Note: Descriptions are shown in the official language in which they were submitted.
CA 02211~27 ls97-08-OX
Set-Top Box
The invention concerns a set-top box according to
patent claim 1.
Broad-band communications systems which are able to
contain a return channel are necessary to provide
interactive services such as e.g. near-video-on-demand,
video-on-demand or telelearning. The video and audio
signals of the interactive services are transmitted by a
server to several subscribers, e.g. in the forward channel
of a hybrid broad-band communications network or via a
satellite link. Each subscriber has a set-top box in which
the video and audio signals are decompressed and decoded,
among other things. To make use of the interactive services
each subscriber must have the possibility of requesting the
desired services from the server. This takes place via a
return channel.
One possibility of implementing the return channel is
known from the article "New Concept Links TV and Telephone"
from the magazine Funkschau 19/1989, pages 46 to 51. The
interactive services are transmitted to several subscribers
via the forward channel of a broad-band communications
network. The return channel is implemented via an
integrated services digital network, the so-called ISDN.
The transmission of the request signals takes place via an
ISDN-telephone installation in a user information channel,
the so-called B channel. This has the disadvantage ~hat
while the video-on-demand service is being used, e.g. 90
minutes per video film, the user information channel is
occupied and cannot be used for telephoning for example.
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Furthermore a low data rate, e.g. 10 kbit/s, is sufficient
to transmit the request signals. In this way only a small
part of the 64 kbit/s of the user information channel is
being utilized.
In addition the article "Set-Top-Boxes for Digital TV"
in the magazine Funkschau 23/1995, pages 22 to 29 describes
a set-top box with among other things a video decoder, an
audio decoder, a processor, a RAM (Random Access Memory)
memory and several interfaces, among them an interface for
connecting the set-top box to a telephone line.
It is the task of the invention to provide a device
whereby a subscriber can transmit request signals to a
server. This task is fulfilled by the principle of patent
claim 1. Advantageous configurations can be found in the
dependent patent claims 2 to 4.
A special advantage of the invention ls the
possibility of the simultaneous use of interactive services
and telephone services for subscribers who have only one
user information channel available.
Another advantage of the invention is the better
utilization of the signalling channel in the integrated
services digital network.
The invention will be explained in the following by
means of a configuration example with the help of figures 1
and 2, wherein:
Figure 1 is a schematic illustration of a broad-band
communications system able to contain a return
channel, and
Figure 2 is a schematically illustrated construction of a
set-top box according to the invention.
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The configuration example is described next by means
of figure 1, which illustrates a broad-band communications
system BK able to contain a return channel. Among other
things, the return-channel-capable broad-band communications
system BK is used to provide interactive services such as
e.g. video-on-demand or home banking. The basis of the
broad-band communications system BK is a cable television
distribution network CATV and an integrated services digital
network ISDN. Television and radio programs are fed to the
cable television distribution network CATV by a television
and radio station TVR and transmitted to several subscriber
installations. In addition upon request from a subscriber,
video and audio signals are fed by a server SERVER to the
cable television distribution network CATV and transmitted
to the subscriber. The transmission of the subscriber's
request signals, which can also be used e.g. for forwarding
and rewinding activities, freeze frames or account orders,
takes place via the integrated services digital network
ISDN. To that end the subscriber installation TN comprises
a television set TV, a set-top box STB and an infrared
remote control IR.
The television programs as well as the video signals
are displayed on the screen of the television set TV.
The set-top box is used for receiving television and
radio programs as well as video and audio signals which are
transmitted via the cable television distribution network
CATV, for receiving control signals from the integrated
services digital network ISDN, for receiving infrared
signals from the infrared remote control, for transmitting
the received and processed television and radio programs as
well as the received and processed video and audio signals
to the television set, and for transmitting request signals
via the integrated services digital network ISDN.
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The request signals are transmitted in a packet-switched
mode via an interface S0 in a signalling channel of the
integrated services digital network ISDN. The signalling
channel represents the return channel.
A switching center of the integrated services digital
network ISDN receives the request signals from several
subscribers in packet data form and combines them in the
multiplex mode, so that the request signals from a group of
subscribers can be transmitted e.g. in a user information
channel which is a dedicated connection for example, from
the switching center to the server SERVER via the integrated
services digital network ISDN.
The configuration example will now be explained
further by means of figure 2 which illustrates a set-top box
STB of a subscriber of the broad-band communications system
in figure 1. The set-top box comprises a decoding unit DEK,
a control unit CTRL, an interface S0 and an infrared
receiver unit IR.
