Note: Descriptions are shown in the official language in which they were submitted.
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EXTRACTING DATA SECTIONS FROM A TRANSMITTED DATA STREAM
The present invention relates to an apparatus for and a method of storing one
or more
sections of a transmitted data stream such as=an MPEG bitstream containing
video and
' audio television data in addition to the sections of data.
The advent of digital transmission systems intended primarily for broadcasting
television signals, in particular but not exclusively satellite television
systems, has
opened up the possibility of using such systems for other purposes. One of
these is to
provide interactivity with the end user.
One way of doing this is to run an application on the receiver/decoder through
which
the television signal is received. The code for the application could be
permanently
stored in the receiver/decoder. However, this would be rather limiting.
Preferably, the
receiver/decoder should be able to download the code for a required
application. In
this way, more variety may be provided, and applications can be updated as
required
without any action on the part of the user.
In computer systems, particularly systems where the computer system is
incorporated
in some larger system such as a receiver/decoder for digital television, the
amount of
memory is often limited. This means that the memory must be organized so that
the
use of inemory space by the various functions required by the system is
minimized.
In addition, it may also be necessary to minimize the time required to access
at least
some parts of the memory.
Accordingly, the present invention is particularly, but not exclusively,
concerned with
the downloading into the memory of the receiver/decoder only that data
specifically
required by an application.
In a first aspect the present invention provides a method of storing at least
one of a
plurality of sections of a transmitted data stream, said one section having at
least one
section characteristic, said method comprising the steps of:
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receiving the data stream;
filtering said one section from said data stream according to at least said
one
section characteristic; and
storing said one section.
This filtering step enables only the sections required by an application to be
loaded
into the memory of a receiver/decoder.
In a preferred embodiment, the filtering step comprises the steps of:
specifying at least one filtering characteristic, each characteristic
comprising
a filtering criterion and a value for that filtering criterion;
comparing the or each section characteristic with a respective filtering
characteristic; and
filtering said one section from said data stream when the or each section
characteristic corresponds to the respective filtering characteristic.
A second aspect of the present invention provides a method of storing a
plurality of
sections of a transmitted data stream using the above method, each section
being
stored in a respective memory location.
Preferably, this method further comprises the step of:
specifying at least one data filtering characteristic, each data filtering
characteristic comprising a data filtering criterion and a value for that data
filtering
criterion;
comparing data stored in each stored section with a respective data filtering
characteristic; and
enabling said stored section to be replaced in said memory when said data
stored in that stored section does not correspond with the respective data
filtering
characteristic.
Preferably, the method further comprises the step of supplying a section
identification
signal to an application when said data stored in said stored section
corresponds to
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said respective data filtering characteristic.
= The section identification signal preferably comprises the storage address
of said one
section.
In a third aspect, the present invention provides a method of storing a group
of
sections according to the above method, said sections being cyclically
transmitted in
said data stream, each group including a first section and a last section;
said method
comprising the steps of:
storing the first section;
subsequently downloading sections successively transmitted immediately after
said first section, each section being successively stored in a respective
memory
location, until either said last section is downloaded or a predetermined
number of
sections have been stored.
In a fourth aspect, the present invention provides a method of storing a group
of
sections according to the above method, said sections being cyclically
transmitted in
said data stream, said group including a first section and a last section;
said method
comprising the steps of:
downloading the first section;
subsequently downloading sections successively transmitted immediately after
said first section, each section being successively stored in a respective
memory
location, until either said last section is downloaded or a predetermined
number of
sections have been stored whereupon the sections stored in the memory
locations are
successively overwritten by subsequently downloaded sections until said last
section
is downloaded; and
storing said last section in said memory.
In a fifth aspect, the present invention provides a method of storing a group
of
sections cyclically transmitted in a data stream, said group including a first
section and
a last section; said method comprising the steps of:
receiving the data stream;
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downloading the first section and storing it in a memory;
subsequently downloading sections successively transmitted immediately after
said first section, each section being successively stored in a respective
memory
location, until either said last section is downloaded or a predetermined
number of
sections have been stored in said memory.
In a sixth aspect, the present invention provides a method of storing a group
of
sections cyclically transmitted in a data stream, said group including a first
section and
a last section; said method comprising the steps of:
receiving the data stream;
downloading the first section;
subsequently downloading sections successively transmitted immediately after
said first section, each section being successively stored in a respective
memory
location, until either said last section is downloaded or a predetermined
number of
sections have been stored, whereupon the sections stored in the memory
locations are
successively overwritten by subsequently downloaded sections until said last
section
is downloaded; and
storing said last section in said memory.
By virtue of the above third to sixth aspects of the present invention, only
those
sections required from a group of sections are stored in the memory of the
receiver/decoder. For example, when viewing a list of, say, three television
programmes scheduled for transmission at a particular time, by means of the
third and
fifth aspects only the first four sections of the group are downloaded from
the data
stream, enabling an end user quickly to scroll down the list, starting from
the first
programme shown at that time. By means of the fourth and sixth aspects only
the last
four sections of the group are downloaded from the data stream, enabling the
end user
to scroll quickly up the list, starting from the last programme shown at that
time and
allowing the memory of the receiver/decoder to be minimised.
