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'19' on line 1562 looks like a reference -- Missing reference section? '20' on line 1568 looks like a reference -- Missing reference section? '21' on line 1573 looks like a reference -- Missing reference section? '24' on line 1586 looks like a reference Summary: 5 errors (**), 0 flaws (~~), 8 warnings (==), 28 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 ICNRG S. Lederer 2 Internet Draft D. Posch 3 Intended status: Informational C. Timmerer 4 Expires: August 31, 2015 Alpen-Adria University Klagenfurt 5 C. Westphal, Ed. 6 A. Azgin 7 S. Liu 8 Huawei 9 C. Mueller 10 Bitmovin 11 A.Detti 12 University of Rome Tor Vergata 13 D. Corujo 14 University of Aveiro 16 February 23, 2015 18 Adaptive Video Streaming over ICN 19 draft-irtf-icnrg-videostreaming-03.txt 21 Status of this Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. This document may not be modified, 28 and derivative works of it may not be created, and it may not be 29 published except as an Internet-Draft. 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. This document may not be modified, 33 and derivative works of it may not be created, except to publish it 34 as an RFC and to translate it into languages other than English. 36 This document may contain material from IETF Documents or IETF 37 Contributions published or made publicly available before November 38 10, 2008. The person(s) controlling the copyright in some of this 39 material may not have granted the IETF Trust the right to allow 40 modifications of such material outside the IETF Standards Process. 41 Without obtaining an adequate license from the person(s) controlling 42 the copyright in such materials, this document may not be modified 43 outside the IETF Standards Process, and derivative works of it may 44 not be created outside the IETF Standards Process, except to format 45 it for publication as an RFC or to translate it into languages other 46 than English. 48 Internet-Drafts are working documents of the Internet Engineering 49 Task Force (IETF), its areas, and its working groups. Note that 50 other groups may also distribute working documents as Internet- 51 Drafts. 53 Internet-Drafts are draft documents valid for a maximum of six 54 months and may be updated, replaced, or obsoleted by other documents 55 at any time. It is inappropriate to use Internet-Drafts as 56 reference material or to cite them other than as "work in progress." 58 The list of current Internet-Drafts can be accessed at 59 http://www.ietf.org/ietf/1id-abstracts.txt 61 The list of Internet-Draft Shadow Directories can be accessed at 62 http://www.ietf.org/shadow.html 64 This Internet-Draft will expire on August 24, 2015. 66 Copyright Notice 68 Copyright (c) 2015 IETF Trust and the persons identified as the 69 document authors. All rights reserved. 71 This document is subject to BCP 78 and the IETF Trust's Legal 72 Provisions Relating to IETF Documents 73 (http://trustee.ietf.org/license-info) in effect on the date of 74 publication of this document. Please review these documents 75 carefully, as they describe your rights and restrictions with 76 respect to this document. 78 Abstract 80 This document considers the consequences of moving the underlying 81 network architecture to an Information-Centric Network (ICN) 82 architecture on video distribution. As most of the traffic in future 83 networks is expected to be video, we consider how to modify the 84 existing video streaming mechanisms. Several important topics 85 related to video distribution over ICN are presented, covering a 86 wide range of scenarios: we look at how to evolve DASH to work over 87 ICN, and leverage the recent ISO/IEC MPEG Dynamic Adaptive Streaming 88 over HTTP (DASH) standard; we consider layered encoding over ICN; 89 P2P mechanisms introduce distinct requirements for video and we look 90 at how to adapt PPSP for ICN; IPTV adds delay constraints, and this 91 will create more stringent requirements over ICN as well. As part of 92 the discussion on video, we discuss DRMs in ICN. Finally, in 93 addition to consider how existing mechanisms would be impacted by 94 ICN, this document lists some research issues to design ICN specific 95 video streaming mechanisms. 97 Table of Contents 98 1. Introduction....................................................... 4 99 2. Conventions used in this document.................................. 5 100 3. Use case scenarios for ICN and Video Streaming..................... 5 101 4. Video download..................................................... 6 102 5. Video streaming and ICN............................................ 7 103 5.1. Introduction to client-driven streaming and DASH ............... 7 104 5.2. Layered Encoding ............................................... 8 105 5.3. Interactions of Video Streaming with ICN ....................... 8 106 5.3.1. Interaction of DASH and ICN ................................ 8 107 5.3.2. Interaction of ICN with Layered Encoding .................. 11 108 5.4. Possible Integration of Video streaming and ICN architecture .. 11 109 5.4.1. DASH over CCN ............................................. 11 110 5.4.2. Testbed, Open Source Tools, and Dataset ................... 13 111 6. P2P video distribution and ICN.................................... 14 112 6.1. Introduction to PPSP .......................................... 14 113 6.2. PPSP over ICN: deployment concepts ............................ 16 114 6.2.1. PPSP short background ..................................... 16 115 6.2.2. From PPSP messages to ICN named-data ...................... 16 116 6.2.3. Support of PPSP interaction through a pull-based ICN API .. 17 117 6.2.4. Abstract layering for PPSP over ICN ....................... 18 118 6.2.5. PPSP interaction with the ICN routing plane ............... 19 119 6.2.6. ICN deployment for PPSP ................................... 19 120 6.3. Impact of MPEG DASH coding schemes ............................ 20 121 7. IPTV and ICN...................................................... 21 122 7.1. IPTV challenges ............................................... 21 123 7.2. ICN benefits for IPTV delivery ................................ 22 124 8. Digital Rights Managements in ICN................................. 24 125 8.1. Broadcast Encryption for DRM in ICN............................ 25 126 8.2. AAA Based DRM for ICN Networks................................. 28 127 9. Future Steps for Video in ICN..................................... 29 128 9.1. Large Scale Live Events ....................................... 29 129 9.2. Video Conferencing and Real-Time Communications ............... 29 130 9.3. Store-and-Forward Optimized Rate Adaptation ................... 29 131 9.4. Heterogeneous Wireless Environment Dynamics ................... 30 132 9.5. Network Coding for Video Distribution in ICN .................. 32 133 10. Security Considerations.......................................... 32 134 11. IANA Considerations.............................................. 32 135 12. Conclusions...................................................... 32 136 13. References....................................................... 33 137 13.1. Normative References ......................................... 33 138 13.2. Informative References ....................................... 33 139 14. Authors' Addresses............................................... 36 140 15. Acknowledgements................................................. 37 142 1. Introduction 144 The unprecedented growth of video traffic has triggered a rethinking 145 of how content is distributed, both in terms of the underlying 146 Internet architecture and in terms of the streaming mechanisms to 147 deliver video objects. 149 In particular, the IRTF ICN working group has been chartered to 150 study new architectures centered upon information; the main 151 contributor to Internet traffic (and information dissemination) is 152 video, and this is expected to stay the same in the short- to mid- 153 term future. If ICN is expected to become prominent, it will have to 154 support video streaming efficiently. 156 As such, it is necessary to discuss along two directions: 158 . Can the current video streaming mechanisms be leveraged and 159 adapted to an ICN architecture? 161 . Can (and should) new, ICN-specific video streaming mechanisms 162 be designed to fully take advantage of the new abstractions 163 exposed by the ICN architecture? 165 This document intends to focus on the first question, in an attempt 166 to define the use cases for video streaming and some requirements. 168 This document focuses on a few scenarios, namely Netflix-like video 169 streaming, peer-to-peer video sharing and IPTV, and identifies how 170 the existing protocols can be adapted to an ICN architecture. In 171 doing so, it also identifies the main issues with these protocols in 172 this ICN context. 174 Some documents have started to consider the ICN-specific 175 requirements of dynamic adaptive streaming [2][3][4][6]. 177 In this document, we give a brief overview of the existing solutions 178 for the selected scenarios. We then consider the interactions of 179 such existing mechanisms with the ICN architecture and list some of 180 the interactions any video streaming mechanism will have to 181 consider. We then identify some areas for future research. 183 2. Conventions used in this document 185 In examples, "C:" and "S:" indicate lines sent by the client and 186 server respectively. 188 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 189 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 190 document are to be interpreted as described in RFC-2119 [RFC2119]. 192 In this document, these words will appear with that interpretation 193 only when in ALL CAPS. Lower case uses of these words are not to be 194 interpreted as carrying RFC-2119 significance. 196 In this document, the characters ">>" preceding an indented line(s) 197 indicates a compliance requirement statement using the key words 198 listed above. This convention aids reviewers in quickly identifying 199 or finding the explicit compliance requirements of this RFC. 201 3. Use case scenarios for ICN and Video Streaming 203 For ICN specific descriptions, we refer to the other working group 204 documents. For our purpose, we assume here that ICN means an 205 architecture where content is retrieved by name and with no binding 206 of content to a specific network location. 