will first define requirements for three modes 1285 of content internetworking: interoperation of request-routing 1286 systems, interoperation of distribution systems, and 1287 interoperation of accounting systems. These requirements are 1288 intended to lead to a follow-on effort to define protocols for 1289 interoperation of these systems. 1290 o In its initial form, the working group is not chartered to deliver 1291 those protocols [...] 1293 " 1295 Thus, the CDI working group touched on the same problem space as the 1296 present document. 1298 The CDI working group published 3 Informational RFCs: 1300 o RFC 3466 [RFC3466] - "A Model for Content Internetworking (CDI)". 1301 o RFC 3568 [RFC3568] - "Known Content Network (CN) Request-Routing 1302 Mechanisms". 1303 o RFC 3570 [RFC3570] - "Content Internetworking (CDI) Scenarios". 1305 B.2.2. 3GPP 1307 3GPP was the first organization that released a specification related 1308 to adaptive streaming over HTTP. 3GPP Release 9 specification on 1309 adaptive HTTP streaming was published in March 2010, and there have 1310 been some bug fixes on this specification since the publication. In 1311 addition, 3GPP has produced an extended version for Release 10, which 1312 was published in 2011. This release will include a number of 1313 clarifications, improvements and new features. 1315 [3GP-DASH] is defined as a general framework independent of the data 1316 encapsulation format. It has support for fast initial startup and 1317 seeking, adaptive bitrate switching, re-use of HTTP origin and cache 1318 servers, re-use of existing media playout engines, on-demand, live 1319 and time-shifted delivery. It specifies syntax and semantics of 1320 Media Presentation Description (MPD), format of segments and delivery 1321 protocol for segments. It does not specify content provisioning, 1322 client behavior or transport of MPD. 1324 The content retrieved by a client using [3GP-DASH] adaptive streaming 1325 could be obtained from a CDN but this is not discussed or specified 1326 in the 3GPP specifications as it is transparent to [3GP-DASH] 1327 operations. Similarly, it is expected that [3GP-DASH] can be used 1328 transparently from the CDNs as a delivery protocol (between the 1329 delivering CDN surrogate and the User Agent) in a CDN Interconnection 1330 environment. [3GP-DASH] could also be a candidate for content 1331 acquisition between CDNs in a CDN Interconnection environment. 1333 B.2.3. ISO MPEG 1335 Within ISO MPEG, the Dynamic Adaptive Streaming over HTTP (DASH) ad- 1336 hoc group adopted the 3GPP Release 9 [3GP-DASH] specification as a 1337 starting point and has made some improvements and extensions. 1338 Similar to 3GPP SA4, the MPEG DASH ad-hoc group has been working on 1339 standardizing the manifest file and the delivery format. 1340 Additionally, the MPEG DASH ad-hoc group has also been working on the 1341 use of MPEG-2 Transport Streams as a media format, conversion from/to 1342 existing file formats, common encryption, and so on. The MPEG DASH 1343 specification could also be a candidate for delivery to the User 1344 Agent and for content acquisition between CDNs in a CDN 1345 Interconnection environment. The Draft International Standard (DIS) 1346 version [MPEG-DASH] is currently publicly available since early 1347 February 2011. 1349 In the 95th MPEG meeting in January 2011, the DASH ad-hoc group 1350 decided to start a new evaluation experiment called "CDN-EE". The 1351 goals are to understand the requirements for MPEG DASH to better 1352 support CDN-based delivery, and to provide a guidelines document for 1353 CDN operators to better support MPEG DASH streaming services. The 1354 ongoing work is still very preliminary and does not currently target 1355 looking into CDN Interconnection use cases. 1357 B.2.4. ATIS IIF 1359 ATIS ([ATIS]) IIF is the IPTV Interoperability Forum (within ATIS) 1360 that develops requirements, standards, and specifications for IPTV. 1362 ATIS IIF is developing the "IPTV Content on Demand (CoD) Service" 1363 specification. This includes use of a CDN (referred to in ATIS IIF 1364 CoD as the "Content Distribution and Delivery Functions") for support 1365 of a Content on Demand (CoD) Service as part of a broader IPTV 1366 service. However, this only covers the case of a managed IPTV 1367 service (in particular where the CDN is administered by the service 1368 provider) and does not cover the use, or interconnection, of multiple 1369 CDNs. 1371 B.2.5. CableLabs 1373 "Founded in 1988 by cable operating companies, Cable Television 1374 Laboratories, Inc. (CableLabs) is a non-profit research and 1375 development consortium that is dedicated to pursuing new cable 1376 telecommunications technologies and to helping its cable operator 1377 members integrate those technical advancements into their business 1378 objectives." [CableLabs] 1380 CableLabs has defined specifications for CoD Content Metadata as part 1381 of its VOD Metadata project. 