Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: BANDWIDTH i~iANAGEMENT ON A HYBRID POINT TO POINT BROADCAST
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to interactive television systems and more particularly
to optimization of data
delivery in an interactive television system which has both a broadcast
channel and a point-to-point channel.
2. Description of the Related Art
Interactive television systems can be used to provide a wide variety of
services to viewers. Interactive
television systems are capable of delivering typical video program streams,
interactive television applications,
text and graphic images, web pages and other types of information. Interactive
television systems are also
capable of registering viewer actions or responses. Interactive television
systems can be used for such purposes
as marketing, entertainment and education. Users may interact with the systems
by ordering advertised products
or services, competing against contestants in a game show, requesting
specialized information regarding
particular programs, or navigating through pages of information.
Typically, a broadcast service provider generates an interactive television
signal for transmission to a
viewer's television. The interactive television signal may include an
interactive portion consisting of application
code or control information, as well as an audio-video portion consisting of a
television program or other
informational displays. The broadcast service provider combines the audio-
video and interactive portions into a
single signal for transmission to a receiver connected to the user's
television. The signal is generally compressed
prior to transmission and transmitted through typical broadcast channels, such
as cable television (CATV) lines or
direct satellite transmission systems.
The interactive functionality of the television is controlled by a set-top box
connected to the television.
The set-top box receives the signal transmitted by the broadcast service
provider, separates the interactive portion
from the audio-video portion and decompresses the respective portions of the
signal. The set-top box uses the
interactive information, for example, to execute an application while the
audio-video information is transmitted to
the television. The set-top box may combine the audio-video information with
interactive graphics or audio
generated by the interactive application prior to transmitting the information
to the television. The interactive
graphics and audio may present additional information to the viewer or may
prompt the viewer for input. The
set-top box may provide viewer input or other information to the broadcast
service provider via a modem
connecrion.
By their nature, interactive television systems provide various different
pieces of information which may
be displayed to a particular viewer. The interaction of the viewer with the
system determines which of the
information is presented to him or her as well as what information is
transmitted from the viewer back to the
system. Interactive television systems may therefore have to transmit large
amounts of information to a group of
viewers because each of the viewers may request different pieces of the
information. As a result of the demand
for such large amounts of data, the bandwidth of the system may be
insufficient to provide the information to the
viewers within a sufficiently short response time.
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SUMMARY OF THE INVENTION
The invention provides a method and apparatus for managing an interactive
television system to
optimize usage of the available bandwidth and minimize the system's response
time. In one embodiment, the
interactive television system comprises a broadcast station, a plurality of
receiving stations, a broadcast channel
through which data can be transmitted from the broadcast station to the
receiving stations, and a plurality of
point-to-point channels, each of which is between a corresponding one of the
receiving stations and the broadcast
station. Data can be transmitted from the broadcast station over each of the
point-to-point channels to the
respective receiving stations, as well as from the receiving stations to the
broadcast station. The broadcast station
monitors the demand for particular pieces of information and determines
whether the information should be
delivered via the broadcast channel or the point-to-point channels.
In one embodiment, the interactive television system is configured to deliver
requested web pages from
the broadcast station to the receiving stations. Each of the receiving
stations is configured to transmit requests for
particular web pages to the broadcast station and to display the requested
pages when they are received from the
broadcast station. The broadcast station is configured to cyclically broadcast
a certain number of web pages on
the broadcast channel. After each of the pages has been broadcast once, the
series repeats and each of the pages is
broadcast again. The broadcast station is also configured to transmit
individual web pages on the point-to-point
channels.
The broadcast station monitors the requests from the receiving stations and
determines which of the
requested pages are in higher demand. The pages which have the greatest demand
are transmitted to all of the
receiving stations on the broadcast chatmel. Pages which were requested by a
particular receiving station are
displayed by that receiving station. Pages which were not requested are
ignored. Pages which have been
requested by fewer receiving stations can be transmitted via the point-to-
point channels of the respective
receiving stations. Thus, the broadcast channels are used primarily to
transmit pages which are requested by a
large number of viewers, while the point-to-point channels are used to
transmit pages which are requested by a
small number of viewers. The use of the system's available bandwidth is
thereby used in a way that minimizes
the response time between a receiving station's request for a page and
delivery of the page to the receiving
station. While this embodiment comprises a system for delivering web pages, it
is understood that other
embodiments may be configured to deliver interactive television applications,
multimedia data, or other types of
information.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent upon
reading the following detailed
description and upon reference to the accompanying drawings in which:
Fig. 1 is a block diagram illustrating the distribution of interactive
television applications and television
programs from their sources to a series of viewers.
