Robert Kuschnig

An evaluation of TCP-based rate-control algorithms for adaptive internet streaming of H.264/SVC

Recent work in TCP video streaming indicates that multimedia streaming via TCP provides satisfactory performance when the achievable TCP throughput is approximately twice the media bit rate. However, these conditions may not be achievable on the Internet, e.g., when the delivery path offers insufficient bandwidth or becomes congested due to competing traffic. Therefore, adaptive streaming for videos over TCP is required and a number of rate-control algorithms for video streaming have been proposed and evaluated in the literature.\\ In this paper, we evaluate and compare three existing rate-control algorithms for TCP streaming in terms of the (PSNR) quality of the delivered video and in terms of the timeliness of delivery. The contribution of the paper is that, to the best of our knowledge, this is the first evaluation of TCP-based streaming in an Internet-like setting making use of the scalability features of the H.264/SVC video codec. Two simple bandwidth estimation algorithms and a priority-/deadline-driven approach are described to adapt the bit rates of, and transmit, the H.264/SVC video in a rate-distortion optimal manner. The results indicate that the three algorithms perform robustly in terms of video quality and timely delivery, both on under-provisioned links and in case of competing TCP flows. The priority-/deadline-driven technique is even more stable in terms of packet delays and jitter; thus, client buffers can be dimensioned more easily.

Improving Internet Video Streaming Performance by Parallel TCP-Based Request-Response Streams

TCP-based video streaming encounters difficulties in unreliable networks with unanticipated packet loss. In combination with high round trip times, the effective throughput deteriorates rapidly and TCP connection resets or stalls may occur. In this paper, we propose a client-driven video transmission scheme which utilizes multiple HTTP/TCP streams. The scheme is largely insensitive to unanticipated packet loss and thereby reduces throughput fluctuations. Since it is based on HTTP, the scheme can easily be deployed in existing network infrastructures. It fosters scalability on the server side by shifting complexity from the server to the clients. Certain features of request-response schemes allow maintaining fairness, despite of using multiple HTTP streams. Making use of TCP, the scheme inherently adapts to congested network links.

Evaluation of HTTP-based request-response streams for internet video streaming

Adaptive video streaming based on TCP/HTTP is becoming popular because of its ability to adapt to changing network conditions. We present an in-depth experimental analysis of the use of HTTP-based request-response streams for video streaming. In this scheme, video fragments are fetched by a client from the server, in smaller units called chunks, potentially via multiple parallel HTT P requests (TCP connections). A model for the achievable throughput is formulated.The model is validated by a broad range of streaming experiments, including an evaluation of TCP-friendliness. Our findings include that request-response streams are able to scale with the available bandwidth by increasing the chunk size or the number of concurrent streams. Several combinations of system parameters exhibiting TCP-friendliness are presented. We also evaluate the video streaming performance in terms of video quality in the presence of packet loss. Multiple request-response streams are able to maintain satisfactory performance, while a single TCP connection deteriorates rapidly with increasing packet loss. The results provide experimental evidence that HTTP-based request-response streams are a good alternative to classical TCP streaming

Achieving air-ground communications in 802.11 networks with three-dimensional aerial mobility

Increasing availability of autonomous small-size aerial vehicles leads to a variety of applications for aerial exploration and surveillance, transport, and other domains. Many of these applications rely on networks between aerial nodes, that will have high mobility dynamics with vehicles moving in all directions in 3D space and positioning in different orientations, leading to restrictions on network connectivity. In this paper, we propose a simple antenna extension to 802.11 devices to be used on aerial nodes. Path loss and small-scale fading characteristics of air-to-ground links are analyzed using signal strength samples obtained via real-world measurements at 5 GHz. Finally, network performance in terms of throughput and number of retransmissions are presented. Results show that a throughput of 12Mbps can be achieved at distances in the order of 300m.

Channel measurements over 802.11a-based UAV-to-ground links

We analyze unmanned aerial vehicle (UAV)-to-ground links for an 802.11a-based small quadrotor UAV network with two on-board antennas via a set of field experiments. The paper presents our first results toward modeling the uplink and downlink channel and provide the path loss exponents for an open field and a campus scenario. We illustrate the impact of antenna orientation on the received signal strength and UDP throughput performance for different heights, yaws, and distances. When both antennas are horizontal (parallel to the flight direction plane), yaw differences can be handled, whereas a vertical antenna can assist against signal loss due to tilting of the UAV during acceleration/deceleration. Further work is required to analyze fading as well as UAV-UAV links in a multi-UAV network.

