Wireless IPTV Development Platform Antti Heikkinen
Jukka-Pekka Laulajainen
Jari Korva
Johannes Peltola
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VTT Technical Research Centre of Finland P.O.Box 1100, FIN-90571, Oulu, Finland Abstract In this paper, we present an open wireless IPTV development platform which provides a cost-effective and realistic environment for testing and developing video transmission technologies and services. We describe the components of the platform and give examples of how the platform has been used. The platform supports video delivery to mobile users in various networks, e.g., WLAN, WiMAX, and 3G. Furthermore, the platform includes support for managing client mobility and quality of service (QoS). The environment comprises of a controlled laboratory environment including a network emulator as well as actual networks with wide coverage and regular users. Keywords IPTV, Wireless, Mobility, QoS, H.264, IPv6, Platform. INTRODUCTION Wireless IPTV (Internet protocol television) aims to make the traditional IPTV and related services available to users anywhere, anytime, on any device, and through any network. This goal requires advanced technology where networks, services, and content are highly adaptive, and thus able to respond to the needs of consumers in different use situations, accounting user’s preferences and the limitations in capabilities of the mobile devices and networks. Compared to fixed network environment, this task is especially challenging in wireless networks because of the error-prone radio channel. Additionally, there are usually no QoS guarantees available in currently used IP networks, which can cause big variations in the transmission capability of the network. In fixed networks this problem can be taken care of by overprovisioning, but in wireless networks this is not possible. Also the mobility of the terminals affects the connection, especially if it includes switching from one network technology to another (e.g. 3G to 2G or WLAN to 3G) or between networks belonging to different administrative domains. Adaptive transmission of video and other media over wireless networks has been studied extensively [1-5]. Basic components for adaptive media transmission over wireless networks are a source encoder, transmission unit, transport network, network monitoring mechanism, client and feedback or control channel. The network monitoring
mechanism provides control information about network conditions by gathering end-to-end connection statistics. Generally, the monitoring mechanism utilizes an application layer control protocol like RTCP [3] or a transport layer control protocol like TCP [5]. The monitoring mechanism can also exploit information from other layers, e.g. network or physical layer. Based on this information the source encoder or the transmission unit adjusts the source data rate. In order to develop the above mentioned mechanisms and services in a converging network environment, we need a platform that corresponds to the characteristics of the real networks and allows us to test actual scenarios without losing the ability to control and observe the network. Although a great deal of development uses only simulated network environments, a platform that contains realistic and controlled test networks is needed in order to test and develop new applications, algorithms and protocols. In this paper, we describe an open wireless development platform which provides a cost-effective and realistic environment for testing and development of wide range of video transmission technologies. The platform makes it possible to integrate new services and applications such as IPTV into the platform. These services can be tested and validated in a realistic and controlled network which supports QoS, IPv6, mobility and network monitoring. Furthermore the platform supports several mobile devices and clients. The rest of the paper is organized into three sections. The first one describes the wireless IPTV platform architecture while the second shows the applicability of the platform by describing some research and development examples that have been conducted on the testbed. Finally, the last section concludes the paper. PLATFORM ARCHITECTURE The wireless IPTV development platform shown in Figure 1 consists of a media server, test network, network monitoring tool, mobility management mechanisms, and video clients for different devices. The platform is built of off-the-self and custom components, but instead of being a static structure, new technologies such as applications, codecs, and protocols can be easily integrated into the platform.
Figure 1. The architecture of the wireless IPTV development platform.
Media Server The media server can capture, encode and stream videos on the network. The media input can be for example a digital video broadcast (DVB) receiver, external video camera, media file, or a network stream. The media server includes several video codecs such as MPEG-2, MPEG-4, and H.264. Hence, we can use real-time transcoding to change the coding parameters of the video stream, adjust spatial or temporal resolution, or change the video format. Furthermore, the media server includes an interface for controlling data by initializing and adjusting the video encoder parameters during the encoding. The streaming server supports a large number of Internet protocols such as HTTP, TCP, UDP, and IPv6. The server streams the videos over a network to the end user by using either unicast or multicast communication. Test Network The development platform includes a controlled network environment connecting the client devices to the media server. The network consists of a wired backbone network and several wireless access networks using different technologies. These technologies are IEEE 802.11g and pre-standard IEEE 802.11n wireless LANs, cellular 3G/HSDPA, and IEEE 802.16d WiMAX. As all the networks are included in the development platform, the network between client and server can be freely configured to best suit the research and development purposes. It is
also possible to get information from different protocol layers on the network, which is infeasible when using commercial networks. However, separated laboratory network does not alone provide a very realistic environment for testing. To solve this problem, we have a rate control tool for inducing impairments like additional delay, jitter, bandwidth limitations, or packet losses to the network. Additionally, we participate to a metropolitan WLAN effort, which currently supports around 6000 monthly users with 600 access points around the city and thus allows more realistic tests and field trials. Mobility and Multihoming Support In order to support mobility, the platform has been equipped with a home agent which is a key enabler for Mobile IP. The core network has been adapted for mobility experiments by deploying an emulated multi-operator IPv6 testbed solution developed in the European ANEMONE project [6]. This allows us to analyze the effects of performing handovers between differently administered networks and experimenting with multihoming, i.e. a technology which allows a network or a terminal to be concurrently connected via several access networks so that for example different data flows to be transported via different networks. Network Monitoring for Media Adaptation The platform includes a network monitoring tool which monitors the client-server connections end-to-end and