Fig. 2 is a block diagram illustrating the interconnection of a broadcast
station and several receiving
stations in one embodiment of the invention.
Fig. 3 is a functional block diagram illustrating the flow of information
through the broadcast station in
one embodiment of the invention.
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Fig. 4 is a block diagram of a set-top box used in one embodiment of the
invention.
While the invention is susceptible to various modifications and alternative
forms, specific embodiments
thereof are shown by way of example in the drawings and will herein be
described in detail. It should be
understood, however, that the drawings and detailed description thereto are
not intended to limit the invention to
the particular form disclosed, but on the contrary, the intention is to cover
all modifications, equivalents and
alternatives falling within the spirit and scope of the present invention as
defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
One embodiment of the invention is described below. In this embodiment, an
interactive television
system includes a broadcast station and a number of receiving stations. The
broadcast station and receiving
stations are coupled by a broadcast channel such as direct satellite
transmission. ("Broadcast" is used herein to
refer to transmission of a single signal to all subscribing receivers.
"Direct" satellite transmission as used herein
contemplates transmissions received by the interactive television receiver,
through its antenna, directly from the
satellite.) The broadcast station and receiving stations are also connected by
several point-to-point channels, each
of which forms a direct channel between the broadcast station and one of the
receiving stations.
The broadcast and point-to-point channels may both be used to transmit various
pieces of data to the
receiving stations. The data may be audio-video-interactive information, such
as interactive application modules,
or any other type of data, such as web pages. The embodiment described below
is configured to transmit web
pages. The description of this embodiment, however, is intended to be
illustrative rather than limiting, and the
transmitted data can represent any type of information, such as application
code, raw data or graphical
information.
In the described embodiment, the receiving stations are configured to transmit
information requests to
the broadcast station. The information requests transmitted by a particular
receiving station correspond to web
pages which the user at the receiving station wishes to view. The broadcast
station receives the requests and
retrieves the requested pages from the appropriate sources. After the
requested pages have been retrieved by the
broadcast station, they must be transmitted to the receiving stations which
submitted the corresponding requests.
The retrieved pages may be transmitted to the receiving stations via either
the broadcast channel or the
point-to-point channels. Data transmitted via the broadcast channel is
distributed to all of the receiving stations,
whether they requested the transmitted pages or not. Data transmitted via the
point-to-point channels is
distributed only to those receiving stations which requested it, but the
broadcast station can only transmit a limited
amount of data at one time.
Rather than using only one of these channels to transmit data to the receiving
stations, this embodiment
of the invention can use both. That is, a particular piece of data such as a
web page can be transmitted over either
channel. Because the point-to-point channel is not limited to transmitting
only narrow-band data, entire web
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pages can be transmitted over this channel. The broadcast station need not
strip out narrow-band data for
transmission over the point-to-point channel while wide-band data is
transmitted over the broadcast channel.
Similar data (e.g., wide-band data) can be transmitted over either the
broadcast channel or the point-to-point
channel. Consequently, the decision to transmit particular data over one
channel or the other can be based on
delivery times or other quality-of service criteria.
There are a number of factors which influence the decision to transmit data
over one channel or the
other. For example, since some of the retrieved pages may have been requested
by more than one receiving
station, it may be more efficient to transmit these pages via the broadcast
channel, while pages requested by a
single receiving station may be more efficiently transmitted via the point-to-
point channel. In another example,
interactive application modules which are needed by larger numbers of
subscribers may be transmitted via the
broadcast channel, while modules which are needed by fewer subscribers may be
transmitted via the point-to-
point channels.
Thus, in some instances, it may be advantageous to transmit data over the
broadcast channel. For
example, when the point-to-point channel would require an inordinately large
amount of time to deliver the data
or when transmission over the broadcast channel is necessary to meet quality-
of service criteria, the broadcast
channel is selected for transmission of the data. The broadcast station may
therefore monitor the requests from
the receiving stations to determine which of the pages are in greater demand
(i.e., which are requested by a
greater number of receiving stations.) When the requested pages are retrieved,
those which are in the greatest
demand are transmitted via the broadcast channel.
