1 Type of Question

Task-oriented Question that should eventually result in Recommendations.

2 Motivation

A return path is sometimes needed from the user's premises to the programme provider, in order to implement interactive services in the secondary distribution of television. The degree of interactivity needed may be different depending on the kind of service provided; such need may concern the main service for which the secondary distribution network is intended, namely the distribution of television to the home; it may also concern some additional services that may be provided through the same network, separately from the main service provided. Examples are various forms of pay television, video-on-demand and so on.

The characteristics of the return channel from the user to the programme provider, that the network may provide, will generally influence the degree of interactivity possible. Conversely, the degree of interactivity required by the planned services will influence the design of the secondary distribution network conceived to be able to also provide those services.

A typical example is Video on Demand (VoD), where it is generally found that a cost-effective way to implement the service is by means of asymmetric networks. These networks provide a wideband forward channel from the service provider to the home user, to deliver the demanded television programme, and a narrow-band return channel from the user to the service provider, used to convey the demand messages. Such asymmetric networks are almost unique to cable television distribution on demand and they require an optimized architecture that is often different from the one employed for the conventional symmetric networks used for general telecommunication purposes.

In some cases it is possible to trade data capacity of the return channel for data capacity of the forward channel; an example is the teletext service, where all the information is periodically delivered to the user, and the interactivity only operates within the user's premises.

It is important to identify the degree of interactivity required by the various interactive services that may be carried on a television secondary distribution network, and to study the means to provide such interactivity. The aim is to achieve if possible a degree of uniformity in the design of television secondary distribution networks, and to provide guidelines on the technical solutions to be preferred in order to meet the interactivity requirements peculiar to different services.

3 Items for study

• Identification and listing of the main and of the additional services that could be provided through a television secondary distribution network, e.g.:
• digital cable television networks;
• cabled sections of Master Antenna Television (MATV) systems;
• cabled sections of Satellite Master Antenna Television (SMATV) systems;
• cabled sections of Multichannel Multipoint Distribution Systems (MMDS);
• cabled sections of Local Multichannel Distribution Systems (LMDS).
• Study of the interactivity requirements peculiar to the interactive services identified, such as, for example VoD or NVoD (near video on demand)¹.
• Recommendation(s) on the characteristics of the return channel (or channels) that can be used to provide the interactivity required by the various services.
• Recommendation(s) on the technical solutions that can be adopted, in order to provide a return channel or return channels having the characteristics required by the various services, both for the case of cable distribution networks and for the case of collective antenna systems (MATV, SMATV, MMDS and LMDS networks).
• Recommendation(s) on the operating solutions (such as concentrating the users' return data streams) that can be adopted in order to use the available return channel(s) in the most effective way.

4 Expected results and anticipated target dates

A consistent number of additional Recommendations are in preparation, and it is expected that they will be approved between 2002 and 2004.

5 Relationships

The work will need to take into account the studies of ITU-R Study Group 6, that is responsible to specify in general terms the picture and sound quality to be provided by television distribution services.

The work will also need to take into account studies of ITU-T Study Groups 15 and 16 in general, with special attention on studies concerning the characteristics of some audiovisual and data services that may be carried as additional services on a television secondary distribution network.

Liaison should be established with ITU-T Study Group 11 with regard to the provision of an open network and signalling access to the provider of additional services.

Liaison should also be established with ITU-T Study Group 13 with regard to the studies on the Global Information Infrastructure (GII).

^[1] Near video on demand (NVoD) is a service in which the same programme is sent over several cable television channels, starting at short and regularly spaced time intervals. The user that requests the programme must only wait a few minutes to receive it from the start, and will have the same impression of the service as if it were a true VoD service. Indeed, the main difference between the VoD and the NVoD services is in the internal mode of operation of the cable head‑end, not in the way the demand or the demanded video are transmitted on the cable television network.