GB2341746A

GB2341746A - Digital TV service protector

Info

Publication number: GB2341746A
Application number: GB9819784A
Authority: GB
Inventors: Bruce Fairbairn Devlin; Christopher David Ridley
Original assignee: Snell and Wilcox Ltd
Current assignee: Snell Advanced Media Ltd
Priority date: 1998-09-10
Filing date: 1998-09-10
Publication date: 2000-03-22
Also published as: GB9819784D0; AU5752899A; WO2000016558A1

Abstract

A digital television service protector receives multiplexed program streams. In addition to checking the integrity of all program streams, the protector monitors selected parameters of each stream; so that on detection of a loss in integrity, a failed program stream can be replaced with a substitution stream constructed by the protector to have appropriate parameters matching those of the failed stream. The appropriate parameters may be, for example, program identification taken from the input bitstream which it is replacing. The substitution stream may be error messages, test signals, repeats of information or other appropriate information in suitable form such as image, audio or textual.

Description

2341746 DIGITAL BROADCASTING This invention relates to digital

broadcasting and is particularly concerned with the consequences of failures at points in the digital television transmission chain.

The international standard ISO/IEC13818 (generic coding of moving pictures and associated audio information), known commonly as MPEG2, has been globally adopted as the method of encoding media and binding them together in a multiplex for transmission as digital services. In this system, media are compressed by removing temporally and spatially 10 redundant information. Psycho-visual and psycho-acqustic models also reduce information content. The resulting digital data can be packetised and bound together with other compressed and uncompressed services to form a transport stream. The data streams within a transport stream are grouped into collections of services which in the case of digital television comprise 15 one or more video channels, one or more audio channels and optionally data streams for program support and enhancement. Digital television transmission systems are complex and relatively untried. The possibility of component or system failures must be addressed and, particularly, the effect of such failures on viewers. 20 According to the present invention, there is provided digital television service protection apparatus comprising a television service input terminal for receiving a plurality of compressed bitstreams; a television service output terminal; a monitoring unit for monitoring selected parameters of the respective input bitstreams; an integrity checking unit for continuously 25 checking the integrity of each input bitstream; a bitstream construction unit for constructing a substitution bitstream having appropriate parameters chosen to accord with those of the monitored input bitstream and a switcher actuated from said integrity checking unit to switch the apparatus from a normal mode in which the television service at the input terminal is passed transparently to the output terminal, to a failure mode in which one or more bitstreams at the output terminal are substituted by a bitstream from said bitstream construction unit, on detection of a loss in integrity.

By placing a device according to this document after a potential point of failure in a transmission system:

the transmitted multiplex may be replaced in the event of failure; the receiving equipment or receiving person may be informed of the failure; the transmitted multiplex may be partially replaced to correct or limit the effect of a partial failure of the system; the transmitted multiplex may be modified or partially replaced to prevent complete loss of service at receiving equipment; or the transmitted multiplex may be modified or partially replaced to prevent undesirable effects in receiving equipment.

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a block diagram of a typical transmission system, and Figure 2 is a block diagram illustrating one use of apparatus according to the present invention.

Most digital television transmission systems are characterized as having one or more sites as sources of services; an optional concatenation point followed by a communications link to one or more radiation points. Such a typical system is illustrated in Figure 1.

Typical modes of failure for such a system are at the following points:

A. A full or partial failure at the program source to assemble the service.

B. A failure of the link to the concatenation point causing all or some of the components of a service to fail.

C. A failure at the concatenation point to assemble correctly the out going stream.

D. The concatenation facility fails to add any necessary data streams or information to the out going stream.

E. Partial or complete failure of the link to the radiation points.

F. Failure of the equipment at the radiation point.

These point A to F are marked in Figure 1.

To protect against loss of part or the entire stream, service protection apparatus according to the present invention can be added at several points in the system. Figure 2 shows one such device placed at each point of radiation.

Apparatus according to the present invention is illustrated in Figure 3.