In a seventh aspect, the present invention provides apparatus for storing at
least one
of a plurality of sections of a transmitted data stream, said one section
having at least
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one section characteristic, said apparatus comprising:
means for receiving the data stream;
means for.filtering said one section from said data stream according to at
least
said one section characteristic; and
means for storing said one section.
Preferably, said filtering means comprises:
means for specifying at least one filtering characteristic, each
characteristic
comprising a filtering criterion and a value for that filtering criterion;
means for comparing the or each one section characteristic with a respective
filtering characteristic; and
means for filtering said one section from said data stream when the or each
section characteristic corresponds to the respective filtering characteristic.
In an eighth aspect, the present invention provides apparatus as described
above for
downloading a plurality of such sections, said storing means comprising a
plurality of
memory locations for storing respective sections.
Preferably, the apparatus further comprises:
means for specifying at least one data filtering characteristic, each data
filtering
characteristic comprising a data filtering criterion and a value for that data
filtering
criterion;
means for comparing data stored in each stored section with a respective data
filtering characteristic; and
means for enabling said stored section to be replaced in said memory when
said data stored in that stored section does not correspond with the
respective data
filtering characteristic.
The apparatus may also comprise:
means for supplying a section identification signal to an application when
said
data stored in said stored section corresponds to said respective data
filtering
characteristic.
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The above method or apparatus may be used with such a data stream in the form
of
an MPEG bitstream which also includes video and audio television data in
addition to said
sections.
In accordance with another broad aspect of the present invention, there is
provided a
method for processing a data stream in a video processing device. The method
comprises: a)
receiving the data stream, wherein the data stream comprises sections, each
section containing
a header and a payload, the section header comprising parameters, the
processing device being
able to filter received sections according to at least a section header
parameter; b) filtering from
the data stream a first group of sections, wherein the first group of sections
comprises a first
section, a plurality of subsequent sections, and a last section according to
the at least one given
section header parameter; c) storing the first section of the first group; and
d) filtering the data
stream for further sections according to the at least one section header
parameter until an
application-defined predetermined number of sections have been stored, wherein
the
application-defined predetermined number of sections stored are a subset of
sections from the
filtered first group of sections.
In accordance with another broad aspect of the present invention, there is
provided a
method for processing a data stream in a video processing device. The method
comprises: a)
receiving the data stream, wherein the data stream comprises sections, each
section containing
a header and a payload, the section header comprising parameters, the
processing device being
able to filter received sections according to at least a section header
parameter; b) filtering from
the data stream a first group of sections, wherein the first group of sections
comprises a first
section, a plurality of subsequent sections, and a last section according to
the at least one given
section header parameter; c) storing the first section of the first group; and
d) filtering the data
stream for further sections according to the at least one section header
parameter, wherein the
filtered sections are stored in a circular buffer that can contain an
application-defined
predetermined number of sections until reception of the last section, wherein
a subset of
sections from the filtered first group of sections is loaded into memory for
the application.
In accordance with yet another broad aspect of the present invention, there is
provided a video processing device for storing a plurality of sections of a
transmitted data
stream. The video processing device comprises: means for receiving the data
stream, wherein
the data stream comprises sections, each section containing a header and a
payload, the section
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header comprising parameters; means for filtering from the data stream a first
group of
sections, wherein the first group of sections comprises a first section, a
plurality of subsequent
sections, and a last section according to at least one given section header
parameter; means for
storing the first group of sections; the filtering means and the storage means
being arranged to
filter the data stream for sections according to the at least one section
header parameter until an
application-defined predetermined number of sections have been stored, wherein
the
application-defined predetermined number of sections stored are a subset of
sections from the
filtered first group of sections.
In accordance with a further broad aspect of the present invention, there is
provided
a video processing device for storing a plurality of sections of a transmitted
data stream. The
video processing device comprises: means for receiving the data stream,
wherein the data
stream comprises sections, each section containing a header and a payload, the
section header
comprising parameters; means for filtering from the data stream a first group
of sections,
wherein the first group of sections comprises a first section, a plurality of
subsequent sections,
and a last section according to at least one given section header parameter;
means for storing
the first group of sections; the filtering means and said storage means being
arranged to filter
the data stream for sections according to the at least one section header
parameter, and to store
filtered sections from the first group in a circular buffer that can contain
an application-defined
predetermined number of sections until reception of the last section of the
first group, wherein
a subset of sections from the filtered first group of sections is loaded into
the circular buffer for
the application.
Preferred features of the present invention will now be described, purely by
way of
example, with reference to the accompanying drawings, in which:
Figure 1 shows the overall architecture of a digital television system
according to
the preferred embodiment of the present invention;
Figure 2 shows the architecture of an interactive system of the digital
television
system;
Figure 3 shows the arrangement of files within a module downloaded into the
memory of an interactive receiver/decoder;
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Figure 4 shows the arrangement of a section;
Figure 5 shows the arrangement of memory volumes of the memory of the
interactive receiver/decoder;
Figure 6 is a schematic diagram of interfaces of the receiver/decoder;
Figure 7 shows the architecture of the software in the receiver/decoder;
Figure 8 shows the architecture of a receiver system for downloading sections
from
an MPEG data stream;
Figure 9 shows the arrangement of bytes in a section which are used by a
hardware
prefilter;
Figure 10 shows an example of a hardware filter mask array and a hardware
filter
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value array of a hardware filter;
Figure 11 shows the arrangement of bytes in a section which are used by a
software
prefilter;
Figure 12 shows an example of the loading of a table;
Figure 13 shows an example of an arrangement of sections in a group of
sections;
Figure 14 shows an example of a following mode.download of a group of
sections;
Figure 15 shows an example of a preceding mode download of a group of
sections;
Figure 16 shows the arrangement of fields in a descriptor of a group of
sections: and
Figure 17 shows the arrangement of fields in a descriptor of a table of
sections.
