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Description  |
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TECHNICAL FIELD
This invention relates to interactive television systems and more
particularly to methods and apparatus by which a subscriber to an
interactive television service can receive specifically tailored programs
assembled from program segments broadcast throughout a cable television
system.
BACKGROUND OF THEN INVENTION
Cable television systems have made possible the transmission of many
channels of television programs to the homes of subscribers. Instead of
being limited to the number of VHF and UHF channels that can be
transmitted and received in a given area, the number of channels in cable
systems is limited only by the transmission characteristics of the cable
itself and the ability to compress the information in television programs
into narrower-bandwidth channels. The advent of fiber-optic transmission
systems for use in cable television networks has also vastly increased the
number of channels available.
Such increase in channels has also given rise to proposals for interactive
television systems wherein a subscriber can transmit information or
requests back into the system, which information or requests may
subsequently affect programs or information directed to such subscriber.
There are a wide variety of applications for interactive television
systems, such as video games, video catalog shopping, teaching systems,
movies on demand and audio programs. Each application can be tailored for
an individual subscriber, for example, a subscriber may be able to select
the language of the soundtrack in a movie. However, such systems typically
require the ability (i) to control specific programs or information sent
to each subscriber and (ii) to receive input messages or requests from the
subscriber.
A headend-to-subscriber channel does not need the full bandwidth of the
usual television cable channel if compression can be used. For example a
number of compressed and digitized television signals can be transmitted
over a single conventional 6 Mhz cable channel. Other program information,
such as high-fidelity audio, still video pictures or text can also be sent
in compressed form. By using a large number of conventional channels for
1TV purposes, such as is now possible with optical fiber distribution
systems, together with compression, it is conceivable that hundreds of
virtual channels could be made available.
Even with such a large number of channels, it may not be possible to
transmit a different program from the cable headend to each subscriber.
However, the needs of subscribers may overlap. For example, a number of
subscribers may wish to view the same movie, but at different times, or
with sound tracks in different languages. There may also be applications
where it is desired to transmit different combinations of program segments
to different subscribers, but where at any given time, a particular
program segment is being transmitted to more than one subscriber. One
example of such an application is the transmission of different commercial
messages to different subscribers watching the same program. Other
examples are applications in which one or more segments of a program has
alternatives and subscribers are given the ability to interactively select
particular alternatives for a given segment. For example, a movie could be
made with multiple ratings for different audiences, but with only certain
segments that are critical for the ratings needing to be different. Still
other examples are applications where subscribers have the ability to
select program segments as the program progresses; for example, a
subscriber may be able to select among different endings to a movie.
In many cable television systems, a special converter is used at the
subscriber location to allow the subscriber to select among the various
available channels, and possibly to "unscramble" premium channels for
which extra fees are payable. Such converters usually provide an output on
one of the channels that a standard television receiver can receive, such
as Channel 3. More recently, television receivers and video recorders have
been made available that are "cable ready," that is, with the ability to
receive and select among all the channels transmitted over the cable
system, but without the ability to unscramble premium channels. A
converter is still needed for the premium channels.
Many cable-ready television receivers have additional features, such as
picture-within-picture and remote-control tuning, that cannot be used
conveniently with cable converters that provide an output over a single
channel. Similarly, video recorders capable of being programmed to record
selected channels at selected times are defeated by such a converter.
Accordingly, it is desired to provide a converter for use in interactive
television systems that is "transparent" to unrestricted channels on the
cable system and that permits use of cable-ready features on television
receivers and video recorders.
SUMMARY OF THE INVENTION
One or more channels in a multi-channel cable television distribution
system are used for the transmission of interactive television (ITV)
signals in the form of packetized digital information from the cable
system headend to subscribers. A converter at each subscriber location is
connected between the cable system and the subscriber's television
receiver. Such converter contains a receiver for the ITV channels. Control
packets in the ITV signals are addressed to individual converters to
enable the receipt of one or more virtual channels by a converter. The
converter decodes and expands the packetized digital information in such
enabled channels and generates a conventional video signal, which is
transmitted to the subscriber's television receiver on one of the channels
used for the ITV signal from the headend, replacing the packetized digital
information.