In other instances, it may be advantageous to transmit data over the point-to-
point channel. For example,
when the broadcast channel is heavily loaded with transmission of high-demand
data, it may be preferable to
transmit a module which has been requested by a single subscriber via the
point-to-point channel. There may also
be instances in which the transmission quality of the point-to-point channel
is greater than that of the broadcast
channel, in which case certain modules may need to be transmitted via the
point-to-point channel.
Referring to Fig. 1, a block diagram illustrating the distribution of
information such as web pages from
their sources to a series of viewers is shown. (It should be noted that web
pages are exemplary, rather than
limiting, of the types of data which may be transmitted and other types of
data, such as application modules,
image data, and the like may also be transmitted in the various embodiments of
the invention.) Broadcast station
10 has several program sources 11. In one embodiment, sources 11 are web
servers which may be accessed by
broadcast station 10 to obtain web pages. In other embodiments, the sources
may include remote broadcast
network feeds, videotape recorders, computers, data storage devices, and the
like. Sources 11 provide audio-
video information which is to be included in the interactive television
signal. The information from sources 11 is
transmitted to receiving station 20 via either a broadcast channel or a point-
to-point channel . The broadcast
channel is depicted in the figure as a direct satellite broadcast channel
formed by broadcast antenna 12,
communications satellite 15 and receiving antenna 19. Although the figure
illustrates a satellite transmission, it is
contemplated that any broadcast medium, including non-satellite, CATV (cable),
telco (telephone), MMDS
(microwave) and terrestrial transmissions, may be used. The point-to-point
channel may comprise an ordinary
telephone line 13 connected to a transmitting modem in the broadcast station
and a receiving modem in the
receiving station (not shown). The point-to-point channel may comprise other
transmission media in other
4
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embodiments. The point-to-point channel is typically used to transmit user
data from the receiving station to the
broadcast station. The point-to-point channel also provides an alternate path
for web pages and other pieces of
information from sources 11 to be delivered to receiving station 20.
Referring to Fig. 2, the interconnection of broadcast station 10 and several
receiving stations 20 is
shown. (For convenience, items having reference numerals followed by a letter
are collectively referred to by the
reference numeral without a letter.) The figure illustrates that broadcast
channel 14 transmits a single broadcast
signal to each of receiving stations 20, while point-to-point channels 13
separately connect each of the receiving
stations to the broadcast station. A signal on one of the point-to-point
channels is therefore independent of the
signals on the other point-to-point channels.
Referring to Fig. 3, a functional block diagram illustrating the flow of
information through broadcast
station 10 is shown. In one embodiment, web pages are received from web
servers via modem 21. The web
pages may be compressed by compression units 22 in order to conserve
bandwidth. Any one of a number of
compression algorithms may be used if appropriate for a particular program or
application. Some web pages may
not be easily or effectively compressed, so some of the information may bypass
compression units 22 and be
passed from the modem to packetization units 23 without compressing the
information. Packetization units 23
accept the compressed (or uncompressed) information and format it into packets
for transmission over the
broadcast channel. The figure also shows storage unit 24, which may provide
previously obtained information,
stored data or some other type of information to compression unit 22 and
packetization unit 23. The components
of broadcast station 10 are coupled to a control unit (not shown) which
manages the functions of the broadcast
station.
The packets from packetization units 23 are fed into multiplexing unit 25,
which may intersperse the
packets with each other or with control information prior to transmission. The
interspersed packets are then
passed to proxy server 26. Proxy server 26 monitors the web page requests
submitted by the users and determines
the demand for the different web pages. Typically, high-demand pages are
transmitted on the broadcast channel,
while lower-demand pages are transmitted via the point-to-point channel. In
the illustrated embodiment, the
point-to-point channel is represented by modem 27, which transmits the page to
a single user via a phone line (nat
shown).
While other types of controllers or processors could be used to implement the
monitoring function of the
broadcast station, a proxy server is used in this embodiment. In addition to
monitoring the information requests,
the proxy server can perform other functions, such as filtering the requests
or caching information responsive to
the requests. The use of a proxy server may also increase the scalability of
the system, as more proxy servers can
be added to handle the load from the receiving stations.
