A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Video communication over lossy packet networks such as the Internet is hampered by limited bandwidth and packet loss. This paper presents a system for providing reliable video communication over these networks, where the system is composed of two subsystems: (1) multiple state video encoder/decoder and (2) a path diversity transmission system. Multiple state video coding combats the problem of error propagation at the decoder by coding the video into multiple independently decodable streams, each with its own prediction process and state. If one stream is lost the other streams can still be decoded to produce usable video, and furthermore, the correctly received streams provide bidirectional (previous and future) information that enables improved state recovery for the corrupted stream. This video coder is a form of multiple description coding (MDC), and its novelty lies in its use of information from the multiple streams to perform state recovery at the decoder. The path diversity transmission system explicitly sends different subsets of packets over different paths, as opposed to the default scenarios where the packets proceed along a single path, thereby enabling the end- to-end video application to effectively see an average path behavior. We refer to this as path diversity. Generally, seeing this average path behavior provides better performance than seeing the behavior of any individual random path. For example, the probability that all of the multiple paths are simultaneously congested is much less than the probability that a single path is congested. The resulting path diversity provides the multiple state video decoder with an appropriate virtual channel to assist in recovering from lost packets, and can also simplify system design, e.g. FEC design. We propose two architectures for achieving path diversity, and examine the effectiveness of path diversity in communicating video over a lossy packet network. <s> BIB001 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Wireless link losses result in poor TCP throughput since losses are perceived as congestion by TCP, resulting in source throttling. In order to mitigate this effect, 3G wireless link designers have augmented their system with extensive local retransmission mechanisms. In addition, in order to increase throughput, intelligent channel state based scheduling have also been introduced. While these mechanisms have reduced the impact of losses on TCP throughput and improved the channel utilization, these gains have come at the expense of increased delay and rate variability. In this paper, we comprehensively evaluate the impact of variable rate and variable delay on long-lived TCP performance. We propose a model to explain and predict TCP's throughput over a link with variable rate and/or delay. We also propose a network-based solution called Ack Regulator that mitigates the effect of variable rate and/or delay without significantly increasing the round trip time, while improving TCP performance by up to 40%. <s> BIB002 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Multipath streaming protocols have recently attracted much attention because they provide an effective means to provide high-quality streaming over the Internet. However, many existing schemes require a long start-up delay and thus are not suitable for interactive applications such as video conferencing and tele-presence. In this paper, we focus on real-time live streaming applications with stringent end-to-end latency requirement, say several hundreds of milliseconds. To address these challenges, we take a joint multipath and FEC approach that intelligently splits the FEC-encoded stream among multiple available paths. We develop an analytical model and use asymptotic analysis to derive closed-form, optimal load splitting solutions, which are surprisingly simple yet insightful. To our best knowledge, this is the first work that provides such closed-form optimal solutions. Based on the analytical insights, we have designed and implemented a novel Encoded Multipath Streaming (EMS) scheme for real-time live streaming. EMS strives to continuously satisfy the application's QoS requirements by dynamically adjusting the load splitting decisions and the FEC settings. Our simulation results have shown that EMS can not only outperform the existing multipath streaming schemes, but also adapt to the dynamic loss and delay characteristics of the network with minimal overhead. <s> BIB003 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> TCP has traditionally been considered inappropriate for real-time applications. Nonetheless, popular applications such as Skype use TCP since UDP packets cannot pass through restrictive network address translators (NATs) and firewalls. Motivated by this observation, we study the delay performance of TCP for real-time media flows. We develop an analytical performance model for the delay of TCP. We use extensive experiments to validate the model and to evaluate the impact of various TCP mechanisms on its delay performance. Based on our results, we derive the working region for VoIP and live video streaming applications and provide guidelines for delay-friendly