Different components of television programs, such as the video and audio
components or different time segments of the program, are assigned to
different virtual channels. A particular subscriber's converter is
configured to receive a particular subset of program components by
enabling the converter to receive the virtual channels carrying the
components in such subset. An embodiment is disclosed in which different
combinations of program segments are enabled for different subscribers.
Another embodiment is disclosed in which the viewing of a program by
multiple subscribers who begin viewing at different times is synchronized
by using "filler" program segments having different lengths.
These and other aspects of the invention will become apparent from the
attached drawings and detailed description.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic block diagram of a cable television system adapted
for use by an interactive television system in accordance with the
invention.
FIG. 2 is a block diagram of a converter for use at subscriber locations of
an interactive television system.
FIG. 3 is a flow chart showing the operation of controller 114 in FIG. 2
upon receipt of a packet of information from the cable system.
FIGS. 4 and 5 are diagrams showing various time relationships among program
segments in a multicasting environment.
FIG. 6 is a flow chart showing the operation of ITV server/20 in FIG. 1 in
scheduling program segments in one embodiment of the invention.
DETAILED DESCRIPTION
FIG. 1 is a schematic block diagram of a cable television system adapted
for use by an interactive television system in accordance with the
invention. A typical cable television system comprises headend equipment
101 at a central location, a distribution network consisting of various
feeders 102 and branches 103 and connections to subscriber locations such
as 104, where converters and television receivers (or cable-ready
television receivers alone) receive the signals from the distribution
network. In a typical cable television system, various television programs
are fed into the different channels of the system by headend equipment
101. Such programs may be received, for example, from local broadcasts by
broadcast receivers 110, from communications satellites by satellite
receivers 111 or directly from local sources 112.
Interactive television (ITV) subscribers are served via dedicated
distribution channels of the cable television system from ITV server 120.
Server 120 obtains its programming material from such sources as
programming center 121, or program library 122. Program library 122
contains stored versions of movies, musical selections, texts, pictorial
information and other materials that may be accessed by ITV subscribers in
conjunction with an ITV service or application. Programming center 121 may
be a direct source of program material for server 120 or may prepare such
material for library 122.
ITV server 120, programming center 121 and program library 122 may be at
the same or different locations and may themselves be connected in
networks. There can be multiple servers 120 for different cable systems.
Program library 122 may consist of a number of libraries at different
locations. However, there will typically be a server 120 dedicated to a
particular cable system to interact with the ITV subscribers on that
systems distribution network.
There arc a wide variety of possible configurations for server 120, all of
which will typically include at least one central processor to control
programs and other information transmitted to subscribers 104 over the
dedicated ITV channels in the cable system and to receive and respond to
uplink messages from subscribers 104.
Using well-known compression techniques, a number of full-motion television
signals can be transmitted in packetized form over a cable channel in a
cable television system. For example, a full-motion NTSC television signal
can be compressed and digitized for transmission at 1.5 Mbits/second. By
packetizing such digital information and interleaving such packets, it is
possible that as many as 16 such television signals (24 Mbits/second) can
be sent via "virtual channels" in a standard 6 MHz cable channel. If a
lower bandwidth signal (such as an audio signal) is to be sent over a
virtual channel, fewer packets need be transmitted for such virtual
channel per unit of time.
A typical packet consists of two bytes for a polling address, two bytes
identifying the virtual channel of which the packet is a part and 48 data
bytes. The data bytes contain the compressed video, audio or other
information being transmitted in the virtual channel. One virtual channel
(for example, channel 00) is reserved for control messages. A typical
control message includes a field containing the address of the converter
for which the message is intended, a field identifying the virtual channel
to which the message relates, a field specifying the kind of data to be
transmitted on such virtual channel (i.e. still pictures, full motion
video, stereo audio, text) and other control information. A television
signal is typically transmitted over two virtual channels: one for the
video portion, the other for the audio. Control messages are also used to
initialize converters.
FIG. 2 is a block diagram of a converter 200 for connection between a cable
system and a television receiver at a subscriber's premises. Input cable
202 is typically a coaxial cable or an optical fiber cable connected to
the cable distribution system. Cable 202 is connected to inputs of
band-stop filter 204, selectable channel receiver 206 and ITV channel
receiver 208 and to the output of uplink modulator 210. Cable 202 is part
of an input circuit (not shown) that also contains any interface
apparatus, such as optical/electrical transducers and amplification and
buffering circuits needed to connect the cable system to filter 204,
receivers 206 and 208 and modulator 210. Such interface apparatus and
amplification and buffering circuits are well known to those skilled in
the art.
