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Otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (November 24, 2015) is 3077 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Missing reference section? '2' on line 1580 looks like a reference -- Missing reference section? '3' on line 1586 looks like a reference -- Missing reference section? '4' on line 1593 looks like a reference -- Missing reference section? '6' on line 1602 looks like a reference -- Missing reference section? 'RFC2119' on line 200 looks like a reference -- Missing reference section? '7' on line 1609 looks like a reference -- Missing reference section? '25' on line 1686 looks like a reference -- Missing reference section? '1' on line 1576 looks like a reference -- Missing reference section? 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Timmerer 4 Expires: May 23, 2016 Alpen-Adria University Klagenfurt 5 C. Westphal, Ed. 6 Aytac 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 15 J. Wang 16 City University of Hong-Kong 17 Marie-Jose Montpetit 18 Niall Murray 19 Athlone Institute of Technology 21 November 24, 2015 23 Adaptive Video Streaming over ICN 24 draft-irtf-icnrg-videostreaming-05.txt 26 Status of this Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 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, and it may not be 34 published except as an Internet-Draft. 36 This Internet-Draft is submitted in full conformance with the 37 provisions of BCP 78 and BCP 79. 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Please review these documents 80 carefully, as they describe your rights and restrictions with 81 respect to this document. 83 Abstract 85 This document considers the consequences of moving the underlying 86 network architecture from the current Internet to an Information- 87 Centric Network (ICN) architecture on video distribution. As most of 88 the traffic in future networks is expected to be video, we consider 89 how to modify the existing video streaming mechanisms. Several 90 important topics related to video distribution over ICN are 91 presented, covering a wide range of scenarios: we look at how to 92 evolve DASH to work over ICN, and leverage the recent ISO/IEC MPEG 93 Dynamic Adaptive Streaming over HTTP (DASH) standard; we consider 94 layered encoding over ICN; P2P mechanisms introduce distinct 95 requirements for video and we look at how to adapt Peer to Peer 96 Streaming Protocol (PPSP) for ICN; IPTV adds delay constraints, and 97 this will create more stringent requirements over ICN as well. As 98 part of the discussion on video, we discuss DRMs in ICN. Finally, in 99 addition to consider how existing mechanisms would be impacted by 100 ICN, this document lists some research issues to design ICN specific 101 video streaming mechanisms. 103 Table of Contents 104 1. Introduction....................................................... 4 105 2. Conventions used in this document.................................. 5 106 3. Use case scenarios for ICN and Video Streaming..................... 5 107 4. Video download..................................................... 7 108 5. Video streaming and ICN............................................ 7 109 5.1. Introduction to client-driven streaming and DASH ............... 7 110 5.2. Layered Encoding ............................................... 8 111 5.3. Interactions of Video Streaming with ICN ....................... 9 112 5.3.1. Interaction of DASH and ICN ................................ 9 113 5.3.2. Interaction of ICN with Layered Encoding .................. 11 114 5.4. Possible Integration of Video streaming and ICN architecture .. 12 115 5.4.1. DASH over CCN ............................................. 12 116 5.4.2. Testbed, Open Source Tools, and Dataset ................... 14 117 6. P2P video distribution and ICN.................................... 15 118 6.1. Introduction to PPSP .......................................... 15 119 6.2. PPSP over ICN: deployment concepts ............................ 16 120 6.2.1. PPSP short background ..................................... 16 121 6.2.2. From PPSP messages to ICN named-data ...................... 17 122 6.2.3. Support of PPSP interaction through a pull-based ICN API .. 18 123 6.2.4. Abstract layering for PPSP over ICN ....................... 18 124 6.2.5. PPSP interaction with the ICN routing plane ............... 19 125 6.2.6. ICN deployment for PPSP ................................... 20 126 6.3. Impact of MPEG DASH coding schemes ............................ 21 127 7. IPTV and ICN...................................................... 22 128 7.1. IPTV challenges ............................................... 22 129 7.2. ICN benefits for IPTV delivery ................................ 23 130 8. Digital Rights Managements in ICN................................. 24 131 8.1. Broadcast Encryption for DRM in ICN ........................... 25 132 8.2. AAA Based DRM for ICN Networks ................................ 28 133 8.2.1. Overview .................................................. 28 134 8.2.2. Implementation ............................................ 29 135 9. Future Steps for Video in ICN..................................... 29 136 9.1. Large Scale Live Events ....................................... 30 137 9.2. Video Conferencing and Real-Time Communications ............... 30 138 9.3. Store-and-Forward Optimized Rate Adaptation ................... 30 139 9.4. Heterogeneous Wireless Environment Dynamics ................... 31 140 9.5. Network Coding for Video Distribution in ICN .................. 33 141 9.6. Synchronization Issues for Video Distribution in ICN .......... 33 142 10. Security Considerations.......................................... 34 143 11. IANA Considerations.............................................. 34 144 12. Conclusions...................................................... 34 145 13. References....................................................... 35 146 13.1. Normative References ......................................... 35 147 13.2. Informative References ....................................... 35 148 14. Authors' Addresses............................................... 38 149 15. Acknowledgements................................................. 39 151 1. Introduction 153 The unprecedented growth of video traffic has triggered a rethinking 154 of how content is distributed, both in terms of the underlying 155 Internet architecture and in terms of the streaming mechanisms to 156 deliver video objects. 158 In particular, the IRTF ICN working group has been chartered to 159 study new architectures centered upon information; the main 160 contributor to Internet traffic (and information dissemination) is 161 video, and this is expected to stay the same in the short- to mid- 162 term future. If ICN is expected to become prominent, it will have to 163 support video streaming efficiently. 165 As such, it is necessary to discuss along two directions: 167 . Can the current video streaming mechanisms be leveraged and 168 adapted to an ICN architecture? 170 . Can (and should) new, ICN-specific video streaming mechanisms 171 be designed to fully take advantage of the new abstractions 172 exposed by the ICN architecture? 174 This document intends to focus on the first question, in an attempt 175 to define the use cases for video streaming and some requirements. 177 This document focuses on a few scenarios, namely Netflix-like video 178 streaming, peer-to-peer video sharing and IPTV, and identifies how 179 the existing protocols can be adapted to an ICN architecture. In 180 doing so, it also identifies the main issues with these protocols in 181 this ICN context. 183 Some documents have started to consider the ICN-specific 184 requirements of dynamic adaptive streaming [2][3][4][6]. 186 In this document, we give a brief overview of the existing solutions 187 for the selected scenarios. We then consider the interactions of 188 such existing mechanisms with the ICN architecture and list some of 189 the interactions any video streaming mechanism will have to 190 consider. We then identify some areas for future research. 192 2. Conventions used in this document 194 In examples, "C:" and "S:" indicate lines sent by the client and 195 server respectively. 197 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 198 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 199 document are to be interpreted as described in RFC-2119 [RFC2119]. 201 In this document, these words will appear with that interpretation 202 only when in ALL CAPS. Lower case uses of these words are not to be 203 interpreted as carrying RFC-2119 significance. 205 In this document, the characters ">>" preceding an indented line(s) 206 indicates a compliance requirement statement using the key words 207 listed above. This convention aids reviewers in quickly identifying 208 or finding the explicit compliance requirements of this RFC. 210 3. Use case scenarios for ICN and Video Streaming 212 For ICN specific descriptions, we refer to the other working group 213 documents. For our purpose, we assume here that ICN means an 214 architecture where content is retrieved by name and with no binding 215 of content to a specific network location. 217 The consumption of multimedia content comes along with timing 218 requirements for the delivery of the content, for both, live and on- 219 demand consumption. Additionally, real-time use cases such as audio- 220 /video conferencing [7], game streaming, etc., come along with more 221 strict timing requirements. Long startup delays, buffering periods, 222 image freeze, etc., should be avoided to achieve a good Quality of 223 Experience (QoE) to the consumer of the content. (For a definition 224 of QoE in the context of video distribution, please refer to [25]. 225 The working definition is: "Quality of Experience (QoE) is the 226 degree of delight or annoyance of the user of an application or 227 service. It results from the fulfillment of his or her expectations 228 with respect to the utility and / or enjoyment of the application or 229 service in the light of the user's personality and current state.") 231 Of course, these requirements are heavily influenced by routing 232 decisions and caching, which are central parts of ICN and which have 233 to be considered when streaming video in such infrastructures. 235 Due to this range of requirements, we find it useful to narrow the 236 focus on four scenarios (more can be included later): 238 - a video delivery architecture similar to that of iTune, where the 239 whole file is being downloaded to the client and can be replayed 240 there multiple times; 241 - a video streaming architecture for playing back movies; this is 242 relevant for the naming and caching aspects of ICN, as well as the 243 interaction with the rate adaptation mechanism necessary to 244 deliver the best QoE to the end-user; 245 - a peer-to-peer architecture for sharing videos; this introduces 246 more stringent routing requirements in terms of locating copies of 247 the content, as the location of the peers evolves and peers join 248 and leave the swarm they use to exchange video chunks; 249 - IPTV; this introduces requirements for multicasting and adds 250 stronger delay constraints. 