208 The consumption of multimedia content comes along with timing 209 requirements for the delivery of the content, for both, live and on- 210 demand consumption. Additionally, real-time use cases such as audio- 211 /video conferencing [7], game streaming, etc., come along with more 212 strict timing requirements. Long startup delays, buffering periods 213 or poor quality, etc., should be avoided to achieve a good Quality 214 of Experience (QoE) to the consumer of the content. Of course, these 215 requirements are heavily influenced by routing decisions and 216 caching, which are central parts of ICN and which have to be 217 considered when streaming video in such infrastructures. 219 Due to this range of requirements, we find it useful to narrow the 220 focus on four scenarios (more can be included later): 222 - a video delivery architecture similar to that if itune, where the 223 whole file is being downloaded to the client and can be replayed 224 there multiple times; 225 - a video streaming architecture for playing back movies; this is 226 relevant for the naming and caching aspects of ICN, as well as the 227 interaction with the rate adaptation mechanism necessary to 228 deliver the best QoE to the end-user; 229 - a peer-to-peer architecture for sharing videos; this introduces 230 more stringent routing requirements in terms of locating copies of 231 the content, as the location of the peers evolves and peers join 232 and leave the swarm they use to exchange video chunks; 233 - IPTV; this introduces requirements for multicasting and adds 234 stronger delay constraints. 236 Other scenarios, such as video-conferencing and real-time video 237 communications are not explicitly discussed in this document, while 238 they are in scope. Also, events of mass-media distribution, such as 239 a large crowd in a live event, are also adding new requirements to 240 be included in later version. 242 We discuss how the current state-of-the-art protocols in an IP 243 context can be modified for the ICN architecture. The remainder of 244 this document is organized as follows. In the next section, we 245 consider video download. Then in Section 5, we briefly describe DASH 246 [1], and Layered Encoding (MDC, SVC). P2P is the focus of Section 6, 247 where we describe PPSP. Section 7 highlights the requirements of 248 IPTV, while Section 8 describes the issues of DRM. Section 9 lists 249 some research issues to be solved for ICN-specific video delivery 250 mechanisms. 252 This research items include videoconferencing and real-time video 253 communications, which will be detailed more in future versions of 254 this document; as well as the mass distribution of content at live 255 large-scale events (stadium, concert hall, etc) for which there is 256 no clearly adopted existing protocol. 258 4. Video download 260 Video download, namely the fetching of a video file from a server or 261 a cache down to the user's local storage, is a natural application 262 of ICN. It should be supported natively without requiring any 263 specific considerations. 265 This is supported now by a host of protocols (say, scp, ftp, or over 266 http), which would need to be replaced by the protocols to retrieve 267 content in ICNs. 269 However, current mechanisms are built atop existing transport 270 protocol. Some ICN proposals (say, CCN or NDN for instance) attempt 271 to leverage the work down upon these transport protocol and it has 272 been proposed to use mechanisms such as the TCP congestion window 273 (and the associated Adaptive Increase, Multiplicative Decrease - 274 AIMD) to decide how many object requests ("interests" in CCN/NDN 275 terminology) should be in flight at any point in time. 277 It should be noted that ICN intrinsically supports different 278 transport mechanisms, which could achieve better performance than 279 TCP, as they subsume TCP into a special case. For instance, one 280 could imagine a link-by-link transport coupled with caching. This is 281 enabled by the ICN architecture, and would facilitate the point-to- 282 point download of video files. 284 5. Video streaming and ICN 286 5.1. Introduction to client-driven streaming and DASH 288 Media streaming over the hypertext transfer protocol (HTTP) and in a 289 further consequence streaming over the transmission control protocol 290 (TCP) has become omnipresent in today's Internet. Content providers 291 such as Netflix, Hulu, and Vudu do not deploy their own streaming 292 equipment but use the existing Internet infrastructure as it is and 293 they simply deploy their own services over the top (OTT). This 294 streaming approach works surprisingly well without any particular 295 support from the underlying network due to the use of efficient 296 video compression, content delivery networks (CDNs), and adaptive 297 video players. Earlier video streaming research mostly recommended 298 to use the user datagram protocol (UDP) combined with the real time 299 transport protocol (RTP). It assumed it would not be possible to 300 transfer multimedia data smoothly with TCP, because of its 301 throughput variations and large retransmission delays. This point of 302 view has significantly evolved today. HTTP streaming, and especially 303 its most simple form known as progressive download, has become very 304 popular over the past few years because it has some major benefits 305 compared to RTP streaming. As a consequence of the consistent use of 306 HTTP for this streaming method, the existing Internet 307 infrastructure, consisting of proxies, caches and CDNs, could be 308 used. Originally, this architecture was designed to support best 309 effort delivery of files and not real time transport of multimedia 310 data. Nevertheless, real time streaming based on HTTP could also 311 take advantage of this architecture, in comparison to RTP, which 312 could not leverage any of the aforementioned components. Another 313 benefit that results from the use of HTTP is that the media stream 314 could easily pass firewalls or network address translation (NAT) 315 gateways, which was definitely a key for the success of HTTP 316 streaming. However, HTTP streaming is not the holy grail of 317 streaming as it also introduces some drawbacks compared to RTP. 318 Nevertheless, in an ICN-based video streaming architecture these 319 aspects also have to be considered. 321 The basic concept of DASH [1] is to use segments of media content, 322 which can be encoded at different resolutions, bitrates, etc., as 323 so-called representations. These segments are served by conventional 324 HTTP Web servers and can be addressed via HTTP GET requests from the 325 client. As a consequence, the streaming system is pull-based and the 326 entire streaming logic is located on the client, which makes it 327 scalable, and allows to adapt the media stream to the client's 328 capabilities. 330 In addition to this, the content can be distributed using 331 conventional CDNs and their HTTP infrastructure, which also scales 332 very well. In order to specify the relationship between the 333 contents' media segments and the associated bitrate, resolution, and 334 timeline, the Media Presentation Description (MPD) is used, which is 335 a XML document. The MPD refers to the available media segments using 336 HTTP URLs, which can be used by the client for retrieving them. 338 5.2. Layered Encoding 340 Another approach for video streaming consist in using layered 341 encoding. Namely, scalable video coding formats the video stream 342 into different layers: a base layer which can be decoded to provide 343 the lowest bit rate for the specific stream, and enhancement layers 344 which can be transmitted separately if network conditions allow. The 345 higher layers offer higher resolutions and enhancement of the video 346 quality, while the layered approach allows to adapt to the network 347 conditions. This is used in MPEG-4 scalable profile or H.263+. 348 H264SVC is available, but not much deployed. JPEG2000 has a wavelet 349 transform approach for layered encoding, but has not been deployed 350 much either. 352 It is not clear if the layered approach is fine-grained enough for 353 rate control. 355 5.3. Interactions of Video Streaming with ICN 357 5.3.1. Interaction of DASH and ICN 359 Video streaming, and DASH in particular, have been designed with 360 goals that are aligned with that of most ICN proposals. Namely, it 361 is a client-based mechanism, which requests items (in this case, 362 chunks of a video stream) by name. 364 ICN and MPEG-DASH [1] have several elements in common: 366 - the client-initiated pull approach; 367 - the content being dealt with in pieces (or chunks); 368 - the support of efficient replication and distribution of content 369 pieces within the network; 370 - the scalable, session-free nature of the exchange between the 371 client and the server at the streaming layer: the client is free 372 to request any chunk from any location; 373 - the support for potentially multiple sources. 375 As ICN is a promising candidate for the Future Internet (FI) 376 architecture, it is useful to investigate its suitability in 377 combination with multimedia streaming standards like MPEG-DASH. In 378 this context, the purpose of this section is to present the usage of 379 ICN instead of HTTP in MPEG-DASH 381 However, there are some issues that arise from using a dynamic rate 382 adaptation mechanism in an ICN architecture: 384 o Naming of the data in DASH does not necessarily follow the ICN 385 convention of any of the ICN proposals. Several chunks of the 386 same video stream might currently go by different names that for 387 instance do not share a common prefix. There is a need to 388 harmonize the naming of the chunks in DASH with the naming 389 conventions of the ICN. The naming convention of using a 390 filename/time/encoding format could for instance be made 391 compatible with the convention of CCN. 393 o While chunks can be retrieved from any server, the rate 394 adaptation mechanism attempts to estimate the available network 395 bandwidth so as to select the proper playback rate and keep its 396 playback buffer at the proper level. Therefore, there is a need 397 to either include some location semantics in the data chunks so 398 as to properly assess the throughput to a specific location; or 399 to design a different mechanism to evaluate the available network 400 bandwidth. 402 o The typical issue of access control and accounting happens in 403 this context, where chunks can be cached in the network outside 404 of the administrative control of the content publisher. It might 405 be a requirement from the owner of the video stream that access 406 to these data chunks needs to be accounted/billed/monitored. 