Canadian Patents Database / Patent 1302554 Summary

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(12) Patent: (11) CA 1302554
(21) Application Number: 598651
(54) English Title: VIDEO SIGNAL DISTRIBUTION SYSTEM
(54) French Title: SYSTEME DE DISTRIBUTION DE SIGNAUX VIDEO
(52) Canadian Patent Classification (CPC):
  • 350/24
(51) International Patent Classification (IPC):
  • H04J 99/00 (2009.01)
  • H04N 7/14 (2006.01)
  • H04N 7/173 (2006.01)
(72) Inventors :
  • GRAVES, ALAN FRANK (Canada)
  • DITTBURNER, ROBERT CARSON (Canada)
  • HAGGLUND, BARRY BENJAMIN (Canada)
(73) Owners :
  • NORTEL NETWORKS LIMITED (Canada)
(71) Applicants :
(74) Agent: SMITH, DALLAS F.
(45) Issued: 1992-06-02
(22) Filed Date: 1989-05-03
(30) Availability of licence: N/A
(30) Language of filing: English

English Abstract





VIDEO SIGNAL DISTRIBUTION SYSTEM


Abstract of the Disclosure
A signal distribution system is disclosed for distributing
television program signals from a central location to a plurality of
subscriber locations via respective optical fibers. At the central
location, 4 of 64 signals are selected and multiplexed for delivery to
each subscriber location. At each subscriber location, an interface
unit selects any 2 of the 4 signals for delivery to each of a
plurality of video port controllers, for supply to an associated
television receiver and video cassette recorder. Requests for program
signals initiated by a subscriber at a video port controller are
handled by the interface unit, being granted, denied, or forwarded to
the central location as appropriate. The system facilitates the
provision of pay per-channel and pay-per-view television program
signals.

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Note: Claims are shown in the official language in which they were submitted.

14
WHAT IS CLAIMED IS:

1. A signal distribution system for distributing video
signals from a central location to a plurality of subscriber locations
via respective communications paths, the system comprising, at the
central location:
means for selecting for each subscriber location, from a
first plurality of video signals a second, lesser, plurality of video
signals and for delivering said second plurality of video signals to
the respective subscriber location via a respective communications
path; and, at each subscriber location:
a plurality of control means each for supplying a respective
video signal to at least one respective video signal receiver
associated therewith; and
interface means coupled to the respective communications
path and to each control means for delivering respective video signals
thereto;
wherein each control means comprises means for requesting
delivery of any of the first plurality of video signals and for
communicating such request to the interface means, and wherein the
interface means comprises means responsive to such request for:
determining whether the requested video signal is one of
said second plurality of video signals delivered thereto via the
respective communications path;
if so, delivering the requested video signal to the
respective control means; and
if not, communicating a request for the requested video
signal to the central location to be selected from the first plurality
of video signals and delivered as one of the second plurality of
video signals.

2. A system as claimed in claim 1 wherein the interface
means comprises means for supplying to each control means a third
plurality, less than the second plurality, of video signals.


3. A system as claimed in claim 2 wherein the first, second,
and third pluralities of video signals comprise at least about 64, 4,
and 2 video signals respectively.

4. A system as claimed in claim 1 and including at the
central location means for multiplexing with each selected signal an
identification of the selected signal.

5. A system as claimed in claim 1 wherein each communications
path comprises a digital signal communications path, the system further
comprising at the central location means for supplying each of the
first plurality of video signals as a digital signal.

6. A system as claimed in claim 5 wherein each control means
comprises means for converting a respective digital video signal
delivered thereto into an analog video signal for supply to the
respective video signal receiver.

7. A system as claimed in claim 5 wherein the communications
paths comprise optical fiber communications paths.

8. A method of distributing television program signals from
a central location selectively to a plurality of subscriber locations,
comprising the steps of:
at a plurality of points at a subscriber location, requesting
television program signals for delivery thereto;
at the central location, selecting for the respective
subscriber location a plurality of requested television program
signals from a larger number of available television program signals;
supplying the selected signals from the central location to
the subscriber location via a respective communications path; and
at a central point at the subscriber location, receiving
requests for television program signals from said plurality of points,
receiving the selected signals from the central location via the
respective communications path, determining whether requested
television program signals are received from the central location

16
and if so delivering the requested television program signals received
from the central location to said plurality of points in dependence
upon the received requests, and communicating to the central location
requests for selecting television program signals at the central
location for supply to the subscriber location.

9. A method as claimed in claim 8 wherein the television
program signals are supplied as time division multiplexer digital
signals via the respective communications paths.

Note: Descriptions are shown in the official language in which they were submitted.