The decoding unit DEK is connected to the cable
television distribution network CATV, the television set TV
and the control unit CTRL. It is used to filter out those
of the received video and audio signals which are requested
by subscribers, to process them and transmit them to the
television set TV. Among other things the processing
comprises the decompressing, demodulating, deprogramming and
decoding. The video and/or audio signals are compressed
e.g. in accordance with the inter/intra-method, modulated in
accordance with the quadrature phase modulation, programmed
in accordance with the MPEG-2 method and coded by means of
an asymmetric coding method. The steps of the individual
processing stages and the required components as well as
their circuitry are known to the professional. The decoding
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unit DEK furthermore has the interfaces and system
characteristics of the Nokia DVB 9500 S (d-box) from the
article "Set-Top-Boxes for Digital TV" on page 23 in
Funkschau 23/1995.
The interface S0 is an interface which is defined in
the integrated services digital network ISDN with two user
information channels, the so-called B channels with 64
kbit/s of transmission capacity each, and with a signalling
channel, the so-called D channel with 16 kbit/s of
transmission capacity.
The infrared receiver unit IR is used to receive the
request signals emitted by the infrared remote control, to
convert the request signals into electrical signals and to
route the electrical signals further to the control unit
CTRL.
The control unit CTRL comprises a means M for
transmitting the request signals via the interface S0 to the
integrated services digital network ISDN, a converter unit U
for converting protocols, a multiplexer MIJX, a processor
unit designed as a microprocessor ~P, and a memory MEMO
designed as a RAM and EPROM (Erasable Programmable Read Only
Memory).
The electrical request signals are fed to the
microprocessor IlP. In the microprocessor ~P the
identification number of the set-top box STB, which is
stored in the memory MEMO, is added to the electrical
request signals as well as control and test bits, e.g.
parity bits which are computed in the microprocessor ~P.
The resulting bit sequence is fed to the multiplexer MUX.
In the multiplexer MUX the bit sequences with the request
signals and monitoring signals, which originate from the
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decoding unit DEK, are transmitted to the converter unit U
in the time division multiplex mode. The monitoring signals
for example contain information about which video film is
currèntly being transmitted to the television set TV or
whether the output of the received signal is sufficient for
a predetermined picture quality. In the converter unit U a
protocol conversion of the output signals of the multiplexer
MUX into a packet data protocol takes place, which can be
transmitted in the packet-switched mode via the signalling
channel of the integrated services digital network ISDN.
The converted bit sequences and monitoring signals are
routed via the means M and the interface S0 to the switching
center where a multiplex formation takes place. They finally
reach the server via the integrated services digital network
ISDN.
The means M are used both for sending signals in the
packet data protocol and for receiving signals in the packet
data protocol, which are routed further to the converter
unit U. To that end the means M comprises a dialing device,
a D channel monitoring unit, a receiver for receiving packet
data and a sender for transmitting the request signals with
the added bits and the monitoring signals in the packet-
switched mode via the interface S0 in a signalling channel
of the integrated services digital network ISDN.
The means M receives control signals in the packet
data protocol via the interface S0. The received control
signals are routed to the converter unit U for the protocol
conversion. After the protocol conversion they are
transmitted to the decoding unit DEK via the microprocessor
~P. The control signals are used e.g. to acknowledge the
request signals received by the server SERVER, to carry out
the deprogramming of the requested service, to confirm the
debiting of bank accounts or to indicate the current account
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status. Transmitting the control signals in the integrated
services digital network ISDN provides increased safety
against interception (wire-tapping), as compared to
transmitting the control signals via the cable television
distribution network CATV. It furthermore reduces the
transmission density in the cable television distribution
network, which reduces the susceptibility to interference
and thereby improves the signal quality.
In the configuration example the video and audio
signals are transmitted from the server to the subscribers
via a cable television distribution network. The cable
television distribution network is e.g. a purely optical,
purely electrical or a hybrid one. The video and audio
signals could also be transmitted to the subscribers via a
satellite link, which would reduce the transmission density
in the cable television distribution network.
In the configuration example the control signals are
transmitted from the server to the subscribers via the
integrated services digital network. Instead of via the
integrated services digital network, the control signals can
also be transmitted in open channels of the cable television
distribution network or the satellite link.
In the configuration example the set-top box and the
television set are two separate devices. The set-top box
can also be integrated in the television set, which e.g.
simplifies the availability of the operating voltage for the
set-top box.