252 Other scenarios, such as video-conferencing and real-time video 253 communications are not explicitly discussed in this document, while 254 they are in scope. Also, events of mass-media distribution, such as 255 a large crowd in a live event, are also adding new requirements to 256 be included in later version. 258 We discuss how the current state-of-the-art protocols in an IP 259 context can be modified for the ICN architecture. The remainder of 260 this document is organized as follows. In the next section, we 261 consider video download. Then in Section 5, we briefly describe DASH 262 [1], and Layered Encoding (MDC, SVC). P2P is the focus of Section 6, 263 where we describe PPSP. Section 7 highlights the requirements of 264 IPTV, while Section 8 describes the issues of DRM. Section 9 lists 265 some research issues to be solved for ICN-specific video delivery 266 mechanisms. 268 Videoconferencing and real-time video communications will be 269 detailed more in future versions of this document; as well as the 270 mass distribution of content at live large-scale events (stadium, 271 concert hall, etc) for which there is no clearly adopted existing 272 protocol. 274 4. Video download 276 Video download, namely the fetching of a video file from a server or 277 a cache down to the user's local storage, is a natural application 278 of ICN. It should be supported natively without requiring any 279 specific considerations. 281 This is supported now by a host of protocols (e.g. SCP, FTP, or over 282 HTTP), which would need to be replaced by the protocols to retrieve 283 content in ICNs. 285 However, current mechanisms are built on top of existing transport 286 protocols. Some ICN proposals (say, CCN or NDN for instance) attempt 287 to leverage the work done upon these transport protocol and it has 288 been proposed to use mechanisms such as the TCP congestion window 289 (and the associated Adaptive Increase, Multiplicative Decrease - 290 AIMD) to decide how many object requests ("interests" in CCN/NDN 291 terminology) should be in flight at any point in time. 293 It should be noted that ICN intrinsically supports different 294 transport mechanisms, which could achieve better performance than 295 TCP, as they subsume TCP into a special case. For instance, one 296 could imagine a link-by-link transport coupled with caching. This is 297 enabled by the ICN architecture, and would facilitate the point-to- 298 point download of video files. 300 5. Video streaming and ICN 302 5.1. Introduction to client-driven streaming and DASH 304 Media streaming over the hypertext transfer protocol (HTTP) and in a 305 further consequence streaming over the transmission control protocol 306 (TCP) has become omnipresent in today's Internet. Content providers 307 such as Netflix, Hulu, and Vudu do not deploy their own streaming 308 equipment but use the existing Internet infrastructure as it is and 309 they simply deploy their own services over the top (OTT). This 310 streaming approach works surprisingly well without any particular 311 support from the underlying network due to the use of efficient 312 video compression, content delivery networks (CDNs), and adaptive 313 video players. Earlier video streaming research mostly recommended 314 to use the user datagram protocol (UDP) combined with the real time 315 transport protocol (RTP). It assumed it would not be possible to 316 transfer multimedia data smoothly with TCP, because of its 317 throughput variations and large retransmission delays. This point of 318 view has significantly evolved today. HTTP streaming, and especially 319 its most simple form known as progressive download, has become very 320 popular over the past few years because it has some major benefits 321 compared to RTP streaming. Unlike HTTP streaming, RTP could not 322 easily make use of the existing Internet infrastructure, consisting 323 of proxies, caches and CDNs. Originally, this architecture was 324 designed to support best effort delivery of files and web traffic, 325 and not real time transport of multimedia data. Nevertheless, it has 326 proved very efficient with streaming. Another benefit from the use 327 of HTTP (instead of RTP) is that the media stream could easily pass 328 firewalls or network address translation (NAT) gateways, which was 329 definitely a key for the success of HTTP streaming. However, HTTP 330 streaming is not the holy grail of streaming as it also introduces 331 some drawbacks compared to RTP. The use of UDP in RTP for instance 332 enables timeliness over reliability; RTP also supports multi-cast 333 sessions, unlike HTTP. Nevertheless, in an ICN-based video streaming 334 architecture these aspects also have to be considered. 336 The basic concept of DASH [1] is to use segments of media content, 337 which can be encoded at different resolutions, bit rates, etc., as 338 so-called representations. These segments are served by conventional 339 HTTP Web servers and can be addressed via HTTP GET requests from the 340 client. As a consequence, the streaming system is pull-based and the 341 entire streaming logic is located on the client, which makes it 342 scalable, and allows to adapt the media stream to the client's 343 capabilities. 345 In addition to this, the content can be distributed using 346 conventional CDNs and their HTTP infrastructure, which also scales 347 very well. In order to specify the relationship between the 348 contents' media segments and the associated bit rate, resolution, 349 and timeline, the Media Presentation Description (MPD) is used, 350 which is a XML document. The MPD refers to the available media 351 segments using HTTP URLs, which can be used by the client for 352 retrieving them. 354 5.2. Layered Encoding 356 Another approach for video streaming consist in using layered 357 encoding. Namely, scalable video coding formats the video stream 358 into different layers: a base layer which can be decoded to provide 359 the lowest bit rate for the specific stream, and enhancement layers 360 which can be transmitted separately if network conditions allow. The 361 higher layers offer higher resolutions and enhancement of the video 362 quality, while the layered approach allows to adapt to the network 363 conditions. This is used in MPEG-4 scalable profile or H.263+. 364 H.264SVC is available, but not much deployed. JPEG2000 has a wavelet 365 transform approach for layered encoding, but has not been deployed 366 much either. 368 It is not clear if the layered approach is fine-grained enough for 369 rate control. 371 5.3. Interactions of Video Streaming with ICN 373 5.3.1. Interaction of DASH and ICN 375 Video streaming, and DASH in particular, have been designed with 376 goals that are aligned with that of most ICN proposals. Namely, it 377 is a client-based mechanism, which requests items (in this case, 378 chunks of a video stream) by name. 380 ICN and MPEG-DASH [1] have several elements in common: 382 - the client-initiated pull approach; 383 - the content being dealt with in pieces (or chunks); 384 - the support of efficient replication and distribution of content 385 pieces within the network; 386 - the scalable, session-free nature of the exchange between the 387 client and the server at the streaming layer: both are not 388 restricted to classical end-to-end or host-to-host communications. 389 - the support for potentially multiple source locations. 391 For the last point, DASH may list multiple source URLs in a 392 manifest, and ICN is agnostic to the location of a copy it is 393 receiving. We do not imply that current video streaming mechanisms 394 attempt to draw the content from multiple sources concurrently. This 395 is a potential benefit of ICN, but is not considered in the current 396 approaches mentioned in this document. 398 As ICN is a promising candidate for the Future Internet (FI) 399 architecture, it is useful to investigate its suitability in 400 combination with multimedia streaming standards like MPEG-DASH. In 401 this context, the purpose of this section is to present the usage of 402 ICN instead of HTTP in MPEG-DASH 404 However, there are some issues that arise from using a dynamic rate 405 adaptation mechanism in an ICN architecture: 407 o Naming of the data in DASH does not necessarily follow the ICN 408 convention of any of the ICN proposals. Several chunks of the 409 same video stream might currently go by different names that for 410 instance do not share a common prefix. There is a need to 411 harmonize the naming of the chunks in DASH with the naming 412 conventions of the ICN. The naming convention of using a 413 filename/time/encoding format could for instance be made 414 compatible with the convention of CCN. 416 o While chunks can be retrieved from any server, the rate 417 adaptation mechanism attempts to estimate the available network 418 bandwidth so as to select the proper playback rate and keep its 419 playback buffer at the proper level. Therefore, there is a need 420 to either include some location semantics in the data chunks so 421 as to properly assess the throughput to a specific location; or 422 to design a different mechanism to evaluate the available network 423 bandwidth. 425 o The typical issue of access control and accounting happens in 426 this context, where chunks can be cached in the network outside 427 of the administrative control of the content publisher. It might 428 be a requirement from the owner of the video stream that access 429 to these data chunks needs to be accounted/billed/monitored. 431 o Dynamic streaming multiplies the representations of a given video 432 stream, therefore diminishing the effectiveness of caching: 433 namely, to get a hit for a chunk in the cache, it has to be for 434 the same format and encoding values. Alternatively, to get the 435 same hit rate as for a stream using a single encoding, the cache 436 size must be scaled up to include all the possible 437 representations. 439 o Caching introduces oscillatory dynamics as it may modify the 440 estimation of the available bandwidth between the end user and 441 the repository where it is getting the chunks from. For instance, 442 if an edge cache holds a low resolution representation near the 443 user, the user getting this low resolution chunks will observe a 444 good performance, and will then request higher resolution chunks. 445 If those are hosted on a server with poor performance, then the 446 client would have to switch back to the low representation. This 447 oscillation may be detrimental to the perceived QoE of the user. 449 o The ICN transport mechanism needs to be compatible to some extent 450 with DASH. To take a CCN example, the rate at which interests are 451 issued should be such that the chunks received in return arrive 452 fast enough and with the proper encoding to keep the playback 453 buffer above some threshold. 455 o The usage of multiple network interfaces is possible in ICN, 456 enabling a seamless handover between them. For the combination 457 with DASH, an intelligent strategy which should focus on traffic 458 load balancing between the available links may be necessary. This 459 would increase the effective media throughput of DASH by 460 leveraging the combined available bandwidth of all links, 461 however, it could potentially lead to high variations of the 462 media throughput. 464 o DASH does not define how the MPD is retrieved; hence, this is 465 compatible with CCN. However, the current profiles defined within 466 MPEG-DASH require the MPD to contain HTTP-URLs (incl. http and 467 https URI schemes) to identify segments. To enable a more 468 integrated approach as described in this document, an additional 469 profile for DASH over CCN has to be defined, enabling ICN/CCN- 470 based URIs to identify and request the media segments. 472 We describe in Section 5.4 a potential implementation of a dynamic 473 adaptive video stream over ICN, based upon DASH and CCN [5]. 475 5.3.2. Interaction of ICN with Layered Encoding 477 Issues of interest to an Information-Centric network architecture in 478 the context of layered video streaming include: 480 . Caching of the multiple layers. The caching priority should go 481 to the base layer, and defining caching policy to decide when 482 to cache enhancement layers; 483 . Synchronization of multiple content streams, as the multiple 484 layers may come from different sources in the network (for 485 instance, the base layer might be cached locally while the 486 enhancement layers may be stored in the origin server). There 487 are both intra-layer synchronization (for the layers of the 488 same video or audio stream) but also inter-stream 489 synchronization to address, for synchronizing the audio and the 490 video streams (see Section 9 for other synchronization aspects 491 to be included in the "Future Steps for Video in ICN"); 492 . Naming of the different layers: when the client requests an 493 object, the request can be satisfied with the base layer alone, 494 aggregated with enhancement layers. Should one request be 495 sufficient to provide different streams? In a CCN architecture 496 for instance, this would violate a one interest-one data packet 497 principle and the client would need to specify each layer it 498 would like to receive. In a Pub/Sub architecture, the 499 rendezvous point would have to make a decision as to which 500 layers (or which pointer to which layer's location) to return. 502 5.4. Possible Integration of Video streaming and ICN architecture 504 5.4.1. DASH over CCN 506 DASH is intended to enable adaptive streaming, i.e., each content 507 piece can be provided in different qualities, formats, languages, 508 etc., to cope with the diversity of todays' networks and devices. As 509 this is an important requirement for Future Internet proposals like 510 CCN, the combination of those two technologies seems to be obvious. 511 Since those two proposals are located at different protocol layers - 512 DASH at the application and CCN at the network layer - they can be 513 combined very efficiently to leverage the advantages of both and 514 potentially eliminate existing disadvantages. As CCN is not based on 515 classical host-to-host connections, it is possible to consume 516 content from different origin nodes as well as over different 517 network links in parallel, which can be seen as an intrinsic error 518 resilience feature w.r.t. the network. This is a useful feature of 519 CCN for adaptive multimedia streaming within mobile environments 520 since most mobile devices are equipped with multiple network links 521 like 3G and WiFi. CCN offers this functionality out of the box which 522 is beneficial when used for DASH-based services. In particular, it 523 is possible to enable adaptive video streaming handling both 524 bandwidth and network link changes. That is, CCN handles the network 525 link decision and DASH is implemented on top of CCN to adapt the 526 video stream to the available bandwidth. 528 In principle, there are two options to integrate DASH and CCN: a 529 proxy service acting as a broker between HTTP and CCN as proposed in 530 [6], and the DASH client implementing a native CCN interface. The 531 former transforms an HTTP request to a corresponding interest packet 532 as well as a data packet back to an HTTP response, including 533 reliable transport as offered by TCP. This may be a good compromise 534 to implement CCN in a managed network and to support legacy devices. 535 As such a proxy is already described in [6] this draft focuses on a 536 more integrated approach, aiming at fully exploiting the potential 537 of a CCN DASH Client. That is, we describe a native CCN interface 538 within the DASH client, which adopts a CCN naming scheme (CCN URIs) 539 to denote segments in the Media Presentation Description (MPD). In 540 this architecture, only the network access component on the client 541 has to be modified and the segment URIs within MPD have to be 542 updated according to the CCN naming scheme. 544 Initially, the DASH client retrieves the MPD containing the CCN URIs 545 of the content representations including the media segments. The 546 naming scheme of the segments may reflect intrinsic features of CCN 547 like versioning and segmentation support. Such segmentation support 548 is already compulsory for multimedia streaming in CCN and, thus, can 549 also be leveraged for DASH-based streaming over CCN. The CCN 550 versioning can be adopted in a further step to signal different 551 representations of the DASH-based content, which enables an implicit 552 adaptation of the requested content to the clients' bandwidth 553 conditions. That is, the interest packet already provides the 554 desired characteristics of a segment (such as bit rate, resolution, 555 etc.) within the content name (or potentially within parameters 556 defined as extra types in the packet formats). Additionally, if 557 bandwidth conditions of the corresponding interfaces or routing 558 paths allow so, DASH media segments could be aggregated 559 automatically by the CCN nodes, which reduces the amount of interest 560 packets needed to request the content. However, such approaches need 561 further research, specifically in terms of additional intelligence 562 and processing power needed at the CCN nodes. 564 After requesting the MPD, the DASH client will start to request 565 particular segments. Therefore, CCN interest packets are generated 566 by the CCN access component and forwarded to the available 567 interfaces. Within the CCN, these interest packets leverage the 568 efficient interest aggregation for, e.g., popular content, as well 569 as the implicit multicast support. Finally, the interest packets are 570 satisfied by the corresponding data packets containing the video 571 segment data, which are stored on the origin server or any CCN node, 572 respectively. With an increasing popularity of the content, it will 573 be distributed across the network resulting in lower transmission 574 delays and reduced bandwidth requirements for origin servers and 575 content providers respectively. 577 With the extensive usage of in-network caching, new drawbacks are 578 introduced since the streaming logic is located at the client, i.e., 579 clients are not aware of each other and the network infrastructure 580 and cache states. Furthermore, negative effects are introduced when 581 multiple clients are competing for a bottleneck and when caching is 582 influencing this bandwidth competition. As mentioned above, the 583 clients request individual portions of the content based on 584 available bandwidth, which is calculated using throughput 585 estimations. This uncontrolled distribution of the content 586 influences the adaptation process of adaptive streaming clients. The 587 impact of this falsified throughput estimation could be tremendous 588 and leads to a wrong adaptation decision which may impact the 589 Quality of Experience (QoE) at the client, as shown in [8]. In ICN, 590 the client does not have the knowledge from which source the 591 requested content is actually served or how many origin servers of 592 the content are available, as this is transparent and depends on the 593 name-based routing. This introduces the challenge that the 594 adaptation logic of the adaptive streaming client is not aware of 595 the event when the ICN routing decides to switch to a different 596 origin server or content is coming through a different 597 link/interface. As most algorithms implementing the adaption logic 598 are using bandwidth measurements and related heuristics, the 599 adaptation decisions are no longer valid when changing origin 600 servers (or links) and potentially cause playback interruptions and, 601 consequently, stalling. Additionally, ICN supports the usage of 602 multiple interfaces and a seamless handover between them, which 603 again comes together with bandwidth changes, e.g., switching between 604 fixed and wireless, 3G/4G and WiFi networks, etc. Considering these 605 characteristics of ICN, adaptation algorithms merely based on 606 bandwidth measurements are not appropriate anymore, as potentially 607 each segment can be transferred from another ICN node or interface, 608 all with different bandwidth condition. Thus, adaptation algorithms 609 taking into account these intrinsic characteristics of ICN are 610 preferred over algorithms based on mere bandwidth measurements. 612 5.4.2. Testbed, Open Source Tools, and Dataset 614 For the evaluations of DASH over CCN, a testbed with open source 615 tools and datasets is provided in [9]. In particular, it provides 616 two client player implementations, (i) a libdash extension for DASH 617 over CCN and (ii) a VLC plugin implementing DASH over CCN. For both 618 implementations the CCNx implementation has been used as a basis. 620 The general architecture of libdash is organized in modules, so that 621 the library implements a MPD parser and an extensible connection 622 manager. The library provides object-oriented interfaces for these 623 modules to access the MPD and the downloadable segments. These 624 components are extended to support DASH over CCN and available in a 625 separate development branch of the github project available at 626 http://www.github.com/bitmovin/libdash. libdash comes together with 627 a fully featured DASH player with a QT-based frontend, demonstrating 628 the usage of libdash and providing a scientific evaluation platform. 629 As an alternative, patches for the DASH plugin of the VLC player are 630 provided. These patches can be applied to the latest source code 631 checkout of VLC resulting in a DASH over CCN-enabled VLC player. 633 Finally, a DASH over CCN dataset is provided in form of a CCNx 634 repository. It includes 15 different quality representation of the 635 well-known Big Buck Bunny Movie, ranging from 100 kbps up to 4500 636 kbps. The content is split into segments of two seconds, and 637 described by an associated MPD using the presented naming scheme in 638 Section 4.1. This repository can be downloaded from [9], and is also 639 provided by a public accessible CCNx node. Associated routing 640 commands for the CCNx namespaces of the content are provided via 641 scripts coming together with the dataset and can be used as a public 642 testbed. 644 6. P2P video distribution and ICN 646 Another form of distributing content - and video in particular- 647 which ICNs need to support is Peer-to-Peer distribution (P2P). We 648 see now how an existing protocol such as PPSP can be modified to 649 work in an ICN environment. 651 6.1. Introduction to PPSP 653 P2P video Streaming (PPS) is a popular approach to redistribute live 654 media over Internet. The proposed Peer-to-Peer Video Streaming 655 (P2PVS) solutions can be roughly classified in two classes: 657 - Push/Tree based 659 - Pull/Mesh based 661 The Push/Tree based solution creates an overlay network among peers 662 that has a tree shape. Using a progressive encoding (e.g. Multiple 663 Description Coding or H.264 Scalable Video Coding), multiple trees 664 could be set up to support video rate adaptation. On each tree an 665 enhancement stream is sent. The more the number of stream received, 666 the higher the video quality. A peer control video rate by fetching 667 or not the streams delivered on the distribution trees. 669 The Pull/Mesh based solution is inspired by the BitTorrent file 670 sharing mechanism. A Tracker collects information about the state of 671 the swarm (i.e. set of participating peers). A peer forms a mesh 672 overlay network with a subset of peers, and exchange data with them. 673 A peer announces what data items it disposes and requests missing 674 data items that are announced by connected peers. In case of live 675 streaming, the involved data set includes only a recent window of 676 data items published by the source. Also in this case, the use of a 677 progressive encoding can be exploited for video rate adaptation. 679 Pull/Mesh based P2PVS solutions are the more promising candidate for 680 the ICN deployment, since most of ICN approach provides a pull-based 681 API [5][10][11][12]. In addition, Pull/Mesh based P2PVS are more 682 robust than Push/Tree based one [13] and the Peer to Peer Streaming 683 Protocol (PPSP) working group [14] is also proposing a Pull/Mesh 684 based solution. 686 +------------------------------------------------+ 687 | | 688 | +--------------------------------+ | 689 | | Tracker | | 690 | +--------------------------------+ | 691 | | ^ ^ | 692 |Tracker | | Tracker |Tracker | 693 |Protocol| | Protocol |Protocol | 694 | | | | | 695 | V | | | 696 | +---------+ Peer +---------+ | 697 | | Peer |<----------->| Peer | | 698 | +---------+ Protocol +---------+ | 699 | | ^ | 700 | | |Peer | 701 | | |Protocol | 702 | V | | 703 | +---------------+ | 704 | | Peer | | 705 | +---------------+ | 706 | | 707 +------------------------------------------------+ 708 Figure 1: PPSP System Architecture (source [RFC6972]) 710 Figure 1 reports the PPSP architecture presented in [RFC6972]. PEERs 711 announce and share video chunks and a TRACKER maintains a list of 712 PEERs participating in a specific audio/video channel or in the 713 distribution of a streaming file. The tracker functionality may be 714 centralized in a server or distributed over the PEERs. PPSP 715 standardize the Peer and Tracker Protocols, which can run directly 716 over UDP or TCP. 718 This document discusses some preliminary concepts about the 719 deployment of PPSP on top of an ICN that exposes a pull-based API, 720 meanwhile considering the impact of MPEG DASH streaming format. 722 6.2. PPSP over ICN: deployment concepts 724 6.2.1. PPSP short background 726 PPSP specifies peer protocol (PPSPP) [15] and tracker protocol 727 (PPSP-TP)[16]. 729 Some of the operations carried out by the tracker protocol are the 730 followings. When a peer wishes to join the streaming session it 731 contacts the Tracker (CONNECT message), obtains a PEER_ID and a list 732 of PEER_IDs (and IP addresses) of other peers that are participating 733 to the SWARM and that the tracker has singled out for the requesting 734 peer (this may be a subset of the all peers of the SWARM). In 735 addition to this join operation, a peer may contact the tracker to 736 request to renew the list of participating peers (FIND message), to 737 periodically update its status to the tracker (STAT_REPORT message), 738 etc. 740 Some of the operations carried out by the peer protocol are the 741 following. Using the list of peers delivered by the tracker, a peer 742 establishes a session with them (HANDSHAKE message). A peer 743 periodically announces to neighboring peers which chunks it has 744 available for download (HAVE message). Using these announcements, a 745 peer requests missing chunks from neighboring peers (REQUEST 746 messages), which will send back them (DATA message). 748 6.2.2. From PPSP messages to ICN named-data 750 ICN provides users with data items exposed by names. The bundle name 751 and data item is usually referred as named-data, named-content, etc. 752 To transfer PPSP messages though an ICN the messages should be be 753 wrapped as named-data items, and receivers should request them by 754 name. 756 A PPSP entity receives messages from peers and/or tracker. Some 757 operations require gathering the messages generated by another 758 specific host (peer or tracker). For instance, if a peer A wishes to 759 gain information about video chunks available from peer B, the 760 former shall fetch the PPSP HAVE messages specifically generated by 761 the later. We refer to these kinds of named-data as "located-named- 762 data", since they should be gathered from a specific location (e.g. 763 peer B). 765 For other PPSP operations, like to fetch a DATA message (i.e. a 766 video chunk), what it is relevant for a peer is just to receive the 767 requested content, independently from who is the endpoint that 768 generate the data. We refer to this information with the generic 769 term "named-data". 771 The naming scheme differentiates named-data and located-named-data 772 items. In case of named-data, the naming scheme only includes a 773 content identifier (e.g. the name of the video chunk), without any 774 prefix identifying who provides the content. For instance, a DATA 775 message containing the video chunk #1 may be named as 776 "ccnx:/swarmID/chunk/chunkID", where swarmID is a unique identifier 777 of the streaming session, "chunk" is a keyword and chunkID is the 778 chunk identifier (e.g. a integer number). 780 In case of located-named-data, the naming scheme includes a 781 location-prefix, which uniquely identifies the host generating the 782 data item. This prefix may be the PEER_ID in case the host was a 783 peer or a tracker identifier in case the host was the tracker. For 784 instance, a HAVE message generated by a peer B may be named as 785 "ccnx:/swarmID/peer/PEER_ID/HAVE", where "peer" is a keyword, 786 PEER_ID_B is the identifier of peer B and HAVE is a keyword. 788 6.2.3. Support of PPSP interaction through a pull-based ICN 789 API 791 The PPSP procedures are based both on pull and push interactions. 792 For instance, the distribution of chunks availability can be 793 classified as a push-based operation, since a peer sends an 794 "unsolicited" information (HAVE message) to neighboring peers. 795 Conversely the procedure used to receive video chunks can be 796 classified as pull-based, since it is supported by a 797 request/response interaction (i.e. REQUEST, DATA messages). 799 As we said, we refer to an ICN architecture which provides a pull- 800 based API. Accordingly, the mapping of PPSP pull-based procedure is 801 quite simple. For instance, using the CCN architecture [5] a PPSP 802 DATA message may be carried by a CCN Data message and a REQUEST 803 message can transferred by a CCN Interest. 805 Conversely, the support of push-based PPSP operations may be more 806 difficult. We need of an adaptation functionality that carries out a 807 push-based operation using the underlying pull-based service 808 primitives. For instance, a possible approach is to use the 809 request/response (i.e. Interest/Data) four ways handshakes proposed 810 in [7]. Another possibility is that receivers periodically send out 811 request messages of the named-data that neighbors will push and, 812 when available, sender inserts the pushed data within a response 813 message. 815 6.2.4. Abstract layering for PPSP over ICN 817 +-----------------------------------+ 818 | Application | 819 +-----------------------------------+ 820 | PPSP (TCP/IP) | 821 +-----------------------------------+ 822 | ICN - PPSP Adaptation Layer (AL) | 823 +-----------------------------------+ 824 | ICN Architecture | 825 +-----------------------------------+ 826 Figure 2: Mediator approach 828 Figure 2 provides a possible abstract layering for PPSP over ICN. 829 The Adaptation Layer acts as a mediator (proxy) between legacy PPSP 830 entities based on TCP/IP and the ICN architecture. In facts, the 831 role the mediator is to use ICN to transfer PPSP legacy messages. 833 This approach makes possible to merely reuse TCP/IP P2P applications 834 whose software includes also PPSP functionality. This "all-in-one" 835 development approach may be rather common since the PPSP-Application 836 interface is not going to be specified. Moreover, if the Operating 837 System will provide libraries that expose a PPSP API, these will be 838 initially based on a underlying TCP/IP API. Also in this case, the 839 mediator approach would make possible to easily reuse both the PPSP 840 libraries and the Application on top of an ICN. 842 +-----------------------------------+ 843 | Application | 844 +-----------------------------------+ 845 | ICN-PPSP | 846 +-----------------------------------+ 847 | ICN Architecture | 848 +-----------------------------------+ 850 Figure 3: Clean-slate approach 852 Figure 3 sketches a clean-slate layering approach in which the 853 application directly includes or interacts with a PPSP version based 854 on ICN. Likely such a PPSP_ICN integration could yield a simplier 855 development, also because it does not require implementing a TCP/IP 856 to ICN translation as in the Mediator approach. However, the clean- 857 slate approach requires developing the application (in case of 858 embedded PPSP functionality) or the PPSP library from scratch, 859 without exploiting what might already exist for TCP/IP. 861 Overall, the Mediator approach may be considered as the first step 862 of a migration path towards ICN native PPSP applications. 864 6.2.5. PPSP interaction with the ICN routing plane 866 Upon the ICN API a user (peer) requests a content and the ICN sends 867 it back. The content is gathered by the ICN from any source, which 868 could be the closest peer that disposes of the named-data item, an 869 in-network cache, etc. Actually, "where" to gather the content is 870 controlled by an underlying ICN routing plane, which sets up the ICN 871 forwarding tables (e.g. CCN FIB [5]). 873 A cross-layer interaction between the ICN routing plane and the PPSP 874 may be required to support a PPSP session. Indeed, ICN shall forward 875 request messages (e.g. CCN Interest) towards the proper peer that 876 can handle them. Depending on the layering approach, this cross- 877 layer interaction is controlled either by the Adaptation Layer or by 878 the ICN-PPSP. For example, if a peer A receives a HAVE message 879 indicating that peer B disposes of the video chunk named 880 "ccnx:/swarmID/chunk/chunkID", then former should insert in its ICN 881 forwarding table an entry for the prefix 882 "ccnx:/swarmID/chunk/chunkID" whose next hop locator (e.g. IP 883 address) is the network address of peer B [17]. 885 6.2.6. ICN deployment for PPSP 887 The ICN functionality that supports a PPSP session may be "isolated" 888 or "integrated" with the one of a public ICN. 890 In the isolated case, a PPSP session is supported by an instance of 891 an ICN (e.g. deployed on top of IP), whose functionalities operate 892 only on the limited set of nodes participating to the swarm, i.e. 893 peers and the tracker. This approach resembles the one followed by 894 current P2P application, which usually form an overlay network among 895 peers of a P2P application. And intermediate public IP routers do 896 not carry out P2P functionalities. 898 In the integrated case, the nodes of a public ICN may be involved in 899 the forwarding and in-network caching procedures. In doing so, the 900 swarm may benefit from the presence of in-network caches so limiting 901 uplink traffic on peers and inter-domain traffic too. These are 902 distinctive advantages of using PPSP over a public ICN, rather than 903 over TCP/IP. In addition, such advantages aren't likely manifested 904 in the case of isolated deployment. 906 However, the possible interaction between the PPSP and the routing 907 layer of a public ICN may be dramatic, both in terms of explosion of 908 the forwarding tables and in terms of security. These issues 909 specifically take place for those ICN architectures for which the 910 name resolution (i.e. name to next-hop) occurs en-route, like the 911 CCN architecture. 913 For instance, using the CCN architecture, to fetch a named-data item 914 offered by a peer A the on-path public ICN entities have to route 915 the request messages towards the peer A. This implies that the ICN 916 forwarding tables of public ICN nodes may contain many entries, e.g. 917 one entry per video chunk, and these entries are difficult to be 918 aggregated since peers avail sparse parts of a big content, whose 919 names have a same prefix (e.g. "ccnx:/swarmID"). Another possibility 920 is to wrap all PPSP messages into a located-named-data. In this case 921 the forwarding tables should contain "only" the PEER_ID prefixes 922 (e.g. "ccnx:/swarmID/peer/PEER_ID"), so scaling down the number of 923 entries from number of chunks to number of peers. However, in this 924 case the ICN mechanisms recognize a same video chunk offered by 925 different peers as different contents, so vanishing caching and 926 multicasting ICN benefits. Moreover, in any case routing entries 927 should be updated either the base of the availability of named-data 928 items on peers or on the presence of peers, and these events in a 929 P2P session is rapidly changing so possibly hampering the 930 convergence of the routing plane. Finally, since peers have an 931 impact on the ICN forwarding table of public nodes, this may open 932 obvious security issues. 934 6.3. Impact of MPEG DASH coding schemes 936 The introduction of video rate adaptation may valuably decrease the 937 effectiveness of P2P cooperation and of in-network caching, 938 depending of the kind of the video coding used by the MPEG DASH 939 stream. 941 In case of a MPEG DASH streaming with MPEG AVC encoding, a same 942 video chunk is independently encoded at different rates and the 943 encoding output is a different file for each rate. For instance, in 944 case of a video encoded at three different rates R1,R2,R3, for each 945 segment S we have three distinct files: S.R1, S.R2, S.R3. These 946 files are independent of each other. To fetch a segment coded at R2 947 kbps, a peer shall request the specific file S.R2. The estimation of 948 the best coding rate is usually handled by receiver-driven 949 algorithms, implemented by the video client. 951 The independence among files associated to different encoding rates 952 and the heterogeneity of peer bandwidths, may dramatically reduce 953 the interaction among peers, the effectiveness of in-network caching 954 (in case of integrated deployment), and consequently the ability of 955 PPSP to offload the video server (i.e. a seeder peer). Indeed, a 956 peer A may select a coding rate (e.g. R1) different from the one 957 selected by a peer B (e.g. R2) and this prevents the former to fetch 958 video chunks from the later, since peer B avails of chunks coded at 959 a rate different from the ones needed by A. To overcome this issue, 960 a common distributed rate selection algorithm could force peers to 961 select the same coding rate [17]; nevertheless this approach may be 962 not feasible in the in case of many peers. 964 The use of SVC encoding (Annex G extension of the H.264/MPEG-4 AVC 965 video compression standard) should make rate adaptation possible, 966 meanwhile neither reducing peer collaborations nor the in-network 967 caching effectiveness. For a single video chunk, a SVC encoder 968 produces different files for the different rates (roughly "layers"), 969 and these files are progressively related each other. Starting from 970 a base-layer which provides the minimum rate encoding, the next 971 rates are encoded as an "enhancement layer" of the previous one. For 972 instance, in case the video is coded with three rates R1 (base- 973 layer), R2 (enhancement-layer n.1), R3 (enhancement-layer n.2), then 974 for each DASH segment we have three files S.R1, S.R2 and S.R3. The 975 file S.R1 is the segment coded at the minimum rate (base-layer). The 976 file S.R2 enhances S.R1, so as S.R1 and S.R2 can be combined to 977 obtain a segment coded at rate R2. To get a segment coded at rate 978 R2, a peer shall fetch both S.R1 and S.R2. This progressive 979 dependence among files that encode a same segment at different rates 980 makes peer cooperation possible, also in case peers player have 981 autonomously selected different coding rates. For instance, if peer 982 A has selected the rate R1, the downloaded files S.R1 are useful 983 also for a peer B that has selected the rate R2, and vice versa. 985 7. IPTV and ICN 987 7.1. IPTV challenges 989 IPTV refers to the delivery of quality content broadcast over the 990 Internet, and is typically associated with strict quality 991 requirements, i.e., with a perceived latency of less than 500 ms and 992 a packet loss rate that is multiple orders lower than the current 993 loss rates experienced in the most commonly used access networks. We 994 can summarize the major challenges for the delivery of IPTV service 995 as follows. 997 Channel change latency represents a major concern for the IPTV 998 service. Perceived latency during channel change should be less than 999 500ms. To achieve this objective over the IP infrastructure, we have 1000 multiple choices: 1002 (i) receiving fast unicast streams from a dedicated server (most 1003 effective but not resource efficient); 1004 (ii) connecting to other peers in the network (efficiency depends 1005 on peer support, effective and resource efficient, if also 1006 supported with a dedicated server); 1007 (iii) connecting to multiple multicast sessions at once (effective 1008 but not resource efficient, and depends on the accuracy of 1009 the prediction model used to track user activity). 1011 The second major challenge is the error recovery. Typical IPTV 1012 service requirements dictate the mean time between artifacts to be 1013 approximately 2 hours. This suggests the perceived loss rate to be 1014 around or less than 10^-7. Current IP-based solutions rely on the 1015 following proactive and reactive recovery techniques: (i) joining 1016 the FEC multicast stream corresponding to the perceived packet loss 1017 rate (not efficient as the recovery strength is chosen based on 1018 worst-case loss scenarios), (ii) making unicast recovery requests to 1019 dedicated servers (requires active support from the service 1020 provider), (iii) probing peers to acquire repair packets (finding 1021 matching peers and enabling their cooperation is another challenge). 1023 7.2. ICN benefits for IPTV delivery 1025 ICN presents significant advantages for the delivery of IPTV 1026 traffic. For instance, ICN inherently supports multicast and allows 1027 for quick recovery from packet losses (with the help of in-network 1028 caching). Similarly, peer support is also provided in the shape of 1029 in-network caches that typically act as the middleman between two 1030 peers, enabling therefore earlier access to IPTV content. 1032 However, despite these advantages, delivery of IPTV service over 1033 Information Centric Networks brings forth new challenges. We can 1034 list some of these challenges as follows: 1036 . Messaging overhead: ICN is a pull-based architecture and relies 1037 on a unique balance between requests and responses. A user 1038 needs to make a request for each data packet. In the case of 1039 IPTV, with rates up to, and likely to be, above 15Mbps, we 1040 observe significant traffic upstream to bring those streams. 1041 As the number of streams increase (including the same session 1042 at different quality levels), so as the burden on the routers. 1043 Even if the majority of requests are aggregated at the core, 1044 routers close to the edge (where we observe the biggest 1045 divergence in user requests) will experience a significant 1046 increase in overhead to process these requests. The same is 1047 true at the user side, as the uplink usage multiplies in the 1048 number of sessions a user requests (for instance, to minimize 1049 the impact of bandwidth fluctuations). 1050 . Cache control: As the IPTV content expires at a rapid rate 1051 (with a likely expiry threshold of 1s), we need solutions to 1052 effectively flush out such content to also prevent degradation 1053 impact on other cached content, with the help of intelligently 1054 chosen naming conventions. However, to allow for fast recovery 1055 and optimize access time to sessions (from current or new 1056 users), the timing of such expirations needs to be adaptive to 1057 network load and user demand. However, we also need to support 1058 quick access to earlier content, whenever needed, for instance, 1059 when the user accesses the rewind feature (note that in-network 1060 caches will not be of significant help in such scenarios due to 1061 overhead required to maintain such content). 