A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <s> This paper investigates mobile video delivery in a heterogeneous wireless network from a video server to a multi-homed client. Joint source-channel coding (JSCC) has proven to be an effective solution for video transmission over bandwidth-limited, error-prone wireless networks. However, one major problem with the existing JSCC approaches is that they consider the network between the server and the client as a single transport link. The situation becomes more complicated in the context of multiple available links because involving a low-bandwidth, highly lossy, or long-delay wireless network in the transmission will only degrade the video quality. To address the critical problem, we propose a novel flow rate allocation-based JSCC (FRA-JSCC) approach that includes three key phases: (1) forward error correction redundancy estimation under loss requirement, (2) source rate adaption under delay constraint, and (3) dynamic rate allocation to minimize end-to-end video distortion. We present a mathematical formulation of JSCC to optimize video quality over multiple wireless channels and provide comprehensive analysis for channel distortion. We evaluate the performance of FRA-JSCC through emulations in Exata and compare it with the existing schemes. Experimental results show that FRA-JSCC outperforms the competing models in improving the video peak signal-to-noise ratio as well as in reducing the end-to-end delay. <s> BIB001 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <s> Indoor positioning systems have received increasing attention for supporting location-based services in indoor environments. WiFi-based indoor localization has been attractive due to its open access and low cost properties. However, the distance estimation based on received signal strength indicator (RSSI) is easily affected by the temporal and spatial variance due to the multipath effect, which contributes to most of the estimation errors in current systems. In this work, we analyze this effect across the physical layer and account for the undesirable RSSI readings being reported. We explore the frequency diversity of the subcarriers in orthogonal frequency division multiplexing systems and propose a novel approach called FILA, which leverages the channel state information (CSI) to build a propagation model and a fingerprinting system at the receiver. We implement the FILA system on commercial 802.11 NICs, and then evaluate its performance in different typical indoor scenarios. The experimental results show that the accuracy and latency of distance calculation can be significantly enhanced by using CSI. Moreover, FILA can significantly improve the localization accuracy compared with the corresponding RSSI approach. <s> BIB002 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <s> Load distribution is a key research issue in deploying the limited network resources available to support traffic transmissions. Developing an effective solution is critical for enhancing traffic performance and network utilization. In this paper, we investigate the problem of load distribution for real-time traffic over multipath networks. Due to the path diversity and unreliability in heterogeneous overlay networks, large end-to-end delay and consecutive packet losses can significantly degrade the traffic flow’s goodput , whereas existing studies mainly focus on the delay or throughput performance. To address the challenging problems, we propose a G oodput- A ware L oad distribu T i ON (GALTON) model that includes three phases: (1) path status estimation to accurately sense the quality of each transport link, (2) flow rate assignment to optimize the aggregate goodput of input traffic, and (3) deadline-constrained packet interleaving to mitigate consecutive losses. We present a mathematical formulation for multipath load distribution and derive the solution based on utility theory. The performance of the proposed model is evaluated through semi-physical emulations in Exata involving both real Internet traffic traces and H.264 video streaming. Experimental results show that GALTON outperforms existing traffic distribution models in terms of goodput, video Peak Signal-to-Noise Ratio (PSNR), end-to-end delay, and aggregate loss rate. <s> BIB003 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <s> The growing availability of various wireless access technologies promotes increasing demand for mobile video applications. Stream control transmission protocol (SCTP)-based concurrent multipath transfer (CMT) improves the wireless video delivery performance with its parallel transmission and bandwidth (BW) aggregation features. However, the existing CMT solutions deployed at the transport layer only are not accurate enough due to lower layer uncertainties, such as variations of the wireless channel. In addition, CMT-based video transmission may use excessive BW in comparison with the popular Transmission Control Protocol (TCP)-based flows, which results in unfair sharing of network resources. This paper proposes a novel cross-layer fairness-driven (CL/FD) SCTP-based CMT solution (CMT-CL/FD) to improve video delivery performance, while remaining fair to the competing TCP flows. CMT-CL/FD utilizes a cross-layer approach to monitor and analyze path quality, which includes wireless channel measurements at the data-link layer and rate/BW estimations at the transport layer. Furthermore, an innovative window-based mechanism is applied for flow control to balance delivery fairness and efficiency. Finally, CMT-CL/FD intelligently distributes video data over different paths depending on their estimated quality to mitigate packet reordering and loss, under the constraint of TCP-friendly flow control. Simulation results show how CMT-CL/FD outperforms existing solutions in terms of both video delivery performance and TCP-friendliness. <s> BIB004 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <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> BIB005 