1383 B.2.6. ETSI MCD 1385 ETSI MCD (Media Content Distribution) is the ETSI technical committee 1386 "in charge of guiding and coordinating standardization work aiming at 1387 the successful overall development of multimedia systems (television 1388 and communication) responding to the present and future market 1389 requests on media content distribution". 1391 MCD created a specific work item on interconnection of heterogeneous 1392 CDNs ("CDN Interconnection, use cases and requirements") in March 1393 2010. MCD very recently created a working group to progress this 1394 work item. However, no protocol level work has yet started in MCD 1395 for CDN Interconnection. 1397 B.2.7. ETSI TISPAN 1399 ETSI TISPAN has published two sets of IPTV specifications, one of 1400 which is based on IMS. In addition, TISPAN has published a CDN 1401 architecture supporting delivery of various content services such as 1402 time-shifted TV and VoD to TISPAN devices (UEs) or regular PCs. The 1403 use cases allow for hierarchically and geographically distributed CDN 1404 scenarios, along with multi-CDN cooperation. As a result, the 1405 architecture contains reference points to support interconnection of 1406 other TISPAN CDNs. The protocol definition phase for the 1407 corresponding CDN architecture was kicked-off at the end of 2010 as 1408 is still in progress. In line with its long history of leveraging 1409 IETF protocols, ETSI could potentially leverage CDNI interfaces 1410 developed in the IETF for their related protocol level work on 1411 interconnections of CDNs. 1413 B.2.8. ITU-T 1415 SG13 is developing standards related to the support of IPTV services 1416 (i.e.. multimedia services such as television/VoD/audio/text/ 1417 graphics/data delivered over IP-based managed networks). 1419 ITU-T Recommendation Y.1910 [Y.1910] provides the description of the 1420 IPTV functional architecture. This architecture includes functions 1421 and interfaces for the distribution and delivery of content. This 1422 architecture is aligned with the ATIS IIF architecture. 1424 Based upon ITU-T Rec. Y.1910, ITU-T Rec. Y.2019 [Y.2019] describes in 1425 more detail the content delivery functional architecture. This 1426 architecture allows CDN Interconnection: some interfaces (such as D3, 1427 D4) at the control level allow relationships between different CDNs, 1428 in the same domain or in different domains. Generic procedures are 1429 described, but the choice of the protocols is open. 1431 B.2.9. Open IPTV Forum (OIPF) 1433 The Open IPTV Forum has developed an end-to-end solution to allow any 1434 OIPF terminal to access enriched and personalized IPTV services 1435 either in a managed or a non-managed network[OIPF-Overview]. Some 1436 OIPF services (such as Network PVR) may be hosted in a CDN. 1438 To that end, the Open IPTV Forum specification is made of 5 parts: 1440 o Media Formats including HTTP Adaptive Streaming 1441 o Content Metadata 1442 o Protocols 1443 o Terminal (Declarative or Procedural Application Environment) 1444 o Authentication, Content Protection and Service Protection 1446 B.2.10. TV-Anytime Forum 1448 Version 1 of the TV-Anytime Forum specifications were published as 1449 ETSI TS 102 822-1 through ETSI TS 102 822-7 "Broadcast and On-line 1450 Services: Search, select, and rightful use of content on personal 1451 storage systems ("TV-Anytime")". It includes the specification of 1452 content metadata in XML schemas (ETSI TS 102 822-3) which define 1453 technical parameters for the description of CoD and Live contents. 1454 The specification is referenced by DVB and OIPF. 1456 The TV-anytime Forum was closed in 2005. 1458 B.2.11. SNIA 1460 The Storage Networking Industry Association (SNIA) is an association 1461 of producers and consumers of storage networking products whose goal 1462 is to further storage networking technology and applications. 1464 SNIA has published the Cloud Data Management Interface (CDMI) 1465 standard ([SNIA-CDMI]). 1467 "The Cloud Data Management Interface defines the functional interface 1468 that applications will use to create, retrieve, update and delete 1469 data elements from the Cloud. As part of this interface the client 1470 will be able to discover the capabilities of the cloud storage 1471 offering and use this interface to manage containers and the data 1472 that is placed in them. In addition, metadata can be set on 1473 containers and their contained data elements through this interface." 