An overview of a digital television system 1000 is shown in Figure 1. The
invention
includes a mostly conventional digital television system 2000 which uses the
known
MPEG-2 compression system to transmit compressed digital signals. In more
detail,
MPEG-2 compressor 2002 in a broadcast centre receives a digital signal stream
(typically a stream of video signals). The compressor 2002 is connected to a
multiplexer and scrambler 2004 by linkage 2006. The multiplexer 2004 receives
a
plurality of further input signals, assembles one or more transport streams
and
transmits compressed digital signals to a transmitter 2008 of the broadcast
centre via
linkage 2010, whi h can of course take a wide variety of forms including
telecom
links. The transmitter 2008 transmits electromagnetic signals via uplink 2012
towards
a satellite transponder 2014, where they are electronically processed and
broadcast via
notional downlink 2016 to earth receiver 2018, conventionally in the form of a
dish
owned or rented by the end user. The signals received by receiver 2018 are
transmitted to an integrated receiver/decoder 2020 owned or rented by the end
user
and connected to the end user's television set 2022. The receiver/decoder 2020
~ _ -_ _ -- - - .
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decodes the compressed MPEG-2 signal into a television signal for the
television set
2022.
A conditional access system 3000 is connected to the multiplexer 2004 and the
receiver/decoder 2020, and is located partly in the broadcast centre and
partly in the
decoder. It enables the end user to access digital television broadcasts from
one or
more broadcast suppliers. A smartcard, capable of deciphering messages
relating to
commercial offers (that is, one or several television programmes sold by the
broadcast
supplier), can be inserted into the receiver/decoder 2020. Using the decoder
2020 and
smartcard, the end user may purchase commercial offers in either a
subscription mode
or a pay-per-view mode.
An interactive system 4000, also connected to the multiplexer 2004 and the
receiver/decoder 2020 and again located partly in the broadcast centre and
partly in
the decoder, enables the end user to interact with various applications via a
modemmed back channel 4002.
Figure 2 shows the general architecture of the interactive television system
4000 of
the digital television system 1000 of the present invention.
For example, the interactive system 4000 allows an end user to buy items from
on-
screen catalogues, consult local news and weather maps on demand and play
games
through his television set.
The interactive system 4000 comprises in overview four main elements:
an authoring tool 4004 at the broadcast centre (or elsewhere) for enabling a
broadcast supplier to create, develop, debug and test applications;
an application and data server 4006 the broadcast centre, connected to the
authoring tool 4004 for enabling a broadcast supplier to prepare, authenticate
and
format applications and data for delivery to the multiplexer and scrambler
2004 for
insertion into the MPEG-2 transport stream (typically the private section
thereof) to
be broadcast to the end user;
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a virtual machine including a run time engine (RTE) 4008, which is an
executable code installed in the receiver/decoder 2020 owned or rented by the
end user
for enabling an end user to receive, authenticate, decompress, and load
applications
into the working memory 2024 of the receiver/decoder 2020 for execution. The
engine 4008 also runs resident, general-purpose applications. The engine 4008
is
independent of the hardware and operating system; and
a modemmed back channel 4002 between the receiver/decoder 2020 and the
application and data server 4006 to enable signals instructing the server 4006
to insert
data and applications into the MPEG-2 transport stream at the request of the
end user.
The interactive television system operates using "applications" which control
the
functions of the receiver/decoder and various devices contained therein.
Applications
are represented in the engine 4008 as "resource files". A "module" is a set of
resource
files and data. Several modules may be required to make up an application. A
"memory volume" of the receiver/decoder is a storage space for modules. An
"interface" is used to download modules. Modules may be downloaded into the
receiver/decoder 2020 from the MPEG-2 transport stream.
The elements mentioned in the previous paragraph are now described in more
detail.
For the purposes of this specification, an application is a piece of computer
code for
controlling high level functions of preferably the receiver/decoder 2020. For
example,
when the end user positions the focus of a remote controller on a button
object seen
on the screen of the television set 2022 and presses a validation key, the
instruction
sequence associated with the button is run.
An interactive application proposes menus and executes commands at the request
of
the end user and provides data related to the purpose of the application.
Applications
may be either resident applications, that is, stored in the ROM (or FLASH or
other
non-volatile memory) of the receiver/decoder 2020, or broadcast and downloaded
into
the RAM or FLASH memory of the receiver/decoder 2020.
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Examples of applications are:-
= An Initiating Application. The receiver/decoder 2020 is equipped with a
resident initiating application which is an adaptable collection of modules
(this
term being defined in more detail hereunder) enabling the receiver/decoder
2020 to be immediately operative in the, MPEG-2 environment. The
application provides core features which can be modified by the broadcast
supplier if required. It also provides an interface between the resident
application and downloaded applications.