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <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> BIB006 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <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> BIB007 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <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> BIB008 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <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> BIB009 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> D. Cross Layer Approaches <s> This document describes, surveys, and classifies the protocol ::: mechanisms provided by existing IETF protocols, as background for ::: determining a common set of transport services. It examines the ::: Transmission Control Protocol (TCP), Multipath TCP, the Stream Control ::: Transmission Protocol (SCTP), the User Datagram Protocol (UDP), UDP- ::: Lite, the Datagram Congestion Control Protocol (DCCP), the Internet ::: Control Message Protocol (ICMP), the Real-Time Transport Protocol ::: (RTP), File Delivery over Unidirectional Transport / Asynchronous ::: Layered Coding (FLUTE/ALC) for Reliable Multicast, NACK- Oriented ::: Reliable Multicast (NORM), Transport Layer Security (TLS), Datagram ::: TLS (DTLS), and the Hypertext Transport Protocol (HTTP), when HTTP is ::: used as a pseudotransport. This survey provides background for the ::: definition of transport services within the TAPS working group. <s> BIB010
Although it is possible to estimate throughput or bandwidth and other network parameters at the application layer, they are not as accurate as the transport or network layer measurements. Different layers have different knowledge levels. For instance, the application layer is aware of video features, player buffer and deadlines. The transport layer is able to calculate the bandwidth and RTT, and it also has a congestion control mechanism. The network layer accesses IP level and routing paths, and the link layer has wireless parameter access. Therefore, the interaction between different layers has the benefit of utilizing the advantages of different layers by signaling messages among them. This interaction is known as cross layer and was epitomized in the Transport Services (TAPS) working group by IETF BIB010 . Mostly, lower layers gather network information and feed them to higher layers BIB005 . In cross layer approaches, usually application layer or transport layer becomes the main layer. The main layer could decide a path for data transferring and manage load balancing or apply a method to save energy. The main layer could even change other layers behaviors. For example, application layer could change the TCP window size in order to control throughput, modifies routing tables, disconnect and reconnect the interfaces to manage failure or energy saving BIB005 . Therefore, we categorize our surveyed works into two groups: decision by application layer, and decision by transport layer, depending on which layer can be considered the main one, as discussed further in this subsection and summarized in Table III . 1) Application Layer Decision: Corbillon et al. BIB006 proposed a cross layer approach with interaction between application and transport layer. In this approach, an adaptive mechanism is used to select the segments on application layer and MPTCP is used as transport protocol. The main goal of this approach is to maximize the amount of data that is received on time to destination. Therefore, it utilizes the benefit of being application aware to estimate playback deadline and it only sends the video units that have chance to arrive in time. As there is no cross layer feedback available in MPTCP, it is assumed that such a feedback exists and can be used. The feedback should indicate which path should be selected by MPTCP to send the next packet and only after that the cross layer scheduler would give MPTCP the data to send on this selected path (only one packet at a time). Therefore, the scheduler, which is content-aware, can decide if and when a video unit is given to the transport layer. Ojanpera et al. BIB007 proposed a cross layer approach with interaction between application and network layer. The goal of this approach is to improve quality and availability of video streaming. The approach utilizes DASH to provide transparently bit rate adaptation support and MPTCP with default settings (coupled congestion control and default scheduling strategy) to provide multipath transmission capability. As explained in Section IV-A2, rate adaptation method available in DASH system could perform more efficiently if it could access accurate network information. Therefore, in this work, a network management system, built upon the Distributed Decision Engine (DDE) framework, is proposed. DDE provides network information, including QoS, load, and capacity. Consequently, the client is adjusted to support DDE in order to incorporate the gathered network information into the bit rate adaptation decision in order to cope with changes in the network available bandwidth. Then, the MPTCP scheduler on the server side is responsible for mapping data on the different paths. For achieving network load balancing, the operator network management (of DDE) can dynamically disable the access network for the client by DDE signaling. MPTCP reacts to the event by stopping the usage of the corresponding path and mapping the traffic to other available paths. Finally, the results of the work show that using more network information for client bit rate adaptation decision outperforms standalone throughput-based by improving the stability of the video. Wu et al. BIB003 developed a model, Goodput-Aware Load distribuTiON (GALTON), in application-network layer. GAL-TON optimizes the goodput performance of video streaming over multipath networks. Goodput is an application level throughput, a key parameter for video QoS and refers to the successfully received data at the receiver within the deadline. In GALTON, the receiver monitors network status (e.g., available bandwidth, RTT, PLR) and informs this information to the sender via feedback. The