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Claims  |
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What is claimed is:
1. A method of processing logical addresses specifying Internet content
associated with a television program, the method comprising the acts of:
receiving batch mode logical addresses associated with a program in advance
of the program being broadcast;
receiving a video signal by which the program is broadcast;
retrieving a real-time logical address and associated data by extracting a
sequence of data having a predetermined syntax from a data service channel
of the video signal;
selecting a logical address from among the real-time logical address and at
least one of the batch mode logical addresses using predefined rules; and
enabling the selected logical address to be used to retrieve Internet
content specified by the selected logical address.
2. The method of claim 1, further comprising the act of decoding the
real-time logical address by translating predetermined patterns of one or
more Electronic Industries Association 608 standard character set
characters within the real-time logical address into a single character in
a set of characters from which URLs are comprised.
3. The method of claim 1, wherein the data service channel is one of T1,
T2, T3, T4, CC1, CC2, CC3, or CC4 of a vertical blanking interval of the
video program.
4. The method of claim 1, wherein the act of receiving batch mode logical
addresses comprises the act of receiving the batch mode logical addresses
from a Web server.
5. The method of claim 1, wherein the act of receiving batch mode logical
addresses comprises the act of receiving the batch mode logical addresses
as part of an electronic program guide.
6. The method of claim 1, wherein the act of receiving batch mode logical
addresses comprises the act of receiving the batch mode logical addresses
on a computer-readable medium.
7. The method of claim 1, wherein the selected logical address comprises a
Uniform Resource Locator.
8. The method of claim 1, wherein the predetermined rules specify that:
the real-time logical address is valid for a predetermined amount of time
after receipt; and
the at least one of the batch mode logical addresses is valid for a defined
time interval.
9. The method of claim 1, wherein the predetermined rules specify that if
the real-time logical address is associated with a commercial sponsor, the
real-time link is to be used rather than the at least one batch mode
logical addresses.
10. The method of claim 1, wherein the predetermined rules specify that the
real-time logical address is to replace the at least one batch mode
logical addresses, such that the at least one batch mode logical addresses
are not used to retrieve associated Internet content.
11. The method of claim 1, wherein the predetermined rules specify that the
real-time logical address supplements the at least one batch mode logical
addresses, such that both the real-time logical address and the at least
one batch mode logical addresses can be used to retrieve Internet content.
12. The method of claim 1, wherein the data service channel comprises
either a text service channel or a captioning service channel.
13. A method of processing logical addresses specifying Internet content
associated with a television program that is broadcast by a video signal
having a vertical blanking interval, the method comprising the acts of:
receiving batch mode logical addresses associated with a program in advance
of the program being broadcast;
receiving the video signal;
retrieving a real-time logical address and associated data by extracting a
sequence of data having a predetermined syntax from a data service channel
encoded in the vertical blanking interval of the video signal, the data
service channel comprising either a text service channel or a captioning
service channel;
selecting a logical address from among the real-time logical address and at
least one of the batch mode logical addresses using predefined rules; and
enabling the selected logical address to be used to retrieve Internet
content specified by the selected logical address.
14. The method of claim 13, wherein the act of retrieving a real-time
logical address comprises the act of extracting a Uniform Resource
Locator.
15. The method of claim 14, further comprising the act of translating
predetermined patterns of one or more characters within the Uniform
Resource Locator into a single character in a set of characters from which
Uniform Resource Locators are comprised.
16. The method of claim 14, wherein the video signal is one of a National
Television Standards Committee (NTSC), Phase Alternate Lines (PAL),
Sequential Couleur Avec Memoire (SECAM), or High Definition Television
(HDTV) video signal.
17. The method of claim 14, further including the acts of:
determining if the sequence of data has been corrupted by generating a
16-bit checksum for the sequence of data; and
comparing the 16-bit checksum to a predetermined value.
18. The method of claim 14, further including the act of extracting one or
more attributes associated with the URL from the sequence of data.
19. The method of claim 18, wherein the one or more attributes include a
type indicating to what the Uniform Resource Locator relates.
20. The method of claim 18, wherein the one or more attributes include a
title for the Internet resource.
21. The method of claim 14, wherein the predetermined syntax has the
following general form:
<url>{[attribute.sub.1 :value.sub.1 ]} {[attribute.sub.2 :value.sub.2
]} . . . {[attribute.sub.n :valve.sub.n ]} [checksum];
where "<," ">," "[,"and "]" represent divider characters, "url"
represents the Uniform Resource Locator, "checksum" represents a checksum
in hexadecimal format, and the attribute value pairs in curly brackets are
optional.