TCP settings. Our research indicates that simple application-level schemes, such as packet splitting and parallel connections, can reduce the delay of real-time TCP flows by as much as 30% and 90%, respectively. <s> BIB004 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> In this paper, we propose an effective end-to-end virtual path construction system, which exploits path diversity over heterogeneous wireless networks. The goal of the proposed system is to provide a high quality live video streaming service over heterogeneous wireless networks. First, we propose a packetization-aware fountain code to integrate multiple physical paths efficiently and increase the fountain decoding probability over wireless packet switching networks. Second, we present a simple but effective physical path selection algorithm to maximize the effective video encoding rate while satisfying delay and fountain decoding failure rate constraints. The proposed system is fully implemented in software and examined over real WLAN and HSDPA networks. <s> BIB005 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Poor connectivity is common when we use wireless networks on the go. A natural way to tackle the problem is to take advantage of the multiple network interfaces on our mobile devices, and use all the networks around us. Using multiple networks at a time makes makes possible faster connections, seamless connectivity and potentially lower usage charges. The goal of this paper is to explore how to make use of all the networks with today's technology. Specifically, we prototyped a solution on an Android phone. Using our prototype, we demonstrate the benefits (and difficulties) of using multiple networks at the same time. <s> BIB006 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Although wireless broadband technologies have evolved significantly over the past decade, they are still insufficient to support the fast-growing mobile traffic, especially due to the increasing popularity of mobile video applications. Wireless multicast, aiming to exploit the wireless broadcast advantage, is a viable approach to bridge the gap between the limited wireless networking capacity and the ever-increasing mobile video traffic demand. In this work, we propose MuVi, a Multicast Video delivery scheme in OFDMA-based 4G wireless networks, to optimize multicast video traffic. MuVi differentiates video frames based on their importance in reconstructing the video and incorporates an efficient radio resource allocation algorithm to optimize the overall video quality across all users in the multicast group. MuVi is a lightweight solution with most of the implementation in the gateway, slight modification in the base-station, and no modification at the clients. We implement MuVi on a WiMAX testbed and compare its performance to a Naive wireless multicast scheme that employs the most robust MCS (Modulation and Coding Scheme), and an Adaptive scheme that employs the highest MCS supportable by all clients. Experimental results show that MuVi improves the average video PSNR (Peak Signal-to-Noise Ratio) by up to 13 and 7 dB compared to the Naive and the Adaptive schemes, respectively. MuVi does not require modification to the video encoding scheme or the air interface. Thus it allows speedy deployment in existing systems. <s> BIB007 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> CH1: MULTIMEDIA NETWORKING AND COMMUNICATION / CH2: ERROR RESILIENT VIDEO / CH3: ERROR RESILIENT AUDIO / CH4: BANDWIDTH ADAPTATION MECHANISMS / CH5: SCALABLE VIDEO CODING FOR ADAPTIVE STREAMING APPLICATIONS / CH6: SCALABLE AUDIO CODING / CH7: CHANNEL PROTECTION FUNDAMENTALS / CH8: CHANNEL MODELING AND ANALYSIS FOR THE INTERNET / CH9: FORWARD ERROR CONTROL / CH10: NETWORK-ADAPTIVE MEDIA TRANSPORT / CH11: MAC-LAYER WIRELESS CHANNEL MODELS / CH12: CROSS-LAYER WIRELESS MULTIMEDIA / CH13: QOS SUPPORT IN WIRELESS ENVIRONMENTS / CH14: STREAMING MEDIA ON DEMAND / CH15: REAL TIME COMMUNICATION / CH16: ADAPTIVE MEDIA PLAYOUT / CH17: PATH DIVERSITY / CH18: DISTRIBUTED VIDEO CODING AND APPLICATIONS / CH19: MEDIA OVERLAYS <s> BIB008 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Modern mobile devices are equipped with multiple network interfaces, including 3G/LTE and WiFi. Bandwidth aggregation over LTE and WiFi links offers an attractive opportunity of supporting bandwidth-intensive services, such as high-quality video streaming, on mobile devices. However, achieving effective bandwidth aggregation in mobile environments raises several challenges related to deployment, link heterogeneity, network fluctuation, and energy consumption. We present GreenBag, an energy-efficient bandwidth aggregation middleware that supports real-time data-streaming services over asymmetric wireless links, requiring no modifications to the existing Internet infrastructure and servers. GreenBag employs several techniques, including medium load balancing, efficient segment management, and energy-aware mode control, to resolve such challenges. We implement a prototype of GreenBag on Android-based mobile devices which hosts, to the best knowledge of the authors, the first LTE-enabled bandwidth aggregation prototype for energy-efficient real-time video streaming. Our