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VIDEO SIGNAL DISTRIBUTION SYSTEM
This invention relates to a signal distribution system for
distributing video signals from a central location to a plurality of
subscriber locations via respective communications pa-ths.
Background of the Invention
It is well known to distribute television program signals
from a central location to subscriber locations via coaxial cable
distribution systems. ~hilst such systems have long been used for
broadcast television program signals, i.e. signals which are available
1~ to all subscribers without payment of further fees, they must be
supplemented or modified to accommodate newer video signal services,
such as pay-per-channel (PPC) and pay-per-view (PPV) television
program signals. In addition, such systems have a limited capacity,
i.e. a limited number of program channels which can be carried,
because all of the channels available to all of the subscribers must
be broadcast simultaneously.
With PPC signals, commonly the signal is scrambled at the
central location and, for a payment of a fee for the channel, the
subscriber is provided with a descrambler for use at his location to
return the signal to its normal, receivable, form. Such procedures
have led to the existence of unauthorized descramblers enabling
subscribers to receive programs without payment of the fee for the
channel, and to the theft oF authorized scramblers.
With PPV television program signals, similar or more complex
scrambling procedures may be used, but there is an additional
requirement for the subscriber to communicate to the central location
his desire to receive, and his agreement to pay for, a particular
program. This communication requires an upstream communications path
from the subscriber location to the central location, in addition to
the downstream communications path via which the television program
signals are distributed. Such an upstream communications path is not
conveniently provided by cable distribution systems, and generally
must be provided via other equipment, such as the telephone system or
other equipment at the subscriber's location. Furthermore, the
communications and addressable decoders which are involved with PPV
signals lead to undesirable congestion in broadcast networks.
In each of these instances, the fact that the television
program signals are distributed in a general manner from the central




,.. .~, ,,~. . . .

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location to all of the subscriber locations means that control oF the
signals by their distributor is lost, and the signals are exposed to
theft with consequent loss of revenues.
With increasing bandwidths available on communications paths
which have conventionally served for only telephone communications,
for example through the use of optical fiber communications paths and
especially the extension of such paths from a central location to
subscriber locations, it is increasingly becoming possible to use such
communications paths not only For telephone communications but also
for other services, such as video signal distribution, enabling the
provision of cable distribution systems to subscriber locations to be
dispensed with.
Accordingly an object of this invention is to provide an
improved signal distribution system for distributing video signals.
Summary of the Invention
According to this invention there is provided a signal
distribution system ~or distributin~ video signals from a central
location to a plurality of subscriber locations via respective
communications paths, the system comprising: means at the central
location for selecting for each subscriber location, from a first
plurality of signals, a second, lesser, plurality of signals and for
delivering said second plurality of signals to the subscriber location
via a respective communications path; and, at each subscriber
location: a plurality of control means each for supplying a
respective video signal to a-t least one respective video signal
receiver associated therewith; and interface means coupled to the
respective communications path and to each control means for
delivering respective video signals thereto.
In an embodiment of the invention described in detail below,
the means at the central location is constituted by a video services
switching unit (VSS) and, for each subscriber location, each control
means is constituted by a video port controller (VPC) and the
interface means is constituted by an optical network interface un,t
~ONI~.
The interface means preferably comprises means for supplying
to each control means a third plurality, less than the second
plurality, of video signals. Advantageously the first, second, and
third pluralities of video signals comprise at least about 64, 4, and




.. ...

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~ 3
2 video signals respectively. These numbers enable each subscriber
location to have simultaneous access to 4 of a total of 64 video
signals, with any 2 of the 4 signals being simultaneously supplied to
each control means for delivery for example to a co-located television
receiver and video cassette recorder.
Preferably the control means comprises means for requesting
delivery of any of the first plurality of signals and for
communicating such request to the interface means, and the interface
means comprises means responsive to such request for selectively:
delivering the requested signal to the respective control means if the
requested signal is one of said second plurality of signals delivered
thereto via the respective communications path; and communicating a
request for the requested signal to the central location to be
delivered as one of the second plurality of signals.
Conveniently each communications path comprises a digital
signal communications path, the system further comprising at the
central location means for supplying each of the first plurality of
signals as a digital signal. This facilitates the provision of
multiplexed digital signals, each with baseband video quality, to a
co-located television receiver and VCR associated with each control
means. In this case each control means preferably comprises means for
converting a respective digital video signal delivered thereto into an
analog video signal for supply to the respective video signal
receiver. Advantageously the communications paths comprise optical
fibers.
To facilitate selection, delivery, and confirmation of
signals, preferably the system includes at the central location means
for multiplexing with each selected signal an identification of the
selected signal.
The invention also extends to a method of distributing
television program signals from a central location selectively to a
plurality of subscriber locations, comprising the steps of:
at a plurality of points at a subscriber location, requesting
television program signals for delivery thereto;
at the central location, selecting for the respective
subscriber location a plurality of requested television program
signals from a larger number of available television program signals;

