Imagine the following: you are in your sofa and you just switched on your television set and your brand new set-top box. The first thing you notice is the Portal TV of TV Cabo, with several options – such as the Electronic Programming Guide, Digital Video Recording, Internet -, but you decide to skip this and to watch television.
The newscast begins and the anchorman gives you an update about the Middle East situation, and a “Go Interactive” invitation button pops-up in the screen - which means the set-top box received an interactive television link and activated the invitation. Since you are not fully aware of the latest developments, you decide to press the “Go Interactive” button in you remote control.
The page request is sent to Microsoft TV server that on its turn access the external web page. This page is downloaded to the Microsoft TV server, which optimised it for television viewing. Finally, the web page is downloaded for the set-top box and you have before your eyes the information you requested. All this took less than a second, and you did not even had time to think about the complex process that brought that information to you.
To access the Portal TV features the process is basically the same. Since it is not one of the thesis objectives to describe how the Microsoft TV platform works in detail, it will only include a brief explanation of how it works. In order to understand how the content is delivered, one has to understand how the front and back channels work. The front channel can be considered as the coaxial video cable, while the back channel is the coaxial cable connected to a modem that provided that capability for two-way communication.
As for modes of transmitting interactive television content, the ATVEF specification defines two methods of delivering interactive television content: Transport A and Transport B. According to the Microsoft manual “Building Interactive Entertainment and E-commerce Content”, Transport A is by far the most popular mode of transmitting interactive content in the analog video space:
“In a Transport A scenario, the URL address to a Web page is sent via the video cable (front channel) as an ATVEF trigger (Link). This trigger appears on-screen as a prompt to tell the viewer that interactive TV content is available. When the prompt appears, the user initiates an Internet (back channel) connection by pressing a button on an infrared remote control or wireless keyboard.”179
On the other hand, the Transport B is distinguished from Transport A by “the way interactive TV content is packaged and which wire carries it”180. Transport B uses TCP/IP packets to send both Web data and triggers on the front channel:
“There is no doubt that if bandwidth in the video signal were free and plentiful, Transport B would be more popular. However, at this time, limited bandwidth restricts the use of Transport B”181.
Another important technical concept is the Vertical Blanking Interval (VBI), that provides a way for digital information to be transported in an analog signal. Briefly, each time a television picture redraws, there are ten black lines at the top of the screen available for the transport of data:
“With the Transport A method, the trigger is encoded into the VBI, and interactive data is delivered via the back channel. With the Transport B method, both the data and the triggers are encoded into the VBI or a digital signal and delivered via the front channel182.”
That’s about it, for now, as far as the technical aspects of the TV Cabo Interactive Television service are concerned. Regarding content, there is still much to say. As it was mentioned before, TV Cabo divided the Interactive Television service in two distinct types of services: Televisão Interactiva (or Enhanced TV) and Portal TV.
Source: Sapo www.sapo.pt
In a first phase, the Portal TV will have the following Content Channels: