Hewlett-Packard Co reckons that by marrying a conventional HP 9000 Series 800 business server with a specially-designed video delivery system, it has stolen a big march on its rivals in the battle to become king of the hill in the video-on-demand market. The company believes that one of the attractions of its MediaStream Server is it can start small and be built upon, and its latest win is the one in Singapore, where its server is at the heart of a major video-on-demand trail (CI No 2,575). Although there is only one server in the MediaStream range, it is scalable. At the low end it supports 100 concurrent streams of video and Hewlett-Packard says the maximum is 10,000 streams. The MediaStream is made up of two main blocks: the MediaStream Application Server and the Video Transfer Engine. The MediaStream Application Server is the control system and is based on the HP Series 800 running HP-UX. It carries out the functions that the set-top box requires. The Video Transfer Engine is the core of the MediaStream Server and is also based Hewlett-Packard Precision Architecture RISC single board computers. It moves the video data off the disk and out onto the network. As its function is to move data rather than carry out computation, Hewlett-Packard has optimised it for this task, so it does not contain the compute functions of a normal computer. It believes this is one of the server’s unique features because it is designed specifically for the video server task and not a standard machine retrofitted for the task. The Video Transfer Engine runs an operating system derived from the HP-RT real-time Unix.

RAID-like

The server design is based on the need to proide high availability of streams with no single point of failure. Greg Hoberg, manager of broadband solutions in the Video Communications Division said the storage is based on the idea of having ‘back-ups ready to go’. It uses a RAID-like technology that enables information that was on a failed drive to be recreated without needing twice the storage space. The next potential point of failure is in the process of getting the information from storage to the output port. Hewlett-Packard has a system whereby if one part goes down, the server can still have other areas operating. This is done by having functions working in parallel. If the system were to go down, its total performance would be lessened to say 90% or 80%, but it would not stop altogether. Hewlett-Packard added that as the system would rarely run at full capacity anyway, it can be designed to have a buffer built in to allow for any failure. It said the situation could be compared to a telephone company. If everyone picked up their phone at the same time, then not everyone would be able to get through to the person they were calling. The same idea will apply for video-on-demand services. Much of what would really happen using the MediaStream would be up to the service provider, who will decide how to allocate the resources of the server and on the final according to the level of service desired. If there is rush demand for a previously unfancied movie, the system may not be able to provide it to everyone: the server can be reconfigured but someone would need to make the decision.

By Abigail Waraker

Next is the issue of scaling the system to ensure the same kind of performance at an output capacity of 10,000 streams as at 100 streams. Hewlett-Packard claims another unique feature of its server architecture is that the service provider does not need a new computer every time it wants to add streams to the server. The streams can be increased by adding new modules to the Video Transfer Engine. These modules are data streaming devices that get information onto the network and provide a network interface with the telecommunications enviroment. If the service provider were to need fewer than 100 streams, then the firm accepts it would be more cost-effective to use a traditional computer. But the system is suitable for 100 streams and above. The only limitation is that the control comp

uter must be able to handle the transaction calculations for the number of streams that the Video Transfer Engine is providing, so here a different computer might be required. The Video Transfer Engine, which runs the HP-RT derivative, includes the Data Source for delivering the data. The Stream Controller controls the operation of the Data Source, of which there may be more than one. Its role is to bring the Data Sources together as if they are a single media server. The Stream Router enables scalability by making the multiple Data Sources appear to act as a single server and cuts out the need for a high speed bus structure. Both the Stream Controller and Router operate in real time. The software for the MediaStream Server is in two main parts. The Real Time Services part of the software is unique to Hewlett and includes functions such as Session Management, Application Services, Back Channel Signalling, Streaming Control – start, stop, fast-forward, rewind, Performance Tracking, Diagnostics and Dynamic Load Balancing. The Content Management modules carry out storage allocation of video material on the disks and maintains an index to the video material as well as its content and location. The Session Management module determines the connection of each program stream to a specific network stream. Together with the Network Services Management modules, it controls the initiation, maintenance and conclusion of each series of transactions the customer makes with the service provider.

X-rated

The Subscriber Services module controls the specific request each customer has made, such as preventing the downloading of X-rated movies, and the External Services module will send information for customer credit checking, and limit the credit available for shopping channels, for example. A Back Channel module enables the television set-top box to talk back to the server. The MediaStream Server has five main interfaces. There is no standard governing the Forward Channel which is the path for delivering information to the set-top box from the server, but Hewlett is embracing Synchronous Digital Hierarchy with Asynchronous Transfer Mode cells. Non-video data is transported in the private data field of MPEG or in separate Asynchronous Transfer Mode cells destined for the set-top box. The Back Channel is a low bit rate channel and the protocol will typically be TCP/IP over almost any physical layer, the firms says. The Signalling Channel sets up the session using the messaging on this link. The Management Port manages the MediaStream Server remotely using Simple Network Management Protocol and HP OpenView. Finally, the content Input Port is used to load program material onto the MediaStream Server disk subsystems either from a robotic Media Library or other source. The specifications are 60 to 10,000 streams at 3Mb per second viewer-client consumption rate and a latency of less than a second from received client request to delivered video, audio and data.