22. A computer program product for implementing, in a processing device
associated with a display device on which a television program can be
displayed, a method of processing logical addresses specifying Internet
content associated with the television program, the computer program
product comprising:
a computer-readable medium carrying computer-executable instructions that,
when executed by the processing device, cause the processing device to
perform the method, including the acts of:
receiving batch mode logical addresses associated with a program in advance
of the program being broadcast;
receiving a video signal by which the program is broadcast;
retrieving a real-time logical address and associated data by extracting a
sequence of data having a predetermined syntax from a data service channel
of the video signal;
selecting a logical address from among the real-time logical address and at
least one of the batch mode logical addresses using predefined rules; and
enabling the selected logical address to be used to retrieve Internet
content specified by the selected logical address.
23. The computer program product of claim 22, wherein the act of receiving
batch mode logical addresses comprises the act of receiving the batch mode
logical addresses from a Web server.
24. The computer program product of claim 22, wherein the act of receiving
batch mode logical addresses comprises the act of receiving the batch mode
logical addresses as part of an electronic program guide.
25. The computer program product of claim 22, wherein the predetermined
rules specify that:
the real-time logical address is valid for a predetermined amount of time
after receipt; and
the at least one of the batch mode logical addresses is valid for a defined
time interval.
26. The computer program product of claim 22, wherein the predetermined
rules specify that if the real-time logical address is associated with a
commercial sponsor, the real-time link is to be used rather than the at
least one batch mode logical addresses.
27. The computer program product of claim 22, wherein the predetermined
rules specify that the real-time logical address is to replace the at
least one batch mode logical addresses, such that the at least one batch
mode logical addresses are not used to retrieve associated Internet
content.
28. The computer program product of claim 22, wherein the predetermined
rules specify that the real-time logical address supplements the at least
one batch mode logical addresses, such that both the real-time logical
address and the at least one batch mode logical addresses can be used to
retrieve Internet content.
29. The computer program product of claim 22, wherein the data service
channel comprises either a text service channel or a captioning service
channel. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The invention relates generally to the integration of broadcast television
programming with content from the Internet, World-Wide Web, Intranet,
and/or other remote or local resources. More specifically, the invention
relates to transporting logical addresses for such content as part of a
broadcast television signal.
BACKGROUND OF THE INVENTION
The World-Wide Web (the Web) is a collection of formatted hypertext pages
located on numerous computers around the world that are logically
connected by the Internet. The Web has become a valuable resource for
information relating to almost any subject, including entertainment,
business, travel, and education, to name just a few. Web browsers,
software providing user interfaces to the Web, allow individuals to access
Internet content from personal computers. Internet terminals, such as
those pioneered by WebTV Networks, Inc., of Mountain View, Calif. have
made the Web accessible to an even larger segment of the population by
providing access to the Web without the use of a personal computer.
Internet terminals (also commonly referred to as set-top boxes) provide
individuals with access to Web pages using an ordinary television (TV) set
as a display and a remote control or wireless keyboard for user input.
Many Web sites include content relating to popular television programs,
specific episodes, and their characters, for example. It would be
desirable to provide a mechanism for integrating broadcast television
programming with the Web to facilitate the retrieval and viewing of this
and other content concurrently with the television broadcast or at a later
time at the option of the viewer. In particular, it would be desirable to
provide a practical mechanism for communication of logical addresses, such
as Uniform Resource Locators (URLs), for Internet content relating to a
television broadcast, for example, as part of the television signal.
The Electronic Industries Alliance (EIA) has published a standard relating
to embedding data in line 21 of the vertical blanking interval (VBI) of a
National Television Standards Committee (NTSC) video signal entitled,
"Recommended Practice for Line 21 Data Service," approved Sep. 20, 1994
(hereinafter "EIA-608"). EIA-608 describes various data services, such as
closed captioning, text services, and extended data services (XDS) that
are carried in line 21 of the VBT of an NTSC video signal. Details
regarding these services can be found in EIA-608 which is incorporated
herein by reference.