1475 B.2.12. Summary of existing standardization work 1477 The following sections will summarize the existing work of the 1478 standard bodies listed earlier against the CDNI problem space. 1479 Appendix B.2.12.1 summarizes existing interfaces that could be 1480 leveraged for content acquisition between CDNs and Appendix B.2.12.2 1481 summarizes existing metadata specifications that may be applicable to 1482 CDNI. To date we are not aware of any standardization activities in 1483 the areas of the remaining CDNI interfaces (CDNI Request Routing, 1484 CDNI Control and CDNI Logging). 1486 B.2.12.1. Content Acquisition across CDNs and Delivery to End User 1487 (Data plane) 1489 A number of standards bodies have completed work in the areas of 1490 content acquisition interface between a CSP and a CDN, as well as as 1491 on the delivery interface between the surrogate and the User Agent. 1492 Some of this work is summarized below. 1494 TISPAN, OIPF and ATIS have specified IPTV and/or Content on Demand 1495 (CoD) services, including the data plane aspects (typically different 1496 flavors of RTP/RTCP and HTTP) to obtain content and deliver it to 1497 User Agents. For example, : 1498 o The OIPF data plane includes both RTP and HTTP flavors (HTTP 1499 progressive download, HTTP Adaptive streaming [3GP-DASH]). 1501 o The ATIS IIF specification "IPTV Content on Demand (CoD) Service" 1502 [ATIS-COD] defines a reference point (C2) and the corresponding 1503 HTTP-based data plane protocol for content acquisition between an 1504 authoritative origin server and the CDN. 1505 While these protocols have not been explicitly specified for content 1506 acquisition across CDNs, they are suitable (in addition to others 1507 such as standard HTTP) for content acquisition between CDNs in a CDN 1508 Interconnection environment. Therefore for the purpose of the CDNI 1509 working group there are already multiple existing data plane 1510 protocols that can be used for content acquisition across CDNs. 1512 Similarly, there are multiple existing standards (e.g. the OIPF data 1513 plane mentioned above, HTTP adaptive streaming [3GP-DASH]) or public 1514 specifications (e.g. vendor specific HTTP Adaptive streaming 1515 specifications) so that content delivery can be considered already 1516 solved (or at least sufficiently addressed in other forums). 1518 Thus, specification of the content acquisition interface between CDNs 1519 and the delivery interface between the surrogate and the User Agent 1520 are out of scope for the CDNI working group. The CDNI working group 1521 may only concern itself with the negotiation/selection aspects of the 1522 acquisition protocol to be used in a CDN interonnect scenario. 1524 B.2.12.2. CDNI Metadata 1526 CableLabs, ITU, OIPF and TV-Anytime have work items dedicated to the 1527 specification of content metadata: 1529 o CableLabs has defined specifications for CoD Content Metadata as 1530 part of its VOD Metadata project. "The VOD Metadata project is a 1531 cable television industry and cross-industry-wide effort to 1532 specify the metadata and interfaces for distribution of video-on- 1533 demand (VOD) material from multiple content providers to cable 1534 operators." [CableLabs-Metadata]. However, while the CableLabs 1535 work specifies an interface between a content provider and a 1536 service provider running a CDN, it does not include an interface 1537 that could be used between CDNs. 1538 o ITU Study Group 16 has started work on a number of draft 1539 Recommendations (H.IPTV-CPMD, H.IPTV-CPMD, HSTP.IPTV-CMA, 1540 HSTP.IPTV-UMCI) specifying metadata for content distribution in 1541 IPTV services. 1542 o An Open IPTV Terminal receives the technical description of the 1543 content distribution from the OIPF IPTV platform before receiving 1544 any content. The Content distribution metadata is sent in the 1545 format of a TV-Anytime XSD including tags to describes the 1546 location and program type (on demand or Live) as well as 1547 describing the time availability of the on demand and live 1548 content. 1550 However the specifications outlined above do not include metadata 1551 specific to the distribution of content within a CDN or between 1552 interconnected CDNs, for example geo-blocking information, 1553 availability windows, access control mechanisms to be enforced by the 1554 surrogate, how to map an incoming content request to a file on the 1555 origin server or acquire it from the upstream CDN etc. 1557 The CDMI standard ([SNIA-CDMI]) from SNIA defines metadata that can 1558 be associated with data that is stored by a cloud storage provider. 