1062 . Access accuracy: To receive the up-to-date session data, users 1063 need to be aware of such information at the time of their 1064 request. Unlike IP multicast, since the users join a session 1065 indirectly, session information is critical to minimize 1066 buffering delays and reduce the startup latency. Without such 1067 information, and without any active cooperation from the 1068 intermediate routers, stale data can seriously undermine the 1069 efficiency of content delivery. Furthermore, finding a cache 1070 does not necessarily equate to joining a session, as the look- 1071 ahead latency for the initial content access point may have a 1072 shorter lifetime than originally intended. For instance, if the 1073 user that has initiated the indirect multicast leaves the 1074 session early, the requests from the remaining users need to 1075 experience an additional latency of one RTT as they travel 1076 towards the content source. If the startup latency is chosen 1077 depending on the closeness to the intermediate router, going to 1078 the content source in-session can lead to undesired pauses. 1080 It should be noted that IPTV includes more than just multicast. Many 1081 implementations include "trick plays" (fast forward, pause, rewind) 1082 that often transform a multicast session into multiple unicast 1083 sessions. In this context, ICN is beneficial, as the caching offers 1084 an implicit multicast, but without tight synchronization constraints 1085 in between two different users. One user may rewind, and start 1086 playing forward again, drawing from a nearby cache of the content 1087 recently viewed by another user (whereas in a strict multicast 1088 session, the opportunity of one user lagging off behind would be 1089 more difficult to implement). 1091 8. Digital Rights Managements in ICN 1093 This section discusses the need for Digital Rights Management (DRM) 1094 functionalities for multimedia streaming over ICN. It focuses on two 1095 possible approaches: modifying AAA to support DRM in ICN, and using 1096 Broadcast Encryption. 1098 It is assumed that ICN will be used heavily for digital content 1099 dissemination. It is vital to consider DRM for digital content 1100 distribution. In today's Internet there are two predominant classes 1101 of business models for on-demand video streaming. The first model is 1102 based on advertising revenues. Non-copyright protected (usually 1103 user-generated content, UGC) is offered by large infrastructure 1104 providers like Google (YouTube) at no charge. The infrastructure is 1105 financed by spliced advertisements into the content. In this context 1106 DRM considerations may not be required, since producers of UGC may 1107 only strive for the maximum possible dissemination. Some producers 1108 of UGC are mainly interested to share content with their families, 1109 friends, colleges or others and have no intention to make profit. 1110 However, the second class of business models requires DRM, because 1111 they are primarily profit oriented. For example, large on-demand 1112 streaming platforms like Netflix establish business models based on 1113 subscriptions. Consumers may have to pay a monthly fee in order to 1114 get access to copyright protected content like TV series, movies or 1115 music. This model may be ad-supported and free to the content 1116 consumer, like YouTube Channels or Spotify. But the creator of the 1117 content expects some remuneration for his work. From the perspective 1118 of the service providers and the copyright owners, only clients that 1119 pay the fee (explicitly or implicitly through ad placement) should 1120 be able to access and consume the content. Anyway, the challenge is 1121 to find an efficient and scalable way of access control to digital 1122 content, which is distributed in information-centric networks. 1124 8.1. Broadcast Encryption for DRM in ICN 1126 The section discusses Broadcast Encryption (BE) as a suitable basis 1127 for DRM functionalities in conformance to the ICN communication 1128 paradigm. Especially when network inherent caching is considered the 1129 advantage of BE will be highlighted. 1131 In ICN, data packets can be cached inherently in the network and any 1132 network participant can request a copy of these packets. This makes 1133 it very difficult to implement an access control for content that is 1134 distributed via ICN. A naive approach is to encrypt the transmitted 1135 data for each consumer with a distinct key. This prohibits everyone 1136 other than the intended consumers to decrypt and consume the data. 1137 However, this approach is not suitable for ICN's communication 1138 paradigm since it would reduce the benefits gained from the inherent 1139 network caching. Even if multiple consumers request the same content 1140 the requested data for each consumer would differ using this 1141 approach. A better but still insufficient idea is to use a single 1142 key for all consumers. This does not destruct the benefits of ICN's 1143 caching ability. The drawback is that if one of the consumers 1144 illegally distributes the key, the system is broken and any entity 1145 in the network can access the data. Changing the key after such an 1146 event is useless since the provider has no possibility to identify 1147 the illegal distributer. Therefore this person cannot be stopped 1148 from distributing the new key again. In addition to this issue other 1149 challenges have to be considered. Subscriptions expire after a 1150 certain time and then it has to be ensured that these consumers 1151 cannot access the content anymore. For a provider that serves 1152 millions of daily consumers (e.g. Netflix) there could be a 1153 significant number of expiring subscriptions per day. Publishing a 1154 new key every time a subscription expires would require an 1155 unsuitable amount of computational power just to re-encrypt the 1156 collection of audio-visual content. 1158 A possible approach to solve these challenges is Broadcast 1159 Encryption (BE) [22] as proposed in [23]. From this point on, this 1160 section will focus only on BE as an enabler for DRM functionality in 1161 the use case of ICN video streaming. This subsection continues with 1162 the explanation of how BE works and shows how BE can be used to 1163 implement an access control scheme in the context of content 1164 distribution in ICN. 1166 BE actually carries a misleading name. One might expect a concrete 1167 encryption scheme. However, it belongs to the family of key- 1168 management schemes (KMS). KMS are responsible for the generation, 1169 exchange, storage and replacement of cryptographic keys. The most 1170 interesting characteristics of Broadcast Encryption Schemes (BES) 1171 are: 1173 . A BES typically uses a global trusted entity called the 1174 licensing agent (LA), which is responsible for spreading a set 1175 of pre-generated secrets among all participants. Each 1176 participant gets a distinct subset of secrets assigned from the 1177 LA. 1178 . The participants can agree on a common session key, which is 1179 chosen by the LA. The LA broadcasts an encrypted message that 1180 includes the key. Participants with a valid set of secrets can 1181 derive the session-key from this message. 1182 . The number of participants in the system can change 1183 dynamically. Entities may join or leave the communication group 1184 at any time. If a new entity joins the LA passes on a valid set 1185 of secrets to that entity. If an entity leaves (or is forced to 1186 leave) the LA revokes the entity's subset of keys, which means 1187 that it cannot derive the correct session key anymore when the 1188 LA distributes a new key. 1190 . -Traitors (entities that reveal their secrets) can be traced 1191 and excluded from ongoing communication. The algorithms and 1192 preconditions to identify a traitor vary between concrete BES. 1194 This listing already illustrates why BE is suitable to control the 1195 access to data that is distributed via an information-centric 1196 network. BE enables the usage of a single session key for 1197 confidential data transmission between a dynamically changing subset 1198 or network participants. ICN caches can be utilized since the data 1199 is encrypted only with a single key known by all legitimate clients. 1200 Furthermore, traitors can be identified and removed from the system. 1201 The issue of re-encryption still exists, because the LA will 1202 eventually update the session key when a participant should be 1203 excluded. However, this disadvantage can be relaxed in some way if 1204 the following points are considered: 1206 . The updates of the session key can be delayed until a set of 1207 compromised secretes has been gathered. Note that secrets may 1208 become compromised because of two reasons. First, a traitor 1209 could have illegally revealed the secret. Second, the 1210 subscription of an entity expired. Delayed revocation 1211 temporarily enables some non-legitimate entities to consume 1212 content. However, this should not be a severe problem in home 1213 entertainment scenarios. Updating the session key in regular 1214 (not too short) intervals is a good tradeoff. The longer the 1215 interval last the less computational resources are required for 1216 content re-encryption and the better the cache utilization in 1217 the ICN will be. To evict old data from ICN caches that has 1218 been encrypted with the prior session key the publisher could 1219 indicate a lifetime for transmitted packets. 1220 . Content should be re-encrypted dynamically at request time. 1221 This has the benefit that untapped content is not re-encrypted 1222 if the content is not requested during two session key updates 1223 and therefore no resources are wasted. Furthermore, if the 1224 updates are triggered in non-peak times the maximum amount of 1225 resource needed at one point in time can be lowered 1226 effectively, since in peak times generally more diverse content 1227 is requested. 1228 . Since the amount of required computational resources may vary 1229 strongly from time to time it would be beneficial for any 1230 streaming provider to use cloud-based services to be able to 1231 dynamically adapt the required resources to the current needs. 1232 Regarding to a lack of computation time or bandwidth the cloud 1233 service could be used to scale up to overcome shortages. 1235 Figure 4 show the potential usage of BE in a multimedia delivery 1236 frameworks that builds upon ICN infrastructure and uses the concept 1237 of dynamic adaptive streaming, e.g., DASH. BE would be implemented 1238 on the top to have an efficient and scalable way of access control 1239 to the multimedia content. 