A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Today, mobile devices like laptops and cell phones often come equipped with multiple network interfaces, enabling clients to simultaneously connect to independent access networks. Even though applications, such as multimedia streaming and video-on-demand delivery systems, could potentially benefit greatly from the aggregated bandwidth, implementation and standardization challenges have so far hindered the deployment of multilink solutions. Previously, we have explored the benefits of collaboratively using multiple Internet connections to progressively download and play back large multimedia files. In this paper, we present an improved version of our approach that utilizes HTTP's capability of request pipelining in combination with range retrieval requests. While, in our earlier work, the optimal choice of file segmentation size presented a tradeoff between throughput and startup latency, the enhanced solution is able to overcome this tradeoff. The use of very small segments no longer impairs the efficiency of throughput aggregation, which additionally makes our solution robust against link variances and agnostic to network heterogeneity. <s> BIB001 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Hypertext transfer protocol (HTTP) based streaming solutions for live video and video on demand (VOD) applications have become available recently. However, the existing HTTP streaming solutions cannot provide a low latency experience due to the fact that inherently in all of them, latency is tied to the duration of the media fragments that are individually requested and obtained over HTTP. We propose a low latency HTTP streaming approach using HTTP chunked encoding, which enables the server to transmit partial fragments before the entire video fragment is published. We develop an analytical model to quantify and compare the live latencies in three HTTP streaming approaches. Then, we present the details of our experimental setup and implementation. Both the analysis and experimental results show that the chunked encoding approach is capable of reducing the live latency to one to two chunk durations and that the resulting live latency is independent of the fragment duration. <s> BIB002 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> The distribution of videos over the Internet is drastically transforming how media is consumed and monetized. Content providers, such as media outlets and video subscription services, would like to ensure that their videos do not fail, startup quickly, and play without interruptions. In return for their investment in video stream quality, content providers expect less viewer abandonment, more viewer engagement, and a greater fraction of repeat viewers, resulting in greater revenues. The key question for a content provider or a CDN is whether and to what extent changes in video quality can cause changes in viewer behavior. Our work is the first to establish a causal relationship between video quality and viewer behavior, taking a step beyond purely correlational studies. To establish causality, we use Quasi-Experimental Designs, a novel technique adapted from the medical and social sciences. We study the impact of video stream quality on viewer behavior in a scientific data-driven manner by using extensive traces from Akamai's streaming network that include 23 million views from 6.7 million unique viewers. We show that viewers start to abandon a video if it takes more than 2 seconds to start up, with each incremental delay of 1 second resulting in a 5.8%increase in the abandonment rate. Further, we show that a moderate amount of interruptions can decrease the average play time of a viewer by a significant amount. A viewer who experiences a rebuffer delay equal to 1% of the video duration plays 5% less of the video in comparison to a similar viewer who experienced no rebuffering. Finally, we show that a viewer who experienced failure is 2.32% less likely to revisit the same site within a week than a similar viewer who did not experience a failure. <s> BIB003 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Multipath transport protocols such as Multipath TCP can concurrently use several subflows to transmit a TCP flow over potentially different paths. Since more than one subflow is used, an efficient multipath scheduling algorithm is needed at the sender. The objective of the scheduler is to identify the subflow over which the current data packet should be sent. This paper compares the most important types of schedulers for multipath transfers. We model their performance analytically and derive key metrics, most notably the resulting end-to-end delay over heterogeneous paths. Our results show that a scheduler minimizing the packet delivery delay yields the best overall performance, but it is complex to realize. An alternative scheduler based on the sender queue size is simpler and has sufficient performance for relatively small asymmetry between the multiple paths. Our model results are confirmed by measurements with a real multipath transport protocol. <s> BIB004 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Video streaming is gaining popularity among mobile users. The latest mobile devices, such as smart phones and tablets are equipped with multiple wireless network interfaces. How to efficiently and cost-effectively utilize multiple links to improve the video streaming quality needs to be investigated. In order to maintain high video streaming quality while reduce the wireless service cost, in this paper, the optimal video streaming process with multiple links is formulated as a Markov Decision Process (MDP). The reward function is designed to consider the quality of experience (QoE) requirements for video traffic, such as the interruption rate, average playback quality, playback smoothness and wireless service cost. Using dynamic programming, the MDP can be solved to obtain the optimal streaming policy. To evaluate the performance of the proposed multi-link rate adaptation (MLRA) algorithm, we implement a testbed using the Android mobile phone and the open-source X264 video codec. Experimental results demonstrate the feasibility and effectiveness of the proposed MLRA algorithm for mobile video streaming applications, which outperforms the existing state-of-the-art one. <s> BIB005 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Energy conservation has become a critical issue around the world. In smart phones, battery power capabilities are not keeping up with the advances in other technologies (e.g., processing and memory) and are rapidly becoming a concern, especially in view of the growth in usage of energy-hungry mobile multimedia streaming. The deficiency in battery power and the need for reduced energy consumption provides motivation for researchers to develop energy efficient techniques in order to manage the power consumption in next-generation wireless networks. As there is little analysis in the literature on the relationship between the wireless environment and the mobile device energy consumption, this paper investigates the impact of network-related factors (e.g., network load and signal quality level) on the power consumption of the mobile device in the context of video delivery. This paper analyzes the energy consumption of an Android device and the efficiency of the system in several scenarios while performing video delivery (over UDP or TCP) on an IEEE 802.11g network. The results show that the network load and the signal quality level have a combined significant impact on the energy consumption. This analysis can be further used when proposing energy efficient adaptive multimedia and handover mechanisms. <s> BIB006 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> The Internet infrastructure often supports multiple routes between two communicating hosts and, today, especially mobile hosts usually offer multiple network interfaces, so that disjoint paths between the hosts can be constructed. Having a number of (partly or fully) disjoint paths available may allow applications to distribute their traffic, aggregate capacity of different paths, choose the most suitable subset of paths, and support failover if a path fails. Exploiting multipath characteristics has been explored for TCP, but the requirements for real-time traffic differs notably. In this paper, we devise a multipath communication model for Real-time Transport Protocol (RTP); present minimal set of required protocol extensions; develop algorithms for scheduling RTP traffic across multiple paths at the sender and a corresponding de-jittering algorithm at the receiver side; and evaluate our proposal in varying scenarios using media traffic across different emulated mobile access network setups. <s> BIB007 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Due to its simplicity at the server side, HTTP-based adaptive streaming has become a popular choice for streaming on-line contents to a wide range of user devices. In HTTP-based streaming systems, the server simply stores the video segmented into a series of small chunks coded in many different qualities and sizes, and leaves the decision of which chunk to download next to achieve a high quality viewing experience to the client. This decision making is a challenging task, especially in mobile environment due to unexpected changes in network bandwidth as the user moves through different regions. In this paper, we consider Markov Decision Process (MDP) to derive the optimum chunk selection strategy that maximizes streaming quality and propose three approaches to reduce the computational cost of MDP. The first approach recomputes the solution after downloading