One approach that has been suggested for transmitting URLs as part of an
NTSC video signal is to embed URLs in the Extended Data Service (XDS)
channel. However, this approach has several limitations. For example, XDS
packets are limited to 32 bytes including packet overhead. Since URLs and
data associated therewith will typically exceed 32 bytes, this data would
have to be spread over multiple XDS packets. Additionally, if URLs were to
be transmitted in XDS packets they would compete for the limited bandwidth
available to XDS with V-Chip program rating information. Bandwidth
available to XDS may at times be insufficient to filly support both URLs
and V-Chip rating information. Another problem with this approach is the
difficulty associated with having more than one "active" URL for a program
at the same time. This problem stems from (1) the difference between URLs
and attributes that are typically associated with a program by way of XDS,
such as a scheduled start time, a duration, an elapsed time, a program
title, etc. and (2) the repetitive nature of XDS packets. Typically, only
the most recently received attribute of a program is active. For example,
an earlier elapsed time value associated with a particular program is
replaced by a subsequently received elapsed time value associated with
that program. In contrast, such behavior is undesirable for URLs as it may
often be beneficial to have multiple URLs active at a given time during a
program.
With regard to the repetitive nature of XDS packets, EIA-608 recommends
transmitting XDS packets continuously to fill all available bandwidth
beyond what is used by the captioning and text services and suggests
repetition rate algorithms based on packet priorities. Briefly, as XDS
usage increases, the repetition rate for each of the types of packets is
decreased and XDS packets of the same type (e.g., those having the same
packet ID) may be deleted by downstream encoders to accommodate the
additional XDS traffic. Therefore, the only way to guarantee reception by
the viewer of multiple URLs per television program is to provide unique
packet IDs for each URL to assure they are not deleted as more of the XDS
bandwidth is consumed downstream. However, coordinating such unique packet
IDs among the many potential originators of URLs is not practical.
In light of the foregoing, what is needed is a more intelligent mechanism
for communicating logical addresses associated with local and/or remote
content within a video signal. In particular, it is desirable to
accommodate the need for multiple active URLs at a given time during a TV
program. Additionally, it is desirable to provide for improved error
detection. Further, it is advantageous to choose a portion of the video
signal which does not compete directly for bandwidth with V-Chip rating
information. Finally, it is desirable to utilize a syntax that is suitable
for a broad set of devices.
SUMMARY OF THE INVENTION
A method and apparatus are described for communicating logical addresses
within a broadcast television signal. According to one aspect of the
present invention, a logical address of a resource may be communicated to
a receiving device by way of a data service channel of a video signal. A
sequence of data complying with a predetermined syntax and including the
logical address is embedded in either a text service channel or a
captioning service channel of the video signal. Advantageously, in this
manner, when the video signal is transmitted, it is accompanied by the
logical address.
According to another aspect of the present invention, a logical address of
a resource may be received by way of a data service channel of a video
signal. A video signal including data associated with one or more data
services is received. Subsequently, a sequence of data complying with a
predetermined syntax is retrieved from either a captioning service or a
text service. Ultimately, a logical address may be extracted from the
video signal by parsing the sequence of data.
Other features of the present invention will be apparent from the
accompanying drawings and from the detailed description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example, and not by way of
limitation, in the figures of the accompanying drawings and in which like
reference numerals refer to similar elements and in which:
FIG. 1 is a block diagram illustrating several clients connected to a
server system.
FIG. 2 is a diagram illustrating a client according to one embodiment of
the present invention.
FIG. 3 is a block diagram illustrating exemplary functional units of a
set-top box according to one embodiment of the present invention.
FIG. 4 is a flow diagram illustrating a method of transporting logical
address links according to one embodiment of the present invention.
FIG. 5 is a flow diagram illustrating logical address link reception
processing according to one embodiment of the present invention.
FIG. 6 conceptually illustrates how real-time logical address links and
batch mode logical address links may be combined according to one
embodiment of the present invention.
FIG. 7 is a flow diagram illustrating a method of combining real-time
logical address links and batch mode logical address links according to
one embodiment of the present invention.
DETAILED DESCRIPTION
A method and apparatus are described for transporting logical addresses
within a broadcast television signal. The logical addresses may provide
"links" to Internet, Web, or other local or remote content related or
unrelated to a program being broadcast. A form of logical address (also
referred to as a resource locator) commonly associated with Web content is
a Uniform Resource Locator (URL). A URL is a compact string representation
of a location used to identify an abstract or physical resource on the
Internet. Of course, alternative means of uniquely identifying content may
be employed. For example, it is appreciated that keys (e.g., database
indices), network addresses (e.g., IP addresses), and other identification
mechanisms, alone or in combination, may be employed to uniquely identify
a resource. Therefore, while the term URL refers to a specific type of
content identifier used in connection with the Web, the terms logical
address and/or resource locator are used herein to refer to
content/resource identification mechanisms generally.
