Digital Equipment Corp has now subcontracted Online Media Ltd to supply its ARM RISC set-top boxes for Westminster Cable Ltd’s video-on-demand trials scheduled for November in the London Borough of Westminster, the part of the system that had still to be decided (CI No 2,660). Online Media is unwilling give the value of the contract but said the set-top boxes will be connected to Digital Equipment Corp’s Mediaplex media server at Westminster Cable’s head office rather than installed in every user’s home so fewer boxes will be required. The set-top boxes carry out the digital to analogue conversion of video data from the Mediaplex server to users’ home and the conversion from analogue to digital required when users make requests to the server. The number of boxes therefore depends upon the level of demand for services, said Westminster Cable. The services will be carried over Westminster Cable’s switched-star network, which required upgrading as it had an insufficient channel capacity to carry video on demand services. The company increased the bandwidth within each switch to handle 27 channels and now claims the network will be ready to handle 36 channels by October. The switched-star network was developed in 1983 for video jukebox and home shopping trials but met with technical failure mainly because it used car windscreen wiper motors to pull lasers out of the rack (CI No 2,658). Westminster Cable dismissed claims that 36 channels would still not be enough and said it could compete with the higher channel capacity of tree-and-branch networks used in the Cambridge video-on-demand trial. Indeed the company argued that its switched-star network is more suited to video-on-demand as switches in the network regulate data broadcast into the home and therefore transmit only video data requested. In a tree and branch network all data is broadcast into the user’s home and the set-top box carries out the selection of correct channels to be broadcast. The company claims tree-and-branch networks become clogged with unecessary data that users can’t and don’t want to see, leaving insufficient bandwidth available for users to make requests back to the server. Westminster Cable said its switched network reaches 80,000 home via a switch in every street which is connected to a maximum of 600 co-axial cables direct to users’ homes. Only customers that are connected to the switched-star network will be able to participate in the trial. But Westminster Cable said it is now looking to offer services to some 50,000 customers on its tree-and-branch network. It said it was also talking to cable and satellite companies with a view to increasing the amount of channels offered from the current 200-title library.