408 o Dynamic streaming multiplies the representations of a given video 409 stream, therefore diminishing the effectiveness of caching: 410 namely, to get a hit for a chunk in the cache, it has to be for 411 the same format and encoding values. Alternatively, to get the 412 same hit rate as for a stream using a single encoding, the cache 413 size must be scaled up to include all the possible 414 representations. 416 o Caching introduces oscillatory dynamics as it may modify the 417 estimation of the available bandwidth between the end user and 418 the repository where it is getting the chunks from. For instance, 419 if an edge cache holds a low resolution representation near the 420 user, the user getting this low resolution chunks will observe a 421 good performance, and will then request higher resolution chunks. 422 If those are hosted on a server with poor performance, then the 423 client would have to switch back to the low representation. This 424 oscillation may be detrimental to the perceived QoE of the user. 426 o The ICN transport mechanism needs to be compatible to some extent 427 with DASH. To take a CCN example, the rate at which interests are 428 issued should be such that the chunks received in return arrive 429 fast enough and with the proper encoding to keep the playback 430 buffer above some threshold. 432 o The usage of multiple network interfaces is possible in ICN, 433 enabling a seamless handover between them. For the combination 434 with DASH, an intelligent strategy which should focus on traffic 435 load balancing between the available links may be necessary. This 436 would increase the effective media throughput of DASH by 437 leveraging the combined available bandwidth of all links, 438 however, it could potentially lead to high variations of the 439 media throughput. 441 o DASH does not define how the MPD is retrieved; hence, this is 442 compatible with CCN. However, the current profiles defined within 443 MPEG-DASH require the MPD to contain HTTP-URLs (incl. http and 444 https URI schemes) to identify segments. To enable a more 445 integrated approach as described in this document, an additional 446 profile for DASH over CCN has to be defined, enabling ICN/CCN- 447 based URIs to identify and request the media segments. 449 We describe in Section 5.4 a potential implementation of a dynamic 450 adaptive video stream over ICN, based upon DASH and CCN [5]. 452 5.3.2. Interaction of ICN with Layered Encoding 454 Issues of interest to an Information-Centric network architecture in 455 the context of layered video streaming include: 457 . Caching of the multiple layers. The caching priority should go 458 to the base layer, and defining caching policy to decide when 459 to cache enhancement layers; 460 . Synchronization of multiple content streams, as the multiple 461 layers may come from different sources in the network (for 462 instance, the base layer might be cached locally while the 463 enhancement layers may be stored in the origin server); 464 . Naming of the different layers: when the client requests an 465 object, the request can be satisfied with the base layer alone, 466 aggregated with enhancement layers. Should one request be 467 sufficient to provide different streams? In a CCN architecture 468 for instance, this would violate a one interest-one data packet 469 principle and the client would need to specify each layer it 470 would like to receive. In a Pub/Sub architecture, the 471 rendezvous point would have to make a decision as to which 472 layers (or which pointer to which layer's location) to return. 474 5.4. Possible Integration of Video streaming and ICN architecture 476 5.4.1. DASH over CCN 478 DASH is intended to enable adaptive streaming, i.e., each content 479 piece can be provided in different qualities, formats, languages, 480 etc., to cope with the diversity of todays' networks and devices. As 481 this is an important requirement for Future Internet proposals like 482 CCN, the combination of those two technologies seems to be obvious. 483 Since those two proposals are located at different protocol layers - 484 DASH at the application and CCN at the network layer - they can be 485 combined very efficiently to leverage the advantages of both and 486 potentially eliminate existing disadvantages. As CCN is not based on 487 classical host-to-host connections, it is possible to consume 488 content from different origin nodes as well as over different 489 network links in parallel, which can be seen as an intrinsic error 490 resilience feature w.r.t. the network. This is a useful feature of 491 CCN for adaptive multimedia streaming within mobile environments 492 since most mobile devices are equipped with multiple network links 493 like 3G and WiFi. CCN offers this functionality out of the box which 494 is beneficial when used for DASH-based services. In particular, it 495 is possible to enable adaptive video streaming handling both 496 bandwidth and network link changes. That is, CCN handles the network 497 link decision and DASH is implemented on top of CCN to adapt the 498 video stream to the available bandwidth. 500 In principle, there are two options to integrate DASH and CCN: a 501 proxy service acting as a broker between HTTP and CCN as proposed in 502 [6], and the DASH client implementing a native CCN interface. The 503 former transforms an HTTP request to a corresponding interest packet 504 as well as a data packet back to an HTTP response, including 505 reliable transport as offered by TCP. This may be a good compromise 506 to implement CCN in a managed network and to support legacy devices. 507 As such a proxy is already described in [6] this draft focuses on a 508 more integrated approach, aiming at fully exploiting the potential 509 of a CCN DASH Client. That is, we describe a native CCN interface 510 within the DASH client, which adopts a CCN naming scheme (CCN URIs) 511 to denote segments in the Media Presentation Description (MPD). In 512 this architecture, only the network access component on the client 513 has to be modified and the segment URIs within MPD have to be 514 updated according to the CCN naming scheme. 516 Initially, the DASH client retrieves the MPD containing the CCN URIs 517 of the content representations including the media segments. The 518 naming scheme of the segments may reflect intrinsic features of CCN 519 like versioning and segmentation support. Such segmentation support 520 is already compulsory for multimedia streaming in CCN and, thus, can 521 also be leveraged for DASH-based streaming over CCN. The CCN 522 versioning can be adopted in a further step to signal different 523 representations of the DASH-based content, which enables an implicit 524 adaptation of the requested content to the clients' bandwidth 525 conditions. That is, the interest packet already provides the 526 desired characteristics of a segment (such as bit rate, resolution, 527 etc.) within the content name (or potentially within parameters 528 defined as extra types in the packet formats). Additionally, if 529 bandwidth conditions of the corresponding interfaces or routing 530 paths allow so, DASH media segments could be aggregated 531 automatically by the CCN nodes, which reduces the amount of interest 532 packets needed to request the content. However, such approaches need 533 further research, specifically in terms of additional intelligence 534 and processing power needed at the CCN nodes. 536 After requesting the MPD, the DASH client will start to request 537 particular segments. Therefore, CCN interest packets are generated 538 by the CCN access component and forwarded to the available 539 interfaces. Within the CCN, these interest packets leverage the 540 efficient interest aggregation for, e.g., popular content, as well 541 as the implicit multicast support. Finally, the interest packets are 542 satisfied by the corresponding data packets containing the video 543 segment data, which are stored on the origin server or any CCN node, 544 respectively. With an increasing popularity of the content, it will 545 be distributed across the network resulting in lower transmission 546 delays and reduced bandwidth requirements for origin servers and 547 content providers respectively. 549 With the extensive usage of in-network caching, new drawbacks are 550 introduced since the streaming logic is located at the client, i.e., 551 clients are not aware of each other and the network infrastructure 552 and cache states. Furthermore, negative effects are introduced when 553 multiple clients are competing for a bottleneck and when caching is 554 influencing this bandwidth competition. As mentioned above, the 555 clients request individual portions of the content based on 556 available bandwidth which is calculated using throughput 557 estimations. This uncontrolled distribution of the content 558 influences the adaptation process of adaptive streaming clients. The 559 impact of this falsified throughput estimation could be tremendous 560 and leads to a wrong adaptation decision which may impact the 561 Quality of Experience (QoE) at the client, as shown in [8]. In ICN, 562 the client does not have the knowledge from which source the 563 requested content is actually served or how many origin servers of 564 the content are available, as this is transparent and depends on the 565 name-based routing. This introduces the challenge that the 566 adaptation logic of the adaptive streaming client is not aware of 567 the event when the ICN routing decides to switch to a different 568 origin server or content is coming through a different 569 link/interface. As most algorithms implementing the adaption logic 570 are using bandwidth measurements and related heuristics, the 571 adaptation decisions are no longer valid when changing origin 572 servers (or links) and potentially cause playback interruptions and, 573 consequently, stalling. Additionally, ICN supports the usage of 574 multiple interfaces and a seamless handover between them, which 575 again comes together with bandwidth changes, e.g., switching between 576 fixed and wireless, 3G/4G and WiFi networks, etc. Considering these 577 characteristics of ICN, adaptation algorithms merely based on 578 bandwidth measurements are not appropriate anymore, as potentially 579 each segment can be transferred from another ICN node or interface, 580 all with different bandwidth condition. Thus, adaptation algorithms 581 taking into account these intrinsic characteristics of ICN are 582 preferred over algorithms based on mere bandwidth measurements. 584 5.4.2. Testbed, Open Source Tools, and Dataset 586 For the evaluations of DASH over CCN, a testbed with open source 587 tools and datasets is provided in [9]. In particular, it provides 588 two client player implementations, (i) a libdash extension for DASH 589 over CCN and (ii) a VLC plugin implementing DASH over CCN. For both 590 implementations the CCNx implementation has been used as a basis. 592 The general architecture of libdash is organized in modules, so that 593 the library implements a MPD parser and an extensible connection 594 manager. The library provides object-oriented interfaces for these 595 modules to access the MPD and the downloadable segments. These 596 components are extended to support DASH over CCN and available in a 597 separate development branch of the github project available at 598 http://www.github.com/bitmovin/libdash. libdash comes together with 599 a fully featured DASH player with a QT-based frontend, demonstrating 600 the usage of libdash and providing a scientific evaluation platform. 601 As an alternative, patches for the DASH plugin of the VLC player are 602 provided. These patches can be applied to the latest source code 603 checkout of VLC resulting in a DASH over CCN-enabled VLC player. 605 Finally, a DASH over CCN dataset is provided in form of a CCNx 606 repository. It includes 15 different quality representation of the 607 well-known Big Buck Bunny Movie, ranging from 100 kbps up to 4500 608 kbps. The content is split into segments of two seconds, and 609 described by an associated MPD using the presented naming scheme in 610 Section 4.1. This repository can be downloaded from [9], and is also 611 provided by a public accessible CCNx node. Associated routing 612 commands for the CCNx namespaces of the content are provided via 613 scripts coming together with the dataset and can be used as a public 614 testbed. 616 6. P2P video distribution and ICN 618 Another form of distributing content - and video in particular- 619 which ICNs need to support is Peer-to-Peer distribution (P2P). We 620 see now how an existing protocol such as PPSP can be modified to 621 work in an ICN environment. 623 6.1. Introduction to PPSP 625 P2P video Streaming (PPS) is a popular approach to redistribute live 626 media over Internet. The proposed P2PVS solutions can be roughly 627 classified in two classes: 629 - Push/Tree based 631 - Pull/Mesh based 633 The Push/Tree based solution creates an overlay network among peers 634 that has a tree shape. Using a progressive encoding (e.g. Multiple 635 Description Coding or H.264 Scalable Video Coding), multiple trees 636 could be set up to support video rate adaptation. On each tree an 637 enhancement stream is sent. The more the number of stream received, 638 the higher the video quality. A peer control video rate by fetching 639 or not the streams delivered on the distribution trees. 641 The Pull/Mesh based solution is inspired by the BitTorrent file 642 sharing mechanism. A Tracker collects information about the state of 643 the swarm (i.e. set of participating peers). A peer forms a mesh 644 overlay network with a subset of peers, and exchange data with them. 645 A peer announces what data items it disposes and requests missing 646 data items that are announced by connected peers. In case of live 647 streaming, the involved data set includes only a recent window of 648 data items published by the source. Also in this case, the use of a 649 progressive encoding can be exploited for video rate adaptation. 651 Pull/Mesh based P2PVS solutions are the more promising candidate for 652 the ICN deployment, since most of ICN approach provides a pull-based 653 API [5][10][11][12]. In addition, Pull/Mesh based P2PVS are more 654 robust than Push/Tree based one [13] and the Peer to Peer Streaming 655 Protocol (PPSP) working group [14] is also proposing a Pull/Mesh 656 based solution. 658 +------------------------------------------------+ 659 | | 660 | +--------------------------------+ | 661 | | Tracker | | 662 | +--------------------------------+ | 663 | | ^ ^ | 664 |Tracker | | Tracker |Tracker | 665 |Protocol| | Protocol |Protocol | 666 | | | | | 667 | V | | | 668 | +---------+ Peer +---------+ | 669 | | Peer |<----------->| Peer | | 670 | +---------+ Protocol +---------+ | 671 | | ^ | 672 | | |Peer | 673 | | |Protocol | 674 | V | | 675 | +---------------+ | 676 | | Peer | | 677 | +---------------+ | 678 | | 679 +------------------------------------------------+ 680 Figure 1: PPSP System Architecture (source [RFC6972]) 682 Figure 1 reports the PPSP architecture presented in [RFC6972]. PEERs 683 announce and share video chunks and a TRACKER maintains a list of 684 PEERs participating in a specific audio/video channel or in the 685 distribution of a streaming file. The tracker functionality may be 686 centralized in a server or distributed over the PEERs. PPSP 687 standardize the Peer and Tracker Protocols, which can run directly 688 over UDP or TCP. 690 This document discusses some preliminary concepts about the 691 deployment of PPSP on top of an ICN that exposes a pull-based API, 692 meanwhile considering the impact of MPEG DASH streaming format. 694 6.2. PPSP over ICN: deployment concepts 696 6.2.1. PPSP short background 698 PPSP specifies peer protocol (PPSPP) [15] and tracker protocol 699 (PPSP-TP)[16]. 701 Some of the operations carried out by the tracker protocol are the 702 followings. When a peer wishes to join the streaming session it 703 contacts the Tracker (CONNECT message), obtains a PEER_ID and a list 704 of PEER_IDs (and IP addresses) of other peers that are participating 705 to the SWARM and that the tracker has singled out for the requesting 706 peer (this may be a subset of the all peers of the SWARM). In 707 addition to this join operation, a peer may contact the tracker to 708 request to renew the list of participating peers (FIND message), to 709 periodically update its status to the tracker (STAT_REPORT message), 710 etc. 712 Some of the operations carried out by the peer protocol are the 713 following. Using the list of peers delivered by the tracker, a peer 714 establishes a session with them (HANDSHAKE message). A peer 715 periodically announces to neighboring peers which chunks it has 716 available for download (HAVE message). Using these announcements, a 717 peer requests missing chunks from neighboring peers (REQUEST 718 messages), which will send back them (DATA message). 720 6.2.2. From PPSP messages to ICN named-data 722 An ICN provides users with data items exposed by names. The bundle 723 name and data item is usually referred as named-data, named-content, 724 etc. To transfer PPSP messages though an ICN the messages should be 725 be wrapped as named-data items, and receivers should request them by 726 name. 728 A PPSP entity receives messages from peers and/or tracker. Some 729 operations require gathering the messages generated by another 730 specific host (peer or tracker). For instance, if a peer A wishes to 731 gain information about video chunks available from peer B, the 732 former shall fetch the PPSP HAVE messages specifically generated by 733 the later. We refer to these kinds of named-data as "located-named- 734 data", since they should be gathered from a specific location (e.g. 735 peer B). 737 For other PPSP operations, like to fetch a DATA message (i.e. a 738 video chunk), what it is relevant for a peer is just to receive the 739 requested content, independently from who is the endpoint that 740 generate the data. We refer this information with the generic term 741 "named-data". 743 The naming scheme differentiates named-data and located-named-data 744 items. In case of named-data, the naming scheme only includes a 745 content identifier (e.g. the name of the video chunk), without any 746 prefix identifying who provides the content. For instance, a DATA 747 message containing the video chunk n. 1 may be named as 748 "ccnx:/swarmID/chunk/chunkID", where swarmID is a unique identifier 749 of the streaming session, "chunk" is a keyword and chunkID is the 750 chunk identifier (e.g. a integer number). 752 In case of located-named-data, the naming scheme includes a 753 location-prefix, which uniquely identifies the host generating the 754 data item. This prefix may be the PEER_ID in case the host was a 755 peer or a tracker identifier in case the host was the tracker. For 756 instance, a HAVE message generated by a peer B may be named as 757 "ccnx:/swarmID/peer/PEER_ID/HAVE", where "peer" is a keyword, 758 PEER_ID_B is the identifier of peer B and HAVE is a keyword. 760 6.2.3. Support of PPSP interaction through a pull-based ICN 761 API 763 The PPSP procedures are based both on pull and push interactions. 764 For instance, the distribution of chunks availability can be 765 classified as a push-based operation, since a peer sends an 766 "unsolicited" information (HAVE message) to neighboring peers. 767 Conversely the procedure used to receive video chunks can be 768 classified as pull-based, since it is supported by a 769 request/response interaction (i.e. REQUEST, DATA messages). 771 As we said, we refer to an ICN architecture which provides a pull- 772 based API. Accordingly, the mapping of PPSP pull-based procedure is 773 quite simple. For instance, using the CCN architecture [5] a PPSP 774 DATA message may be carried by a CCN Data message and a REQUEST 775 message can transferred by a CCN Interest. 777 Conversely, the support of push-based PPSP operations may be more 778 difficult. We need of an adaptation functionality that carries out a 779 push-based operation using the underlying pull-based service 780 primitives. For instance, a possible approach is to use the 781 request/response (i.e. Interest/Data) four ways handshakes proposed 782 in [7]. Another possibility is that receivers periodically send out 783 request messages of the named-data that neighbors will push and, 784 when available, sender inserts the pushed data within a response 785 message. 787 6.2.4. Abstract layering for PPSP over ICN 789 +-----------------------------------+ 790 | Application | 791 +-----------------------------------+ 792 | PPSP (TCP/IP) | 793 +-----------------------------------+ 794 | ICN - PPSP Adaptation Layer (AL) | 795 +-----------------------------------+ 796 | ICN Architecture | 797 +-----------------------------------+ 798 Figure 2: Mediator approach 800 Figure 2 provides a possible abstract layering for PPSP over ICN. 801 The Adaptation Layer acts as a mediator (proxy) between legacy PPSP 802 entities based on TCP/IP and the ICN architecture. In facts, the 803 role the mediator is to use ICN to transfer PPSP legacy messages. 805 This approach makes possible to merely reuse TCP/IP P2P applications 806 whose software includes also PPSP functionality. This "all-in-one" 807 development approach may be rather common since the PPSP-Application 808 interface is not going to be specified. Moreover, if the Operating 809 System will provide libraries that expose a PPSP API, these will be 810 initially based on a underlying TCP/IP API. Also in this case, the 811 mediator approach would make possible to easily reuse both the PPSP 812 libraries and the Application on top of an ICN. 814 +-----------------------------------+ 815 | Application | 816 +-----------------------------------+ 817 | ICN-PPSP | 818 +-----------------------------------+ 819 | ICN Architecture | 820 +-----------------------------------+ 822 Figure 3: Clean-slate approach 824 Figure 3 sketches a clean-slate layering approach in which the 825 application directly includes or interacts with a PPSP version based 826 on ICN. Likely such a PPSP_ICN integration could yield a simplier 827 development, also because it does not require implementing a TCP/IP 828 to ICN translation as in the Mediator approach. However, the clean- 829 slate approach requires developing the application (in case of 830 embedded PPSP functionality) or the PPSP library from scratch, 831 without exploiting what might already exist for TCP/IP. 833 Overall, the Mediator approach may be considered as the first step 834 of a migration path towards ICN native PPSP applications. 836 6.2.5. PPSP interaction with the ICN routing plane 838 Upon the ICN API a user (peer) requests a content and the ICN sends 839 it back. The content is gathered by the ICN from any source, which 840 could be the closest peer that disposes of the named-data item, an 841 in-network cache, etc. Actually, "where" to gather the content is 842 controlled by an underlying ICN routing plane, which sets up the ICN 843 forwarding tables (e.g. CCN FIB [5]). 845 A cross-layer interaction between the ICN routing plane and the PPSP 846 may be required to support a PPSP session. Indeed, ICN shall forward 847 request messages (e.g. CCN Interest) towards the proper peer that 848 can handle them. Depending on the layering approach, this cross- 849 layer interaction is controlled either by the Adaptation Layer or by 850 the ICN-PPSP. For example, if a peer A receives a HAVE message 851 indicating that peer B disposes of the video chunk named 852 "ccnx:/swarmID/chunk/chunkID", then former should insert in its ICN 853 forwarding table an entry for the prefix 854 "ccnx:/swarmID/chunk/chunkID" whose next hop locator (e.g. IP 855 address) is the network address of peer B [17]. 857 6.2.6. ICN deployment for PPSP 859 The ICN functionality that supports a PPSP session may be "isolated" 860 or "integrated" with the one of a public ICN. 862 In the isolated case, a PPSP session is supported by an instance of 863 an ICN (e.g. deployed on top of IP), whose functionalities operate 864 only on the limited set of nodes participating to the swarm, i.e. 865 peers and the tracker. This approach resembles the one followed by 866 current P2P application, which usually form an overlay network among 867 peers of a P2P application. And intermediate public IP routers do 868 not carry out P2P functionalities. 870 In the integrated case, the nodes of a public ICN may be involved in 871 the forwarding and in-network caching procedures. In doing so, the 872 swarm may benefit from the presence of in-network caches so limiting 873 uplink traffic on peers and inter-domain traffic too. These are 874 distinctive advantages of using PPSP over a public ICN, rather than 875 over TCP/IP. In addition, such advantages aren't likely manifested 876 in the case of isolated deployment. 878 However, the possible interaction between the PPSP and the routing 879 layer of a public ICN may be dramatic, both in terms of explosion of 880 the forwarding tables and in terms of security. These issues 881 specifically take place for those ICN architectures for which the 882 name resolution (i.e. name to next-hop) occurs en-route, like the 883 CCN architecture. 885 For instance, using the CCN architecture, to fetch a named-data item 886 offered by a peer A the on-path public ICN entities have to route 887 the request messages towards the peer A. This implies that the ICN 888 forwarding tables of public ICN nodes may contain many entries, e.g. 889 one entry per video chunk, and these entries are difficult to be 890 aggregated since peers avail sparse parts of a big content, whose 891 names have a same prefix (e.g. "ccnx:/swarmID"). Another possibility 892 is to wrap all PPSP messages into a located-named-data. In this case 893 the forwarding tables should contain "only" the PEER_ID prefixes 894 (e.g. "ccnx:/swarmID/peer/PEER_ID"), so scaling down the number of 895 entries from number of chunks to number of peers. However, in this 896 case the ICN mechanisms recognize a same video chunk offered by 897 different peers as different contents, so vanishing caching and 898 multicasting ICN benefits. Moreover, in any case routing entries 899 should be updated either the base of the availability of named-data 900 items on peers or on the presence of peers, and these events in a 901 P2P session is rapidly changing so possibly hampering the 902 convergence of the routing plane. Finally, since peers have an 903 impact on the ICN forwarding table of public nodes, this may open 904 obvious security issues. 906 6.3. Impact of MPEG DASH coding schemes 908 The introduction of video rate adaptation may valuably decrease the 909 effectiveness of P2P cooperation and of in-network caching, 910 depending of the kind of the video coding used by the MPEG DASH 911 stream. 913 In case of a MPEG DASH streaming with MPEG AVC encoding, a same 914 video chunk is independently encoded at different rates and the 915 encoding output is a different file for each rate. For instance, in 916 case of a video encoded at three different rates R1,R2,R3, for each 917 segment S we have three distinct files: S.R1, S.R2, S.R3. These 918 files are independent of each other. To fetch a segment coded at R2 919 kbps, a peer shall request the specific file S.R2. The estimation of 920 the best coding rate is usually handled by receiver-driven 921 algorithms, implemented by the video client. 923 The independence among files associated to different encoding rates 924 and the heterogeneity of peer bandwidths, may dramatically reduce 925 the interaction among peers, the effectiveness of in-network caching 926 (in case of integrated deployment), and consequently the ability of 927 PPSP to offload the video server (i.e. a seeder peer). Indeed, a 928 peer A may select a coding rate (e.g. R1) different from the one 929 selected by a peer B (e.g. R2) and this prevents the former to fetch 930 video chunks from the later, since peer B avails of chunks coded at 931 a rate different from the ones needed by A. To overcome this issue, 932 a common distributed rate selection algorithm could force peers to 933 select the same coding rate [17]; nevertheless this approach may be 934 not feasible in the in case of many peers. 936 The use of SVC encoding (Annex G extension of the H.264/MPEG-4 AVC 937 video compression standard) should make rate adaptation possible, 938 meanwhile neither reducing peer collaborations nor the in-network 939 caching effectiveness. For a single video chunk, a SVC encoder 940 produces different files for the different rates (roughly "layers"), 941 and these files are progressively related each other. Starting from 942 a base-layer which provides the minimum rate encoding, the next 943 rates are encoded as an "enhancement layer" of the previous one. For 944 instance, in case the video is coded with three rates R1 (base- 945 layer), R2 (enhancement-layer n.1), R3 (enhancement-layer n.2), then 946 for each DASH segment we have three files S.R1, S.R2 and S.R3. The 947 file S.R1 is the segment coded at the minimum rate (base-layer). The 948 file S.R2 enhances S.R1, so as S.R1 and S.R2 can be combined to 949 obtain a segment coded at rate R2. To get a segment coded at rate 950 R2, a peer shall fetch both S.R1 and S.R2. This progressive 951 dependence among files that encode a same segment at different rates 952 makes peer cooperation possible, also in case peers player have 953 autonomously selected different coding rates. For instance, if peer 954 A has selected the rate R1, the downloaded files S.R1 are useful 955 also for a peer B that has selected the rate R2, and vice versa. 957 7. IPTV and ICN 959 7.1. IPTV challenges 961 IPTV refers to the delivery of quality content broadcast over the 962 Internet, and is typically associated with strict quality 963 requirements, i.e., with a perceived latency of less than 500 ms and 964 a packet loss rate that is multiple orders lower than the current 965 loss rates experienced in the most commonly used access networks. We 966 can summarize the major challenges for the delivery of IPTV service 967 as follows. 969 Channel change latency represents a major concern for the IPTV 970 service. Perceived latency during channel change should be less than 971 500ms. To achieve this objective over the IP infrastructure, we have 972 multiple choices: 974 (i) receiving fast unicast streams from a dedicated server (most 975 effective but not resource efficient); 976 (ii) connecting to other peers in the network (efficiency depends 977 on peer support, effective and resource efficient, if also 978 supported with a dedicated server); 979 (iii) connecting to multiple multicast sessions at once (effective 980 but not resource efficient, and depends on the accuracy of 981 the prediction model used to track user activity). 983 The second major challenge is the error recovery. Typical IPTV 984 service requirements dictate the mean time between artifacts to be 985 approximately 2 hours. This suggests the perceived loss rate to be 986 around or less than 10^-7. Current IP-based solutions rely on the 987 following proactive and reactive recovery techniques: (i) joining 988 the FEC multicast stream corresponding to the perceived packet loss 989 rate (not efficient as the recovery strength is chosen based on 990 worst-case loss scenarios), (ii) making unicast recovery requests to 991 dedicated servers (requires active support from the service 992 provider), (iii) probing peers to acquire repair packets (finding 993 matching peers and enabling their cooperation is another challenge). 