At any rate, supplying links to Internet/Web content provides an easy and
powerful way to bring the richness and interactive nature of the Internet
to TV. Such links may be used by program producers, program sponsors,
networks, local affiliates and other content providers to link TV viewers
to web content specifically designed to complement what the viewers are
watching on TV at a given time. According to one aspect of the present
invention, a means is provided for transmitting logical addresses that
identify content (e.g., Internet content) within a video signal. For
example, content providers may transmit URLs to viewers by employing a
predetermined syntax to insert the URLs within line 21 of the vertical
blanking interval of an analog television signal. According to another
aspect of the present invention, upon receipt of a logical address in a TV
signal, an icon or some other visual indication may be presented to the
viewer to notify the viewer of the availability of Internet content. The
viewer may then select the visual indication to view the content
concurrently with the TV broadcast or save the logical address for later
viewing.
The present invention includes various steps, which will be described
below. The steps can be embodied in machine-executable instructions, which
can be used to cause a general-purpose or special-purpose processor
programmed with the instructions to perform the steps. Alternatively, the
steps of the present invention might be performed by specific hardware
components that contain hardwired logic for performing the steps, or by
any combination of programmed computer components and custom hardware
components.
Importantly, while embodiments of the present invention will be described
with respect to viewing Web content on an Internet terminal system, such
as the WebTV.RTM. Internet terminal, the method and apparatus described
herein are equally applicable to other types of content that may be stored
remotely or content that may be directly accessible to the viewing system
(WebTV is a registered trademark of WebTV Networks, Inc., of Mountain
View, Calif.). For example, logical addresses embedded in a video signal
may refer to content stored on a CD-ROM or other mass storage device, a
company's Intranet server, or other resource. Additionally, certain
aspects of the invention described herein have equal application to
various other TV viewing devices, such as personal computers equipped with
TV tuners, and the like. Moreover, while various embodiments of the
present invention will be described with reference to an NTSC broadcast
video signal, aspects of the present invention are equally applicable to
other broadcast TV systems, such as Phase Alternating Lines (PAL),
Sequential Couleur Avec Memoire (SECAM), and the proposed High Definition
Television (HDTV) standard. Finally, it is appreciated that a variety of
other transport mechanisms may be employed, including digital satellite,
digital TV, and cable TV.
System Overview
Aspects of the present invention may be included in an Internet system
terminal, such as the WebTV internet terminal, for providing a user with
access to the Internet. As will be discussed further below, the Internet
system includes an Internet terminal (also referred to as an Internet
System client) ("client") and an Internet server ("server"). A user of an
Internet terminal generally accesses a server via a direct-dial telephone
(POTS, for "plain old telephone service"), ISDN (Integrated Services
Digital Network), or other similar connection, in order to browse the Web,
send and receive e-mail, and use various other Internet system network
services. Services provided by the Internet system network service, such
as the WebTV network, are typically provided by servers using software
residing within the servers in conjunction with software residing within a
client.
FIG. 1 illustrates a basic configuration of an Internet system network in
which one embodiment of the present invention may be implemented. A number
of clients 1 are coupled to a modem pool 2 via direct-dial, bi-directional
data connections 29, which may be telephone (POTS, i.e., "plain old
telephone service"), ISDN (Integrated Services Digital Network), or any
other similar type of connection. Other connection mechanisms may be
employed such as cable and satellite forward channels, for example. In any
event, the modem pool 2 is coupled typically through a router, such as
that conventionally known in the art, to a number of remote servers 4 via
a conventional network infrastructure 3, such as the Internet. The
Internet system also includes a server 5, which specifically supports the
clients 1. The clients 1 each have a connection to the server 5 through
the modem pool 2 and the Internet 3. Note that the modem pool 2 is a
conventional modem pool, such as those found today throughout the world
providing access to the Internet and private networks.
An Exemplary Client System
FIG. 2 illustrates an Internet system client ("client") 1 known in the art.