sender estimates the path quality based on the reported network information and detects congested paths by ZigZag scheme. There is also a proposed flow rate allocator which is responsible for partitioning flows to several subflows and assigning them to the available paths to optimize the aggregated goodput. It is also responsible for performing load balancing. Then, packets scheduled to the same path would be spread out within imposed deadline through the UDP connections. Besides that, scheduler adjusts probe rate and probing packet sizes dynamically over the congested paths. Wu et al. BIB001 proposed a flow rate allocation-based Joint Source and Channel Coding (FRA-JSCC) approach in an application-physical layer. Joint Source and Channel Coding (JSCC) is an efficient solution for improving error-resilient in wireless video transmission. Therefore, in this work, JSCC is optimized to a FRA-JSCC for mobile video broadcasting in multipath networks. In FRA-JSCC approach, three main methods are proposed. First, FEC redundancy estimation to protect video data against channel losses. Second, source rate adaptation based on the calculated encoding rate. The encoding rate is concerned because high encoding rate makes more channel distortion and imposes high delay due to heavier load and network congestion. On the other hand, low encoding rate cannot provide the video delay requirements. Third, flow rate allocation is responsible to dynamically select the appropriate paths out of all available access networks and assign the transmission rates to them based on Weighted Round Robin (WRR) scheduling strategy. 2) Transport Layer Decision: Han et al. BIB008 proposed MP-DASH framework, with overall goal of enhancing MPTCP to support adaptive video streaming (DASH) under userspecified interface preferences. For this goal, MP-DASH is designed as a cross layer approach with interaction between application and transport layer. In order to implement MP-DASH two components are designed: MP-DASH scheduler, and MP-DASH video adapter, as shown in Figure 12 . MP-DASH scheduler is implemented with MPTCP scheduler with knowledge of network interface preferences from the user and aggregated throughput. MP-DASH video adapter component, which is a lightweight add-on, is implemented to integrate the MP-DASH scheduler with DASH rate adaptation. Video adapter exchanges information between video player and MP-DASH scheduler (segment sizes and deadlines from video player to MP-DASH scheduler, and throughput from MP-DASH scheduler to the video player). This way, DASH algorithms becomes multipath friendly and MP-DASH scheduler becomes aware of delivery deadline. Besides that, MP-DASH splits the MP-DASH scheduling functions into two parts: decision function on the client, and enforcement function on the server. Decision function determines how to manage paths based on information from video player (e.g., segment sizes and deadlines), and enforcement function operates the decisions. The knowledge of network interface preferences is used to reduce cellular data usage while maintaining video QoE. Therefore, the approach starts data transferring with WiFi link and checks WiFi throughput dynamically to see if it is sufficient. If WiFi cannot deliver data before deadline time, the cellular network should be enabled. The results of the work show cellular usage reduced up to 99%, and radio energy consumption reduced up to 85% compared with the default MPTCP. The work in BIB009 proposed a dynamic MPTCP path control using Software-Defined Networking (SDN) (which makes cross layer approach of transport and network layer). The goal of the approach is to cope with out-of-order delivered packets to speed up download rate and improve video QoE in ABR streaming. In this work, the authors show the feasibility of using SDN platform regarding MPTCP. The SDN controller monitors information and estimates path capacity. Then, the SDN controller communicates periodically with the SDN clients to inform which paths are the best. The SDN platform on the client side removes poor and low capacity links because poor links increase the MPTCP reordering queue size. The removed paths attach again when they return to the proper capacity. Throughput measurement is used to find the available path capacity. It also may consider other multiple factors, such as RTT and delay to compute the best paths depending on the applications (e.g., video, VoIP or web surfing). Therefore, SDN application dynamically selects the proper paths and adjusts the number of paths in real-time. The evaluation shows that dynamically switch between MPTCP and SPTCP increases download time. In addition, the results of DASH implementation over the proposed dynamic MPTCP path control shows less bit rate change and rebuffering than without dynamic MPTCP path control. Cross-layer fairness-driven SCTP-based CMT solution (CMT-CL/FD) approach BIB004 is a path quality-aware approach over CMT. In CMT-CL/FD, cross layer evaluates path quality by using loss rate information in effective signal-tonoise ratio (ESNR) (which is calculated at the link layer), and bandwidth or transmission rate information (which are estimated at the transport layer). ESNR is an upgrade calculation for signal-to-noise ratio/noise ratio (SNR) to evaluate wireless communication quality because the default SNR method has some shortcomings. For example, SNR is not accurate in realtime communication, and is not able to capture co-channel interference, frequency-selective fading and signal multipath effects BIB002 . Then, CMT-CL/FD distributes data intelligently over different paths depending on their estimated quality. A loss-cause dependent retransmission (RTX) policy is also introduced to distinguish wireless loss from congestion loss. Consequently, in case of congested network, cwnd is changed and retransmission occurs (as explained in Section IV-B5). Finally, this proposed approach mitigates reordering, losses, and consequently decreases HOL problem. However, none of these works use video content features for the scheduling strategy.