= A Startup Application. The startup application allows any application,
either
downloaded or resident, to run on the receiver/decoder 2020. This application
acts as a bootstrap executed on arrival of a service in order to start the
application. Startup is downloaded into RAM and therefore can be updated
easily. It can be configured so that the interactive applications available on
each channel can be selected and run, either immediately after downloading or
after preloading. In the case of preloading, the application is loaded into
the
memory 2024 and is activated by the startup when required.
= A Program Guide. The Program Guide is an interactive application which
gives full information about programming. For example, it may give
information about, say, one week's television programmes provided on each
channel of a digital television bouquet. By depressing a key on the remote
controller 2026, the end user accesses an add-on screen, overlaid on the event
shown on the screen of the television set 2022. This add-on screen is a
browser giving information on the current and next events of each channel of
the digital TV bouquet. By depressing another key on the remote controller
2026, the end user accesses an application which displays a list of
information
on events over one week. The end user can also search and sort events with
simple and customised criteria. The end user can also access directly a
selected
channel.
= A Pay Per View application. The Pay Per View Application is an interactive
service available on each PPV channel of the digital TV bouquet in
conjunction with the conditional access system 3000. The end user can access
the application using a TV guide or channel browser. Additionally, the
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application starts automatically as soon as a PPV event is detected on the PPV
channel. The end user is then able to buy the current event either through his
daughter smartcard 3020 or via the communication server 3022 (using a
modem, a telephone and DTMF codes, MINITEL or the like). The application
may be either resident in the ROM of the receiver/decoder 2020 or
downloadable into the RAM of the decoder 2020.
= A PC Download application. On request, an end user can download computer
software using the PC download application.
= A Magazine Browser application. The magazine browser application comprises
a cyclic video broadcast of images with end user navigation via on-screen
buttons.
= A Quiz application. The quiz application is preferablly synchronised with a
broadcast quiz programme. As an example, multiple choice questions are
displayed on the screen of the television 2022, and the user can select an
answer using the remote controller 2026. The quiz application can inform the
user whether the answer is correct or not, and can keep count of the user's
score.
= A Teleshopping application. In one example of the teleshopping application,
offers of goods for sale are transmitted to the receiver/decoder 2020 and
displayed on the television 2022. Using the remote controller, the user can
select a particular item to buy. The order for the item is sent via the
modemmed back channel 4002 to the application and data server 4006 or to
a separate sales system the telephone number of which has been downloaded
to the receiver/decoder, possibly with an order to debit the account for a
credit
card which has been inserted into one of the card readers 4036 of the
receiver/decoder 2020.
= A Telebanking application. In one example of the telebanking application,
the
user inserts a bank card into one of the card readers 4036 of the
receiver/decoder 2020. The receiver/decoder 2020 dials up the user's bank,
using a telephone number stored in the bank card or stored in the
receiver/decoder, and then the application provides a number of facilities
which
can be selected using the remote controller 2026, for example for downloading
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via the telephone line a statement of account, transferring funds between
accounts, requesting a cheque book, etc.
0 An Internet Browser application. In one example of the Internet browser
application, instructions from the user, such as a request to view a web page
having a particular URL, are entered using the remote controller 2026, and
these are sent by the modemmed back channel 4002 to the application and data
server 4006. The appropriate web page is then included in the transmissions
from the broadcast centre, received by the receiver/decoder 2020 via the
uplink
2012, transponder 2014 and downlink 2016, and displayed on the television
2022.
Applications are stored in memory locations in the receiver/decoder 2020 and
represented as resource files. The resource files comprise graphic object
description
unit files, variables block unit files, instruction sequence files,
application files and
data files.
The graphic object description unit files describe the screens, the man-
machine
interface of the application. The variables block unit files describe the data
structures
handled by the application. The instruction sequence files describe the
processing
operations of the applications. The application files provide the entry points
for the
applications.
The applications constituted in this way can use data files, such as icon
library files,
image files, character font files, colour table files and ASCII text files. An
interactive
application can also obtain on-line data by effecting inputs and/or outputs.
The engine 4008 only loads into its memory those resource files it needs at a
given
time. These resource files are read from the graphic object description unit
files,
instruction sequence files and application files; variables block unit files
are stored in
memory following a call to a procedure for loading modules and remain locked
there
until a specific call to a procedure for unloading modules is made.
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With reference to Figure 3, a module 4010, such as a tele-shopping module, is
a set
of resource files and data comprising the following:
a single application file 4012;
an undetermined number of graphic'object description unit files 4014;
an undetermined number of variables block unit files 4016;
an undetermined number of instruction sequence files 4018; and
where appropriate, data files 4020 such as icon library files, image files,
character font files, colour table files and ASCII text files.
In the MPEG data stream, each module comprises a group of MPEG tables. Each
MPEG table may be formatted as a number of sections. In the MPEG data stream,
each section has a "size" of up to 4 kbytes. For data transfer via the serial
and
parallel port, for example, modules similarly are split into tables and
sections, the size
of the section varying with the transport medium.