The client 1 includes an electronics unit 10 (hereinafter referred to as
"the set-top box 10"), an ordinary television set 12, and a remote control
11. In an alternative embodiment of the present invention, the set-top box
10 is built into the television set 12 as an integral unit. In the
embodiment depicted, the client 1 uses the television set 12 as a display
device for displaying video data and a graphical user interface. The
set-top box 10 is coupled to the television set 12 by a video link 6. The
video link 6 is an RF (radio frequency), S-video, composite video, or
other equivalent form of video link.
The set-top box 10 includes hardware and/or software for receiving and
decoding a broadcast video signal 8, such as an NTSC, PAL, SECAM or other
TV system video signal, and providing video data to the television set via
video link 6. The set-top box 10 also includes hardware and/or software
for providing the user with a graphical user interface, by which the user
can access various Internet system network services, browse the Web, send
e-mail, and otherwise access the Internet. The user interface includes
means for notifying the user of the presence of encoded data, such as
URLs, embedded in the video signal. The notification may be audible,
visual or a combination of the two. In one embodiment, the notification
comprises temporarily displaying an icon in a portion of the screen.
The client 1 may include both a standard modem and an ISDN modem, such that
the communication link 29 between the set-top box 10 and the server 5 can
be either a telephone (POTS) connection 29a or an ISDN connection 29b. The
set-top box 10 receives power through a power line 7.
Remote control 11 is operated by the user in order to control the client 1
in browsing the Web, sending e-mail, and performing other Internet-related
functions. The set-top box 10 receives commands from remote control 11 via
an infrared (IR) communication link. In alternative embodiments, the link
between the remote control 11 and the set-top box 10 may be RF or any
equivalent mode of transmission.
Exemplary Client System Architecture
FIG. 3 is a block diagram illustrating internal features of the set-top box
10. In this example, operation of the client 1 is controlled by a
processing unit, such as central processing unit (CPU) 21, which is
coupled to an Application-Specific Integrated Circuit (ASIC) 20. The CPU
21 executes software designed to implement various features of the present
invention. ASIC 20 contains circuitry which may be used to implement
certain features provided by the client 1. ASIC 20 is coupled to an audio
digital-to-analog converter (DAC) 25 which provides audio output to
television 12. In addition, ASIC 20 is coupled to a video encoder 26 which
provides video output to television set 12. An IR interface 24 detects IR
signals transmitted by remote control 11 and, in response, provides
corresponding electrical signals to ASIC 20. A standard telephone modem 27
and/or an ISDN modem 30 are coupled to ASIC 20 to provide connections 29a
and 29b, respectively, to the modem pool 2 and, via the Internet 3, to the
remote servers 4. Note that the set-top box 10 also may include a cable
television modem (not shown).
A TV interface 31 is coupled to ASIC 20 to receive broadcast video signals,
such as an NTSC video signal, and provide corresponding electrical signals
to ASIC 20, thereby allowing video data carried in the broadcast video
signal 8 to be presented to the viewer on the TV 12. The TV interface 31
also extracts other data that may be embedded in the video signal. The
data so extracted, or a portion thereof, may be displayed concurrently
with a television program. For example, in one embodiment of the present
invention, titles corresponding to logical addresses that have been
inserted into a text mode data service or a captioning data channel of
line 21 of the VBI are extracted by the TV interface 31 and displayed on
the TV 12. An exemplary syntax for transporting logical addresses in line
21 of the VBI is described below.
Also coupled to ASIC 20 is Read-Only Memory (ROM) 22, which provides
storage of program code for implementing application software to be
executed by the set-top box 10. Note that ROM 22 may be a programmable ROM
(PROM) or any form of erasable PROM (EPROM) or Flash memory. Also coupled
to ASIC 20 is Random Access Memory (RAM) 23. A mass storage device 28 may
optionally be provided and coupled to ASIC 20. The mass storage device 28
may be used to input software or data to the client or to download
software or data received over network connection 29 or data embedded in
broadcast signal 8 . The mass storage device 28 includes any suitable
medium for storing machine-executable instructions, such as magnetic
disks, optical disks, and the like.