Because pages transmitted via the broadcast channel are received by all users,
pages which have been
requested by a large number of users are most efficiently distributed over
this channel. Each of the requests can
be serviced simultaneously and the response time is kept to a minimum. Pages
which are requested by smaller
numbers of users may be more efficiently transmitted via the point-to-point
channels between the broadcast
station and the respective receiving stations. It is also contemplated that
the choice of channels may be based on
anticipated demand, rather than the actual number of requests for particular
pages. For example, if a commercial
for a certain manufacturer is broadcast, it may be anticipated that a large
number of requests for that
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manufacturer's web page will be received. The manufacturer's web page may
therefore be transmitted over the
broadcast channel while other web pages are transmitted over the point-to-
point channels.
It is contemplated that the receiving station may be configured to transmit
pieces of information in a
cyclic manner. That is, a certain number of these pieces of information (e.g.,
web pages) are transmitted one after
the other and then, after each of the pieces of information has been
transmitted a first time, they are transmitted a
second time and a third time and so on. The broadcast station thus
continuously broadcasts data, with each piece
of information being re-broadcast at regular intervals (i.e., each piece of
information is re-broadcast with a certain
frequency). The broadcast station may also be configured to transmit multiple
carousels which have different
periodicities.
As noted above, the pieces of information which are broadcast in this manner
may be referred to as a
carousel. Because there may be a limited number of positions or slots in the
carousel, the broadcast station must
prioritize the requested pieces of information. The determination of whether a
piece of information will be
transmitted via the broadcast channel or the point-to-point channel depends on
its priority and the number of slots
in the carousel. If only a few web pages are requested by users, it may be
possible to transmit all of them,
including low-demand pages, via the broadcast channel. In fact, the need to
meet certain criteria for quality of
service may influence the number of slots in the carousel and the periodicity
of carousel transmissions. On the
other hand, there may be instances in which the number of high-demand pages
exceeds the number of allowable
slots in the carousel, and some of them may have to be transmitted via the
point-to-point channel.
Various strategies may be used to determine which pages are transmitted by
which channel. If one or
more pages are in particularly high demand, they may be allocated two slots in
the carousel so that it is
transmitted with a greater frequency. Responses to requests for these pages
will therefore have a reduced latency
(response time.) If there is a particularly large number of pages for which
there is only a low or moderate
demand, the size of the carousel may be increased. (It should be noted that
the carousel is not a hardware
structure, and that the number of slots in the carousel is determined by the
system software based on system and
performance constraints.) The strategy for routing data via the respective
channels may also take into account
other factors, such as degraded quality of transmissions on the point-to point
channel. For example, if a modem
channel is too noisy to transmit error-free data, or if this channel simply
doesn't meet the quality-of service
criteria, the cyclic broadcast of high-demand data may be interrupted so that
low-demand data can be transmitted
over the broadcast channel.
Receiving station 20 is contemplated to be one of a number of stations which
are subscribers of the
broadcast service provider operating broadcast station 10. The broadcast
signal is collected by receiving antenna
19 and fed to receiving station 20, which in one embodiment is contemplated to
be a set-top box coupled to a
television set. Set-top box 22 processes the packetized signal to reconstruct
the information embodied in the
signal (e.g., web pages.) The reconstructed information is processed in the
set-top box and, if appropriate,
transmitted to the television to be displayed. Web pages may be directed to
the television, while information
comprising an interactive applications may be executed in the set-top box
rather than being displayed. Interactive
applications may, however, generate graphics or audio which are combined with
other information and then
displayed.
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Referring to Fig. 4, a block diagram of a set-top box 22 is shown. The
broadcast signal is received and
fed into tuner 31. Tuner 31 selects a particular broadcast channel on which
the broadcast audio-video-interactive
signal is transmitted and passes the signal to processing unit 32. (Tuner 31
may be replaced by other means, such
as simple input ports, for receiving signals from various signal sources.)
Processing unit 32 demultiplexes the
packets from the broadcast signal if necessary and reconstructs the
information embodied in the signal. The
information is then decompressed by decompression unit 33. The information is
then conveyed to display unit
34, which may perform further processing and conversion of the information
into a suitable television format,
such as NTSC or HDTV audio/video. If the information includes interactive
applications, these applications are
reconstructed and routed to random access memory (RAM) 37. The applications
are then executed by control
unit 35.