Modules are transported in the MPEG data stream in the form of data packets of
typically 188 bytes within respective types of data stream, for example, video
data
streams, audio data streams and teletext data streams. Each packet is preceded
by a
Packet Identifier (PID) of 13 bits, one PID for every packet transported in
the MPEG
data stream. A programme map table (PMT table) contains a list of the
different data
streams and defines the contents of each data stream according to the
respective PID.
A PID may alert a device to the presence of applications in the data stream,
the PID
being identified using the PMT table.
With reference to Figure 4, each section 4300 typically comprises the
following fields:
table ID (TID) 4302, typically having a size of 1 byte, at the beginning of
the
section 4300;
section length identifier 4304, typically having a size of 2 bytes;
section number (SN) 4306 (eg. 1) of that section in the table, the SN
typically
having a size of 1 byte;
the total number of sections (LSN) 4308 (eg. 3) in that table, the LSN
typically
having a size of 1 byte;
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TID extension 4310, typically having a size of 2 bytes;
private data 4312; and
CRC 4314 of the section 4300. The purpose of the CRC 4314 is to check all
of the bytes in the section 4300; if the CRC 4314 correlates with all of the
preceding
data, the section is accepted by the receiver/decoder 2020. Similarly, the
private data
field 4312 may comprise an MD5 signature at the end of the field and
calculated from
all of the preceding contents of that field 4312.
In respect of data received via the serial or parallel interfaces, the fields
of a section
may vary; typically a section received via either= of the aforementioned
interfaces
comprises a reduced amount of data in fields 4302 to 4310 and no CRC 4314.
For a particular module/table, all of the sections making up that table have
the same
TID 4302 and the same TID extension 4310. For a particular application, all of
the
tables making up that application have the same TID but different respective
TID
extensions.
To access a module 4010 from, for example, the MPEG bitstream, both the PID
for
the module and a module directory are required. This directory simply lists
the
modules 4010 which can be downloaded from the carrier signal. Once this
directory
has been downloaded, it is possible for the application to download one or
more
modules 4010.
The concept of modules 4010 together with the concept of downloading small
pieces
of code allows the easy evolution of applications. They can be downloaded into
permanent FLASH memory of the receiver/decoder 2020 as resident software or
broadcast in order to be downloaded into the RAM of the decoder 2020 only when
needed by the end user.
A memory volume is a storage space for modules 4010. Such storage spaces are
located in the memory 2024 of the receiver/decoder 2020. With reference to
Figure
5, the memory 2024 is divided into typically a RAM volume 4022, FLASH volume
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4024, and ROM volume 4026. The memory may further be divided into memory
volumes associated with the various interfaces through which modules are
downloaded
into the receiver/decoder 2020, for example an MPEG volume for storing modules
downloaded from the MPEG bitstream and a serial volume for storing modules
received via a serial interface.
The RAM volume 4022 in turn is divided into a zone dedicated to firmware, a
working space for the engine 4008 and the buffers. The FLASH and other non-
volatile memory can be accessed either by an application or the engine itself
through
a device manager.
Each volume contains a list of modules 4010, each module 4010 containing a
list of
files 4012, 4014, 4016, 4018, 4020. It is possible to have two files bearing
the same
name and which may be located in distinct modules. For example, a version of
the
application is typically stored in the ROM volume 4026, with later versions
being
downloadable into the FLASH volume 4024 to substitute the version stored in
the
ROM volume with that volume stored in the FLASH volume 4024. The contents of
files may be compressed in LZW format, however as decompression of files takes
a
certain period of time they may be received in decompressed format.
Physical interfaces of the receiver/decoder 2020 are used for downloading
data. With
reference to Figure 6, the receiver/decoder 2020 contains, for example, six
downloading media; MPEG flow tuner 4028, serial interface 4030, parallel
interface
4032, modem 4034 and two card readers 4036.
With multiple sources of applications and multiple manufacturing sources of
receiver/decoder 2020, it is important that one application behaves in the
same way
on every receiver/decoder, and each receiver/decoder should execute every
application
in the same, correct manner. With reference to Figure 7, the receiver/decoder
2020
comprises a run time engine 4008 running under the control of a microprocessor
and
a common application programming interface 4054. They are installed in every
receiver/decoder 2020 so that all receiver/decoders 2020 are identical from
the
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application point of view.
Figure 7 shows the architecture of the receiver/decoder 2020 for running
applications
4056. The virtual machine 4007 executes = applications 4056, which may
comprise
applications 4056' coupled directly to the virtual niachine or applications
4056"
downloaded to the receiver/decoder 2020 from, for example, the MPEG data
stream.
The run time engine 4008 also displays graphics and text, calls devices for
services,
receives "events" and uses functions of a library 4058 for specific
computation.
With reference to Figure 7, with respect to an application a function of the
decoder
2020 is "seen" as a device 4060. There may, therefore, be functions of the
receiver/decoder 2020 which may not be seen by any application.
A device 4060 comprises a logical device unit which may correspond to a
component
4062 or physical interface 4064 of the hardware 4066. Such devices are
referred to
as "low level devices" 4068. The output of such a device 4068 may be connected
to
at least one device driver 4070 for converting the logical signals output by
the device
4068 into signals required to drive, for example, a hardware interface 4064.