Logical Address Links
Having described an exemplary environment in which embedded logical
addresses may be employed, logical address links, their syntax, and usage
will now be discussed. Generally, logical address links, such as TV
Crossover.TM. Links, enable seamless integration of television programming
and the Internet by allowing Internet content to be associated with a
television broadcast (TV Crossover.TM.Links is a trademark of WebTV
Networks, Inc., of Mountain View, Calif.). In one embodiment of the
present invention, the client 1 allows Web content and television
programming to be concurrently displayed as described in U.S. patent
application Ser. No. 09/087,354, entitled "Method and Apparatus for
Displaying HTML and Video Simultaneously," filed May 29, 1998, which is
incorporated herein by reference.
Importantly, associations between a television broadcast and Internet
content may be performed in real-time or in batch mode. Real-time logical
address links are sent to the TV viewer's client system during a
television broadcast in line 21 of the VBI. In contrast, batch mode
logical address links are delivered to the client system in advance of the
television broadcast to which they relate. For example, batch mode logical
address links may be downloaded from a Web server to the user's client
system or delivered on CD ROM or other computer readable medium. According
to one embodiment, batch mode logical address links are delivered as part
of an electronic programming guide (EPG) and may be modified and/or
supplemented with real-time logical address links. While real-time logical
address links are valid for a predetermined amount of time after receipt
by the client system, batch mode logical address links typically define a
time interval. For example, a batch mode logical address link may include
a start time and an end time indicating when the link is to be made
available to the viewer.
Syntax for Logical Address Links
Logical addresses may be transmitted in one of the text service channels of
line 21, i.e., First Text Service (T1), Second Text Service (T2), Third
Text Service (T3), or Fourth Text Service (T4), or one of the captioning
data channels of line 21, i.e., Primary Synchronous Caption Service (CC1),
Special Non-synchronous Use Captions (CC2), Secondary Synchronous Caption
Service (CC3), or Special Non-synchronous Use Captions (CC4), by using the
following encoding format for logical address strings on line 21 of the
VBI:
<logical address>[attribute.sub.1 :value.sub.1 ][attribute.sub.2
:value.sub.2 ] . . . [attribute.sub.n :value.sub.n ][checksum]
The logical address (e.g., a URL) is enclosed in angle brackets. One or
more pairs of attributes and values may follow the logical address in
square brackets. Finally, a checksum follows the n.sup.th attribute/value
pair in square brackets. It is appreciated that delimiter characters other
than angle brackets and square brackets may be employed. However, it is
important to avoid employing delimiters that are included in the URL
character set. Additionally, it is preferable that the delimiter be
present in both the standard EIA-608 character set and the US-ASCII
character set to make logical address links relevant to the widest set of
devices.
Attributes
Exemplary attributes include "type" and "name." The type attribute
indicates to what the content associated with the URL relates. For
example, the content may be related to the current television program, to
the broadcast network, or to one of the commercial sponsors of the current
TV program. Table 1 lists exemplary values that may be associated with the
type attribute.
TABLE 1
Meaning of Type Attribute Values
Type Attribute Value Related to
PROGRAM the current program
NETWORK the broadcast network
STATION the local station
SPONSOR a commercial sponsor of the current
program
OPERATOR the service (e.g., cable or satellite) operator
The name attribute provides a concise title for the resource identified by
the logical address. It is preferable to associate a title with a logical
address since the logical address itself doesn't always make clear what
the content of the identified resource is. For example, the URL
http://www.nbc.com/tvcentral/shows/seinfeld/characters/index.html might
identify a web page on NBC's web site that describes frequently appearing
characters on the Seinfeld television program. Therefore, for the viewers'
convenience, a value such as "Seinfeld Stars" may be associated with the
name attribute for this logical address link. Similarly, a web page
relating to guest stars, such as the web page located at
http://www.nbc.com/tvcentral/shows/seinfeld/characters/char2.html, might
be associated with the name "Seinfeld Guest Stars."
Various other attributes are contemplated by the assignee of the present
invention. For example, a mechanism for purging old links may utilize an
attribute that identifies a date or a date and time at which a logical
address link expires. In this manner, after the date indicated, logical
address links having an expires attribute may be purged from the client's
memory.
Importantly, attributes are optional and need not appear in any particular
order. For purposes of illustration, exemplary logical address links are
listed below (note, however, the checksums have not been calculated):
<http://www.nbc.com/tvcentral/show/seinfeld/characters/index.html>
[name:SeinfeldStars][A6F1]
<http://www.tvprogram.com>[type:program] [name:TV Program] [C8C5]
<http://advsponsor.net>[type:sponsor] [name:Special Offer] [BFA0]
<http://madkad_network.com> [type:network] [1128]
<http://www.coolsite.com>[6C1D]
Importantly, it should be appreciated that logical addresses are not
limited to URLs and that URLs are not limited to the "http:" scheme.