experiment results in both emulated and real-world environments show that GreenBag not only achieves good bandwidth aggregation to provide QoS in bandwidth-scarce environments but also efficiently saves energy on mobile devices. Moreover, energy-aware GreenBag can minimize video interruption while consuming 14-25% less energy than the non-energy-aware counterpart in real-world experiments. <s> BIB009 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> With the popularity of mobile devices and the pervasive use of cellular technology, there is widespread interest in hybrid networks and on how to achieve robustness and good performance from them. As most smart phones and mobile devices are equipped with dual interfaces (WiFi and 3G/4G), a promising approach is through the use of multi-path TCP, which leverages path diversity to improve performance and provide robust data transfers. In this paper we explore the performance of multi-path TCP in the wild, focusing on simple 2-path multi-path TCP scenarios. We seek to answer the following questions: How much can a user benefit from using multi-path TCP over cellular and WiFi relative to using the either interface alone? What is the impact of flow size on average latency? What is the effect of the rate/route control algorithm on performance? We are especially interested in understanding how application level performance is affected when path characteristics (e.g., round trip times and loss rates) are diverse. We address these questions by conducting measurements using one commercial Internet service provider and three major cellular carriers in the US. <s> BIB010 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Mobile devices equipped with multiple network interfaces can increase their throughput by making use of parallel transmissions over multiple paths and bandwidth aggregation, enabled by the stream control transport protocol (SCTP). However, the different bandwidth and delay of the multiple paths will determine data to be received out of order and in the absence of related mechanisms to correct this, serious application-level performance degradations will occur. This paper proposes a novel quality-aware adaptive concurrent multipath transfer solution (CMT-QA) that utilizes SCTP for FTP-like data transmission and real-time video delivery in wireless heterogeneous networks. CMT-QA monitors and analyses regularly each path's data handling capability and makes data delivery adaptation decisions to select the qualified paths for concurrent data transfer. CMT-QA includes a series of mechanisms to distribute data chunks over multiple paths intelligently and control the data traffic rate of each path independently. CMT-QA's goal is to mitigate the out-of-order data reception by reducing the reordering delay and unnecessary fast retransmissions. CMT-QA can effectively differentiate between different types of packet loss to avoid unreasonable congestion window adjustments for retransmissions. Simulations show how CMT-QA outperforms existing solutions in terms of performance and quality of service. <s> BIB011 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> With the move towards converged all-IP wireless network environments, managing end-user Quality of Experience (QoE) poses a challenging task, aimed at meeting high user expectations and requirements regarding reliable and cost-effective communication, access to any service, anytime and anywhere, and across multiple operator domains. In this paper, we give a survey of state-of-the-art research activities addressing the field of QoE management, focusing in particular on the domain of wireless networks and addressing three management aspects: QoE modeling, monitoring and measurement, and adaptation and optimization. Furthermore, we identify and discuss the key aspects and challenges that need to be considered when conducting research in this area. <s> BIB012 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Today, most of the smart phones are equipped with two network interfaces: Mobile Broadband (MBB) and Wireless Local Area Network (WLAN). Multi-path transport protocols provide increased throughput or reliability, by utilizing these interfaces simultaneously. However, multi-path transmission over networks with very different QoS characteristics is a challenge. In this paper, we studied Multi-Path TCP (MPTCP) in heterogeneous networks, specifically MBB networks and WLAN. We first investigate the effect of bufferbloat in MBB on MPTCP performance. Then, we propose a bufferbloat mitigation algorithm: Multi-Path Transport Bufferbloat Mitigation (MPT-BM). Using our algorithm, we conduct experiments in real operational networks. The experimental results show that MPT-BM outperforms the current MPTCP implementation by increasing the application goodput quality and decreasing MPTCP's buffer delay, jitter and buffer space requirements. <s> BIB013 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> With the rapid deployment of cellular net- works, modern mobile devices are now equipped with at least two interfaces (WiFi and 3G/4G). As multi-path TCP (MPTCP) has been standardized by the IETF, mobile users running MPTCP can access the Internet via multiple interfaces