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supplying the selected signals from the central location to
the subscriber location via a respective communicati~ns path; and
at a central point at the subscriber location, receiving
requests for television program signals from said plurality of points,
receiving the selected signals from the central location via the
respective communications path, delivering requested television
program signals received from the central location to said plurality
of points in dependence upon the received requests, and communicating
to the central location requests for selecting television program
signals at the central location for supply to the subscriber location.
Brief Description of the Drawings
The invention will be further understood from the following
description with reference to the accompanying drawings, in which:
Fig. 1 is a block diagram illustrating parts of a video signal
distribution system in accordance with an embodiment oF this invention;
Fig. 2 is a block diagram illustrating a video services
switching unit (VSS) of the system of Fig. 1;
Fig. 3 is a block diagram illustrating an optical network
interface unit (ONI) provided for each subscriber in the system of
Fig. 1;
Fig. 4 is a block diagram illustrating a video port controller
(VPC) in the system of Fig. 1;
Fig. 5 illustrates a tdm (time division multiplexed) frame
format of a digiti~ed video signal;
Fig. 6 illustrates a tdm frame format of a VSS-to-ONI signal;
and
Fig. 7 illustrates a tdm frame format of an ONI-to-VPC signal.
Detailed Description of the ~referred Embodiment
Referring to Fig. 1, a video signal distribution system will
be described. The term "video signal" as used herein is intended to
embrace wide bandwidth signals gPnerally, of which video signals are
typical, and not merely signals whose sole purpose is to provide a
visual picture. In particular, this term is used herein to embrace
all of the components, video and audio, of a conventional television
signal.
The distribution system of Fig. 1 includes a video services
switching unit, or VSS, 20 which is located conveniently with respect



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,

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to subscribers of the system. By way of example, the VSS 20 may be
co-located with a telephone central office which provides telephone
and other communications services for the same subscribers. For
simplicity, Fig. 1 shows components of only one subscriber, including
an optical network interface unit, or ONI, 30 which is coupled to the
VSS 20 via a bidirectional s;ngle mode optical fiber 10. The optical
fiber 10 is representative of a bidirectional wideband communications
path between the YSS 20 and the ONI 30, which may alternatively have
other forms such as electrical cables, multiple unidirectional optical
1~ fibers, and so on, which may serve not only for the video signal
distr;bution system described herein but also for the other
communications services for the subscriber. As indicated in Fig. 1,
other optical fibers 12 couple the VSS 20 to ONIs 30 of other
subscribers; for example there may be 128 or more ONIs 30 coupled to
one VSS 20.
As also illustrated in Fig. 1, the VSS 20 is supplied with,
for example, 64 analog video channels. For example, these comprise
television program signals from a CATV source supplied ;n known manner
via an analog video patch panel.
For each subscriber, the system of Fig. 1 includes not only
the ONI 30 but also one or more, for example up to 8, video port
controllers, or VPCs, 40, two of which are illustrated in Fig. 1.
Each VPC 40 is located in the vicinity of a respective television
receiver (TV) 42 and/or video cassette recorder ~VCR) 44 of the
subscriber. The TVs 42 and VCRs 44 are of conventional form and are
not part of the distribution systern itself; they are connected to the
respective VPCs 40 via conventional coaxial cables 46. Each VPC 40 is
connected via a respective coaxial cable 4~ to the ONI 30.
By way of example, for a residential subscriber the GNI may be
located in a garage of the subscriber's residence, and different rooms
of the residence may each include a respective VPC 40 with a TV 42
and a VCR 44 connected thereto. ~ithin the designed limits of the
distribution system which will become evident from the description
below, each such TV 42 and each such VCR 44 may receive any of the ~4
television program signals via the respective units 20, 30, and 40.
These designed limits include, in part;cular, a limit of 4 different