every k chunks. The second approach computes the solution once using global network statistics of a given region. The third approach recomputes the solution every x meters using offline statistics for each x meters of the road. The three approaches are compared using real-world 3G bandwidth and mobility traces. The best performance is achieved with x-MDP. <s> BIB008 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Video streaming is gaining popularity among mobile users. The latest mobile devices, such as smart phones and tablets, are equipped with multiple wireless network interfaces. How to efficiently and cost-effectively utilize multiple links to improve video streaming quality needs investigation. In order to maintain high video streaming quality while reducing the wireless service cost, in this paper, the optimal video streaming process with multiple links is formulated as a Markov Decision Process (MDP). The reward function is designed to consider the quality of service (QoS) requirements for video traffic, such as the startup latency, playback fluency, average playback quality, playback smoothness and wireless service cost. To solve the MDP in real time, we propose an adaptive, best-action search algorithm to obtain a sub-optimal solution. To evaluate the performance of the proposed adaptation algorithm, we implemented a testbed using the Android mobile phone and the Scalable Video Coding (SVC) codec. Experiment results demonstrate the feasibility and effectiveness of the proposed adaptation algorithm for mobile video streaming applications, which outperforms the existing state-of-the-art adaptation algorithms. <s> BIB009 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> HTTP streaming has become a cost-effective means for multimedia delivery nowadays. For adaptivity to networks and terminals, a provider should generate multiple representations of an original video as well as the related metadata. Recently, there have been various adaptation methods to support adaptive HTTP streaming. In this paper, we investigate typical adaptation methods in the context of live video streaming. We first discuss the trade-off among typical adaptation methods. The evaluation and comparison are then carried out not only in terms of bitrate and buffer behaviors but also in terms of the perceptual impact on end users. It is found that the perceptual impact depends not only on adaptation method but also on the content itself. We also show that the preparation of representation sets may affect the behaviors of some adaptation methods. <s> BIB010 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Rate adaption in Dynamic Adaptive Streaming over HTTP (DASH) is widely applied to adapt the transmission rate to varying network capacity. For rate adaption on variable bitrate (VBR) encoded video, it is still a challenge to properly identify and address the dynamics of bandwidth and segment bitrate. In this paper, the trend of client buffer level variation (TBLV) is analyzed to be a more effective metric for detecting the dynamics of bandwidth and segment bitrate compared to previous metrics. Then, a partial-linear trend prediction model is developed to accurately estimate TBLV. Finally, based on the prediction model, a novel simple rate adaption algorithm is designed to achieve efficient and smooth video quality level adjustment. Experimental results show that while maintaining similar average video quality, the proposed algorithm achieves up to 47.3% improvement in rate adaption smoothness compared to the existing work. <s> BIB011 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Adaptive video delivery approaches perform video rate selection based on the streaming client's throughput estimate. In practice, the accuracy of the estimated throughput is limited due to feedback delay and the unawareness of the dynamics of the underlying HTTP/TCP transport layer. As a result, streaming applications employ large playback delays in the order of tens of seconds so as to maintain continuous video rendering with good quality and bandwidth utilization. In this paper, we introduce DASP, an advanced video rate adaptation, to achieve a low-latency adaptive video streaming. The key components of our solution are a server-side mirroring of the streaming client's buffer, which provides a low-delay feedback for the video rate selection, and a hybrid rate adaptation logic based on goodput and buffer information, which stabilizes the adaptive response to the dynamics of transport layer.We demonstrate the performance of our rate selection algorithm by evaluating the stability of the receiver buffer under low-latency and high-definition adaptive video streaming with variable bit rate encoding over an emulated wide-area network link. The results also show that our approach is promising and applicable for dynamic live streaming with a playback delay as low as the chunk duration. <s> BIB012 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> MPEG-2 transport system (TS) and ISO base media file format (ISOBFF) standards developed by MPEG have been widely used by various industries and applications including digital broadcasting systems. Recently MPEG has developed a new standard, MPEG Media Transport or MMT, for next generation broadcasting system considering the emerging convergence of digital broadcasting network and the Internet. MMT assumes HTML5 and Internet protocol (IP) as deployment environment and inherits major features of MPEG-2 TS while simplifying unnecessary complicated features in IP environments. It also considers hybrid delivery of multi-screen services. MMT defines an application layer protocol enabling packetization of opaque objects or files without considering the structure of data and media processing unit (MPU) format specific packetization. Synchronization technology of MMT providing flexible synchronization of multimedia components delivered through hybrid environment over multiple devices is built on top of HTML5. <s> BIB013 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Changing network conditions pose severe problems to video streaming in the Internet. HTTP adaptive streaming (HAS) is a technology employed by numerous video services that relieves these issues by adapting the video to the current network conditions. It enables service providers to improve resource utilization and Quality of Experience (QoE) by incorporating information from different layers in order to deliver and adapt a video in its best possible quality. Thereby, it allows taking into account end user device capabilities, available video quality levels, current network conditions, and current server load. For end users, the major benefits of HAS compared to classical HTTP video streaming are reduced interruptions of the video playback and higher bandwidth utilization, which both generally result in a higher QoE. Adaptation is possible by changing the frame rate, resolution, or quantization of the video, which can be done with various adaptation strategies and related client- and server-side actions. The technical development of HAS, existing open standardized solutions, but also proprietary solutions are reviewed in this paper as fundamental to derive the QoE influence factors that emerge as a result of adaptation. The main contribution is a comprehensive survey of QoE related works from human computer interaction and networking domains, which are structured according to the QoE impact of video adaptation. To be more precise, subjective studies that cover QoE aspects of adaptation dimensions and strategies are revisited. As a result, QoE influence factors of HAS and corresponding QoE models are identified, but also open issues and conflicting results are discussed. Furthermore, technical influence factors, which are often ignored in the context of HAS, affect perceptual QoE influence factors and are consequently analyzed. This survey gives the reader an overview of the current state of the art and recent developments. At the same time, it targets networking researchers who develop new solutions for HTTP video streaming or assess video streaming from a user centric point of view. Therefore, this paper is a major step toward truly improving HAS. <s> BIB014 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> While over-the-top video distribution is now widely deployed, it still suffers from much higher latencies than traditional broadcast, typically from a few seconds up to half a minute. In this paper, we demonstrate a novel DASH system with latency close to broadcast channels, and show how such a system can be used to enable combined broadcast and broadband services while keeping the client buffering requirements on the broadcast link low. <s> BIB015 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Recently, HTTP streaming has become very popular for delivering videos over the Internet. For adaptivity, a provider should generate multiple versions of a video as well as the related metadata. Various adaptation methods have been proposed to support a streaming client in coping with strong bandwidth variations. However, most of existing methods target at constant bitrate (CBR) videos only. In this paper, we present a new method for quality adaptation in on-demand streaming of variable bitrate (VBR) videos. To cope with strong variations of VBR bitrate, we use a local average bitrate as the representative bitrate of a version. A buffer-based algorithm is then proposed to conservatively adapt video quality. Through experiments in the mobile streaming context, we show that our method can provide quality stability as well as buffer stability even under very strong variations of bandwidth and video bitrates. <s> BIB016 