1241 +--------Multimedia Delivery Framework--------+ 1242 | | 1243 | Technologies Properties | 1244 | +----------------+ +----------------+ | 1245 | | Broadcast |<--->| Controlled | | 1246 | | Encryption | | Access | | 1247 | +----------------+ +----------------+ | 1248 | |Dynamic Adaptive|<--->| Multimedia | | 1249 | | Streaming | | Adaptation | | 1250 | +----------------+ +----------------+ | 1251 | | ICN |<--->| Cachable | | 1252 | | Infrastructure | | Data Chunks | | 1253 | +----------------+ +----------------+ | 1254 +---------------------------------------------+ 1256 Figure 4: A potential multimedia framework using BE. 1258 8.2 . AAA Based DRM for ICN Networks 1260 8.2.1. Overview 1262 Recently, a novel approach to Digital Rights Management (DRM) has 1263 emerged to link DRM to usual network management operations, hence 1264 linking DRM to authentication, authorization, and accounting (AAA) 1265 services. ICN provides the abstraction of an architecture where 1266 content is requested by name and could be served from anywhere. In 1267 DRM, the content provider (the origin of the content) allows the 1268 destination (the end user account) to use the content. The content 1269 provider and content storage/cache are at two different entities in 1270 ICC and for traditional DRM only source and destination count and 1271 not the intermediate storage. The proposed solution allows the 1272 provider of the caching to be involved in the DRM policies using 1273 well known AAA mechanisms. It is important to note that this 1274 solution is compatible with the proposes the Broadcast Encryption 1275 (BE) proposed earlier in this draft. The BE proposes a technology as 1276 this solution is more operational. 1278 8.2.2. Implementation 1280 With the proposed AAA-based DRM, when a content is requested by name 1281 from a specific destination, the request could link back to both the 1282 content provider and the caching provider via traditional AAA 1283 mechanisms, and trigger the appropriate DRM policy independently 1284 from where the content is stored. In this approach the caching, DRM 1285 and AAA remain independent entities but can work together through 1286 ICN mechanisms. The proposed solution enables extending the 1287 traditional DRM done by the content provider to jointly being done 1288 by content provider and network/caching provider. 1290 The solution is based on the concept of a "token". The content 1291 provider authenticates the end user and issues an encrypted token to 1292 authenticate the a named content ID or IDs that the user can access. 1293 The token will be shared with the network provider and used as the 1294 interface to the AAA protocols. At this point all content access is 1295 under the control of the network provider and the ICN. The 1296 controllers and switches can manage the content requests and handle 1297 mobility. The content can be accessed from anywhere as long as 1298 the token remains valid or the content is available in the network. 1299 In such a scheme the content provider does not need to be contacted 1300 every time a named content is requested. This reduces the load of 1301 the content provider network and creates a DRM mechanism that is 1302 much more appropriate for the distributed caching and peer-to-peer 1303 storage characteristic of ICN networks. In particular, the content 1304 requested by name can be served from anywhere under the only 1305 condition that the storage/cache can verify that the token is valid 1306 for content access. 1308 The solution is also fully customizable to both content and network 1309 provider's needs as the tokens can be issued based on user accounts, 1310 location and hardware (MAC address for example) linking it naturally 1311 to legacy authentication mechanisms. In addition, since both content 1312 and network providers are involved in DRM policies pollution attacks 1313 and other illegal requests for the content can be more easily 1314 detected. The proposed AAA-based DRM is currently under full 1315 development. 1317 9. Future Steps for Video in ICN 1319 The explosion of online video services, along with their increased 1320 consumption by mobile wireless terminals, further exacerbates the 1321 challenges of Video Adaptation leveraging ICN mechanisms. The 1322 following sections present a series of research items derived from 1323 these challenges, further introducing next steps for the subject. 1325 9.1. Large Scale Live Events 1327 An active area of investigation and a potential use case where ICN 1328 would provide significant benefits, is that of distributing content, 1329 and video in particular, using local communications in large scale 1330 events such as sports event in a stadium, a concert or a large 1331 demonstration. 1333 Such use-case involves locating content that is generated on the fly 1334 and requires discovery mechanisms in addition to sharing mechanisms. 1335 The scalability of the distribution becomes important as well. 1337 9.2. Video Conferencing, Real-Time Communications, Augmented Reality 1338 and Virtual Reality 1340 Current protocols for video-conferencing have been designed, and 1341 this document needs to take input from them to identify the key 1342 research issues. Real-time communication add timing constraints 1343 (both in terms of delay and in terms of synchronization) to the 1344 scenario discussed above. 1346 AR and VR -and immersive multimedia experiences in general- are 1347 clearly an area of further investigation, as they involve combining 1348 multiple streams of data from multiple users into a coherent whole. 1349 This raises issues of multi-source multi-destination multimedia 1350 streams that ICN may be equipped to deal with in a more natural 1351 manner than IP that is inherently unicast. 1353 9.3. Store-and-Forward Optimized Rate Adaptation 1355 One of the benefits of ICN is to allow the network to insert caching 1356 in the middle of the data transfer. This can be used to reduce the 1357 overall bandwidth demands over the network by caching content for 1358 future re-use. But it provides more opportunities for optimizing 1359 video streams. 1361 Consider for instance the following scenario: a client is connected 1362 via an ICN network to a server. Let's say the client is connected 1363 wirelessly to a node that has a caching capability, which is 1364 connected through a WAN to the server. Assume further that the 1365 capacity of each of the links (both the wireless and the WAN logical 1366 links) vary with time. 1368 If the rate adaptation is provided in an end-to-end manner, as in 1369 current mechanisms like DASH, then the maximal rate that can be 1370 supported at the client is that of the minimal bandwidth on each 1371 link. 1373 For instance, if during time period 1, the wireless capacity is 1 1374 and the wired capacity is 2, and during time period 2, the wireless 1375 is 2 due to some hotspot, and the wired is 1 due to some congestion 1376 in the network, then the best end-to-end rate that can be achieved 1377 is 1 during each period. 1379 However, if the cache is used during time period 1 to pre-fetch 2 1380 units of data, then during period 2, there is 1 unit of data at the 1381 cache, and another unit of data, which can be streamed from the 1382 server, and the rate that can be achieved is therefore 2 units of 1383 data. In this case, the average bandwidth rises from 1 to 1.5 over 1384 the 2 periods. 1386 This straw man example illustrate a) the benefit of ICN for 1387 increasing the throughput of the network, and b) the need for the 1388 special rate adaptation mechanisms to be designed so as to take 1389 advantage of this gain. End-to-end rate adaptation can not take 1390 advantage of the cache availability. 1392 9.4. Heterogeneous Wireless Environment Dynamics 1394 With the ever-growing increase in online services being accessed by 1395 mobile devices, operators have been deploying different overlapping 1396 wireless access networking technologies. In this way, in the same 1397 area, user terminals are within range of different cellular, Wi-Fi 1398 or even WiMAX networks. Moreover, with the advent of the Internet of 1399 Things (e.g., surveillance cameras feeding video footage), this list 1400 can be further complemented with more specific short-range 1401 technologies, such as Bluetooth or ZigBee. 1403 In order to leverage from this plethora of connectivity 1404 opportunities, user terminals are coming equipped with different 1405 wireless access interfaces, providing them with extended 1406 connectivity opportunities. In this way, such devices become able to 1407 select the type of access which best suits them according to 1408 different criteria, such as available bandwidth, battery 1409 consumption, access do different link conditions according to the 1410 user profile or even access to different content. Ultimately, these 1411 aspects contribute to the Quality of Experience perceived by the 1412 end-user, which is of utmost importance when it comes to video 1413 content. 1415 However, the fact that these users are mobile and using wireless 1416 technologies, also provides a very dynamic setting, where the 1417 current optimal link conditions at a specific moment might not last 1418 or be maintained while the user moves. These aspects have been amply 1419 analyzed in recently finished projects such as FP7 MEDIEVAL [18], 1420 where link events reporting on wireless conditions and available 1421 alternative connection points were combined with vide requirements 1422 and traffic optimization mechanisms, towards the production of a 1423 joint network and mobile terminal mobility management decision. 1424 Concretely, in [19] link information about the deterioration of the 1425 wireless signal was sent towards a mobility management controller in 1426 the network. This input was combined with information about the user 1427 profile, as well as of the current video service requirements, and 1428 used to trigger the decrease or increase of scalable video layers, 1429 adjusting the video to the ongoing link conditions. Incrementally, 1430 the video could also be adjusted when a new better connectivity 1431 opportunity presents itself. 1433 In this way, regarding Video Adaptation, ICN mechanisms can leverage 1434 from their intrinsic multiple source support capability and go 1435 beyond the monitoring of the status of the current link, thus 1436 exploiting the availability of different connectivity possibilities 1437 (e.g., different "interfaces"). Moreover, information obtained from 1438 the mobile terminal's point of view of its network link, as well as 1439 information from the network itself (i.e., load, policies, and 1440 others), can generate scenarios where such information is combined 1441 in a joint optimization procedure allowing the content to be forward 1442 to users using the best available connectivity option (e.g., 1443 exploiting management capabilities supported by ICN intrinsic 1444 mechanisms as in [20]). 