simultaneously to provide robust data transport and better throughput. However, as cellular networks exhibit large RTTs compared to WiFi, for small data transfers, the delayed startup of additional flows in the current MPTCP design can limit the use of MPTCP. For large data transfers, when exploiting both the WiFi and cellular networks, the inflated and varying RTTs of the cellular flow together with the small and stable RTTs of the WiFi flow can lead to performance degradation. In this paper, we seek to investigate the causes of MPTCP performance issues in wireless environments and will provide analyses and a solution for better performance. In this paper, we study two issues: the impact of the delay startup of additional flows in the current MPTCP design, and the effect of cellular bufferbloat on MPTCP performance. Since Internet traffic is mostly dominated by small downloads (although the tail dis- tributions might be skewed), the delayed startup of additional flows in the current MPTCP implementation can limit the benefits of using MPTCP for small file transfers. To understand when one can start to utilize MPTCP's additional flows, we model the amount of data received from the first flow before the second flow starts and validate the model through measurements. Furthermore, as we observe large and varying RTTs in cellular networks, referred to as bufferbloat, we model and analyze the root cause of this phenomenon. We show how bufferbloat can affect the performance of MPTCP when using both WiFi and cellular networks. Last, we show that, on occasions when bufferbloat is prominent, MPTCP suffers even more because of flow starvation. We provide a solution that can effectively mitigate this performance degradation. The remainder of this paper is organized as follows: Sec. II provides background about MPTCP and Sec. III describes our experimental setup. Sec. IV models the impact of the delayed startup of additional MPTCP flows. We investigate MPTCP performance issues re- lated to cellular networks in Sec. V. Related works are discussed in Sec. VI and Sec. VII concludes this paper. <s> BIB014 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> The Internet is inherently a multipath network: For an underlying network with only a single path, connecting various nodes would have been debilitatingly fragile. Unfortunately, traditional Internet technologies have been designed around the restrictive assumption of a single working path between a source and a destination. The lack of native multipath support constrains network performance even as the underlying network is richly connected and has redundant multiple paths. Computer networks can exploit the power of multiplicity, through which a diverse collection of paths is resource pooled as a single resource, to unlock the inherent redundancy of the Internet. This opens up a new vista of opportunities, promising increased throughput (through concurrent usage of multiple paths) and increased reliability and fault tolerance (through the use of multiple paths in backup/redundant arrangements). There are many emerging trends in networking that signify that the Internet's future will be multipath, including the use of multipath technology in data center computing; the ready availability of multiple heterogeneous radio interfaces in wireless (such as Wi-Fi and cellular) in wireless devices; ubiquity of mobile devices that are multihomed with heterogeneous access networks; and the development and standardization of multipath transport protocols such as multipath TCP. The aim of this paper is to provide a comprehensive survey of the literature on network-layer multipath solutions. We will present a detailed investigation of two important design issues, namely, the control plane problem of how to compute and select the routes and the data plane problem of how to split the flow on the computed paths. The main contribution of this paper is a systematic articulation of the main design issues in network-layer multipath routing along with a broad-ranging survey of the vast literature on network-layer multipathing. We also highlight open issues and identify directions for future work. <s> BIB015 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Utilizing the dormant path diversity through multipath routing in the Internet to reach end users—thereby fulfilling their QoS requirements—is rather logical. While offering better resource utilization, better reliability, and often even much better quality of experience (QoE), multipath routing and provisioning was shown to help network and data center operators achieve traffic engineering in the form of load balancing. In this survey, we first highlight the benefits and basic Internet multipath routing components. We take a top-down approach and review various multipath protocols, from application to link and physical layers, operating at different parts of the Internet. We also describe the mathematical foundations of the multipath operation, as well as highlight the issues and challenges pertaining to reliable data delivery, buffering, and security in deploying multipath provisioning in the Internet. We compare the benefits and drawbacks of these protocols operating at different Internet layers and