provides information about network conditions. This information includes parameters like delay, jitter, and packet loss and it can be used for adapting the applications to maximize the end user experience of the service, in this case to configure the encoding parameters at the media server. Clients The client applications receive and display the video stream. In addition, the client applications may include error resilience features such as error detection and concealment which are important when the video stream is transmitted through an unstable network. The platform is equipped with several video clients for different devices, for instance the VLC media player [7] on PCs and PDAs. We have also implemented our own video client that can be modified easily by adding new codecs and network protocols or by modifying the existing ones. RESEARCH AND DEVELOPMENT EXAMPLES The wireless IPTV development platform is enabling researchers to test and develop new technology. In the following subsections actual case examples illustrate how the platform has been used. DVB Content to Handheld Devices Delivering DVB content to handheld devices requires special attention because the mobile devices may have limited display and processing capabilities. DVB content can be transcoded so that it can be viewed on any of the wireless devices. Generally this means reducing the content bitrate, spatial resolution, or temporal resolution to correspond network and terminal capacity. We have transcoded live digital video broadcast to handheld devices over WLAN connection. Typical mean data rates and characteristic for a single program in DVB-T in Finland are 4-5 Mbit/s in MPEG-2 format with PAL resolution. This single program was transcoded to H.264 format at 512 kbit/s with QVGA (320x240) resolution and it was multicast over the network to handheld devices. QoS-Aware Video Encoding We have developed an application layer QoS control solution that enables video streaming applications to dynamically adapt to the prevailing transmission conditions. The adaptation architecture consists of network monitoring and video adaptation modules. In practice, the network monitoring module provides information about the connection between the server and the client to the adaptation module, which uses this information in order to react to possible problems on the transmission link. If the link is becoming congested due to overload in the network, the adaptation module reacts by decreasing the quality and thereby also the bitrate of the video. This creates a continuous video experience to the user, which is superior to jerky or crashing non-adapted video stream.
Handover Testing As described earlier, the wireless IPTV platform includes support for Mobile IPv6. The main idea of Mobile IPv6 is to maintain existing connections, even if a mobile device roams between networks. We have tested horizontal handovers between two WLANs by using MIPL Mobile IPv6 implementation for Linux [8]. We tested this with different services, including IPTV unicast and VoD, in order to analyze the effects of the mobility and to develop mechanisms which allow the applications and the protocol components to adjust to the situation before or at the time of the handoff. Product Testing Wireless IPTV platform can be used by companies to test and develop their products. The environment includes many different network technologies that can be fully controlled for tests that would not be possible in commercial networks. Our platform has been used, for example, by a company that is developing a new kind of a gaming solution based on video streaming. The target was to find out how the product performs when used over different wireless access technologies. IPTV over WiMAX WiMAX is more and more widely used to provide broadband Internet connectivity to rural areas where it is not affordable to use technologies like DSL or cable modems. We have used our IPTV development platform in order to demonstrate the use of IPTV services to WiMAX connected households. The 10 Mbps maximum bitrate per sector provided by the IEEE 802.16d WiMAX on 3.5 MHz bandwidth is enough for streaming a small number of TV channels but is not suitable for wider use. However, the coming mobile WiMAX version (IEEE 802.16e) could be used for providing IPTV services to mobile devices by using a lower bitrate. CONCLUSION The delivery of multimedia content via IP is continuously gaining momentum. At the same time, different types of new wireless IP networks and terminals are becoming more widely available to the end users. This will increase the complexity in the development of IPTV technology, since end users expect that the services are always available to them. To cope with increased complexity, a controlled but representative development environment is needed in order to research, develop and test tools that are interoperable and allow distributing content efficiently to the end users. In this paper we have presented our wireless IPTV development platform and described how the platform can be utilized for more efficient development and testing. Platform contains modifiable components for adaptive video streaming, network monitoring, and support for different video client implementations. Additionally, the platform contains a mobility-enabled test network including 3G/HSDPA base station and clients, IEEE 802.16d WiMAX, and different types of Wi-Fi access networks.
The platform is used for research and development activities as well as testing existing or emerging products in different network environments. This paper listed some research examples in order to give an overview of the possibilities of the wireless IPTV platform. The research examples included video content adaptation, video streaming optimization, mobility management, WiMAXTV, and commercial product testing. ACKNOWLEDGMENTS This research has been supported by the European FP6 IST project ANEMONE (2006-) and ITEA Magellan project (2004-2006), which was partly funded by TEKES. REFERENCES [1] T. Ahmed, et. al., “Adaptive Packet Video Streaming over IP Networks: a Cross-Layer Approach”, IEEE Journal on Selected Areas in Communications, vol. 23, no. 2, pp. 385-401, 2005. [2] M. Etoh, et al., “Advances in Wireless Video Delivery,” Proc. IEEE, vol. 93, no. 1, pp. 111-122, 2005.
[3] R. Kothari, et al., “Archies: An End-to-End Architecture for Adaptive Live MPEG-4 Video Streaming over Wireless Networks", IEEE International Conference on Wireless and Mobile Computing, Networking and Communications, August 2005. [4] A. Schorr, et al., "Adaptive Media Streaming in Heterogeneous Wireless Networks", IEEE Multimedia Signal Processing 2004, pp. 506-509. [5] D. S. Turaga, et al. “Adaptive Live Streaming over Enterprise Networks”. International conference on Multimedia and Exposition, May 2005. [6] L. Bokor, et al., "ANEMONE: A Pan-European Testbed to Validate IPv6 Mobility Technologies", The Second International Workshop on Network Mobility (WONEMO), January 2007. [7] VideoLAN Project, VideoLAN - Free Software and Open Source Video Streaming Solution: http://www.videolan.org (2007) [8] MIPL Mobile IPv6 for Linux http://www.mipl.mediapoli.com