ITV channel receiver 208 is tuned to receive the cable channel over which
the packetized digital information for the interactive television features
is being transmitted. The actual cable channel or channels used for such
purpose are assigned by the administrators of the cable system. If more
than one such ITV channel is provided, one of the channels is usually
considered the "default" channel, which is the channel used to initialize
converters such as converter 200. Upon initialization, a converter can be
transferred to a different ITV channel by means of a control message. The
output of tuner 208 is a digital bit stream comprising the packetized
digital information, which is forwarded to controller 214.
Controller 214 performs many functions and is typically a microprocessor
with both random-access memory (RAM) and read-only memory (ROM).
Controller 214 sends control and video information to selector/combiner
217, sends control messages to receivers 206 and 208 specifying the
identity of channels to be received, receives manual inputs from manual
input devices 218, sends video packets to decoder 2 15 and audio packets
to decoder 216, and transmits information to the cable headend via uplink
modulator 210. An audio packet can contain information for more than one
audio channel. Controller 214 can also be a source of audio and/or video
information. Such information can be retrieved from memory in controller
214 or generated by computer programs in controller 214 under the control
of messages from receiver 208 or input devices 218. Examples of such
information are symbols, icons, text or other stored images to be used as
video overlays or synthesized sounds to be combined with audio signals.
Decoders 215 and 216 can also be microprocessors, such as digital signal
processors, specifically programmed to decode compressed video or audio
information, as the case may be, in accordance with the appropriate
decoding algorithm, as is well known in the art. Other output devices 220
capable of receiving digital information, such as a printer, can be
connected to controller 214 as desired.
The output of selector/combiner 217 is a television signal, the components
of which can be either (i) selected from one of a number of sources, such
as receiver 206, controller 214, decoder 215 or decoder 216 or (ii)
combined from such sources. In its simplest form, selector/combiner 217
forwards to modulator 222 either the television signal received by
receiver 206 or the television signal obtained by combining video decoded
by decoder 215 with audio decoded by decoder 216. Other versions of
combiner 206 can include apparatus controlled by controller 214 to combine
various video and audio sources into the television signal to be
transmitted to modulator 222. Many techniques are known in the art for
combining video sources, such as overlays, windows and split screens.
Selector/combiner 217 operates on digital representations of video signals
in which each pixel of a scene is represented by a number of bits and on
digital representations of audio signals in which sounds are represented
by digital samples. The outputs of decoders 215 and 216 and any audio or
video outputs from controller 214 are in digital form; also, the
television signal from receiver 206 is converted to digital form in
converting apparatus (not shown). Such converting apparatus is well known
in the art. These digitized video and audio elements are combined in
selector/combiner 217 to produce a sequence of digital frames and digital
audio samples (possibly for more than one audio channel). These samples
are then converted to a conventional television signal, such as an NTSC
signal, by apparatus (not shown) also well known in the art.
Band stop filter 204 deletes at least one of the ITV channels, preferably
the default channel, from the signal received from cable 202, passing the
remaining channels to output cable 230. Modulator 222 modulates the
television signal received from selector/combiner 217 into one of the
blocked 1TV channels on output cable 230. Thus, converter 200 replaces the
packetized digital signal received from the cable system in such ITV
channel with the television signal from selector/combiner 217. Such ITV
channel can then be selected and viewed in the conventional way on a
cable-ready television receiver connected to output cable 230. As
described above, the television signal modulated into such ITV channel can
be produced from ITV packets received over any of the ITV channels.
For applications in which audio programs arc transmitted over an ITV
channel, a separate audio output can be provided, as shown at 240, which
can be used by equipment such as a high-fidelity sound system. Such audio
output can have more than one channel, if desired.