discuss open issues and challenges. <s> BIB016 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <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> BIB017 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <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> BIB018 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> In order to improve the Quality-of-Service (QoS) of latency sensitive applications in next-generation cellular networks, multi-path is adopted to transmit packet stream in real-time to achieve high-quality video transmission in heterogeneous wireless networks. However, multi-path also introduces two important challenges: out-of-order issue and reordering delay. In this paper, we propose a new architecture based on Software Defined Network (SDN) for flow aggregation and flow splitting, and then design a Multiple Access Radio Scheduling (MARS) scheme based on relative Round-Trip Time (RTT) measurement. The QoS metrics including end-to-end delay, throughput and the packet out-of-order problem at the receiver have been investigated using the extensive simulation experiments. The performance results show that this SDN architecture coupled with the proposed MARS scheme can reduce the end-to-end delay and the reordering delay time caused by packet out-of-order as well as achieve a better throughput than the existing SMOS and Round-Robin algorithms. <s> BIB019 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> Recent technological advancements in wireless infrastructures and handheld devices enable mobile users to concurrently receive multimedia contents with different radio interfaces (e.g., cellular and Wi-Fi). However, multipath video transport over the resource-limited and error-prone wireless networks is challenged with key technical issues: 1) conventional multipath protocols are throughput-oriented, and video data are scheduled in a content-agnostic fashion and 2) high-quality real-time video is bandwidth-intensive and delay-sensitive. To address these critical problems, this paper proposes a bandwidth-efficient multipath streaming (BEMA) protocol featured by the priority-aware data scheduling and forward error correction-based reliable transmission. First, we present a mathematical framework to formulate the delay-constrained distortion minimization problem for concurrent video transmission over multiple wireless access networks. Second, we develop a joint Raptor coding and data distribution framework to achieve target video quality with minimum bandwidth consumption. The proposed BEMA is able to effectively mitigate packet reordering and path asymmetry to improve network utilization. We conduct performance evaluation through extensive emulations in Exata involving real-time H.264 video streaming. Compared with the existing multipath protocols, BEMA achieves appreciable improvements in terms of video peak signal-to-noise ratio, end-to-end delay, bandwidth utilization, and goodput. Therefore, BEMA is recommended for streaming high-quality real-time video to multihomed terminals in heterogeneous wireless networks. <s> BIB020 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <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> BIB021 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> The increasing popularity of live video streaming from mobile devices, such as Facebook Live, Instagram Stories, Snapchat, etc. pressurizes the network operators to increase the capacity of their networks. However, a simple increase in system capacity will not be enough without considering the provisioning of quality of experience (QoE) as the basis for network control, customer loyalty, and retention rate and thus increase in network operators revenue. As QoE is gaining strong momentum especially with increasing users’ quality expectations, the focus is now on proposing innovative solutions to enable QoE when delivering video content over heterogeneous wireless networks. In this context, this paper presents an overview of multimedia delivery solutions, identifies the problems and provides a comprehensive classification of related state-of-the-art approaches following three key directions: 1) adaptation; 2) energy efficiency; and 3) multipath content delivery. Discussions, challenges, and open issues on the seamless multimedia provisioning faced by the current and next generation of wireless networks are also provided. <s> BIB022 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> III. BENEFITS AND CHALLENGES OF MULTIPATH VIDEO TRANSMISSION OVER WIRELESS <s> As video traffic dominates the Internet, it is important for operators to detect video Quality of Experience (QoE) in order to ensure adequate support for video traffic. With wide deployment of end-to-end encryption, traditional deep packet inspection based traffic monitoring approaches are becoming ineffective. This poses a challenge for network operators to monitor user QoE and improve upon their experience. To resolve this issue, we develop and present a system for REal-time QUality of experience metric detection for Encrypted Traffic, Requet. Requet uses a detection algorithm we develop to identify video and audio chunks from the IP headers of encrypted traffic. Features extracted from the chunk statistics are used as input to a Machine Learning (ML) algorithm to predict QoE metrics, specifically, buffer warning (low buffer, high buffer), video state (buffer increase, buffer decay, steady, stall), and video resolution. We collect a large YouTube dataset consisting of diverse video assets delivered over various WiFi network conditions to evaluate the performance. We compare Requet with a baseline system based on previous work and show that Requet outperforms the baseline system in accuracy of predicting buffer low warning, video state, and video resolution by 1.12X, 1.53X, and 3.14X, respectively. <s> BIB023