Therefore, the following would also be recognized as valid logical address
links:
<mailto:info@advsponsor.net>[type:sponsor][5FDB]
<news:alt.tv.program][type:program][39 1B]
Checksum
A checksum is appended to the end of the logical address link in order to
detect data corruption that may occur during receipt or transmission of
the logical address link. Preferably, a two byte hexadecimal checksum is
employed such as a checksum that would be produced by the standard TCP/IP
checksum algorithm described in Request For Comments (RFC) 719, "Internet
Protocol", Sep. 1981 which is incorporated herein by reference. According
to one embodiment, the checksum is computed by pairing adjacent characters
in the string (starting with the first delimiter) to form 16-bit integers.
If there are an odd number of characters, the final character is paired
with a byte of zeroes. At any rate, the checksum is computed such that the
one's complement sum of all of the 16-bit integers plus the checksum
equals the 16-bit integer with all 1 bits. That is, the checksum is the
one's complement of the one's complement sum of the 16-bit integers.
Advantageously, in this manner, a great deal less errors go undetected
than in previously suggested 7-bit checksum schemes with only a negligible
increase in the logical address link's overall length.
Transmission of Logical Address Links
Referring now to FIG. 4, a flow diagram illustrating a method of
transporting logical address links according to one embodiment of the
present invention is illustrated. In this embodiment, logical address link
data to be inserted by a content provider, e.g., a program producer,
broadcaster, affiliate, cable or satellite provider, is inserted into
upstream video (the source of video onto which the new data will be
encoded). At step 410, upstream video data is received from a previous
point in the video signal distribution path. At step 420, a determination
is made as to whether or not the current distribution point has one or
more logical address links that are to be associated with the current TV
program being transmitted. If not, processing continues with step 450.
Otherwise, processing proceeds with step 430.
Importantly, the upstream video may or may not contain previously encoded
data, such as logical address links, in line 21 of the VBI. Each content
provider, therefore, is a potential re-encoding point along the
distribution path. At step 430, the existing data is extracted from the
captioning data channel or the text service channel of the video signal.
Subject to certain bandwidth limitations, the content provider then,
embeds one or more logical address links into a captioning or text service
packet of the video signal (step 440). Finally, at step 450, the video
signal is transmitted to the next downstream receiving device(s). This
process may be repeated during video signal processing at each point along
the video signal distribution path.
Reception and Processing of Logical Address Links
Logical address link enabled receiving devices, such as a set-top box 10,
are able to receive and process logical address links embedded in line 21
of the VBI of an NTSC video signal. FIG. 5 is a flow diagram illustrating
logical address link reception processing according to one embodiment of
the present invention. At step 510, a broadcast video signal, such as an
NTSC video signal, is received. Video data extracted from the broadcast
video signal is passed through to the display device, e.g., a TV 12 or
other display device, such as a computer monitor, for presentation to the
viewer.
Encoded data within a captioning or text service channel of the video
signal is extracted at step 520 and it is determined whether or not a
valid logical address link is present (step 530). A valid logical address
link is one that is encoded in a predetermined syntax, such as described
earlier, and whose logical address and attribute/value pairs are not
corrupted as determined by a comparison of a checksum generated by the
receiving device to the checksum accompanying the logical address link. If
a valid logical address link is present, then processing continues with
step 540. At step 540, an indication is provided to the viewer that a
logical address link is associated with the TV program currently being
viewed. According to various embodiments of the present invention, the
indication may be visual, audible, or a combination of one or more audible
and visual indications. For example, an icon may be temporarily displayed
in one of the corners of the display area. Additionally, a tone may
accompany the icon's initial presentation. It is appreciated that various
other alert mechanisms are possible. In any event, continued reception and
processing of the broadcast video signal and embedded logical address
links may be achieved by returning to step 510. Returning to step 530, if
no valid logical address link is present in the video signal, then
processing loops back to step 510.
Combining Real Logical Address Links and Batch Mode Logical Address Links
By providing access to both real-time logical address links and batch mode
logical address links, the advantages of both can be enjoyed. Because
batch mode logical address links are known in advance, the client system
may pre-fetch t | | |