As mentioned above, each packet received in an ITV cable channel contains
identification of a virtual channel. Program information can be
"multicast" on virtual channels for receipt by one or more subscribers. As
also mentioned above, control messages are sent over at least one of the
virtual channels not being used for program information. Different types
of programs can be transmitted in each virtual channel; for example, full
motion video, still pictures, audio or text. When converter 200 is to
receive a program from a virtual channel, a control message addressed to
converter 200 causes controller 214 to store the identification of such
virtual channel. Thereafter, controller 214 processes the contents of each
packet identified as part of such virtual channel. Moreover, controller
214 can be set to process information in more than one virtual channel, if
desired. For example, the audio and video portions of a movie can be sent
simultaneously on different virtual channels, possibly with soundtracks in
different languages on different channels.
Other uses of multiple virtual channels for a single subscriber can be
sequential in nature. For example, it may be desired to transmit different
sequences of program segments to different subscribers. To accomplish
this, the segments are sent over different virtual channels in the correct
time sequence, and the virtual channels corresponding to the sequence of
segments for a particular subscriber are enabled for that subscriber.
Transitions between segments arc synchronized so that at the end of one
segment the next begins. Multicasting will be described in more detail
below.
FIG. 3 is a flow chart showing the overall operation of controller 214 on
receipt of a packet from receiver 208. If the "virtual channel" bytes
indicate that such packet is a control message, (block 302) and the
address field in the control message indicate that the message is intended
for converter 200 (block 304), then controller 214 performs the control
function specified by the remaining contents of the message (block 306).
If the "virtual channel" bytes indicate that such packet is part of a
program channel, such as a channel carrying an encoded and digitized video
signal, and controller 214 is currently enabled to receive from such
virtual channel (block 308), then controller 214 processes the packet
contents in accordance with the type of program in such virtual channel
(block 310), sending data from the packet to the input buffer in the
appropriate output device, such as decoder 215 or decoder 216.
Each packet in which the "polling address" bytes indicate that converter
200 is being polled (block 312) causes such converter to transmit an
uplink message the cable headend (block 314). (The address in the "polling
address" bytes is not necessarily the same as in the address field in a
control message that may be included in the same packet). This uplink
message, typically no more than a few bytes, can contain control
information or information entered manually by the subscriber in one of
manual input devices 218. Because this message is initiated by a downlink
message (from the headend to the converter) having an address known at the
headend, this address can be associated with the uplink message when
received, and there is no need to identify the source of uplink messages.
Uplink messages can be used for a number of purposes, particularly in
interactive situations such as selection programs or program sequences.
Polling and the use of uplink messages for other purposes, such as
initialization and verification purposes, are described in more detail in
U.S. Pat. No. 5,373,288 issued Dec. 13, 1994.
As mentioned above, controller 214 can contain both RAM and ROM. The ROM
includes computer programs that can be permanently loaded, such as
initialization routines; whereas the RAM can be downloaded from the
headend by the use of control messages. Such downloading will typically
occur when a converter is first connected to the cable system or when
programs must be updated. Also, different programs for different purposes
can be downloaded in controller 214 at different times. Such downloading
capability eliminates the need for program-loading capabilities at
converter 200, although such capability could be provided if desired.
Converter 200 forms a facility dedicated to the subscriber, and in many
applications it will be most convenient to have the functions of converter
200 performed at the subscriber's location, as has been described.
However, it is possible, and may be desirable for some applications, to
perform all or part of such functions at a central location, for example,
at the cable head end or in a telephone central office. Such an approach
may permit sharing some of the functions and reducing the amount of
dedicated equipment. However, for the kinds of applications presently
contemplated, such an approach requires at least some equipment dedicated
to each subscriber at the central location and dedicated channels from the
central location to the subscriber for at least one video signal and
stereo audio signals. In the case of a cable television system, such
dedicated channels can be virtual channels as described above and
converter 200 at the subscribers location can be simplified to receive and
decode only such dedicated channels. All the functions relating to channel
selection can be performed at the central location.
When a subscriber becomes inactive, the equipment and channels reserved for
such subscriber can be reassigned to a new subscriber. Thus, dedicated
equipment and channels are needed only for the number of subscribers
expected to be active simultaneously.
FIG. 4 is a graph showing time relationships among various program segments
in different virtual channels in a multicasting environment wherein
different combinations of program segments are transmitted to different
subscribers. The circled numerals relate to virtual channel numbers. For
example, line 401 shows two program segments being transmitted in virtual
channel 1, a first segment being transmitted between t.sub.0 and t.sub.1
and a second segment between t.sub.2 and t.sub.3. Lines 402-407 show
single program segments being transmitted at various times in virtual
channels 2-7, respectively. The starting times, ending times and relative
lengths of the time periods shown are arbitrary and are for illustration
only.