995 7.2. ICN benefits for IPTV delivery 997 ICN presents significant advantages for the delivery of IPTV 998 traffic. For instance, ICN inherently supports multicast and allows 999 for quick recovery from packet losses (with the help of in-network 1000 caching). Similarly, peer support is also provided in the shape of 1001 in-network caches that typically act as the middleman between two 1002 peers, enabling therefore earlier access to IPTV content. 1004 However, despite these advantages, delivery of IPTV service over 1005 Information Centric Networks brings forth new challenges. We can 1006 list some of these challenges as follows: 1008 . Messaging overhead: ICN is a pull-based architecture and relies 1009 on a unique balance between requests and responses. A user 1010 needs to make a request for each data packet. In the case of 1011 IPTV, with rates up to, and likely to be, above 15Mbps, we 1012 observe significant traffic upstream to bring those streams. 1013 As the number of streams increase (including the same session 1014 at different quality levels), so as the burden on the routers. 1015 Even if the majority of requests are aggregated at the core, 1016 routers close to the edge (where we observe the biggest 1017 divergence in user requests) will experience a significant 1018 increase in overhead to process these requests. The same is 1019 true at the user side, as the uplink usage multiplies in the 1020 number of sessions a user requests (for instance, to minimize 1021 the impact of bandwidth fluctuations). 1022 . Cache control: As the IPTV content expires at a rapid rate 1023 (with a likely expiry threshold of 1s), we need solutions to 1024 effectively flush out such content to also prevent degradatory 1025 impact on other cached content, with the help of intelligently 1026 chosen naming conventions. However, to allow for fast recovery 1027 and optimize access time to sessions (from current or new 1028 users), the timing of such expirations needs to be adaptive to 1029 network load and user demand. However, we also need to support 1030 quick access to earlier content, whenever needed, for instance, 1031 when the user accesses the rewind feature (note that in-network 1032 caches will not be of significant help in such scenarios due to 1033 overhead required to maintain such content). 1034 . Access accuracy: To receive the up-to-date session data, users 1035 need to be aware of such information at the time of their 1036 request. Unlike IP multicast, since the users join a session 1037 indirectly, session information is critical to minimize 1038 buffering delays and reduce the startup latency. Without such 1039 information, and without any active cooperation from the 1040 intermediate routers, stale data can seriously undermine the 1041 efficiency of content delivery. Furthermore, finding a cache 1042 does not necessarily equate to joining a session, as the look- 1043 ahead latency for the initial content access point may have a 1044 shorter lifetime than originally intended. For instance, if the 1045 user that has initiated the indirect multicast leaves the 1046 session early, the requests from the remaining users need to 1047 experience an additional latency of one RTT as they travel 1048 towards the content source. If the startup latency is chosen 1049 depending on the closeness to the intermediate router, going to 1050 the content source in-session can lead to undesired pauses. 1052 8. Digital Rights Managements in ICN 1054 This section discusses the need for Digital Rights Management (DRM) 1055 functionalities for multimedia streaming over ICN. It focuses on two 1056 possible approaches: modifying AAA to support DRM in ICN, and using 1057 Broadcast Encryption. 1059 It is assumed that ICN will be used heavily for digital content 1060 dissemination. It is vital to consider DRM for digital content 1061 distribution. In today's Internet there are two predominant classes 1062 of business models for on-demand video streaming. The first model is 1063 based on advertising revenues. Non-copyright protected (usually 1064 user-generated content, UGC) is offered by large infrastructure 1065 providers like Google (YouTube) at no charge. The infrastructure is 1066 financed by spliced advertisements into the content. In this context 1067 DRM considerations may not be required, since producers of UGC may 1068 only strive for the maximum possible dissemination. Some producers 1069 of UGC are mainly interested to share content with their families, 1070 friends, colleges or others and have no intention to make profit. 1071 However, the second class of business models requires DRM, because 1072 they are primarily profit oriented. For example, large on-demand 1073 streaming platforms like Netflix establish business models based on 1074 subscriptions. Consumers may have to pay a monthly fee in order to 1075 get access to copyright protected content like TV series, movies or 1076 music. This model may be ad-supported and free to the content 1077 consumer, like YouTube Channels or Spotify. But the creater of the 1078 content expects some remuneration for his work. From the perspective 1079 of the service providers and the copyright owners, only clients that 1080 pay the fee (explicitly or implicitly through ad placement) should 1081 be able to access and consume the content. Anyway, the challenge is 1082 to find an efficient and scalable way of access control to digital 1083 content, which is distributed in information-centric networks. 1085 8.1. Broadcast Encryption for DRM in ICN 1087 The section discusses Broadcast Encryption (BE) as a suitable basis 1088 for DRM functionalities in conformance to the ICN communication 1089 paradigm. Especially when network inherent caching is considered the 1090 advantage of BE will be highlighted. 1092 In ICN, data packets can be cached inherently in the network and any 1093 network participant can request a copy of these packets. This makes 1094 it very difficult to implement an access control for content that is 1095 distributed via ICN. A naive approach is to encrypt the transmitted 1096 data for each consumer with a distinct key. This prohibits everyone 1097 other than the intended consumers to decrypt and consume the data. 1098 However, this approach is not suitable for ICN's communication 1099 paradigm since it would reduce the benefits gained from the inherent 1100 network caching. Even if multiple consumers request the same content 1101 the requested data for each consumer would differ using this 1102 approach. A better but still insufficient idea is to use a single 1103 key for all consumers. This does not destruct the benefits of ICN's 1104 caching ability. The drawback is that if one of the consumers 1105 illegally distributes the key, the system is broken and any entity 1106 in the network can access the data. Changing the key after such an 1107 event is useless since the provider has no possibility to identify 1108 the illegal distributer. Therefore this person cannot be stopped 1109 from distributing the new key again. In addition to this issue other 1110 challenges have to be considered. Subscriptions expire after a 1111 certain time and then it has to be ensured that these consumers 1112 cannot access the content anymore. For a provider that serves 1113 millions of daily consumers (e.g. Netflix) there could be a 1114 significant number of expiring subscriptions per day. Publishing a 1115 new key every time a subscription expires would require an 1116 unsuitable amount of computational power just to re-encrypt the 1117 collection of audio-visual content. 1119 A possible approach to solve these challenges is Broadcast 1120 Encryption (BE) [22] as proposed in [23]. From this point on, this 1121 section will focus only on BE as an enabler for DRM functionality in 1122 the use case of ICN video streaming. This subsection continues with 1123 the explanation of how BE works and shows how BE can be used to 1124 implement an access control scheme in the context of content 1125 distribution in ICN. 1127 BE actually carries a misleading name. One might expect a concrete 1128 encryption scheme. However, it belongs to the family of key- 1129 management schemes (KMS). KMS are responsible for the generation, 1130 exchange, storage and replacement of cryptographic keys. The most 1131 interesting characteristics of Broadcast Encryption Schemes (BES) 1132 are: 1134 . A BES typically uses a global trusted entity called the 1135 licensing agent (LA), which is responsible for spreading a set 1136 of pre-generated secrets among all participants. Each 1137 participant gets a distinct subset of secrets assigned from the 1138 LA. 1139 . The participants can agree on a common session key, which is 1140 chosen by the LA. The LA broadcasts an encrypted message that 1141 includes the key. Participants with a valid set of secrets can 1142 derive the session-key from this message. 1143 . The number of participants in the system can change 1144 dynamically. Entities may join or leave the communication group 1145 at any time. If a new entity joins the LA passes on a valid set 1146 of secrets to that entity. If an entity leaves (or is forced to 1147 leave) the LA revokes the entity's subset of keys, which means 1148 that it cannot derive the correct session key anymore when the 1149 LA distributes a new key. 1150 . -Traitors (entities that reveal their secrets) can be traced 1151 and excluded from ongoing communication. The algorithms and 1152 preconditions to identify a traitor vary between concrete BES. 1154 This listing already illustrates why BE is suitable to control the 1155 access to data that is distributed via an information-centric 1156 network. BE enables the usage of a single session key for 1157 confidential data transmission between a dynamically changing subset 1158 or network participants. ICN caches can be utilized since the data 1159 is encrypted only with a single key known by all legitimate clients. 1160 Furthermore, traitors can be identified and removed from the system. 1161 The issue of re-encryption still exists, because the LA will 1162 eventually update the session key when a participant should be 1163 excluded. However, this disadvantage can be relaxed in some way if 1164 the following points are considered: 1166 . The updates of the session key can be delayed until a set of 1167 compromised secretes has been gathered. Note that secrets may 1168 become compromised because of two reasons. First, if the secret 1169 has been illegally revealed by a traitor. Second, if the 1170 subscription of an entity expires. Delayed revocation 1171 temporarily enables some non-legitimate entities to consume 1172 content. However, this should not be a severe problem in home 1173 entertainment scenarios. Updating the session key in regular 1174 (not too short) intervals is a good tradeoff. The longer the 1175 interval last the less computational resources are required for 1176 content re-encryption and the better the cache utilization in 1177 the ICN will be. To evict old data from ICN caches that has 1178 been encrypted with the prior session key the publisher could 1179 indicate a lifetime for transmitted packets. 