1559 While the metadata currently defined do not match the needs of CDN 1560 Interconnection, it is worth considering CDMI as one of the existing 1561 pieces of work that may potentially be leveraged for the CDNI 1562 Metadata interface (e.g by extending the CDMI metadata to address 1563 more specific CDNI needs). 1565 B.3. Related Research Projects 1567 B.3.1. IRTF P2P Research Group 1569 Some information on CDN interconnection motivations and technical 1570 issues were presented in the P2P RG at IETF 77. The presentation can 1571 be found in [P2PRG-CDNI]. 1573 B.3.2. OCEAN 1575 OCEAN (http://www.ict-ocean.eu/) is an EU funded research project 1576 that started in February 2010 for 3 years. Some of its objectives 1577 are relevant to CDNI. It aims, among other things, at designing a 1578 new architectural framework for audiovisual content delivery over the 1579 Internet, defining public interfaces between its major building 1580 blocks in order to foster multi-vendor solutions and interconnection 1581 between Content Networks (the term "Content Networks" corresponds 1582 here to the definition introduced in [RFC3466], which encompasses 1583 CDNs). 1585 OCEAN has not yet published any open specifications, nor common best 1586 practices, defining how to achieve such CDN interconnection. 1588 B.3.3. Eurescom P1955 1590 Eurescom P1955 was a 2010 research project involving a four European 1591 Network operators, which studied the interests and feasibility of 1592 interconnecting CDNs by firstly elaborating the main service models 1593 around CDN interconnection, as well as analyzing an adequate CDN 1594 interconnection technical architecture and framework, and finally by 1595 providing recommendations for telcos to implement CDN 1596 interconnection. The Eurescom P1955 project ended in July 2010. 1598 The authors are not aware of material discussing CDN interconnection 1599 protocols or interfaces made publicly available as a deliverable of 1600 this project. 1602 B.4. Relationship to relevant IETF Working Groups 1604 B.4.1. ALTO 1606 As stated in the ALTO Working Group charter [ALTO-Charter]: 1608 "The Working Group will design and specify an Application-Layer 1609 Traffic Optimization (ALTO) service that will provide applications 1610 with information to perform better-than-random initial peer 1611 selection. ALTO services may take different approaches at balancing 1612 factors such as maximum bandwidth, minimum cross-domain traffic, 1613 lowest cost to the user, etc. The working group will consider the 1614 needs of BitTorrent, tracker-less P2P, and other applications, such 1615 as content delivery networks (CDN) and mirror selection." 1617 In particular, the ALTO service can be used by a CDN Request Routing 1618 system to improve its selection of a CDN surrogate to serve a 1619 particular User Agent request (or to serve a request from another 1620 surrogate). [I-D.jenkins-alto-cdn-use-cases] describes a number of 1621 use cases for a CDN to be able to obtain network topology and cost 1622 information from an ALTO server(s) and discusses how CDN Request 1623 Routing could be used as an integration point of ALTO into CDNs. It 1624 is possible that the ALTO service could be used in the same manner in 1625 a multi-CDN environment based on CDN Interconnection. For example, 1626 an upstream CDN may take advantage of the ALTO service in its 1627 decision for selecting a downstream CDN to which a user request 1628 should be delegated. 1630 However, the current work of ALTO is complementary to and does not 1631 overlap with the work described in this document because the 1632 integration between ALTO and a CDN is an internal decision for a 1633 specific CDN and is therefore out of scope for the CDNI working 1634 group. One area for further study is whether additional information 1635 should be provided by an ALTO service to facilitate CDNI CDN 1636 selection. 1638 B.4.2. DECADE 1640 The DECADE Working Group [DECADE-Charter] is addressing the problem 1641 of reducing traffic on the last-mile uplink, as well as backbone and 1642 transit links caused by P2P streaming and file sharing applications. 1643 It addresses the problem by enabling an application endpoint to make 1644 content available from an in-network storage service and by enabling 1645 other application endpoints to retrieve the content from there. 