As previously stated, providing high/optimal QoE for the final user in the wireless video streaming scenario requires high bandwidth and low transmission delay. This is a challenging task, considering the several aspects involved in wireless transmission, such as bandwidth constraints, lossy wireless channels, delay, lack of coverage and congested networks. Adding multipath transmission ability can help with this challenge and its benefits can be summarized as: • Reliability and seamless connectivity: using multipath allows the user to simultaneously utilize multiple available network connections. A better coverage is achieved and the probability of keeping an end-to-end connection alive is increased. In the case of failure or congestion in one network path, multipathing provides a resilient alternative, resulting in improved user video experience; • Throughput increase: by aggregating bandwidth and distributing video traffic over multiple network paths, faster transmission can be achieved, which is essential for real-time video streaming applications BIB006 ; • Load balancing: refers to efficiently distribute video traffic through the available network paths in order to relieve congestion BIB015 . Load balancing improves stability by achieving lower variability and inter-packet delay (jitter); • Reduction of burst loss length: burst loss length refers to the continuous packet losses which is harmful to perceived video streaming quality BIB001 . This is because decoder can recover the loss of a small number of video packets by exploiting correlations in the previously received video sequence to conceal the lost information. However, the effectiveness of this recovery decreases dramatically in case of losing large number of continuous video packets. Using multipath streaming benefits to convert burst losses to isolated losses, and consequently, probability of recovering lost packets would be increased. • Delay decrease: Using multiple paths contributes to having video data ready at the receiver faster, thus, decreasing the effective delay especially from an applicaiton perspective. Probing multiples paths enables to get the data from the lowest delay path, reducing the Time To First Byte (TTFB), i.e., the time between the video request being sent and the first packet received after the request BIB023 . • Security: video split over multiple paths improves protection to some security threats BIB016 once that each network path only carries parts of the whole video stream. Fortunately, with recent development, many of current devices [69] ,  are already equipped with both cellular and WiFi interfaces. Multiple interface devices, which could be equipped with two or more than two interfaces, having the ability to connect simultaneously to multiple network paths are known as multihomed devices, as illustrated in Figure 3 . Multihomed devices can utilize multipath communication by aggregating the available bandwidth from multiple Radio Access Technologies (RATs). With multiple interfaces, users can receive data through parallel paths with multiple IP addresses. Despite all of its benefits, attempting to deploy a multipath solution for video delivery can bring the following potential roadblocks from a practical perspective: Compatibility. Implementation of a general multipath solution usually requires changing one or both of server and client sides, modifying standardized protocols, improving operating systems kernel and/or changing third-party network equipment. Networks heterogeneity. Heterogeneous wireless networks vary based on different bandwidth constraints, delays, jitters and packet loss rates. These different physical properties cause asymmetric communication for video transmission, and consequently, may decrease the overall streaming quality. For instance, a large difference between LTE and WiFi bandwidth decreases the bandwidth aggregation performance BIB009 . Second and third generation (2G and 3G) of cellular networks do not provide enough bandwidth to support live video streaming due to high data rate BIB005 ,  , BIB010 . In addition, the retransmission mechanism in 3G BIB010 may increase the Round-Trip Time (RTT) and the rate variability. 