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Even though cellular networks offer a ubiquitous access to the Internet for mobile devices, their throughput is often insufficient for the rising demand for mobile video. Classical video streaming approaches can not cope with bandwidth fluctuations common in those networks. As a result adaptive approaches for video streaming have been proposed and are increasingly adopted on mobile devices. However, existing adaptive video systems often rely on available network resources alone. As video content properties have a large influence on the perception of occurring quality adaptations our belief is that this is not sufficient. In this work, we thus present a support service for a content-aware video adaptation on mobile devices. Based on the actual video content the adaptation process is improved for both the available network resources and the perception of the user. By leveraging the content properties of a video stream, the system is able to keep a stable video quality and at the same time reduce the network load. <s> BIB017 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> With wireless networks becoming ever more ubiquitous and the capabilities of the devices connected to them rivalling those of desktop computers, there is an acute need for the communications in these networks to be managed as efficiently and autonomously as possible. Moreover, as the number of connected devices is rapidly increasing, the problem is becoming all the more complex and the amount of up-to-date status information needed for the management is multiplying. In order to meet the needs of future network management in terms of knowledge building and dissemination, this paper presents an architecture for collecting, processing, and disseminating vast amounts of network management information efficiently in wireless networks. The information may originate from the different layers of the networking protocol stack either on the wireless clients or network devices, and the architecture facilitates its signalling within a distributed network management system. Also, as described in this paper with practical examples, the architecture has been validated in a laboratory with real devices in the context of multiple use cases ranging from enhanced multimedia delivery for mobile clients to balancing the workload of network nodes. In addition, this paper evaluates the performance of the Event Cache prototype in terms of its capability of handling event dissemination in a real testbed environment. <s> BIB018 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> The MPEG has recently developed a new standard, MPEG Media Transport MMT, for the next-generation hybrid media delivery service over IP networks considering the emerging convergence of digital broadcast and broadband services. MMT is intended to overcome the current limitations of available standards for media streaming by providing a streaming format that is transport- and file-format-friendly, cross-layer optimized between the video and transport layers, error-resilient for MPEG streams, and convertible between transport mechanisms and content adaptation to different networks. In this paper, we overview on the MPEG MMT technology and describe its application to hybrid media delivery over heterogeneous networks. <s> BIB019 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Owing to the increase in consumption of multimedia content and the improvement of device capacity, user demand for high-quality content has increased. However, it is difficult to transport such large amounts of content over the existing broadcasting network with limited bandwidth. To provide high-definition broadcasting, some studies suggest methods of transporting multimedia over heterogeneous networks after encoding content hierarchically. MPEG Media Transport (MMT), standardized by Moving Picture Experts Group (MPEG), is a solution that enables large-volume media transport over heterogeneous networks such as digital broadcasting networks and packet-switched networks. In the case of delivering a scalable encoded video over different networks, synchronization of each stream is an important issue. MMT defines a synchronization scheme, but does not contain sufficient functions to implement it. In this paper, we propose a synchronization scheme for media streams that are encoded hierarchically, divided into layers, and transported over heterogeneous networks. We implement our scheme using MMT and HTTP, and experimented using three encapsulated video streams with different durations. As a result, we show that the proposed scheme can reduce the waiting time to display high-quality video, relative to Dynamic Adaptive Streaming over HTTP-Scalable Video Coding (DASH-SVC) by requesting segments of enhanced layers after calculating the transmission time. Additionally, we find out that the selection of durations have a relation to the characteristics of the video. <s> BIB020 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> HTTP-based adaptive protocols dominate today's video streaming over the Internet, and operate using multiple quality levels that video players request one segment at a time. Despite their popularity, studies have shown that performance of video streams still suffers from stalls, quality switches and startup delay. In wireless networks, it is well-known that high variability in network bandwidth affects video streaming. MultiPath TCP (MPTCP) is an emerging paradigm that could offer significant benefits to video streaming by combining bandwidth on multiple network interfaces, in particular for mobile devices that typically support both WiFi and cellular networks. In this paper, we explore whether MPTCP always benefits mobile video streaming. Our experimental study on video streaming using two wireless interfaces yields mixed results. While beneficial to user experience under ample and stable bandwidth, MPTCP may not offer any advantage under some network conditions. We find that when additional bandwidth on the secondary path is not sufficient to sustain an upgrade in video quality, it is generally better not to use MPTCP. We also identify that MPTCP can harm user experience when an unstable secondary path is added to the stable primary path. <s> BIB021 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> The sever-initiated push mechanism is one of the most prominent features in the next generation HTTP/2 protocol, having shown its capability on saving network traffic and improving the web page retrieval latency. Our prior work has investigated the server push-based mechanism for HTTP video streaming and proposed a k-push scheme, where the server pushes k video segments following the response to a request. In this study, we further conduct an analysis and evaluation of the k-push scheme in HTTP streaming. Our results uncover that the push mechanism can efficiently increase the network utilization (under certain conditions) compared to regular HTTP streaming. However the results also show that the k-push scheme deteriorates network adaptability and leads to the "over-push" problem, in which the pushed video content waste network resources due to user abandonment behaviors. To overcome these limitations, we propose a new " adaptive-push" scheme, which dynamically adjusts the parameter k to adapt to the runtime environment. To evaluate the performance of adaptive-push, we implemented a prototype system. The experimental results show that compared to k-push, adaptive-push can improve the network adaptability. Furthermore, our real-world trace based simulation results show that adaptive-push can effectively alleviate the over-push problem. <s> BIB022 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> End-users in online video services are sensitive to the overall quality of the video at screen, but also, and more importantly, to other factors, including the latency between the video generation and the playback for live videos. If the improvement of the quality of the perceived video has been well investigated by the multimedia community, the impact of delay, latency, and re-buffering has not received a significant attention. Adaptive streaming technologies, which have been widely adopted in the recent years, contribute to this lack of consideration since vendors usually recommend the introduction of significant extra-latency. In this paper, we address the problem of low-latency live video streaming. We propose an implementation of multi-path video delivery at the applicative level, which exploits the information provided in the latest version of the video delivery standards. We present an implementation of a video player, which takes advantage of multi-path networking to enable video playback using TCP with a latency below 100 ms. By initiating the multi-path delivery from the client side, our mechanism is compatible with current network equipments and does not require any change neither at the server nor in the middleboxes. <s> BIB023 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Making networks aware of applications and vice versa is a current trend in the design of emerging network management and service architectures. Additionally, new protocols and application adaptation approaches have been proposed in order to enhance the transmission of Quality of Service (QoS) sensitive data in the best effort Internet. This paper contributes to the field by studying means to improve the quality and availability of video streaming services in multi-access networks through controlled bitrate adaptation and multipath capabilities. The paper proposes a network management system to achieve advanced control and improved performance for