Alternatively, the device 4068 may itself drive a component or interface of
the
receiver/decoder 2020, that is, the output of the device may be connected
directly to
the hardware 4066.
Examples of low level devices 4068 are described below.
An LCARD device enables a program to communicate with the smartcard contained
in one smartcard reader 4036, and an RCARD device enables a program to
communicate with the smartcard contained in the other smartcard reader 4036.
For
example, these devices enable a program to read the state of the card, read
the card
history and send an input message to the card. The devices also inform a
program of
the insertion of a card in to the reader, removal of a card from a reader and
card reset
if not requested by the program. The LCARD and RCARD devices are specific to
the
protocol used for running the card. Typically an IS07816 protocol is used.
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An SCTV device enables a program to verify and configure of a scart outlet to
the
= television set 2022. For example, this device enables a program to request
information about the sound characteristic of the scart outlet, perform a
"MUTE" on
the sound and dynamically program RGB levels.
A TUNER device enables a program to use the tuner 4028. For example, the
device
enables a program to perform a scan from either a minimum frequency or a
current
frequency of the tuner, read the tuner parameters and program the tuner.
A SERIAL device enables a program to communicate with equipment via a serial
link
and a PARALLEL device enables a program to communicate with equipment via a
parallel link. For example, these devices enable a program to send a message
via the
respective link and inform a program of the reception of a message via that
link.
A MODEM device allows the receiver decoder to communicate with a data service
via an internal half-duplex modem supporting V23. The MODEM device requests
the dialling of a number, the sending of a message to the data server and
disconnection of the modem, and signals reception of a message, the detection
of
errors and the loss or detection of a carrier.
Remote devices, executed in a remote location, can be any of the local
devices, except
that a port and protocol must be defined.
In addition to "low level devices" the receiver/decoder 2020 may also include
"high
level devices" 4072 which control operations of the receiver/decoder 2020.
With respect to sections loaded from an MPEG data stream, a device 4072
referred
to as an "MLOAD device" allows an application to load an MPEG section, a
complete
MPEG table or a group of MPEG sections corresponding to hardware and software
filtering criteria.
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With reference to Figure 8, electromagnetic signals are received by receiver
2018 and
transmitted to MPEG tuner 4028. The tuner typically scans a range of
frequencies,
a stopping only when carrier frequency is detected within that range. The thus
detected signals are transmitted to demodulator 4500, which demodulates the
signals
and transmits them to demultiplexer 4502. Demultiplexer 4502 is connected to
MPEG
chip 4504, which in turn is connected to television 2022. The demultiplexer
4502 is
also connected to hardware filter 4506 which typically provides up to 32
outputs
connected to RAM volume 4022 of the receiver/decoder 2020.
The electromagnetic signals received by the demtiltiplexer 4502 comprise a
number
of data streams of data packets, typically comprising a stream of video
packets, a
stream of audio packets, a stream of teletext packets and a stream of subtitle
packets
for a service provided by the broadcast supplier. These data packets are
demultiplexed
by the demultiplexer 4502 and transmitted to MPEG chip 4504 for decoding into
signals for the television set 2022.
The data packets relating to applications are transmitted to the hardware
filter 4506.
With reference to Figure 9, the hardware filter, or prefilter, 4506 utilises
one or more
of typically 8 bytes of a section 4508 of the data stream, typically offset
byte 0 (4510)
and offset bytes 3 to 9 (4512) to filter sectioris from the data stream. These
bytes
include the TID 4302, section number 4306, last section number 4308 and TID
extension 4310 of the MPEG section 4508.
To define the hardware prefilter characteristic, the application specifies
which bits of
the section 4508 to take into account and the expected value of each selected
bit.
Accordingly, the hardware prefilter 4506 comprises a filter mask array 4514
and a
filter value array 4516 respectively, an example of each being shown in Figure
10.
In Figure 10, bits 4518, 4520 and 4522 are chosen using filter mask 4514 and
the
value of each of these bits, 0, 1 and 0 respectively, is chosen using filter
value 4516.
With those filtering criteria, MPEG section 4524 would be output to the
buffers of the
RAM 4022 of the receiver/decoder 2020, whereas MPEG section 4526 would not be
output to the buffers.
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The hardware prefilter 4506 operates by means of a demultiplexer chip,
avoiding
wasting processor power within the main processor.
The microprocessor may utilise the RAM 4022 of the receiver/decoder 2020 in
which
the sections are stored as a software filter 4526. By means of the software
filter 4526,
it is possible to select which of the sections loaded in the buffers of the
RAM volume
4022 will be brought to the application.
The principles of software filtering are similar to those of hardware
filtering. The
software filter 4526 uses typically 8 consecutive 'bytes 4528 of data in the
MPEG
section 4508. As shown in Figure 11, the position of the first byte 4530 of
these 8
consecutive bytes is defined with an offset 4532 based on the first byte 4510
in the
section 4508.
If after loading via the hardware filter the data stored in an MPEG section
does not
correspond to the criteria for software filtering, the buffer in which the
MPEG section
is stored may be used to load another MPEG section.