The integrity of the input television service at terminal 20 is checked repeatedly in integrity checking unit 22. This may simply check for the presence of the expected bitstreams but will preferable conduct a continuous analysis of each the bitstreams and compare selected parameters with predetermined legitimate thresholds. Provided that all critical parameters remain within the legitimate thresholds, the integrity checking unit 22 will control the switching unit 24 such that the input television service passes transparently to the output terminal 26.

If a loss of integrity is detected, the integrity checking unit causes the switching unit to substitute for the failed bitstream or each of the failed bitstreams, a substitute bitstream constructed in the bitstream constructor unit 28.

In one form of the invention, the substitute bitstream is constructed simply from test or other fixed picture, audio or data signals from store 30.

Preferably, however, the bitstream constructor unit 28 makes use of information from the bitstream gathered prior to the failure in bitstream monitor 32, to construct a substitute bitstream having appropriate parameters, such as - for example - the program identification, taken from the input bitstream which it is replacing. The substitute stream or streams which are sent to sustain the service may be error messages, test signals, repeats of information collected earlier from the input or other appropriate information in whatever form of media is suitable; image, audio or textual.

When intervening in the transmitted stream, effort will be made to recover to a basically functional service with the greatest speed and least demand upon receiving equipment.

Thus, the apparatus can be arranged, by way of example, so that:

Should any program identification or PSI need to be replaced, the last known good version of that information may be repeated.

Should an image need to be replaced, a suitable static or dynamic replacement will be sent. This may include a logo or other program specific material that is selected from the contents of the test store, in dependence upon the last valid program identification.

Should an audio stream need to be replaced, a suitable test signal, error message, locally encoded audio signal or silence may be inserted.

Should a data service need to be replaced, a suitable textual or other media stream may be sent.

It is further ensured that the position, timing and location within the out going stream (i.e. the PID of each data stream) remain as constant and consistent across the bitstream substitution process.

It will be understood that the invention has been described by way of example only and that a wide variety of modifications are possible without departing from the scope of this invention. Thus, the apparatus may be arranged on detection of a loss of integrity to replace only those parts of the service which are unusable or logically in error. Alternatively, detection of a loss of integrity in one part of a service may trigger replacement of a larger or other parts of the service. If it is convenient, the integrity checking may be performed in separate apparatus and appropriate control signals sent to the other described elements of the apparatus. Such remote integrity checking apparatus may additionally provide error or alarm messages to a transmission controller and maintain logs facilitating subsequent diagnosis of the causes of failure.

Claims

1. Digital television service protection apparatus comprising a television service input terminal for receiving at least one compressed bitstream; a television service output terminal; a monitoring unit for monitoring selected parameters of the respective input bitstreams; an integrity checking unit for continuously checking the integrity of each input bitstream; a bitstream construction unit for constructing a substitution bitstrearn having appropriate parameters chosen to accord with those of the monitored input bitstrearn and a switcher actuated from said integrity checking unit to switch the apparatus from a normal mode in which the television service at the input terminal is passed transparently to the output terminal, to a failure mode in which one or more bitstreams at the output terminal are substituted by a bitstream from said bitstream construction unit, on detection of a loss in integrity.

2. Digital television service protection apparatus comprising a television service input terminal for receiving at least one compressed bitstream; a television service output terminal; a monitoring unit for monitoring selected parameters of the respective input bitstreams; a control input terminal for receiving a control signal from an integrity checking unit; a bitstream construction unit for constructing a substitution bitstream having appropriate parameters chosen to accord with those of the monitored input bitstream and a switcher actuated from the control signal to switch the apparatus from a normal mode in which the television service at the input terminal is passed transparently to the output terminal, to a failure mode in which one or more bitstreams at the output terminal are substituted by a bitstream from said bitstream construction unit, on detection of a loss in integrity.

3. Digital television service protection apparatus comprising a television service input terminal for receiving at least one compressed bitstream; a television service output terminal; an integrity checking unit for continuously checking the integrity of each input bitstream; a bitstrearn construction unit for constructing a substitution bitstream and a switcher actuated from said integrity checking unit to switch the apparatus from a normal mode in which the television service at the input terminal is passed transparently to the output terminal, to a failure mode in which one or more bitstreams at the output terminal are substituted by a bitstream from said bitstrearn construction unit, on detection of a loss in integrity.