multipath adaptive HTTP video streaming in multi-access networks. The management system builds upon the Distributed Decision Engine (DDE) framework and it is partially implemented and evaluated in the paper using a multi-access network testbed. <s> BIB024 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Today's video streaming services utilize widely adaptive streaming techniques implemented over HTTP. While the approach is robust and compatible with today's internet architecture, middleboxes, and CDNs, it leaves several places for optimization. This paper proposes enhancements to the video bitrate adaptation solution of adaptive HTTP streaming by defining two network-assisted adaptation approaches based on a cognitive network management architecture. The architecture considered in the paper supports enhanced network and service awareness and distributed control over video bitrate adaptation. The presented bandwidth management concepts are experimented in a testbed environment, including prototypes of the proposed algorithms, signaling framework, and video streaming service supporting MPEG-DASH. The implementation details and evaluation results of the work introduced in this overview paper are planned to be included into a follow-up paper. <s> BIB025 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Dynamic adaptive streaming over HTTP (DASH) is a simple, but effective, technology for video streaming over the Internet. It provides adaptive streaming while being highly scalable at the side of the content providers. However, the mismatch between TCP and the adaptive bursty nature of DASH traffic results in underperformance of DASH streams in busy networks. This paper describes a networking architecture based on the Software Defined Networking (SDN) paradigm. Controllers in the network with a broad overview on the network activity provide two mechanisms for adaptation assistance: explicitly signaling target bitrates to DASH players and dynamic traffic control in the network. We evaluate how each of these mechanisms can contribute to the delivery of a stable and high quality stream. It shows that our architecture improves the quality of experience by doubling the video bitrate and reducing disturbing quality switches. As such, this paper contributes insights on how to implement DASH-aware networking that also enables internet service providers, network administrators, and end-users to configure their networks to their requirements. <s> BIB026 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> MPEG DASH provides formats that are suitable to stream segmented media content over HTTP. DASH clients follow a client-pull paradigm by adapting their requests based on the available bandwidth and other local resources. This has proven to be easier to deploy over CDN infrastructure than server-push technologies. However, this decentralised nature introduces new challenges such as offering a consistent and higher quality of service for premium users. MPEG is addressing this issue in the to-be-published new MPEG DASH part 5, Server and Network-assisted DASH (SAND). The key features of SAND are asynchronous network-to-client and network-to-network communication of quality-related assisting information. In addition, DASH-IF is further defining interoperable guidelines to optimise SAND deployments in a variety of environments: home network, over-the-top, etc. MPEG is expected to publish SAND by end of 2016 while DASH-IF aims for the course of 2017. <s> BIB027 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Transport protocols that can exploit multiple paths, especially MPTCP, do not match the requirements of video streaming: high average transmission delay, too strict reliability, and frequent head-of-line phenomenons resulting in abrupt throughput drops. In this paper, we address this mismatch by introducing a cross-layer scheduler, which leverages information from both application and transport layers to re-order the transmission of data and prioritize the most significant parts of the video. Our objective is to maximize the amount of video data that is received in time at the client. We show that current technologies enable the implementation of this cross-layer scheduler without much overhead. We then demonstrate the validity of our approach by studying the performance of an optimal cross-layer scheduler. The gap between the performance of the traditional scheduler versus the optimal scheduler justifies our motivation to implement a cross-layer scheduler in practice. We propose one implementation with basic cross-layer awareness. To evaluate the performance of our proposal, we aggregate a dataset of real MPTCP sessions and we use video stream encoded with HEVC. Our results show that our cross-layer proposal outperforms the traditional scheduler. Viewers not only benefit from the inherent advantages of using MPTCP (such as a better resilience to path failure) but also get a better QoE compared to the traditional scheduler. <s> BIB028 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Compared with using only a single wireless path such as WiFi, leveraging multipath (e.g., WiFi and cellular) can dramatically improve users' quality of experience (QoE) for mobile video streaming. However, Multipath TCP (MPTCP), the de-facto multipath solution, lacks the support to prioritize one path over another. When applied to video streaming, it may cause undesired network usage such as substantial over-utilization of the metered cellular link. In this paper, we propose MP-DASH, a multipath framework for video streaming with the awareness of network interface preferences from users. The basic idea behind MP-DASH is to strategically schedule video chunks' delivery and thus satisfy user preferences. MP-DASH can work with a wide range of off-the-shelf video rate adaptation algorithms with very small changes. Our extensive field studies at 33 locations in three U.S. states suggest that MP-DASH is very effective: it can reduce cellular usage by up to 99% and radio energy consumption by up to 85% with negligible degradation of QoE, compared with off-the-shelf MPTCP. <s> BIB029 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> MPTCP (MultiPath TCP) boosts application network performance by aggregating bandwidth over multiple paths. However, it may cause poor performance due to the large number of out-of-order packets especially when the paths have different delays. To resolve this issue, we propose to dynamically add or remove MPTCP paths with the leverage of software-defined networking (SDN). The key idea is to track the available capacity of connected paths and pick the most appropriate paths depending on varying network conditions. To show the feasibility of our approach, we create an SDN platform using Mininet over Wi-Fi networks. Our analysis shows that a faster download and improved quality of experience (QoE) in adaptive rate video streaming is possible with our dynamic MPTCP path control mechanism using SDN. <s> BIB030 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Smart devices equipped with multiple network interfaces are becoming commonplace. Nevertheless, even though multiple interfaces can be used to connect to the Internet, their capabilities have not been fully utilized yet because the default TCP/IP stack supports only a single interface for communication. This situation is now changing due to the emergence of multipath protocols on different network stack layers. For example, many IP level approaches have been proposed utilizing tunneling mechanisms for hiding multipath transmission from the transport protocols. Several working groups under IEEE and IETF are actively standardizing multipath transmission on the link layer and transport layer. Application level approaches enable multipath transmission capability by establishing multiple transport connections and distributing data over them. Given all these efforts, it is beneficial and timely to summarize the state-of-the-art, compare their pros and cons, and discuss about the future directions. To that end, we present a survey on multipath transmission and make several major contributions: 1) we present a complete taxonomy pertaining to multipath transmission, including link, network, transport, application, and cross layers; 2) we survey the state-of-the-art for each layer, investigate the problems that each layer aims to address, and make comprehensive assessment of the solutions; and 3) based on the comparison, we identify open issues and pinpoint future directions for multipath transmission research. <s> BIB031 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Multipathing in communication networks is gaining momentum due to its attractive features of increased reliability, throughput, fault tolerance, and load balancing capabilities. In particular, wireless environments and datacenters are envisioned to become largely dependent on the power of multipathing for seamless handovers, virtual machine (VM) migration and in general, pooling less proficient resources together for achieving overall high proficiency. The transport layer, with its knowledge about end-to-end path characteristics, is well placed to enhance performance through better utilization of multiple paths. Realizing the importance of transport-layer multipath, this paper investigates the modernization of traditional connection establishment, flow control, sequence number splitting, acknowledgement, and flow scheduling mechanisms for use with multiple paths.Multipath rate control defines the fundamental feature of the transport layer. Thus, we study the restructuring of classical utility maximization framework and analyze its stability and convergence. We also examine