Control unit 35 may include a microprocessor, micro-controller, digital signal
processor (DSP), or some
other type of software instruction processing device. RAM 37 may include
memory units which are static (e.g.,
SRAM), dynamic (e.g., DRAM), volatile or non-volatile (e.g., FLASH), as
required to support the functions of
the set-top box. When power is applied to the set-top box, control unit 35
executes operating system code which
is stored in ROM 36. The operating system code executes continuously while the
set-top box is powered in the
same manner the operating system code of a typical personal computer (PC) and
enables the set-top box to act on
control information and execute interactive and other applications. The set-
top box also includes modem 38.
Modem 38 is connected to the telephone line which provides the point-to-point
channel between the receiving
station and the broadcast station. This channel may serve both as a means for
transmitting requested data from
the broadcast station to the receiving station and as a return path by which
the user can transmit information
requests to the broadcast station.
Set-top box 22 may include a module manager unit 30 contained within control
unit 35. Since the
receiving station is not aware of the whether it has requested modules which
are in high demand from other
receiving stations, module manager unit 30 monitors tuner 31 and modem 38 for
the requested information.
(Tuner 31 in this case is the receiving station's connection to the broadcast
channel and modem 38 is its
connection to the point-to-point channel.) In other embodiments, the receipt
of requested information may be
controlled in a different manner. For example, the broadcast station may be
configured to transmit notification to
the receiving station on a predetermined channel to inform the receiving
station which of the channels will be
used to transmit the requested information. In one embodiment, module manager
unit 30 is implemented in
software, but it may also be implemented in hardware or a combination of
hardware and software. Module
Manager unit 30 may be used to control the receipt of audio-video information
via the broadcast and point-to-
point channels.
Although the term "set-top box" is used herein, it is understood that this
term refers to any receiver or
processing unit for receiving and processing a transmitted signal and
conveying the processed signal to a
television or other monitor. The set-top box may be in a housing which
physically sits on top of a television, it
may be in some other location external to the television (e.g., on the side or
back of the television or remotely
located from the television), or it may be incorporated into the television
itself. Set-top box 22 serves to
demodulate the signal received from broadcast station 10 and to separate the
components of the signal, such as
web pages, television programs and interactive applications. Similarly, the
television set may be a television or a
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video monitor employing any suitable television format (e.g., NTSC or HDTV, or
it may be replaced by other
devices, such as a video recorder.
In the embodiment described above, the broadcast channel is a direct satellite
transmission channel. The
broadcast channel may alternately utilize various transmission media and is
contemplated to include media such
as coaxial cable and free space (e.g., as used for direct satellite
transmissions.) The return path typically consists
of a pair of modems, one in the receiving station and one in the broadcast
station, each connected to a standard
telephone line. Other means for establishing a return path, however, are also
contemplated. For example, a
portion of the bandwidth of the transmission path could be used as the return
path. If the return path utilizes a
portion of the broadcast bandwidth, it is contemplated that the broadcast
station may still employ a separate point-
to-point channel (e.g., a telephone line) to transmit requested data to the
receiving station.
In considering the alternate embodiments of the invention, it may be helpful
to view the channels of
communication between the broadcast station and receiving station as three
logical links: a broadcast link; a
point-to-point link; and a return link. As described above, the broadcast link
is used to transmit data to multiple
receiving stations. The point-to-point link is used to transmit data to
individual receiving stations. The return
link is used to transmit data to the broadcast station. These logical links
may be mapped to a wide variety of
physical media, some of which are shared (e.g., satellite transmissions) and
some of which are separate, or point-
to-point (e.g., telephone lines). More specifically, the broadcast logical
link must be mapped to one of the shared
media. The point-to-point and return links may be mapped to either the shared
media, or the separate media. It is
even possible to split the logical links and map them to more than one medium.
For example, a point-to-point
logical link may be mapped to a shared medium such as a satellite (for
transmissions to the receiving station) and
at the same time mapped to a separate medium such as a telephone line (for
transmissions to the broadcast
station).
Just as various aspects of the invention described above may vary in different
embodiments of the
invention, other details of these embodiments may also be modified without
departing from the spirit and scope of
the invention as defined by the appended claims. The embodiments described
above are intended to be
exemplary rather than limiting, and it is contemplated that the scope of the
invention includes various
modifications and embodiments which will be apparent to those skilled in the
art of the invention.