1446 In fact, ICN base mechanisms can further be exploited in enabling 1447 new deployment scenarios such as preparing the network for mass 1448 requests from users attending a large multimedia event (i.e., 1449 concert, sports), allowing video to be adapted according to content, 1450 user and network requirements and operation capabilities in a 1451 dynamic way. 1453 The enablement of such scenarios require further research, with the 1454 main points highlighted as follows: 1456 . Development of a generic video services (and obviously content) 1457 interface allowing the definition and mapping of their 1458 requirements (and characteristics) into the current capabilities 1459 of the network; 1461 . How to define a scalable mechanism allowing either the video 1462 application at the terminal, or some kind of network management 1463 entity, to adapt the video content in a dynamic way; 1465 . How to develop the previous research items using intrinsic ICN 1466 mechanisms (i.e., naming and strategy layers); 1468 . Leverage intelligent pre-caching of content to prevent stalls and 1469 poor quality phases, which lead to bad Quality of Experience of 1470 the user. This includes in particular the usage in mobile 1471 environments, which are characterized by severe bandwidth changes 1472 as well as connection outages, as shown in [21]; 1474 . How to take advantage of the multi-path opportunities over the 1475 heterogeneous wireless interfaces. 1477 9.5. Network Coding for Video Distribution in ICN 1479 An interesting research area for combining heterogeneous sources is 1480 to use network coding [24]. Network coding allows to asynchronously 1481 combine multiple sources by having each of them send information 1482 that is not duplicated by the other but can be combined to retrieve 1483 the video stream. 1485 However, this creates issues in ICN in terms of: defining the proper 1486 rate adaptation for the video stream; securing the encoded data; 1487 caching the encoded data; timeliness of the encoded data; overhead 1488 of the network coding operations both in network resources and in 1489 added buffering delay, etc. 1491 Network coding has shown promise in reducing buffering events in 1492 unicast, multicast and P2P setting. [26] considers strategies using 1493 network coding to enhance QoE for multimedia communications. Network 1494 coding can be applied to multiple streams, but also within a single 1495 stream as an equivalent of a composable erasure code. Clearly, there 1496 is a need for further investigation of network coding in ICN, 1497 potentially as a topic of activity in the research group. 1499 9.6. Synchronization Issues for Video Distribution in ICN 1501 ICN de-couples the fetching of video chunks from the location of 1502 these chunks. This means an audio chunk may be received from one 1503 network element (cache/storage/server) while a video chunk may be 1504 received from another one while another chunk (say, the next one, or 1505 another layer from the same video stream) may come from a third 1506 element. This introduces disparity in the retrieval times and 1507 locations of the different elements of a video stream that need to 1508 be played at the same (or almost same) time. Synchronization of such 1509 delivery and playback may require specific synchronization tools for 1510 video delivery in ICN. 1512 Other synchronization aspects involve: 1514 - synchronizing within a single stream, for instance the consecutive 1515 chunks of a single stream, or the multiple layers of a layered 1516 scheme, when sources and transport layers may be different. Re- 1517 ordering the packets of a stream distributed over multiple sources 1518 at the video client, or ensuring that multiple chunks coming from 1519 multiple sources arrive within an acceptable time window; 1520 - synchronizing multiple streams, such as the audio and video 1521 components of a video stream, which can be received from 1522 independent sources; 1523 - synchronizing multiple streams from multiple sources to multiple 1524 destinations, such as mass distribution of live events. For 1525 instance, for live video streams or video-conferencing, some level 1526 of synchronization is required so that people watching the stream 1527 view the same events at the same time. 1529 Some of these issues were addressed in [27] in the context of social 1530 video consumption. Network coding, with traffic engineering, is 1531 considered as a potential solution for synchronization issues. Other 1532 approaches could be considered that are specific for ICN as well. 1534 Traffic engineering in ICN [28,29] may be required to provide proper 1535 synchronization of multiple streams. 1537 10. Security Considerations 1539 This is informational. Security considerations are TBD. 1541 11. IANA Considerations 1543 This is informational. IANA considerations are TBD. 1545 12. Conclusions 1547 This draft proposed adaptive video streaming for ICN, identified 1548 potential problems and presented the combination of CCN with DASH as 1549 a solution. As both concepts, DASH and CCN, maintain several 1550 elements in common, like, e.g., the content in different versions 1551 being dealt with in segments, combination of both technologies seems 1552 useful. Thus, adaptive streaming over CCN can leverage advantages 1553 such as, e.g., efficient caching and intrinsic multicast support of 1554 CCN, routing based on named data URIs, intrinsic multi-link and 1555 multi-source support, etc. 1557 In this context, the usage of CCN with DASH in mobile environments 1558 comes together with advantages compared to today's solutions, 1559 especially for devices equipped with multiple network interfaces. 1560 The retrieval of data over multiple links in parallel is a useful 1561 feature, specifically for adaptive multimedia streaming, since it 1562 offers the possibility to dynamically switch between the available 1563 links depending on their bandwidth capabilities, transparent to the 1564 actual DASH client. 1566 13. References 1568 13.1. Normative References 1570 [RFC6972] Y. Zhang, N. Zong, "Problem Statement and Requirements of 1571 the Peer-to-Peer Streaming Protocol (PPSP)", RFC6972, July 1572 2013 1574 13.2. Informative References 1576 [1] ISO/IEC DIS 23009-1.2, Information technology - Dynamic 1577 adaptive streaming over HTTP (DASH) - Part 1: Media 1578 presentation description and segment formats 1580 [2] Lederer, S., Mueller, C., Rainer, B., Timmerer, C., 1581 Hellwagner, H., "An Experimental Analysis of Dynamic Adaptive 1582 Streaming over HTTP in Content Centric Networks", in 1583 Proceedings of the IEEE International Conference on Multimedia 1584 and Expo 2013, San Jose, USA, July, 2013 1586 [3] Liu, Y., Geurts, J., Point, J., Lederer, S., Rainer, B., 1587 Mueller, C., Timmerer, C., Hellwagner, H., "Dynamic Adaptive 1588 Streaming over CCN: A Caching and Overhead Analysis", in 1589 Proceedings of the IEEE international Conference on 1590 Communication (ICC) 2013 - Next-Generation Networking 1591 Symposium, Budapest, Hungary, June, 2013 1593 [4] Grandl, R., Su, K., Westphal, C., "On the Interaction of 1594 Adaptive Video Streaming with Content-Centric Networks", 1595 eprint arXiv:1307.0794, July 2013. 1597 [5] V. 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Braynard, "VoCCN: Voice 1611 over content-centric networks," in ACM ReArch Workshop, 2009 1613 [8] Christopher Mueller, Stefan Lederer and Christian Timmerer, A 1614 proxy effect analysis and fair adaptation algorithm for 1615 multiple competing dynamic adaptive streaming over HTTP 1616 clients, In Proceedings of the Conference on Visual 1617 Communications and Image Processing (VCIP) 2012, San Diego, 1618 USA, November 27-30, 2012. 1620 [9] DASH Research at the Institute of Information Technology, 1621 Multimedia Communication Group, Alpen-Adria Universitaet 1622 Klagenfurt, URL: http://dash.itec.aau.at 1624 [10] A. Detti, N. Blefari-Melazzi, S. Salsano, and M. Pomposini 1625 CONET: A content centric inter-networking architecture," in ACM 1626 Workshop on Information-Centric Networking (ICN), 2011. 1628 [11] W. K. Chai, N. Wang, I. Psaras, G. Pavlou, C. Wang, G. C. de 1629 Blas, F. Ramon-Salguero, L. Liang, S. Spirou, A. Beben, and E. 1630 Hadjioannou, "CURLING: Content-ubiquitous resolution and 1631 delivery infrastructure for next-generation services," IEEE 1632 Communications Magazine, vol. 49, no. 3, pp. 112-120, March 1633 2011 1635 [12] NetInf project Website http://www.netinf.org 1637 [13] N. Magharei, R. Rejaie, Yang Guo, "Mesh or Multiple-Tree: A 1638 Comparative Study of Live P2P Streaming Approaches," INFOCOM 1639 2007. 26th IEEE International Conference on Computer 1640 Communications. IEEE , vol., no., pp.1424,1432, 6-12 May 2007 1642 [14] PPSP WG Website https://datatracker.ietf.org/wg/ppsp/ 1644 [15] A. Bakker, R. Petrocco, V. Grishchenko, "Peer-to-Peer Streaming 1645 Peer Protocol (PPSPP)", draft-ietf-ppsp-peer-protocol-08 1647 [16] Rui S. Cruz, Mario S. Nunes, Yingjie Gu, Jinwei Xia, Joao P. 1648 Taveira, Deng Lingli, "PPSP Tracker Protocol-Base Protocol 1649 (PPSP-TP/1.0)", draft-ietf-ppsp-base-tracker-protocol-02 1651 [17] A.Detti, B. Ricci, N. 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Authors' Addresses 1711 Stefan Lederer, Christian Timmerer, Daniel Posch 1712 Alpen-Adria University Klagenfurt 1713 Universitaetsstrasse 65-67, 9020 Klagenfurt, Austria 1715 Email: {firstname.lastname}@itec.aau.at 1717 Cedric Westphal, Aytac Azgin. Shucheng (Will) Liu 1718 Huawei 1719 2330 Central Expressway, Santa Clara, CA95050, USA 1721 Email: {cedric.westphal,aytac.azgin,liushucheng}@huawei.com 1723 Christopher Mueller 1724 bitmovin GmbH 1725 Lakeside B01, 9020 Klagenfurt, Austria 1727 Email: christopher.mueller@bitmovin.net 1728 Andrea Detti 1729 Electronic Engineering Dept. 1730 University of Rome Tor Vergata 1731 Via del Politecnico 1, Rome, Italy 1733 Email: andrea.detti@uniroma2.it 1735 Daniel Corujo, 1736 Advanced Telecommunications and Networks Group 1737 Instituto de Telecomunicacoes 1738 Campus Universitario de Santiago 1739 P-3810-193 Aveiro, Portugal 1741 Email: dcorujo@av.it.pt 1743 Jianping Wang 1744 City University of Hong Kong 1745 Hong Kong, China 1747 Email: jianwang@cityu.edu.hk 1749 Marie-Jose Montpetit 1751 Email: marie@mjmontpetit.com 1753 Niall Murray 1754 Dept. of Electronic, Computer and Software Engineering 1755 Athlone Institute of Technology 1756 Dublin Rd., Athlone, Ireland 1758 Email: nmurray@research.ait.ie 1760 15. Acknowledgements 1762 This work was supported in part by the EC in the context of the 1763 SocialSensor (FP7-ICT-287975) project and partly performed in the 1764 Lakeside Labs research cluster at AAU. SocialSensor receives 1765 research funding from the European Community's Seventh Framework 1766 Programme. The work for this document was also partially performed 1767 in the context of the FP7/NICT EU-JAPAN GreenICN project, 1768 http://www.greenicn.org. Apart from this, the European Commission 1769 has no responsibility for the content of this draft. The information 1770 in this document is provided as is and no guarantee or warranty is 1771 given that the information is fit for any particular purpose. The 1772 user thereof uses the information at its sole risk and liability.