the topic of multipath congestion control in the light of TCP fairness. To the best of our knowledge, this is the first in-depth survey paper that has chronicled the evolution of the transport layer of the Internet from the traditional single-path TCP to the recent development of the modern multipath TCP (MPTCP) protocol. Along with describing the history of this evolution, we also highlight in this paper the remaining challenges and research issues. Graphical abstractDisplay Omitted <s> BIB032 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> MPEG has developed a new multimedia transport protocol namely MMT for heterogeneous network transport. Considering the characteristics of both broadcast network and internet, MMT has many advantages compared to traditional transport protocols like MPEG2-TS, RTP and so on. Although MMT has defined a detailed transport protocol for broadcast delivery, the broadband transport protocol of MMT has not been implemented specifically. Nowadays, HTTP is the first choice in most MMT systems. In this paper, we develop a new MMT system using QUIC which is developed by Google as a transport protocol atop UDP as the broadband protocol. This system combines the advantages of MMT and QUIC, thus can achieve better performance than existing MMT systems. We also conduct experiments to compare the performance of the two systems. The experiment results verify that using QUIC in MMT can improve the broadband media transport in MMT system. <s> BIB033 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> HTTP adaptive streaming (HAS) is the most recent attempt regarding video quality adaptation. It enables cheap and easy to implement streaming technology without the need for a dedicated infrastructure. By using a combination of TCP and HTTP it has the advantage of reusing all the existing technologies designed for ordinary web. Equally important is that HAS traffic passes through firewalls and works well when NAT is deployed. The rate adaptation controller of HAS, commonly called adaptive bitrate selection (ABR), is currently receiving a lot of attention from both industry and academia. However, most of the research efforts concentrate on a specific aspect or a particular methodology without considering the overall context. This paper presents a comprehensive survey of the most significant research activities in the area of client-side HTTP-based adaptive video streaming. It starts by decomposing the ABR module into three subcomponents, namely: resource estimation function, chunk request scheduling, and adaptation module. Each subcomponent encapsulates a particular function that is vital to the operation of an ABR scheme. A review of each of the subcomponents and how they interact with each other is presented. Furthermore, those external factors that are known to have a direct impact on the performance of an ABR module, such as content nature, CDN, and context, are discussed. In conclusion, this paper provides an extensive reference for further research in the field. <s> BIB034 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Downlink data rates can vary significantly in cellular networks, with a potentially non-negligible effect on the user experience. Content providers address this problem by using different representations (e.g., picture resolution, video resolution and rate) of the same content and switch among these based on measurements collected during the connection. If it were possible to know the achievable data rate before the connection establishment, content providers could choose the most appropriate representation from the very beginning. We have conducted a measurement campaign involving 60 users connected to a production network in France, to determine whether it is possible to predict the achievable data rate using measurements collected, before establishing the connection to the content provider, on the operator's network and on the mobile node. We show that it is indeed possible to exploit these measurements to predict, with a reasonable accuracy, the achievable data rate. <s> BIB035 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Client-side video players employ adaptive bitrate (ABR) algorithms to optimize user quality of experience (QoE). Despite the abundance of recently proposed schemes, state-of-the-art ABR algorithms suffer from a key limitation: they use fixed control rules based on simplified or inaccurate models of the deployment environment. As a result, existing schemes inevitably fail to achieve optimal performance across a broad set of network conditions and QoE objectives. We propose Pensieve, a system that generates ABR algorithms using reinforcement learning (RL). Pensieve trains a neural network model that selects bitrates for future video chunks based on observations collected by client video players. Pensieve does not rely on pre-programmed models or assumptions about the environment. Instead, it learns to make ABR decisions solely through observations of the resulting performance of past decisions. As a result, Pensieve automatically learns ABR algorithms that adapt to a wide range of environments and QoE metrics. We compare Pensieve to state-of-the-art ABR algorithms using trace-driven and real world experiments spanning a wide variety of network conditions, QoE metrics, and video properties. In all considered scenarios, Pensieve outperforms the best state-of-the-art scheme, with improvements in average QoE of 12%--25%. Pensieve also generalizes well, outperforming existing schemes even on networks for which it was not explicitly trained. <s> BIB036 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> This article investigates several network-assisted streaming approaches that rely on active cooperation between video streaming applications and the network. We build a Video Control Plane that enforces Video Quality Fairness among concurrent video flows generated by heterogeneous client devices. For this purpose, a max-min fairness optimization problem is solved at runtime. We compare two approaches to actuate the optimal solution in an Software Defined Networking network: The first one allocates network bandwidth slices to video flows, and the second one guides video players in the video bitrate selection. We assess performance through several QoE-related metrics, such as Video Quality Fairness, video quality, and switching frequency. The impact of client-side adaptation algorithms is also investigated. <s> BIB037 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> This document discusses the use of One Way Latency (OWL) for enhancing ::: multipath transmission in QUIC. Several representative usages of OWL, ::: such as congestion control mechanism, retransmission policy, crucial ::: data scheduling are analyzed. Two kinds of OWL measurement approaches ::: are also provided and compared. More explorations related with OWL ::: will be researched to improve the performance of QUIC. <s> BIB038 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Currently, most multimedia applications utilize a combination of real- ::: time transport protocol (RTP) and user datagram protocol (UDP). ::: Application programs at the source end format payload data into RTP ::: packets using RTP specifications and dispatch them using unreliable ::: UDP along a single path. Multipath transport is an important way to ::: improve the efficiency of data delivery. In order to apply the ::: framework of multipath transport system based on application-level ::: relay (MPTS-AR) to RTP-based multimedia applications, this document ::: defines a multipath real-time transport protocol based on application- ::: level relay (MPRTP-AR), which is a concrete application-specific ::: multipath transport protocol (MPTP). Packet formats and packet types ::: of MPRTP-AR follow the common rules specified in MPTP profile. Based ::: on MPRTP-AR, RTP-based multimedia applications can make full use of ::: the advantages brought by MPTS-AR. <s> BIB039 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> Cross Layer <s> Bandwidth constraints and high end-to-end delays are real challenges for achieving and sustaining high quality mobile video streaming services. Diverse multipath transmission techniques are being investigated as possible solutions, since recent developments have enabled mobile devices users to receive video data simultaneously over multiple interfaces (e.g., LTE and WiFi). While some multipath protocols have been recently standardized for this purpose (e.g., MPTCP), being network layer protocols they cannot properly handle challenging transmission scenarios subject to packet losses and congestion, such as lossy wireless channels. In this work, we adopt the MPEG Media Transport (MMT) protocol to propose an improvement for mobile multipath video streaming solutions. MMT is an application layer protocol with inherent hybrid media delivery properties. We propose a novel path-and-content-aware scheduling strategy for MMT by means of full cooperation between network metrics and video content features. Our strategy provides better models to adaptively cope with unstable communication channel conditions and to improve the final user quality of experience (QoE). For the experimental evaluation, we used NS3-DCE to simulate a realistic multipath network scenario which includes channel error models and background traffic. Results for two video sequences are presented in terms of PSNR, SSIM, goodput, delay and packet loss rates. When compared with a simple scheduling strategy for the traditional multipath MMT, our approach yields significant packet loss rate reductions (~90%) and video quality improvements of around 12 dB for PSNR and 0.15 for SSIM. <s> BIB040