Design options and comparison of in-network H.264/SVC adaptation

This paper explores design options and evaluates implementations of in-network, RTP/RTSP based adaptation MANEs (Media Aware Network Elements) for H.264/SVC content streaming. The obvious technique to be employed by such an adaptation MANE is to perform SVC specific bitstream extraction or truncation. Another mechanism that can be used is description (metadata) driven, coding format independent adaptation based on generic Bitstream Syntax Descriptions (gBSD), as specified within MPEG-21 Digital Item Adaptation (DIA). Adaptation MANE architectures for both approaches are developed and presented, implemented in end-to-end streaming/adaptation prototype systems, and experimentally evaluated and compared. For the gBSD based solution, open issues like the granularity of bitstream descriptions and of bitstream adaptation, metadata overhead, metadata packetization and transport options, and error resilience in case of metadata losses, are addressed. The experimental results indicate that a simple SVC specific adaptation MANE does clearly outperform the gBSD based adaptation variants. Yet, the conceptual advantages of the description driven approach, like coding format independence and flexibility, may outweigh the performance drawbacks in specific applications.

An H.264/SVC-based adaptation proxy on a WiFi router

Recent advances in video coding technology like the scalable extension of the MPEG-4 AVC/H.264 video coding standard pave the way for computationally cheap adaptation of video content. In this paper we present our work on a lightweight RTSP/RTP proxy that enables in-network stream processing. Based on an off-the-shelf wireless router that runs a Linux-based firmware we demonstrate that the video adaptation can be performed on-the-fly directly on a network device. The paper covers design and implementation details of the proxy as well as a discussion about the actual adaptation of the SVC stream. Based on experimental evaluations we show that our approach can handle a reasonable number of concurrent sessions for a typical home deployment scenario. Furthermore, the paper covers possible applications in which adaptation on the network device can be beneficial.

Efficient in-network adaptation of encrypted H.264/SVC content

This paper addresses the efficient adaptation of encrypted scalable video content (H.264/SVC). RTP-based in-network adaptation schemes on a media aware network element (MANE) in an IPTV and VoD scenario are considered. Two basic alternatives to implement encryption and adaptation of H.264/SVC content are investigated: (i) full, format-independent encryption making use of Secure RTP (SRTP); (ii) SVC-specific encryption that leaves the metadata relevant for adaptation (NAL unit headers) unencrypted. The SRTP-based scheme (i) is straightforward to deploy, but requires the MANE to be in the security context of the delivery, i.e., to be a trusted node. For adaptation, the content needs to be decrypted, scaled, and re-encrypted. The SVC-specific approach (ii) enables both full and selective encryption, e.g., of the base layer only. SVC-specific encryption is based on own previous work, which is substantially extended and detailed in this paper. The adaptation MANE can now be an untrusted node; adaptation becomes a low-complexity process, avoiding full decryption and re-encryption of the content. This paper presents the first experimental comparison of these two approaches and evaluates whether multimedia-specific encryption can lead to performance and application benefits. Potential security threats and security properties of the two approaches in the IPTV and VoD scenario are elementarily analyzed. In terms of runtime performance on the MANE our SVC-specific encryption scheme significantly outperforms the SRTP-based approach. SVC-specific encryption is also superior in terms of induced end-to-end delays. The performance can even be improved by selective application of the SVC-specific encryption scheme. The results indicate that the efficient adaptation of SVC-encrypted content on low-end, untrusted network devices is feasible.

On path planning strategies for networked unmanned aerial vehicles

In this paper, we compare deterministic and probabilistic path planning strategies for an autonomous unmanned aerial vehicle (UAV) network, where the objective is to explore a given area with obstacles and provide an overview image. We present both online and offline implementations of the algorithms as alternative solutions, where applicable, and analyze the performance of the offline implementations. Results illustrate the benefits and drawbacks of different planning strategies and provide insight into which strategy should be taken, given the constraints of the application of interest.

Implications of the ISO base media file format on adaptive HTTP streaming of H.264/SVC

HTTP streaming has gained significant attraction in the last few years. Currently many commercial as well as standardized streaming systems are already offering adaptive streaming. In most cases, the adaptation is achieved by switching between separately encoded video streams in different qualities. In contrast to that, this paper focuses on the applicability of scalable video coding based on the H.264/SVC standard for adaptive HTTP streaming. Recent work has already highlighted the conceptual advantages like better cache utilization, fine-grained bit rate scalability, and lower storage requirements. This paper discusses the actual realization and design options for implementing priority streaming using the ISO Base Media File Format (BMFF). We propose three different strategies for organizing the scalable video bit stream that consider both the possibilities as well as limitations of the ISO BMFF. The proposed strategies are discussed and evaluated both conceptually and quantitatively. For that purpose, we provide a detailed analysis based on modeling both the overhead of the file format and the HTTP encapsulation. The results for all three priority streaming strategies show that the limitations of the ISO BMFF result in a high relative overhead in the case of low bit rate content. However, when applied to high quality content, priority streaming of H.264/SVC can be implemented at a very low cost. Depending on the number of layers and the offered scalability dimensions, different strategies should be chosen to minimize the overhead. Based on the analytical model and the discussion, this paper provides guidance for selecting the most efficient strategy.