As mentioned above, a converter can be enabled for more than one virtual
channel at a time. Lines 408-411 show combinations of program segments
received by different subscribers for whom different combinations of
virtual channels are enabled. For example, line 408 shows that a
subscriber having virtual channels 1 and 4 enabled will receive virtual
channel 1 during the period from t.sub.0 to t.sub.1, virtual channel 4
during the period from t.sub.1 to t.sub.2 and virtual channel 1 during the
period from t.sub.2 to t.sub.3. Line 409 shows that a subscriber having
virtual channels 1 and 5 enabled will receive from virtual channels 1, 5
and 1, respectively, during such periods. Such an arrangement could result
where virtual channel 1 is carrying a television program and virtual
channels 4 and 5 are carrying different sets of commercials. Lines 410 and
411 show sequences of program segments that could result when three
virtual channel segments are enabled for different subscribers.
It should be emphasized here that there can be many more virtual channel
identities assigned and enabled than the number of actual virtual channels
that can be active at any given time. For example, seven different virtual
channels are identified in FIG. 4 but no more than they are being used at
any one time. The number of active virtual channels is limited by the
bandwidth of the distribution system, but the number of identities is
limited, for practical purposes, only by the capacity of the memory
elements storing virtual channel identities and the lengths of control
messages enabling virtual channels.
FIG. 5 shows programming segments in another multicasting application where
the same program is to be received by a number of subscribers but with
staggered starting times. An example of such an arrangement is an
interactive television system wherein a subscriber can request a movie for
viewing. During a given time period, many requests to view a currently
popular movie might be received, but at different times. It is desirable
to respond to a subscriber's request by starting the movie without delay,
but it is not desirable to fill up virtual channels with too many
time-staggered versions of the same movie. Thus, a number of different
versions of the starting portion of the movie are made, each having a
different length, which can be used as "fillers" for use between the time
a request is received and the time the main portion of the movie is next
scheduled to begin. The fillers are of different incremental lengths. For
example, if five different fillers are made with lengths of two, three,
four, five, six and seven minutes, then the main portion of the movie will
never need to be started more frequently than every five minutes, but the
wait for the start as seen by the viewer will never be more than one
minute.
Referring to FIG. 5, lines 501-506 illustrate responses by server 120 to
requests received at staggered times for showings of a movie. The first
request (line 501 ) at time to starts the longest filler on virtual
channel 10 and schedules a start of the main portion of the movie at time
t.sub.1 (when such filler is finished) on virtual channel 1. Virtual
channels 1 and 10 are enabled at the requesting subscriber's converter.
The subsequent requests (lines 502-504), which occur more than the time of
the shortest filler before t.sub.1, have successively shorter fillers
scheduled in virtual channels 11, 12 and 13, respectively, and the
appropriate virtual channels are enabled for the requesting subscribers.
The request in line 505 is too late for the shortest filler to run before
the showing of the main portion starting at t.sub.1, so the longest filler
is started again on virtual channel 14 and a new showing of the main
portion is scheduled to start at t.sub.2 on virtual channel 2, and virtual
channels 2 and 14 are enabled for the requesting subscriber in line 505.
The request in line 506 also makes use of virtual channel 2 for the main
portion, but the filler for such request can reuse channel 10, since the
use of that channel shown in line 501 is completed. However, before
channel 10 is reused, control messages are sent to disable such channel
for subscribers who were receiving such channel during the time period
shown in line 501.
FIG. 6 is a flow chart showing the operation of ITV server 120 in FIG. 1 on
receipt of a request for a movie to be run at different starting times and
with different-length fillers as described above. On receipt of a request
for the movie (block 601 ), if the next start of the main position of the
movie has not been scheduled (block 602), a virtual channel is assigned to
the longest filler and a starting time for such filler is scheduled (block
603). Then a virtual channel is assigned and a next starting time for the
main portion of the movie is scheduled to coincide with the time the
longest filler ends (block 604). Finally, the converter from which the
request originated is enabled to receive the virtual channels to which the
longest filler and the next start of the main portion have been assigned.