Transport Layer Decision CMT-CL/FD [119] Server *BEMA: UDP (for video data transmission) and TCP (for connection establishment and feedback information). control information (e.g., jitter and packet loss). As a result, paths are categorized as congested, mildly congested, and noncongested conditions based on the packet loss information. The scheduler, which is responsible for packet distribution over different paths, assigns more media data on the non-congested path and fewer media data on congested ones. I-frames have the highest priority and are transferred over the path with the highest bandwidth, the least delay and packet losses. The sender is informed to retransmit packets by NACK and also retransmits packets on the path with the highest bandwidth, least delay and packet losses. The approach is not integrated with congestion control but tries to keep the load balancing by using network characteristics. The authors developed a de-jitter algorithm at the receiver side to overcome the variation of RTT and packet reordering with an adaptive playback buffer. An MPRTP sender assigns a subflow ID to each path (in MPRTP, the concept of subflow is used for series of video packets transmitted over an single path) and subflow-specific sequence numbers to determine subflow-related packet jitter, packet loss, and packet discards at the receiver side. The approach is less unfair than RTP with the aim of system balancing and spreading data over paths. Recently, Multipath Real-Time Transport Protocol Based on Application-Level Relay (MPRTP-AR) BIB039 was defined by IETF. As shown in Figure 6 , the proposed MPRTP-AR protocol stack has two sub-layers: RTP sub-layer and multipath transport control (MPTC) sub-layer. The RTP sublayer helps this protocol to be fully compatible with existing RTP applications. Therefore, there is no need to change the Application Programming Interface (API). The MPTC sublayer is responsible for functions such as flow partitioning, subflow packaging and recombination, and also subflow reporting. At the sender side, data from the application layer are formatted in RTP packets which are sent to the MPTC sub-layer. Then, MPTC formats them into MPRTP-AR data packets. At the receiver side, MPTC extracts the fixed header of MPRTP-AR data packets and sends them to the RTP sub- layer. RTCP packets could also be generated by the RTP sub-layer for generating media transport statistics. RTCP data could be packaged in MPRTP-AR data packets which would be distributed over multiple paths by MPTC sub-layer. In addition to MPRTP-AR data packets, MPRTP-AR control packets are defined for providing keep-alive packets and MPRTP-AR reports. MPRTP-AR reports (MPRTP-AR Subflow Receiver Report (SRR) and MPRTP-AR Flow Recombination Report (FRR)) contain transport qualities of active paths (e.g., packet loss rate and jitter) and effects on scheduling and flow partitioning. Flow partitioning methods are categorized into two groups that are named codingaware methods and coding-unaware methods. Coding-aware methods are used for layering coding, multiple description coding or object-oriented coding, and are on RTP sub-layer. In this method, each coding flow is assigned to a subflow, or several coding flows are multiplexed into one subflow. Coding-unaware methods are on MPTC sub-layer, and the RTP/RTCP that are passed from upper layer would evenly spread based on the quality of the associated active paths. Flow reporting is also optionally available for the whole recombined flows. 2) DASH: Dynamic Adaptive Streaming over HTTP (MPEG-DASH)  was standardized in 2011 by MPEG. DASH supports both VoD and live video delivery. We first detail the DASH system and its main performance limitations. Then, we explain rate adaptation methods. Finally, we discuss the works that are based on this protocol. DASH system. As explained in Section II, DASH has the same background technology of HTTP adaptive streaming and its system is shown in Figure 7 . In DASH system, representations are fragmented into small segments at the server side. DASH component characteristics (text, video, audio, etc.) are described in a XML document named Media Presentation Description (MPD). Typically, DASH client is responsible for choosing the next media segments and requesting the related HTTP URL. Therefore, a rate adaptation method, named adaptation engine in Figure 7 , is required to select the proper segments' bit rate by considering the segment availability indicated by the MPD, the network conditions and the media playout situation (e.g., playout buffer level) BIB014 . Performance limitations. The rate adaptation method is responsible for key issues that influence QoE, namely, startup delay, stall, and video quality switches. Startup delay refers to the time since the client request a video until it starts to play, namely pre-buffering. This delay occurs because, generally, one or more segments have to be downloaded completely before the video starts to play. Although this delay helps to prevent stalls under poor network conditions, studies show that it often results in users stopping from watching the video BIB003 . It is important to note that while VoD streaming applications can pre-buffer few seconds of video, live and interactive video streaming can only pre-buffer few hundreds of ms of video BIB007 . Stall or interruption refers to the pauses during the video playback due to the playback buffer is emptied, and it needs to wait to buffer video (also called re-buffering) BIB004 . Studies show that stalling happens 40 -70% of all sessions BIB021 . Generally, this issue occurs because of insufficient bandwidth. In DASH, each segment is available to transmit after completing the process of coding. In addition, there is a dead time between receiving the last packet of one segment and requesting for the next segment. For example, this process time together with transmission time over TCP takes at least 3s (when segments have 1 second) BIB002 . One approach to mitigate the stall problem is using a dynamic method to find reasonable segment size (segment duration). Studies in BIB022 and  show that segment size has a high effect on live latency. While with shorter size segmentation, latency significantly decreases, but the number of HTTP requests increases and consequently, the available bandwidth decreases BIB005 . Another approach to decrease latency, and consequently solve the stall issue, is applying subsegmentation transmission. In this approach, each segment divides into several subsegments, and receiver fetches subsegments before the whole segment coding terminates BIB015 . This approach is improved by sending subsegments over more than one link simultaneously, which means adding multipath transmission capability, to increase the fetching segment speed. Multipath transmission approach is used in a few works BIB023 , BIB005 , BIB009 to achieve this target. However, the subsegmentation transmission technique also increases HTTP request overhead BIB005 . In particular, the overhead problem is caused by subsegmentation transmission because at the client side after each request, an average of RTT is required to receive the response from the server. In the case of a large file with small segments/subsegments, this overhead causes a high latency. The HTTP pipelining BIB001 is a technique to decrease both number and length of each idle time. In this technique, the client sends the next subsegment request before completing the download of the current subsegment. However, in pipelining, the responses of the requests at the server have to return back in the same order that the requests arrived at the server. Therefore, if it takes a long time to process one request, the other requests would be blocked. For this reason, pipelining is not widely adopted. To mitigate the overhead problem, the new version of HTTP (HTTP/2) could be used due to its ability to push content in advance, and consequently reduce live latency and network traffic BIB022 . Switching between different video quality representations is also a problem that impacts the video quality on the user side and causes annoying of viewers. Video switching happens because of the network bandwidth changing or buffer occupancy status. Therefore, it is important to adapt a suitable rate adaptation method, which could identify the network resources and congestion on time in order to have an optimal user experience BIB024 . Rate adaptation methods. Typically, rate adaptation methods use throughput monitoring, receiver buffer status, or power level in the process of video segment bit rate decision BIB034 . Throughput-based methods estimate the available bandwidth by monitoring throughput. These type of methods try to avoid re-buffering while providing the highest possible video quality. In case of using a throughput-based method, the video quality is unstable BIB016 due to throughput variations, which could be caused by TCP behavior BIB010 , BIB024 . For example, TCP underestimates bandwidth when segmentation sizes are small (because the corresponding congestion window does not increase) or when bandwidth prediction is weak in networks with fast throughput variation such as cellular networks BIB035 . Buffer-based methods choose the video segment bit rate based on the buffer characteristics and usage. The proposed algorithms try to provide a smooth video streaming, but often result in sudden changes in video quality, or freezing when the buffer level (number of unplayed segments in the queue) drops to zero BIB016 , BIB011 . Power-based methods select the video segment bit rate using the battery level. Regarding BIB006 , video streaming consumes twice the energy of playing the same content