To load an MPEG section from the MPEG data stream, the MLOAD device is
supplied typically with the following information:
the PID of the data stream in which the MPEG section is to be found;
a descrambling data array comprising a number of PID ECMs for descrambling
PIDs;
an operator reference, which recognises a particular ECM to be used to
descramble the PID;
the hardware filter value array to be applied;
the hardware filter mask array to be applied;
the software filter offset value to be applied;
the software filter value array to be applied;
the software filter mask array to be applied;
the maximum size of the section (up to 4096 bytes); and
a time out function determining how long the device should wait to load a
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section, a group of sections or a table.
When it is indicated that the maximum size of a section is 512 bytes, the size
of the
section cannot exceed 512 bytes.
The section is loaded all at once into the buffer of the RAM volume 4022
allocated
by the device. When the section has been loaded, and if it corresponds to the
software filtering criteria, the device should free the demultiplexing route
and inform
the application via an "event", which includes an execution report and the
address of
the buffer containing the section. After loading, a section is identified by
the address
of the buffer in which it is stored.
When a table is to be loaded, the device is also supplied with the TID 4302.
Each
section of the table is loaded into the respective buffer allocated therefor
all at once.
However, it is not essential that the tables are loaded by putting sections
end to end
and in section order. As each section of the table is loaded, the device may
inform
the application that that section of the table has been loaded. Alternatively
or
additionally the device may inform the application via an event that the
entire table
has been loaded successfully into the buffers allocated therefor.
With reference to Figure 12, a table is typically loaded in the following way
(description of the software filtering is omitted for reasons of clarity
only);
step 1: specify the hardware filter mask array 4534 and the hardware filter
value array 4536;
step 2: load a first section 4538 corresponding to the hardware (and software)
filter;
step 3: read the value of the LSN 4540 of the section 4538 to determine the
number of sections to be loaded (= LSN + 1) and change the hardware filter
mask
array 4534 and the hardware filter value array 4536 according to the value of
the LSN
4540;
steps 4 to 6: load the remaining sections 4542, 4544 and 4546 according to the
values of the TID and the ISN and send an event to the application.
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Table loading is only complete when an event indicating successful downloading
is
entered into the queue of the run time engine 4006. Before this event is
placed in the
engine queue, abortion of the loading of the table should be successful.
After a table has been loaded, it is identified with fi name assigned to it by
the
application when requesting the downloading of a table.
Information regarding the way in which a table is stored in the memory of the
receiver/decoder 2020 can be accessed via a call which returns a descriptor of
the
table. An example of such a descriptor is shown in Figure 17. The descriptor
4700
includes a field 4702 comprising the total number of sections (LSN + 1) in the
table
and a list 4704 of the buffers containing the sections 4538, 4542, 4544 and
4546
which make up the table commencing with the section 4544 having the SN of "0",
then the section 4546 having the SN of "1" and so on up to the section 4542
having
the SN corresponding to the LSN.
A group of sections comprises all of the sections which correspond to the
hardware
and software filtering criteria. The sections appear cyclically in the MPEG
data
stream.
With reference to Figure 13, a group 4548 is delimited by two sections; a
first section
(SDG) 4550 and a last section (SFG) 4552, each of which corresponds to
respective
filter criteria, with the other sections (SG) 4554 of the group therebetween.
The loading of sections in a group may occur using two different loading
modes.
In the "following mode", a predetermined number of sections 4554 which
immediately
follow the SDG 4550 are loaded. For each type of section (SDG, SG, SFG), the
application identifies the TID, hardware filter, software filter and the
maximum section
length.
With reference to Figure 14, the device preferably first applies hardware and
software
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filtering criteria to enable the downloading and storing of the SDG 4550 only
This
avoids the loading of redundant SGs 4554 in buffers of the RAM memory volume
4022 of the receiver/decoder 2020 prior to the loading of the SDG 4550. Upon
detection, SDG 4550 is stored in a memory =location or buffer 4556. The device
then
applies hardware and software filtering criteria to e3iable the downloading of
the
desired SGs and SFG from the group of MPEG data sections.
In the example shown in Figure 14, three SGs 4554 from a group of MPEG
sections
comprising one SDG, seven SGs and one SFG are to be downloaded from the MPEG
data stream. Following storage of the SDG 4550' in buffer 4556, the first SG
4558
from the group of MPEG sections to be transmitted after the SDG 4550 is stored
in
buffer 4560. Likewise, the second SG 4562 from the group of MPEG sections to
be
transmitted after the SDG 4550 is stored in buffer 4564 and the third SG 4566
from
the group of MPEG sections to be transmitted after the SDG 4550 is stored in
buffer
4568.
Storage of the SGs continues until either the required number of sections 4554
have
been stored or the SFG 4552 is downloaded. If downloaded, the SFG 4552 is not
stored in a memory location.
As each section of the group is loaded, the device may inform the application
via an
event that that section of the group has been loaded. Alternatively, or
additionally,
the device may inform the application of only either the completion of the
storage of
the MPEG sections or the downloading of the SFG 4552 by sending an event to
the
application.
In the "preceding mode", a predetermined number of sections which immediately
precede the SFG are stored in the memory locations. For each type of section
(SDG,
SG, SFG), the application identifies the PID, TID, hardware filter, software
filter and
the maximum section length.
Loading in this mode requires the use of a circular buffer to store MPEG
sections.
