BBC Monitoring
Large scale audio and video streaming and archiving.
BBC Monitoring supplies news, information and comment gathered from the mass media around the world. BBC Monitoring is part of the BBC World Service, a directorate of the British Broadcasting Corporation. They operate around the clock to monitor more than 3,000 radio, TV, press, Internet and news agency sources, translating from up to 100 languages. This extensive and growing range of sources enables them to provide distinctive, authoritative and reliable coverage of political and economic news. Subscribers include: government departments, journalists and academics, businesses with international interests...
A new video and audio distribution system
In July 2001 Cambridge Imaging won a contract to replace the existing analogue video and audio network. In a nutshell, the new digital system provides 60 video streams and over 200 audio streams to 120 users on an Ethernet network. The audio and video streams are archived for 36 hours on a 4TB storage area network.
"Cambridge Imaging have over ten years of experience of providing video and photographic archive systems to government, broadcast and film library customers. Using our in-house development teams we have created a new video distribution and management system. Because of the shor t development timescale we have teamed up with NETIA to provide the audio systems. Although we are based in separate countries and have developed system for different types of market, it has been remarkably easy to combine NETIA's Radio-Assist and our Imagen systems to produce a complete solution for BBC Monitoring." Paul McConkey, Managing Director of Cambridge Imaging Systems Ltd.
Video
The video streams are created with Optibase MGW2000 encoders. The encoded streams are 5Mbit/s MPEG-2. Each MGW2000 can encode six streams simultaneously and currently there are ten MGW2000s installed. The video streams are multicast to ensure that the network is used efficiently.
"We have a sophisticated scheduling application that will ensure that streams are started and stopped at the correct times and that they are correctly identified to the end users. The video servers and scheduling systems are duplicated and are fault tolerant. The system has been designed to give 24/7 operation with no single point of failure."
Audio
Radio-Assist TM is used to encode the Radio sources to 128Kbit/s mono MPEG-1 Layer2 streams which are unicast to the end users. Digigram encoders are used and each encoder shelf can encode twelve sources simultaneously. There are seventeen encoder shelves currently installed. The audio scheduling is managed in a similar way to the video and again the system is designed for 24/7 operation with no single point of failure.
Storage
Three Imagen storage servers are connected to the Gigabit network backbone and to a DataDirect storage area network with 4TB of available space. The storage servers are under the control of the Imagen video servers and they connect to all of the video streams and copy them to the SAN. Radio-Assist writes all of the audio streams directly to the SAN. The archive is able to provide 36 hours of video and audio streams before the data is automatically purged. It is expected to provide up to 72 hours of storage and possibly more in the future. All of the audio is streamed to end users from the SAN and each user is able to listen to the streams in real time and to pause and restart at will. The system is built in such a way that in case of failure of one of the video or audio servers the backup server dynamically takes over with no intervention and with negligible data loss.
Network
A complete network has been installed using Allied Telesyn Rapier Layer 3 switches and a Gigabit backbone. The network has redundant paths and uses Spanning Tree Protocol to reroute traffic in the event of any failure. The network is linked to an existing ATM LAN using a firewall and another pair of redundant L3 switches. The video streams are multicast and the audio streams are unicast onto the network, the system is designed to be expandable. The current bandwidth requirement is for 300Mbit/s of video streams and 25Mbit/s of audio streams.
The users
Most of the users on the network use the TV and Radio sources as part of their information gathering and research. They have a simple user interface that allows them to connect to any TV or Radio station that is available on the network.