offline. Therefore, power-based methods try to maximize the battery life time during a video streaming session. Due to the bit rate selection being more accurate, the work in BIB012 shifted the adaptation logic to the server side by deploying a mirrored client buffer on the server. Wilk et al. BIB017 use a proxy server while Mao et al. BIB036 leverage Pensieve's neural network model on an ABR server to enforce or assist the mobile client adaptation. Such server side approaches have better network utilization compare to the client side approaches BIB034 . However, server side approaches are not considered scalable. Rate adaptation methods also perform more efficiently if they can access the network information BIB025 . For example, SDN is a technology to implement such a mechanism BIB026 , BIB037 . Another example is Server and Network-assisted DASH (SAND)  , BIB027 which is a system standardized recently by MPEG to collect and propagate the network information for DASH bit rate adaptation decision. The proposed architecture in BIB024 is built upon the Distributed Decision Engine (DDE) BIB018 framework to provide more network information (e.g., available capacity, load, QoS) for better rate adaptation decision in multipath scenario. Multipath support. Current DASH version lacks multipath support, but it is being promoted as its future. Table IV presents some efforts to integrate DASH with Multipath separate TCP (e.g., BIB005 , BIB009 , BIB023 ) and MPTCP (e.g., BIB028 , BIB024 , MP-DASH BIB029 , BIB030 and  ). The table shows attention for combining DASH with MPTCP has increased recently. This is due to MPTCP aggregates bandwidth and supports mobility. MPTCP is also middlebox friendly, and it is supported by the Linux kernel. Besides, MPTCP has got high attention in industry BIB031 , BIB032 . More technical details about MPTCP will be provided in Section IV-B4. James et al. BIB021 explored "Whether MPTCP would always benefit mobile video streaming?". This research analyzed the performance of different scenarios for DASH over MPTCP. The results show that having two paths with stable bandwidths is beneficial even with small bandwidth capacity on the secondary path. Another positive impact of an additional link is when the primary path has high bandwidth variability. However, there are some harmful cases too. For example, adding an unstable secondary path could harm the stable primary path or when the bandwidth of the secondary path is not enough to transmit higher video bit rates. Therefore, MPTCP is significantly sensitive to bandwidth fluctuation. The results also show that unnecessary multipath causes more energy consumption, resource wasting or increase cost of the quality switch. One note regarding provide multipath delivery for DASH is about which one of the client or the server is responsible for packet scheduling decisions. In all the surveyed works that spread data over separate TCP connections in Table IV , the client is responsible for choosing the proper path and fetching the suitable segments/subsegments over that path due to the fact that DASH logic is on the client side. But, integration of DASH with MPTCP is challenging when DASH logic resides BIB005 2012 Y N Chowrikoppalu et al.  2013 N Y RTRA BIB009 2014 Y N Houzé et al. BIB023 2016 Y N Corbillon et al. BIB028 2016 N Y Ojanperä et al. BIB024 2016 N Y MP-DASH BIB029 2016 N Y Nam et al. BIB030 2016 N Y on the client side, and MPTCP scheduler is on the server side. Besides, MPTCP is transparent to the application layer. Therefore, in the surveyed works of Table IV , which MPTCP is used as transport protocol, rate adaptation logic is kept at the client side. But, scheduling decisions related to packet selection and distributing them through the paths are placed at the server side or both client and server side. The surveyed works BIB028 , BIB024 , MP-DASH BIB029 and BIB030 are more related to the cross layer protocol stack. So, we will discuss them with details about scheduling strategies in Section IV-D. The other works are explained in more details below. Xing et al. used Markov Decision Process (MDP) BIB008 to formulate video streaming process as a reinforcement learning task in their works BIB005 and BIB009 for non-scalable and Scalable Video Coding (SVC), respectively. The works' goals are decreasing startup delay, improving video quality and achieving better smoothness. In each of these works, the implemented rate adaptation method selects the next segment based on the current queue length and estimated available bandwidth. To estimate an accurate available bandwidth, Markov channel model is used. This way, adaptation logic finds the transit probability of each link in real-time and determines the best action (e.g., using both links, using only WiFi link, client wait or smoothing). There is also a reward function implemented to reward each action with concern of video QoS requirements (by measuring interruption rate, video quality, video smoothness and search time cost). However, the major problem of using MDP is the high computational cost of solving the complex optimization problem, especially in online and high mobile speed users BIB008 . In addition, the approach is not a content-aware solution. Chowrikoppalu et al.  modified DASH protocol in order to utilize multipath capability. In this work, the adaptation logic is fed with a proposed bandwidth estimation algorithm and some proposed parameters, including path stability, total path stability and buffer level. The bandwidth estimation algorithm is based on sniffing packets on the interface level. Path stability and total path stability are defined to show the variation of bandwidth on each path and on MPTCP connection, respectively. However, the main problem of this approach is that it does not access the video content information. Houzé et al. BIB023 implemented a video player utilizing multipath capability over multiple TCP connections. The goal of this scheme is achieving low-latency in DASH video delivery (below 100 ms). In this approach, server encodes frames of each representation and put them in the related segment every x ms (x depends on the frame rate, for example, x is 40 ms for 25 fps). The client has to fetch each whole frame before the deadline (play time of the frame) and in x ms before a new frame becomes available to fetch. For this target, the authors utilized video delivery over multiple paths as a way to reduce latency. Each frame divides to byte ranges to transfer over different paths and the approach has a mechanism to find the best byte range size in order to receive them with a small inter-arrival time. The larger byte ranges are transferred over faster paths, this way, the variation of transfer delay decreases, and consequently, HOL problem mitigates. Besides, another adapted mechanism is proposed to select the proper representation. In this mechanism, when a segment starts, the biggest frame of each representation is considered in making the decision. The biggest frame is commonly the first frame of each representation (I-frame). Therefore, a representation would be selected that the biggest frame has high probability of reaching the destination on time. The problem, however, is that the approach does not consider the video content information. In addition, while the work uses RTT to estimate each path speed, it needs to improve the scheduling strategy to manage the paths. 3) MMT: MPEG Media Transport (MMT)  was standardized by MPEG in 2014. MMT is a part of the ISO/IEC 23008 High Efficiency Coding and Media Delivery in Heterogeneous Environments (MPEG-H) standard BIB013 . This application layer transport protocol supports VoD and live video streaming. MMT has been widely used for Virtual Reality (VR) and Augmented Reality (AR) technologies, three-dimensional (3-D) scene communication, Multi-View Video (MVV), and for major advances in televisual technology worldwide  ,  . We previously explained some of the properties and behaviors of MMT in Section II. Here, firstly, we indicate more properties of the protocol. Then, we explain the related technologies, MMT functions, and data transmission details. Finally, the surveyed works that are based on the MMT protocol are discussed. MMT properties. MMT could be used for all unidirectional, bidirectional, unicast, multicast, multisource and, even, multipath media delivery. Besides, MMT supports both broadcast and broadband video streaming  ,  . It also provides traditional IPTV broadcasting service and all-Internet Protocol (All-IP) networks. Capability of hybrid media delivery is one of the most important properties of MMT. Hybrid media delivery BIB019 refers to the combination of delivered media components over different types of network. For example, it could be one broadcast channel and one broadband, or it could be two broadband channels. MMT has different hybrid service scenarios that are classified into three groups by ISO/IEC 23008-13  : live and non-live, presentation and decoding, and same/different transport schemes. The first one, live and nonlive, refers to the combination of live streaming components or combination of live with pre-stored components. The second group, presentation and decoding, is the combination of the stream components for synchronized presentation or synchronized decoding. The third group, same transport schemes and different transport schemes, supports the combination of just MMT components or MMT components with other format components (e.g., MPEG-2 TS). An instance of hybrid model comprises of MMT (as a broadcast channel) and DASH (as a broadband channel) over heterogeneous networks is also presented in ISO/IEC 23008-13  . The work in BIB033 compared two MMT broadband systems: a