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With reference to Figure 15, the device preferably first applies hardware and
software
filtering criteria to enable the downloading and storing of the SDG 4570 only.
This
avoids the loading of redundant SGs 4544 in the RAM memory volume 4022 of the
receiver/decoder 2020 prior to the loading of the SDG 4570. Upon detection,
SDG
4550 is not stored. The device then applies hardware and software filtering
criteria
to enable the downloading of the desired SGs and SFG from the group of MPEG
data
sections.
In the example shown in Figure 15, three SGs 4544 from a group of MPEG
sections
comprising one SDG, seven SGs and one SFG are'to be downloaded from the MPEG
data stream. Following the downloading of the SDG 4570, the first SG 4572 from
the
group of MPEG sections to be transmitted after the SDG 4570 is stored in
buffer
4574. Likewise, the second SG 4576 from the group of MPEG sections to be
transmitted after the SDG 4550 is stored in buffer 4578 and the third SG 4580
from
the group of MPEG sections to be transmitted after the SDG 4570 is stored in
buffer
4582.
The fourth SG 4584 from the group of MPEG sections to be transmitted after the
SDG
4550 is stored in buffer 4574, that is, the buffer in which the first SG 4572
had been
stored. Similarly, each of the subsequently transmitted SGs 4586, 4588 and
4590 are
stored in buffers 4578, 4582 and 4574 respectively.
Storage of SGs in this cyclic manner is continued until the SFG 4592 is
detected by
the device. This is the case even if the desired number of SGs have not been
loaded
before the SFG is detected. Upon detection, the SFG 4592 is stored in a
buffer, and
an event indicating successful downloading of the group is sent to the
application.
Information regarding the way in which a group is stored in the RAM 4022 of
the
receiver/decoder 2020 can be accessed via a special call which returns a
descriptor of
the group. An example of such a descriptor is shown in Figure 16. The
descriptor
4600 includes a field 4602 comprising the number of sections in the group and
a list
4604 of the buffers containing either the SDG or the SFG (depending on the
loading
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mode) and the sections SG which make up the group in the order of loading.
After the group has been loaded, it is uniquely identified with a name
assigned to it
by the application when requesting the dovWnloading of the group.
It is possible to add a section to a group or to delete a section from a
group. A
section may belong to more than one group.
When the application requests the addition of a section to a group, the
address of the
buffer containing the new section is put at the end of the descriptor 4604,
and the field
4602 is updated. When the application requests the deletion of a section from
a
group, the address of the buffer containing this section is suppressed in the
descriptor
4600, and field 4602 is updated. If the section was not the last section in
the group,
the descriptor is reorganised to remove any empty memory spaces. Thus, it is
possible to have an "empty group" by deleting all of the sections.
Devices are identified with a unique identifier, for example,
"LCARD_DEVICE_ID"
identifies the LCARD device and "RCARD DEVICE ID" identifies the RCARD
device.
When a new device 4062 is created, it can be installed in existing decoders
2020 by
downloading the relevant application 4056 from the broadcast centre. Typically
the
maximum number of devices handled by one manager is 256.
This downloading is performed in the receiver decoder 2020 by an application
4056
which checks the hardware and software versions and, if correct, loads the
software
module representing the new device 4062 and asks a procedure of the toolbox
4058
to install the new device code within the firmware (in FLASH memory). This can
provide a flexible and secure installation of new functions within the decoder
2020
without affecting the rest of the software.
It will be understood that the present invention has been described above
purely by
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way of example, and modifications of detail can be made within the scope of
the
invention.
Each feature disclosed in the description, -and (where appropriate) the claims
and
drawings may be provided independently or in any appropriate combination.
In the aforementioned preferred embodiments, certain features of the present
invention
have been implemented using computer software. However, it will of course be
clear
to the skilled man that any of these features may be implemented using
hardware.
Furthermore, it will be readily understood that'. the functions performed by
the
hardware, the computer software, and such like are performed on or using
electrical
and like signals.
Cross reference is made to our co-pending applications, all bearing the same
filing
date, and entitled Signal Generation and Broadcasting (Attorney Reference no.
PC/ASB/19707), Smartcard for use with a Receiver of Encrypted Broadcast
Signals,
and Receiver (Attorney Reference No. PC/ASB/19708), Broadcast and Reception
System and Conditional Access System therefor (Attorney Reference No.
PC/ASB/19710), Downloading a Computer File from a Transmitter via a
Receiver/Decoder to a Computer (Attorney Reference No. PC/ASB/19711),
Transmission and Reception of Television Programmes and Other Data (Attorney
Reference No. PC/ASB/19712), Downloading Data (Attorney Reference No.
PC/ASB/19713), Computer Memory Organisation (Attorney Reference No.
PC/ASB/19714), Television or Radio Control System Development (Attorney
Reference No. PC/ASB/19715), Extracting Data Sections from a Transmitted Data
Stream (Attorney Reference No. PC/ASB/19716), Access Control System (Attorney
Reference No. PC/ASB/19717), Data Processing System (Attorney Reference No.
PC/ASB/19718), and Broadcast and Reception System, and Receiver/Decoder and
Remote Controller therefor (Attorney Reference No. PC/ASB/19720). The
disclosures
of these documents are incorporated herein by reference. The list of
applications
includes the present application.