1180 . Content should be re-encrypted dynamically at request time. 1181 This has the benefit that untapped content is not re-encrypted 1182 if the content is not requested during two session key updates 1183 and therefore no resources are wasted. Furthermore, if the 1184 updates are triggered in non-peak times the maximum amount of 1185 resource needed at one point in time can be lowered 1186 effectively, since in peak times generally more diverse content 1187 is requested. 1188 . Since the amount of required computational resources may vary 1189 strongly from time to time it would be beneficial for any 1190 streaming provider to use cloud-based services to be able to 1191 dynamically adapt the required resources to the current needs. 1192 Regarding to a lack of computation time or bandwidth the cloud 1193 service could be used to scale up to overcome shortages. 1195 Figure 4 show the potential usage of BE in a multimedia delivery 1196 frameworks that builds upon ICN infrastructure and uses the concept 1197 of dynamic adaptive streaming, e.g., DASH. BE would be implemented 1198 on the top to have an efficient and scalable way of access control 1199 to the multimedia content. 1201 +--------Multimedia Delivery Framework--------+ 1202 | | 1203 | Technologies Properties | 1204 | +----------------+ +----------------+ | 1205 | | Broadcast |<--->| Controlled | | 1206 | | Encryption | | Access | | 1207 | +----------------+ +----------------+ | 1208 | |Dynamic Adaptive|<--->| Multimedia | | 1209 | | Streaming | | Adaptation | | 1210 | +----------------+ +----------------+ | 1211 | | ICN |<--->| Cachable | | 1212 | | Infrastructure | | Data Chunks | | 1213 | +----------------+ +----------------+ | 1214 +---------------------------------------------+ 1216 Figure 4: A potential multimedia framework using BE. 1218 8.2 . AAA Based DRM for ICN Networks 1220 8.2.1. Overview 1222 Recently, a novel approach to Digital Rights Management (DRM) has 1223 emerged to link DRM to usual network management operations, hence 1224 linking DRM to authentication, authorization, and accounting (AAA) 1225 services. ICN provides the abstraction of an architecture where 1226 content is requested by name and could be served from anywhere. In 1227 DRM, the content provider (the origin of the content) allows the 1228 destination (the end user account) to use the content. The content 1229 provider and content storage/cache are at two different entities in 1230 ICC and for traditional DRM only source and destination count and 1231 not the intermediate storage. The proposed solution allows the 1232 provider of the caching to be involved in the DRM policies using 1233 well known AAA mechanisms. It is important to note that this 1234 solution is compatible with the proposes the Broadcast Encryption 1235 (BE) proposed earlier in this draft. The BE proposes a technology as 1236 this solution is more operational. 1238 8.2.2. Implementation 1240 With the proposed AAA-based DRM, when a content is requested by name 1241 from a specific destination, the request could link back to both the 1242 content provider and the cahing provider via traditional AAA 1243 mechanisms, and trigger the appropriate DRM policy independently 1244 from where the content is stored. In this approach the caching, DRM 1245 and AAA remain independent entities but can work together through 1246 ICN mechanisms. The proposed solution enables extending the 1247 traditional DRM done by the content provider to jointly being done 1248 by content provider and network/caching provider. 1250 The solution is based on the concept of a "token". The content 1251 provider authenticates the end user and issues an encrypted token to 1252 authenticate the a named content ID or IDs that the user can access. 1253 The token will be shared with the network provider and used as the 1254 interface to the AAA protocols. At this point all content access is 1255 under the control of the network provider and the ICN. The 1256 controllers and switches can manage the content requests and handle 1257 mobility. The content can be accessed from anywhere as long as 1258 the token remains valid or the content is available in the network. 1259 In such a scheme the content provider does not need to be contacted 1260 every time a named content is requested. This reduces the load of 1261 the content provider network and creates a DRM mechanism that is 1262 much more appropriate for the distributed caching and peer-to-peer 1263 storage characteristic of ICN networks. In particular, the content 1264 requested by name can be served from anywhere under the only 1265 condition that the storage/cache can verify that the token is valid 1266 for content access. 1268 The solution is also fully customizable to both content and network 1269 provider's needs as the tokens can be issued based on user accounts, 1270 location and hardware (MAC address for example) linking it naturally 1271 to legacy authentication mechanisms. In addition, since both content 1272 and network providers are involved in DRM policies pollution attacks 1273 and other illegal requests for the content can be more easily 1274 detected. The proposed AAA-based DRM is currently under full 1275 development. 1277 9. Future Steps for Video in ICN 1279 The explosion of online video services, along with their increased 1280 consumption by mobile wireless terminals, further exacerbates the 1281 challenges of Video Adaptation leveraging ICN mechanisms. The 1282 following sections present a series of research items derived from 1283 these challenges, further introducing next steps for the subject. 1285 9.1. Large Scale Live Events 1287 An active area of investigation and a potential use case where ICN 1288 would provide significant benefits, is that of distributing content, 1289 and video in particular, using local communications in large scale 1290 events such as sports event in a stadium, a concert or a large 1291 demonstration. 1293 Such use-case involves locating content that is generated on the fly 1294 and requires discovery mechanisms in addition to sharing mechanisms. 1295 The scalability of the distribution becomes important as well. 1297 9.2. Video Conferencing and Real-Time Communications 1299 Current protocols for video-conferencing have been designed, and 1300 this document needs to take input from them to identify the key 1301 research issues. Real-time communication add timing constraints 1302 (both in terms of delay and in terms of synchronization) to the 1303 scenario discussed above. 1305 9.3. Store-and-Forward Optimized Rate Adaptation 1307 One of the benefits of ICN is to allow the network to insert caching 1308 in the middle of the data transfer. This can be used to reduce the 1309 overall bandwidth demands over the network by caching content for 1310 future re-use. But it provides more opportunities for optimizing 1311 video streams. 1313 Consider for instance the following scenario: a client is connected 1314 via an ICN network to a server. Let's say the client is connected 1315 wirelessly to a node that has a caching capability, which is 1316 connected through a WAN to the server. Assume further that the 1317 capacity of each of the links (both the wireless and the WAN logical 1318 links) vary with time. 1320 If the rate adaptation is provided in an end-to-end manner, as in 1321 current mechanisms like DASH, then the maximal rate that can be 1322 supported at the client is that of the minimal bandwidth on each 1323 link. 1325 For instance, if during time period 1, the wireless capacity is 1 1326 and the wired capacity is 2, and during time period 2, the wireless 1327 is 2 due to some hotspot, and the wired is 1 due to some congestion 1328 in the network, then the best end-to-end rate that can be achieved 1329 is 1 during each period. 1331 However, if the cache is used during time period 1 to pre-fetch 2 1332 units of data, then during period 2, there is 1 unit of data at the 1333 cache, and another unit of data, which can be streamed from the 1334 server, and the rate that can be achieved is therefore 2 units of 1335 data. In this case, the average bandwidth rises from 1 to 1.5 over 1336 the 2 periods. 1338 This straw man example illustrate a) the benefit of ICN for 1339 increasing the throughput of the network, and b) the need for the 1340 special rate adaptation mechanisms to be designed so as to take 1341 advantage of this gain. End-to-end rate adaptation can not take 1342 advantage of the cache availability. 1344 9.4. Heterogeneous Wireless Environment Dynamics 1346 With the ever-growing increase in online services being accessed by 1347 mobile devices, operators have been deploying different overlapping 1348 wireless access networking technologies. In this way, in the same 1349 area, user terminals are within range of different cellular, Wi-Fi 1350 or even WiMAX networks. Moreover, with the advent of the Internet of 1351 Things (e.g., surveillance cameras feeding video footage), this list 1352 can be further complemented with more specific short-range 1353 technologies, such as Bluetooth or ZigBee. 1355 In order to leverage from this plethora of connectivity 1356 opportunities, user terminals are coming equipped with different 1357 wireless access interfaces, providing them with extended 1358 connectivity opportunities. In this way, such devices become able to 1359 select the type of access which best suits them according to 1360 different criteria, such as available bandwidth, battery 1361 consumption, access do different link conditions according to the 1362 user profile or even access to different content. Ultimately, these 1363 aspects contribute to the Quality of Experience perceived by the 1364 end-user, which is of utmost importance when it comes to video 1365 content. 1367 However, the fact that these users are mobile and using wireless 1368 technologies, also provides a very dynamic setting, where the 1369 current optimal link conditions at a specific moment might not last 1370 or be maintained while the user moves. These aspects have been amply 1371 analyzed in recently finished projects such as FP7 MEDIEVAL [18], 1372 where link events reporting on wireless conditions and available 1373 alternative connection points were combined with vide requirements 1374 and traffic optimization mechanisms, towards the production of a 1375 joint network and mobile terminal mobility management decision. 