combination of MMT with HTTP versus a combination of MMT with Quick UDP Internet Connection (QUIC)  . QUIC is a transport protocol atop UDP for broadband systems, which was developed by Google. QUIC aims to reduce latency because it has zero round trip connection establishment in many cases. For example, when the client talked to the server before and there is some cached context (repeated connections). In addition, QUIC has multiplexed transport with no HOL blocking. Other features of QUIC are utilizing congestion control, FEC protection, and its own retransmission mechanism. The results of BIB033 show that using QUIC is more appropriate than HTTP in the networks with high delay and lossy networks. This experiment is just for a single path and there is room to evaluate it in multipath transmission defined for QUIC BIB038 . Related technologies. ISO/IEC 23008-1  defined some related MMT technologies. For example, Application Layer Forward Error Correction (AL-FEC) to repair data, ARQ to retransmit lost data, MMT data model and built-in hypothetical buffer model. Regarding the MMT data model  ,  , MMT package is a logical entity, illustrated in Figure 8 , that comprises of one or more assets and required information for video delivery, such as Composition Information (CI), Presentation Information (PI) and Asset Delivery Characteristics (ADC). Asset refers to a logical data entity containing a number of Media Processing Units (MPUs). Video, audio, picture, text are some examples of assets. CI provides information on temporal relationships among MPUs written in XML. HTML5 file is referred to PI, which provides initial information on spatial relationships among media elements, and ADC contains QoS information for multiplexing. Built-in hypothetical buffer model  aims to compensate for jitter and multipath delay delivery. In this model, the sending entity runs the hypothetical receiver buffer model (HRBM) to emulate the receiving entity behavior. In this way, the sending entity determines the required buffering delay and buffer size. Then, sending entity signals this information to the receiving entity. Since at the receiver entity, several buffers exist to reconstruct of MPU from the MMT packets, the received signal is used to define operations of the buffers to ensure that at any time the buffer occupancy is within the buffer size requirement. These buffers are FEC decoding buffer to perform FEC decoding. De-jitter buffer to provide the fixed transmission delay, and MMTP de-capsulation buffer to perform MMT packet processing (e.g., de-encapsulation, de-fragmentation/de-aggregation). MMT functions. MMT has three major functional layers, shown in Figure 9 , independent of video codecs BIB019 : encapsulation, signaling, and delivery. Encapsulation functional layer is responsible for encapsulating MPUs, which are complied with ISOBMFF  . Thereby, it enables easy conversion between storage and delivery format BIB013 . MMT is beneficial to the broadcasting system because MPUs are self-contained, which means that they can completely decode at the terminal without requiring any further information. Signaling functional layer is responsible for signaling messages and delivery management (e.g., CI, PI and ADC). Delivery functional area defines the application layer protocol that supports packetized streaming including the payload format through a heterogeneous network environment. Delivery functional area also provides Multiplexing, flow control and cross layer. Cross layer ability provides exchanging QoS between application layer and transport layer. MMT data transmission. Regarding MMT data transmission, each MMTP session consists of one MMTP flow BIB019 . MMTP flow is defined as all packet flows that are delivered to the same IP and port destination. A MMT flow may carry multiple assets, which are identified with a unique packet id. MMTP packet uses two types of sequence number as different purposes: packet counter and packet sequence number. packet counter represents sequence of packets in a delivery session and it is regardless of the value of packet id. packet counter enables packet loss detection. However, packet sequence number is the sequence number specific to each packet id (each asset). Initially, MMT was designed for broadcast networks (over UDP/IP) with reserved channel capacity. Therefore, congestion control was left to the implementation of the senders. However, MMT inherently supports receiver and sender feedback for stream thinning and bitstream switching. It also may support any Receiver-driven Layered Multicast (RLM)-based congestion control algorithms (e.g., WEBRC, TFMCC). MMT has four modes for payload format; MPU mode to transport MPU packetized streaming, Signaling mode to transfer signaling information, Repair symbol mode to carry FEC repair data, and also Generic File Delivery (GFD) mode, which transports all types of files. Multipath support. Regarding multipath delivery, Kolan et al.  defined a method to establish multipath delivery over MMT, Afzal et al. BIB040 proposed a path-and-contentaware scheduling strategy for packet distribution, and Sohn et al. BIB020 proposed a synchronization scheme for hierarchical video streams over heterogeneous networks. Next we explain each work in more detail. kolan et al.  defined a method to establish multipath delivery over MMT. In this method, MMT protocol utilizes signaling protocols such as RTSP or HTTP to establish and control multipath sessions between sender and receiver (transport connection could be either TCP or UDP). For example, in RTSP, the client and the server could be aware of the multipath capability by sending OPTIONS request to each other. This new option tag, called "multipath", could be implemented in the header of the OPTIONS request. The same way, while HTTP is used to set up multipath sessions, the client includes "Multipthid" header to tell the server about its multipath capability. It is also possible to add or drop a network path during the connection. While media is delivering, MMT periodically sends feedbacks to the sender to inform about the path quality information (e.g., loss, delay and jitter). Therefore, the sender could have a view of different paths' situations and dynamically select better performing paths for packets. Afzal et al. BIB040 proposed a novel path-and-content-aware scheduling strategy for MMT to stream real-time video over heterogeneous wireless networks. The authors claim to be the first work attempting to improve the MMT standard by adding multipath scheduling strategies. The path-and-contentaware scheduling strategy, implemented at the server side, applies some methods to improve the perceived video quality based on adaptive video traffic split schemes, Markovianbased techniques, in addition to a discard and a content-aware strategy. Adaptive video traffic split scheme allocates a proper bit rate for each transmission path considering heterogeneous network context with the aim of executing load balancing, relieve congestion, and proper utilizing of each path capacity. The Markovian-based method estimates path conditions and transition probabilities. Discard strategy reduces congestion by avoiding sending packets that would probably be lost. Contentaware strategy protects packets with high priority (I frames and the closest n P frames, named as near-I (NI) frames in this work) by duplicating or assigning them to the best path. The client constantly monitors the path condition, calculates the path metrics which are sent as feedback information packets to the server through the best path. For this purpose, the feedback signaling mechanisms defined in the MMT standard are leveraged. Finally, the proposed path-and-content-aware scheduling strategy lead to QoE improvements around 12 dB for PSNR and 0.15 for SSIM by significant packet loss rate reductions (∼ 90%). It is important to note that the approach does not require any change in the protocol itself since the scheduler can be implemented as part of the client/server applications. Sohn et al. BIB020 proposed a synchronization scheme for hierarchical video streams over heterogeneous networks. This scheme is a combination of MMT (for broadcasting) and HTTP (for broadband) video streaming. The work utilizes scalable video streaming. Each layer is segmented in time (in seconds), and duration value can vary according to the user's definition. SHVC-encoded stream is used in the experiment with 3-layers: base layer (HD), first enhanced layer (Full HD (FHD): 2K) and second enhanced layer (UHD: 4K). Base layer and first enhanced layer of video are transferred over the broadcast network (MMT supports multiplexing on packet level), and the second enhanced layer is transferred over broadband network. If the receiver's display has HDresolution, it will drop the data of the first enhanced layer among data delivered over the broadcasting channel, and it does not need to have a connection with the server for the second enhanced layer, even if it can connect the networks. PI contains essential information, such as the content resolution, location of content, and MMT eXtension Document (MXD), and can also be transferred on broadcast paths. MXD is inserted in PI and mimics the MPD of DASH-SVC. MXD synchronizes the contents over heterogeneous networks, and organizes content synchronization information. The synchronization scheme is implemented at the receiver side. Receiver requests the segments that can deliver on time. For this target, the expected time to download each segment is computed based on bandwidth calculation and segment size information from MXD. This approach is not aware of video content and there is no scheduling strategy to manage the paths.