How it works - Technical Breakdown (original) (raw)
The Open.... Interactive Television Service -
A Technical Summary
The Service Proposition
The Open.... service delivers on-line shopping, banking, information services and e-mail with all the look, feel and immediacy which customers expect from television. Customers can transact with the Open.... service in complete safety thanks to the secure link created between the Sky Digital Set Top Box (STB) and Open.... Goods can be paid for by credit card in safety and delivered direct to the customer's home.
The Open.... service is possible because of the opportunities offered by digital television which relies on a digital STB to create a series of television pictures from data rather than merely displaying pre-formatted pictures.
The Image
The television images created by Open…. combine video, still images and animation to create an entertaining and captivating service. These media assets can be delivered by satellite, particularly for video and high quality images such as backgrounds which are accessed by many people; by telephone line, for text or pictures which change frequently or are specific to individual customers. Some assets such as frequently used logos may be stored temporarily in the STB.
The pictures appearing on the screen are constructed by the Open…. service in the STB in response to customers' instructions entered by from the remote control. Following the simple on-screen menus the STB will look for content from the satellite, or dial the Open…. computers to retrieve data.
Digital Television
Digital television is a pre-requisite for interactive television. It allows video to be manipulated along with other images, still and animated, by providing processing power in an STB. The primary task of the STB is to reconstruct a digital data stream into moving pictures on the screen. This is slightly more difficult than it sounds because the pictures are compressed before being stored and transmitted.
International bodies have defined the MPEG standard used to compress video from around 140Mbit/s used in analogue television to between 2 and 6Mbit/s, by logically relating successive frames; ie a beachball bouncing across a beach is fairly simply represented by a ball moved fractionally across a static background.
The STB's job is to do the calculations to reconstruct the picture in an MPEG decoder - a relatively simple matter in the case of the beachball, not so simple in the heat of a soccer match. The smaller bandwidth required by digital TV signals also explains its other attraction - more channels in the same bandwidth.
Interactive Television
The concept of interactivity in television means very different things to different people. Strictly, Pay TV is "interactive" in that movies can be ordered by sending small messages from the STB. The concept adopted by Open.... is to provide the richest TV experience with as much data as possible being accessed over the on-line connection. This allows a full range of services such as shopping, banking, games and information.
The Set Top Box
The Open.... concept of interactivity puts great demands on the STB. As well as the MPEG decoding required to show video, the richness of the Open.... service requires that the box can decode JPEGs (another internationally defined compression technique for still pictures) and audio sequences, and handle the communication protocols required by the on-line connection, as independently as possible to avoid glitching.
As a further refinement the Open.... STB uses three display layers, a background MPEG layer, a second video layer and an OSD or graphics layer used principally for overlay text. In essence the STB is a PC, without discs or keyboard, but with a number of other sophisticated peripherals contained in one small enclosure. In many ways an STB is identical to the Network Computers being used in managed business environments.
The power of the STB is achieved in a very cost effective manner using sophisticated software techniques. Typical boxes have the power of a high end 486 PC but with much less memory. There is no disc drive so the operating system is held in flash (electrically alterable) memory. Thus the operating system is always available when the STB is switched on, and it can be upgraded by satellite to add new features. The box always keeps a copy of the last working operating system in as a backup during to the upgrade process.
Bandwidth
Even with MPEG compression, full-screen videos require 2-6Mbit/s of bandwidth. Although several Telcos have experimented with ADSL (Asynchronous Digital Subscriber Loop) technology which will support these bandwidths over normal telephone lines, cost-effective transmission of such bandwidths currently require satellite or cable transmission. Open.... will begin its service with 68Mbit/s of transmission capacity on 2 transponders of an Astra satellite. Digital transmission makes high quality graphics and images and CD quality sound available to all customers through the broadcast stream whilst the viewer interacts via the STB telephone or cable line.
Detailed information required by individual customers is collected from the on-line server across the telephone network using a 28.8kbit/s modem.
The Service
Services are carried by satellite as an application which will run on the STB plus the associated high quality graphics which give the menus their look and feel. Using the high bandwidth available on the satellite, an application and its screens can be delivered as a repeating carousel only 2 seconds long. Each customer runs the application in their own STB, navigating in their own time in any way they wish. On average their STB will find the next screen from the satellite carousel in around a second. Additional information about products and services will be called from the on-line server using the telephone connection.
All Open…. customers will be able to have their own e-mail address as will all members of their household. A simple user interface will allow short messages to be created or responded to using the remote control. Customers who make more use of the system may wish to use the optional cordless keyboard.
The Platform
The services are created using a Service Creation Environment (SCE), a package of hardware and software incorporating Open TV's own authoring tool, OpenAuthor. Code is delivered to the Service Delivery platform where it is checked then split between the Broadcast Server for delivery to the satellite and the On-line Server.
Orders are placed on the On-line Server and credit card details checked using the Transaction Management System (TMS). In Standard Retail the orders are batched and transmitted to the retailers who subsequently advise when goods are shipped for TMS to debit credit card accounts.
The computers which power the platform are located in three principle sites; the broadcasting platform in BT Tower, the on-line platform in a central London location, and the commissioning and operational systems in Open…. House. The Open… uplink site is in Docklands and the customer management centre is in Livingston. The dial-in network is provided by BT and is the largest on-line network in the country; it will support 0.5m customers on Day 1 compared to the largest Internet Provider who currently has 184k customers.
On-line Security
All code is encrypted before transmission and decoded using the CA (Conditional Access) controls in the STB, enabled by the code on the customer's Sky card. Calls to the On-line Server are validated using the Authentication Server and all data is encrypted.