1376 Concretely, in [19] link information about the deterioration of the 1377 wireless signal was sent towards a mobility management controller in 1378 the network. This input was combined with information about the user 1379 profile, as well as of the current video service requirements, and 1380 used to trigger the decrease or increase of scalable video layers, 1381 adjusting the video to the ongoing link conditions. Incrementally, 1382 the video could also be adjusted when a new better connectivity 1383 opportunity presents itself. 1385 In this way, regarding Video Adaptation, ICN mechanisms can leverage 1386 from their intrinsic multiple source support capability and go 1387 beyond the monitoring of the status of the current link, thus 1388 exploiting the availability of different connectivity possibilities 1389 (e.g., different "interfaces"). Moreover, information obtained from 1390 the mobile terminal's point of view of its network link, as well as 1391 information from the network itself (i.e., load, policies, and 1392 others), can generate scenarios where such information is combined 1393 in a joint optimization procedure allowing the content to be forward 1394 to users using the best available connectivity option (e.g., 1395 exploiting management capabilities supported by ICN intrinsic 1396 mechanisms as in [20]). 1398 In fact, ICN base mechanisms can further be exploited in enabling 1399 new deployment scenarios such as preparing the network for mass 1400 requests from users attending a large multimedia event (i.e., 1401 concert, sports), allowing video to be adapted according to content, 1402 user and network requirements and operation capabilities in a 1403 dynamic way. 1405 The enablement of such scenarios require further research, with the 1406 main points highlighted as follows: 1408 . Development of a generic video services (and obviously content) 1409 interface allowing the definition and mapping of their 1410 requirements (and characteristics) into the current capabilities 1411 of the network; 1413 . How to define a scalable mechanism allowing either the video 1414 application at the terminal, or some kind of network management 1415 entity, to adapt the video content in a dynamic way; 1417 . How to develop the previous research items using intrinsic ICN 1418 mechanisms (i.e., naming and strategy layers); 1420 . Leverage intelligent pre-caching of content to prevent stalls and 1421 poor quality phases, which lead to bad Quality of Experience of 1422 the user. This includes in particular the usage in mobile 1423 environments, which are characterized by severe bandwidth changes 1424 as well as connection outages, as shown in [21]. 1426 9.5. Network Coding for Video Distribution in ICN 1428 An interesting research area for combining heterogeneous sources is 1429 to use network coding [24]. Network coding allows to asynchronously 1430 combine multiple sources by having each of them send information 1431 that is not duplicated by the other but can be combined to retrieve 1432 the video stream. 1434 However, this creates issues in ICN in terms of defining the proper 1435 rate adaptation for the video stream; securing the encoded data; 1436 caching the encoded data; timeliness of the encoded data; overhead 1437 of the network coding operations both in network resources and in 1438 added buffering delay, etc. 1440 10. Security Considerations 1442 This is informational. Security considerations are TBD. 1444 11. IANA Considerations 1446 This is informational. IANA considerations are TBD. 1448 12. Conclusions 1450 This draft proposed adaptive video streaming for ICN, identified 1451 potential problems and presented the combination of CCN with DASH as 1452 a solution. As both concepts, DASH and CCN, maintain several 1453 elements in common, like, e.g., the content in different versions 1454 being dealt with in segments, combination of both technologies seems 1455 useful. Thus, adaptive streaming over CCN can leverage advantages 1456 such as, e.g., efficient caching and intrinsic multicast support of 1457 CCN, routing based on named data URIs, intrinsic multi-link and 1458 multi-source support, etc. 1460 In this context, the usage of CCN with DASH in mobile environments 1461 comes together with advantages compared to today's solutions, 1462 especially for devices equipped with multiple network interfaces. 1463 The retrieval of data over multiple links in parallel is a useful 1464 feature, specifically for adaptive multimedia streaming, since it 1465 offers the possibility to dynamically switch between the available 1466 links depending on their bandwidth capabilities, transparent to the 1467 actual DASH client. 1469 13. References 1471 13.1. Normative References 1473 [RFC6972] Y. Zhang, N. Zong, "Problem Statement and Requirements of 1474 the Peer-to-Peer Streaming Protocol (PPSP)", RFC6972, July 1475 2013 1477 13.2. Informative References 1479 [1] ISO/IEC DIS 23009-1.2, Information technology - Dynamic 1480 adaptive streaming over HTTP (DASH) - Part 1: Media 1481 presentation description and segment formats 1483 [2] Lederer, S., Mueller, C., Rainer, B., Timmerer, C., 1484 Hellwagner, H., "An Experimental Analysis of Dynamic Adaptive 1485 Streaming over HTTP in Content Centric Networks", in 1486 Proceedings of the IEEE International Conference on Multimedia 1487 and Expo 2013, San Jose, USA, July, 2013 1489 [3] Liu, Y., Geurts, J., Point, J., Lederer, S., Rainer, B., 1490 Mueller, C., Timmerer, C., Hellwagner, H., "Dynamic Adaptive 1491 Streaming over CCN: A Caching and Overhead Analysis", in 1492 Proceedings of the IEEE international Conference on 1493 Communication (ICC) 2013 - Next-Generation Networking 1494 Symposium, Budapest, Hungary, June, 2013 1496 [4] Grandl, R., Su, K., Westphal, C., "On the Interaction of 1497 Adaptive Video Streaming with Content-Centric Networks", 1498 eprint arXiv:1307.0794, July 2013. 1500 [5] V. 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Braynard, "VoCCN: Voice 1514 over content-centric networks," in ACM ReArch Workshop, 2009 1516 [8] Christopher Mueller, Stefan Lederer and Christian Timmerer, A 1517 proxy effect analysis and fair adaptation algorithm for 1518 multiple competing dynamic adaptive streaming over HTTP 1519 clients, In Proceedings of the Conference on Visual 1520 Communications and Image Processing (VCIP) 2012, San Diego, 1521 USA, November 27-30, 2012. 1523 [9] DASH Research at the Institute of Information Technology, 1524 Multimedia Communication Group, Alpen-Adria Universitaet 1525 Klagenfurt, URL: http://dash.itec.aau.at 1527 [10] A. Detti, N. Blefari-Melazzi, S. Salsano, and M. Pomposini, 1528 "CONET: A content centric inter-networking architecture," 1529 in ACM Workshop on Information-Centric Networking (ICN), 1530 2011. 1532 [11] W. K. Chai, N. Wang, I. Psaras, G. Pavlou, C. Wang, G. C. de 1533 Blas, F. Ramon-Salguero, L. Liang, S. Spirou, A. Beben, 1534 and E. Hadjioannou, "CURLING: Content-ubiquitous 1535 resolution and delivery infrastructure for next-generation 1536 services," IEEE Communications Magazine, vol. 49, no. 3, 1537 pp. 112-120, March 2011 1539 [12] NetInf project Website http://www.netinf.org 1541 [13] N. Magharei, R. Rejaie, Yang Guo, "Mesh or Multiple-Tree: A 1542 Comparative Study of Live P2P Streaming Approaches," 1543 INFOCOM 2007. 26th IEEE International Conference on 1544 Computer Communications. IEEE , vol., no., pp.1424,1432, 1545 6-12 May 2007 1547 [14] PPSP WG Website https://datatracker.ietf.org/wg/ppsp/ 1549 [15] A. Bakker, R. Petrocco, V. Grishchenko, "Peer-to-Peer Streaming 1550 Peer Protocol (PPSPP)", draft-ietf-ppsp-peer-protocol-08 1552 [16] Rui S. Cruz, Mario S. Nunes, Yingjie Gu, Jinwei Xia, Joao P. 1553 Taveira, Deng Lingli, "PPSP Tracker Protocol-Base Protocol 1554 (PPSP-TP/1.0)", draft-ietf-ppsp-base-tracker-protocol-02 1556 [17] A.Detti, B. Ricci, N. 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Springer Berlin / Heidelberg, 1994. 1581 [23] Posch D., Hellwagner H., Schartner P., "On-Demand Video 1582 Streaming based on Dynamic Adaptive Encrypted Content Chunks", th in Proceedings of the 8 International Workshop on Secure 1583 Network Protocols (NPSec' 13), Los Alamitos, IEEE Computer 1584 Society Press, October, 2013. 1586 [24] Montpetit M.J., Westphal C., Trossen D., "Network Coding Meets 1587 Information Centric Networks," in Proceedings of the workshop 1588 on Name-Oriented Mobility (NOM), jointly with ACM MobiHoc 2013, 1589 Hilton Head, SC, June 2013. 1591 14. Authors' Addresses 1593 Stefan Lederer, Christian Timmerer, Daniel Posch 1594 Alpen-Adria University Klagenfurt 1595 Universitaetsstrasse 65-67, 9020 Klagenfurt, Austria 1597 Email: {firstname.lastname}@itec.aau.at 1599 Cedric Westphal, Aytac Azgin, Sucheng (Will) Liu 1600 Huawei 1601 2330 Central Expressway, Santa Clara, CA95050, USA 1603 Email: {cedric.westphal, aytac.azgin, liushucheng}@huawei.com 1605 Christopher Mueller 1606 bitmovin GmbH 1607 Lakeside B01, 9020 Klagenfurt, Austria 1609 Email: christopher.mueller@bitmovin.net 1611 Andrea Detti 1612 Electronic Engineering Dept. 1613 University of Rome Tor Vergata 1614 Via del Politecnico 1, Rome, Italy 1616 Email: andrea.detti@uniroma2.it 1618 Daniel Corujo, 1619 Advanced Telecommunications and Networks Group 1620 Instituto de Telecomunicacoes 1621 Campus Universitario de Santiago 1622 P-3810-193 Aveiro, Portugal 1624 Email: dcorujo@av.it.pt 1626 15. Acknowledgements 1628 This work was supported in part by the EC in the context of the 1629 SocialSensor (FP7-ICT-287975) project and partly performed in the 1630 Lakeside Labs research cluster at AAU. SocialSensor receives 1631 research funding from the European Community's Seventh Framework 1632 Programme. The work for this document was also partially performed 1633 in the context of the FP7/NICT EU-JAPAN GreenICN project, 1634 http://www.greenicn.org. Apart from this, the European Commission 1635 has no responsibility for the content of this draft. The information 1636 in this document is provided as is and no guarantee or warranty is 1637 given that the information is fit for any particular purpose. The 1638 user thereof uses the information at its sole risk and liability. 1639 The authors would like to Dr. Jianping Wang (City University Hong Kong) 1640 and Marie-Jose Montpetit of MIT for their help in writing the AAA for DRM 1641 section.