1647 Exchanging data through the in-network storage service in this 1648 manner, instead of through direct communication, provides significant 1649 gain where: 1651 o The network capacity/bandwidth from in-network storage service to 1652 application endpoint significantly exceeds the capacity/bandwidth 1653 from application endpoint to application endpoint (e.g. because of 1654 an end-user uplink bottleneck); and 1655 o Where the content is to be accessed by multiple instances of 1656 application endpoints (e.g. as is typically the case for P2P 1657 applications). 1659 While, as is the case for any other data distribution application, 1660 the DECADE architecture and mechanisms could potentially be used for 1661 exchange of CDNI control plane information via an in-network-storage 1662 service (as opposed to directly between the entities terminating the 1663 CDNI interfaces in the neighbor CDNs), we observe that: 1665 o CDNI would operate as a "Content Distribution Application" from 1666 the DECADE viewpoint (i.e. would operate on top of DECADE). 1667 o There does not seem to be obvious benefits in integrating the 1668 DECADE control plane responsible for signaling information 1669 relating to control of the in-network storage service itself, and 1670 the CDNI control plane responsible for application-specific CDNI 1671 interactions (such as exchange of CDNI metadata, CDNI request 1672 redirection, transfer of CDNI logging information). 1673 o There would typically be limited benefits in making use of a 1674 DECADE in-network storage service because the CDNI interfaces are 1675 expected to be terminated by a very small number of CDNI clients 1676 (if not one) in each CDN, and the CDNI clients are expected to 1677 benefit from high bandwidth/capacity when communicating directly 1678 to each other (at least as high as if they were communicating via 1679 an in-network storage server). 1681 The DECADE in-network storage architecture and mechanisms may 1682 theoretically be used for the acquisition of the content objects 1683 themselves between interconnected CDNs. It is not expected that this 1684 would have obvious benefits in typical situations where a content 1685 object is acquired only once from an Upstream CDN to a Downstream CDN 1686 (and then distributed as needed inside the Downstream CDN). But it 1687 might have benefits in some particular situations. Since the 1688 acquisition protocol between CDNs is outside the scope of the CDNI 1689 work, this question is left for further study. 1691 The DECADE in-network storage architecture and mechanisms may 1692 potentially also be used within a given CDN for the distribution of 1693 the content objects themselves among surrogates of that CDN. Since 1694 the CDNI work does not concern itself with operation within a CDN, 1695 this question is left for further study. 1697 Therefore, the work of DECADE may be complementary to but does not 1698 overlap with the CDNI work described in this document. 1700 B.4.3. PPSP 1702 As stated in the PPSP Working Group charter [PPSP-Charter]: 1704 "The Peer-to-Peer Streaming Protocol (PPSP) working group develops 1705 two signaling and control protocols for a peer-to-peer (P2P) 1706 streaming system for transmitting live and time-shifted media content 1707 with near real-time delivery requirements." and "The PPSP working 1708 group designs a protocol for signaling and control between trackers 1709 and peers (the PPSP "tracker protocol") and a signaling and control 1710 protocol for communication among the peers (the PPSP "peer 1711 protocol"). The two protocols enable peers to receive streaming data 1712 within the time constraints required by specific content items." 1714 Therefore PPSP is concerned with the distribution of the streamed 1715 content itself along with the necessary signaling and control 1716 required to distribute the content. As such, it could potentially be 1717 used for the acquisition of streamed content across interconnected 1718 CDNs. But since the acquisition protocol is outside the scope of the 1719 work proposed for CDNI, we leave this for further study. Also, 1720 because of its streaming nature, PPSP is not seen as applicable to 1721 the distribution and control of the CDNI control plane and CDNI data 1722 representations. 1724 Therefore, the work of PPSP may be complementary to but does not 1725 overlap with the work described in this document for CDNI. 1727 Authors' Addresses 1729 Ben Niven-Jenkins 1730 Velocix (Alcatel-Lucent) 1731 326 Cambridge Science Park 1732 Milton Road, Cambridge CB4 0WG 1733 UK 1735 Email: ben@velocix.com 1736 Francois Le Faucheur 1737 Cisco Systems 1738 Greenside, 400 Avenue de Roumanille 1739 Sophia Antipolis 06410 1740 France 1742 Phone: +33 4 97 23 26 19 1743 Email: flefauch@cisco.com 1745 Nabil Bitar 1746 Verizon 1747 40 Sylvan Road 1748 Waltham, MA 02145 1749 USA 1751 Email: nabil.bitar@verizon.com