The longest filler can be scheduled to begin immediately, but it may be
desirable to wait a short interval to catch additional requests so that
such filler is not run for just one subscriber.
If an additional request is received before the main portion starts, the
time remaining until such start is determined (block 610) and, if the time
is longer than the shortest filler (block 611 ), the longest filler that
will fit in such remaining time is selected (block 612). If the selected
filler has not already been scheduled (block 613), then a virtual channel
is assigned to such filler and a starting time scheduled (block 614). Such
starting time is chosen so that the filler ends when the main portion
begins. Then, the requesting converter is enabled to receive the virtual
channels to which the selected filler and the next start of the main
portion have been assigned (block 615).
If an additional request arrives too late for the shortest filler to run
before the next start of the main portion (block 611), then new starts of
the longest filler and the main portion are scheduled and new virtual
channels assigned (blocks 603, 604 and 605). As mentioned above, it may be
desirable to delay the start of the longest filler for a short interval to
catch more requests. Such delay should be no more than the difference in
running time between the longest filler and the next longest; for example,
the delay can be thirty seconds if such difference is one minute.
When the running of a particular filler or the main portion has been
completed, then the virtual channel used for such portion is disabled at
all converters that were set to receive it by means of control messages
sent to such converters and such virtual channels can then be reassigned.
As can be seen, the number of virtual channels needed for multiple
showings of the same movie at staggered times is reduced by the method
described above.
The above-described technique can be used with more than one level of
fillers, if desired, to cope with a large number of starting times but
without a large number of simultaneous runnings of the main body of a
movie. For example, a set of "fine" fillers such as described above having
one-minute length differences (say two to seven minutes long) can be used
in conjunction with a set of "coarse" fillers having five-minute
differences (say five to fifteen minutes long). The possible combinations
of one fine filler and one coarse filler range from seven to twenty-two
minutes in length, and the main body of the movie will need to be
restarter no more frequently than every fifteen minutes. Such technique
will necessitate the assignment of three virtual channels for each
subscriber: one for the fine filler, one for the coarse filler and one for
the main body of the movie. It will be apparent that the filler times
described above are merely exemplary and that other times can be used in
accordance with the invention, if desired. All that is necessary is to
have a combination of one or more fillers that, when taken together,
substantially fill the time between a request and the next start of the
main body of the movie.
In addition to using fillers at the start of a movie, the same techniques
as described above can be used to insert fillers at preselected
intermediate points in the movie to permit subscribers to interrupt their
viewing and resume after a pause.
As mentioned above, another application of multicasting in accordance with
the invention can be the transmission Of a television program with
different audio signals for different subscribers, such as a movie with
the sound track in different languages. The video portion of the movie can
be transmitted over one virtual channel and each language version of the
soundtrack can be transmitted on an additional virtual channel.
Alternatively, the video portion and sound track in one language can be
transmitted on a conventional cable channel and sound tracks in other
languages on virtual channels. Since the bandwidth needed for audio is
much less than that needed for a movie with both audio and video, the
number of packets per unit time for such soundtrack will be less than that
for the movie and more virtual channels for such soundtracks can be packed
into one ITV channel. Note that in this particular application of
multicasting two virtual channels are being used simultaneously, not
sequentially, as in the applications described previously.
One skilled in the art will realize that combinations of different
soundtracks, staggered starting times and/or sequences of program segments
can be used in accordance with the methods of the invention, but that such
combinations may require larger numbers of virtual channels.
The aspects of the invention have been described above mainly in the
context of terrestrial cable television systems wherein the number of
usable channels is augmented by virtual channels resulting from the
transmission of digital packets in at least one of the conventional
channels. However, the principles of the invention can be used in
conjunction with other signal distribution systems in which signals are
broadcast from a central location to multiple subscribers. For example,
multichannel radio or television broadcasting systems could also make use
of the invention, as could systems wherein signals are broadcast from
satellites. All that is necessary is the ability to transmit control
messages from the server to facilities dedicated to the subscriber, such
as converter 200 at the subscriber location, able to receive one or more
channels as prescribed by the control messages and to detect and decode
the signals in such channels to recreate the appropriate audio, video or
other signals for use by the subscriber.
The invention has been shown and described with reference to particular
embodiments. However, it will be understood by those skilled in the art
that various change may be made therein without departing from the spirit
and scope of the invention.
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