4G LTE offers higher data transmission rate and signal coverage than 2G/3G BIB007 , BIB010 . When comparing 4G to WiFi, there relevant differences in terms of bandwidth, packet loss, and round-trip time can be observed BIB011 , BIB010 . These aspects, in addition to wireless losses being recognized as congestion by some protocols (e.g. TCP) resulting in decreased network throughput BIB002 , turn multipath communications over heterogeneous wireless networks a truly challenging task. Out-of-order packets. Spreading data over heterogeneous paths with different RTTs, throughput fluctuations, and jitter existence introduces the out-of-order packets problem. This phenomenon causes unnecessary packets retransmissions, wasted bandwidth, and consequently, network congestion. In addition, more time is required to recover the ordered data. A robust multipath transmission solution is required to cope with packet reordering in heterogeneous wireless networks BIB017 to avoid video quality degradation. Head-of-Line (HOL) blocking. When many packets are stored in the destination buffer waiting for delayed packets, the buffer may become full and blocked. This issue is referred as Head-of-Line blocking BIB018 , BIB013 . Generally, buffer blocking occurs with reliable protocols that guarantee inorder packet delivery, such as TCP, and it may become worse in case of multipath delivery. The Bufferbloat phenomenon is the main reason of HOL blocking, contributing to high latency, especially in 3G/4G cellular networks BIB014 , BIB013 . Bufferbloat occurs because of significantly large network buffers (e.g., large router queues) that avoid packet loss at the cost of adding high latencies under congestion. The problem can become worse in case of multipath delivery because if bufferbloat occurs in one of the paths, those packets arrive at the destination with high delay and out-of-order, resulting in HOL blocking. Consequently, HOL blocking not only increases End-to-End delay and jitter but successfully arrived packets may become obsolete (i.e. discarded) due to the long waiting time in the destination buffer. End-to-End delay. Real-time video streaming requires a bounded End-to-End delay BIB019 , which refers to the measured delay from the generation of a video frame to the moment when it can be decoded. End-to-End delay includes holding time of a video frame at both sender and receiver sides, and the transmission delay. It could also include the queuing delay, propagation delay, access delay, and reordering delay. The queuing delay refers to packet buffering in the sender, receiver and other nodes in the network during packet transmission. The transmission delay and radio access delay occur in the physical transmitter to map the data from packets to bits on physical radio interface's hardware. The distance between entities causes the propagation delay. The access points introduce transfer and propagation delay. In the case of video streaming on multipath networks, reordering delay can be increased BIB004 . Overdue packets. Video data packets arriving at the destination after decoding deadlines are expired and known as overdue packets. While overdue packets for UDP-like transmissions may cause video distortions (i.e., degradation of the visual video fidelity BIB021 ) similar to lost packets, in reliable transport protocols like TCP the effects surface as stalling (i.e., video freezes) or rebuffering. Avoiding stalls becomes most critical in live streaming scenarios. Thus, this kind of real-time applications, even when based on TCP-like solutions, consider the overdue packets as lost packets since they are discarded. This concept is called liveness BIB021 . Therefore, suitable multipath streaming strategies need to consider potential decoding deadlines of the receivers. Wrapping up the Challenges. Figure 4 aims at putting together all key issues and possible adverse effects of multipath wireless video streaming. The design of any multipath wireless video streaming solution, it is important to avoid or at least minimize such effects. In other words, optimization of QoS-related parameters leads to improved QoE BIB012 . QoS measurements may differ based on the type of video streaming service BIB008 , BIB021 such as VoD, live or real-time. VoD is a video streaming service which encoded media is pre-stored at the server, and the user can select and watch it at any time (e.g., Netflix movies). In contrast, in live and real-time video streaming services (e.g., live sport streaming, real-time video including interactive video call, gaming, etc.) the video content is not pre-stored/available when the streaming starts. In live streaming, the buffer is smaller compared to VoD streaming to avoid long delays and it also has stricter deadlines. Realtime video streaming has even shorter delay constraint. For example, according to  and BIB020 , a large delay of 5 seconds may be acceptable for VoD and around 1 second delay is acceptable for live streaming, but in order to achieve excellent real-time streaming quality, the solution should provide the End-to-End delay not exceed 150 ms. Besides, packet loss rates higher than 1% are not acceptable for live video streaming solutions  , BIB003 . In some applications with high scenes variability, such as football, it was reported  that subjects already become uncomfortable for packet loss rate slightly above 0.3%. Finally, meeting all QoS requirements does not necessarily guarantee high(est) user QoE. Devices' operating system, hardware, battery, operator pricing, light, people around the user and emotion are some examples of factors that impact the users experience BIB022 , BIB012 .