A Holistic Survey of Wireless Multipath Video Streaming <s> C. Video Compression and Error Concealment <s> This article provides an overview of H.263, the new ITU-T Recommendation for low-bit-rate video communication. H.263 specifies a coded representation for compressing the moving picture component of audio-visual signals at low bit rates. The basic structure of the video source coding algorithm is taken from ITU-T Recommendation H.261 and is a hybrid of interpicture prediction to reduce temporal redundancy and transform coding of the prediction residual to reduce spatial redundancy. The source coder can operate on five standardized picture formats: sub-QCIF, QCIF, CIF, 4CIF, and 16CIF. The decoder has motion compensation capability with half-pixel precision, in contrast to H.261 which uses full-pixel precision and employs a loop filter. H.263 includes four negotiable coding options which provide improved coding efficiency: unrestricted motion vectors, syntax-based arithmetic coding, advanced prediction, and PB-frames. <s> BIB001 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> C. Video Compression and Error Concealment <s> With the introduction of the H.264/AVC video coding standard, significant improvements have recently been demonstrated in video compression capability. The Joint Video Team of the ITU-T VCEG and the ISO/IEC MPEG has now also standardized a Scalable Video Coding (SVC) extension of the H.264/AVC standard. SVC enables the transmission and decoding of partial bit streams to provide video services with lower temporal or spatial resolutions or reduced fidelity while retaining a reconstruction quality that is high relative to the rate of the partial bit streams. Hence, SVC provides functionalities such as graceful degradation in lossy transmission environments as well as bit rate, format, and power adaptation. These functionalities provide enhancements to transmission and storage applications. SVC has achieved significant improvements in coding efficiency with an increased degree of supported scalability relative to the scalable profiles of prior video coding standards. This paper provides an overview of the basic concepts for extending H.264/AVC towards SVC. Moreover, the basic tools for providing temporal, spatial, and quality scalability are described in detail and experimentally analyzed regarding their efficiency and complexity. <s> BIB002 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> C. Video Compression and Error Concealment <s> We examine the visual effect of whole-frame loss by different decoders. Whole-frame losses are introduced in H.264/AVC compressed videos which are then decoded by two different decoders with different common concealment effects: frame copy and frame interpolation. The videos are seen by human observers who respond to each glitch they spot. We found that about 39% of whole-frame losses of B frames are not observed by any of the subjects, and over 58% of the B frame losses are observed by 20% or fewer of the subjects. Using simple predictive features that can be calculated inside a network node with no access to the original video and no pixel level reconstruction of the frame, we develop models that can predict the visibility of whole B frame losses. The models are then used in a router to predict the visual impact of a frame loss and perform intelligent frame dropping to relieve network congestion. Dropping frames based on their visual scores proves superior to random dropping of B frames. <s> BIB003 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> C. Video Compression and Error Concealment <s> As the density of wireless networks continues to grow with more clients, more base stations, and more traffic, designing cost-effective wireless solutions with efficient resource usage and ease to manage is an increasing challenging task due to the overall system complexity. A number of vendors offer scalable and high-performance wireless networks but at a high cost and commonly as a single-vendor solution, limiting the ability to innovate after roll-out. Recent Software-Defined Networking (SDN) approaches propose new means for network virtualization and programmability advancing the way networks can be designed and operated, including user-defined features and customized behaviour even at run-time. However, means for rapid prototyping and experimental evaluation of SDN for wireless environments are not yet available. This paper introduces Mininet-WiFi as a tool to emulate wireless OpenFlow/SDN scenarios allowing high-fidelity experiments that replicate real networking environments. Mininet-WiFi augments the well-known Mininet emulator with virtual wireless stations and access points while keeping the original SDN capabilities and the lightweight virtualization software architecture. We elaborate on the potential applications of Mininet-Wifi and discuss the benefits and current limitations. Two use cases based on IEEE 802.11 demonstrate available functionality in our open source developments. <s> BIB004 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> C. Video Compression and Error Concealment <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> BIB005
Several video codecs were used in the surveyed works cited in Table IX , such as H.263 BIB001 , H.264/AVC  , H.264/SVC BIB002 , HEVC  , and SHVC  . After video transmission, if protection methods are not able to recover the lost packets, the decoder itself can employ error concealment. This way, decoder exploits correlations in the previously received video sequence to conceal the lost information. JM, for instance, performs frame copy while FFmpeg performs Real-time temporal interpolation. According to BIB003 , in case of whole-frame losses, when isolated B-frames were lost and concealed by either JM or FFmpeg, about 40% of the losses were not even noticed by observers. Our surveyed works used JM  , x264 [225], JSVM  , FFmpeg  , HM  for error concealment. Table IX shows that experimental evaluation is mostly dominated by network simulators, such as OPNET  , NS2 [230] , NS3 [231] , EXata  , NetEm  ,  . Only few works, mainly due to costs, scale, and scope, carried their evaluation on real testbeds. Wireless-enabled network emulators like Mininet-WiFi BIB004 are also another category of experimental environments. We also cover some additional implementation details. For example, which type of network interfaces are used in experiments, or if the simulation uses disjoint paths (no common link or node). Using disjoint paths improves bandwidth aggregation and has the benefit of additional fault-tolerance compared with non-disjoint paths BIB005 , altogether contributing to the users video experience.