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program signals which can be simultaneously carried on the optical
fiber 10 to any particular subscriber.
Referring now to Fig. 2, the YSS 20 will be described in more
detail. As illustrated in Fig. 2, the VSS comprises an analog to
digital converter (ADC) 21Q and a multiplexer 212 in respect of each
of the 64 analog video channels. In addition, the VSS includes, for
each subscriber, a respective selector 220, multiplexer 222, control
unit 224, electro-optical transmittPr (Tx) 226, opto-electrical
receiver (Rx) and decoder 228, and directional optical coupler 230.
Each ADC 210 serves to convert the respective incoming analog
video signal into a digital video signal, with for example 8-bit bytes
at a rate of 13.44MB/s (megabytes per second) wh;ch are supplied to
the multiplexer 212. Although various forms of television signal ADC
are known and may be used, each ADC is preferably of the form
described and claimed in Canadian patent application Serial No.
573,872 filed August 4, 19~8 in the name of A.F. Graves and entitled
"D;git;zat;on of Video Signals". In such an ADC, the modulated audio
signal is summed with the picture signal of a television program and
the summed signal is sampled at a relatively high sampling rate,
typically more than three times the color subcarrier frequency,
synchronously related to a rate at which the digitized samples are to
be transmitted.
The 13.44MB/s digital video signal, having a bit rate of
107.52Mb/s (megabits per second), is multiplexed by the multiplexer
212 with a channel identity (ID) also supplied to the multiplexer, to
produce a multiplexed digital video signal at a bit rate of 108.8Mb/s
having a tdm frame format which is illustrated in Fig. 5.
As shown in Fig. 5, each frame has a period of 3.125us
(microseconds) and thus comprises 340 bits. The 340 bits in each
frame are constituted by 42 bytes of the 13.44MB/s video signal, the 8
bits of each byte being represented in Fig. 5 by the bits V7, V6,
...V0 in order of decreasing significance, and 4 identical bits each
represented Cn in Fig. 5. ~ver a superframe period o~ 21.875us or 7
frames, each Cn bit has a value represented sequentially in Fig. 5 as
T, C5, C4, ...C0. T represents a toggle bit which has a value
alternating between 1 and 0 in successive superframes, and the 6 bits

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C5 to CO r~present the channel identity. As 26=64, these 6 bits allow
each of the 64 analog video channels to be uniquely identified.
Referring again to Fig. 2, each selector 220 is supplied with
all 64 digitized video signals and serves, under the control of its
control unit 224 as described further below, to select 4 of these and
supply them to the multiplexer 222. The channel identities are
supplied to the control unit 224 and are replaced, in the signals
multiplexed by the multiplexer 222, by overhead information ~O/H) at a
corresponding bit rate of 5.12Mb/s. Consequently the multiplexer 222
multiplexes 4 digital video signals from the selector 220 at an
average bit rate of 107.52Mb/s with the 5.12Mb/s overhead information
to produce a mult;plexed signal at a bit rate of 435.2Mb/s, hav;ng a
frame format as shown in Fig. 6. This downstream (i.e. in the
direction from the VSS to the ONI and VPC) signal is transmitted
optically by the transmitter 226 and is coupled to the fiber 10 via
the coupler 230. An upstream signal on the ~iber 10 and having a bit
rate of 2.56Mb/s is coupled via the coupler 230 to the receiver and
decoder 228 and thence to the control unit 224. In addition, the
control unit 224 is supplied via a line 230, for example from CATV
equipment (not shown), with information for each subscriber as to
video signal channels available to the subscriber, in accordance with
which the control unit 224 maintains in memory a service provisioning
map for the subscribers.
Referring to Fig. 6, the downstream signal frame format
consists of frames each with a period of 3.125us and hence comprising
1360 bits or 170 bytes. Of these, the first 16 bits or 2 bytes are
constituted by the overhead information, and the remaining 1344 bits
or 168 bytes are constituted by 42 bytes of each of the 4 selected
digital video signals. These video bytes are bit interleaved as shown
by Fig. 6; thus denoting the 4 selected video signals or channels as
a, b, c, and d, video signal bits Vd7, Vc7, Vb7, Va7, Vd6, etc. are
multiplexed in sequence as shown in Fig. 6.
The 16 bits of overhead information comprise a video frame
byte, 10010101 as shown in Fig. 6, followed by 4 bits X and 4 bits Cd,
Cc, Cb, and Ca. The latter 4 bits (C bits) represent the channel
identities of the selected channels d to a respectively, in superframe
periods of 21.785us, as shown in Fig. 6, in exactly the same manner as

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in F;g. 5. The 4 bits X in each frame constitute a downstream
message channel at a bit rate of 1.28Mb/s. As shown in FigA 6, over a
superframe period of 500us (160 3.125us frames) this message channel
provides a frame of 80 bytes, comprising a message frame byte which,
except for an alternating or toggle bit T, is the inverse of the video
frame byte, 78 data bytes, and a final integrity (parity) byte.
Referring now to Fig. 3, the ONI 30 is illustrated in more
detail. The ONI serves to select, for supply to each of the coaxial
cables 48 and hence to each VPC 40, 2 of the 4 digital Yideo signals
which are present or can be supplied in the downstream signal on the
fiber 10.
To this end, the ONI 30 includes a selector 310 and a control
unit 312. The downstream signal on the fiber 10 is coupled via a
directional optical coupler 314 to an electro-optical receiver 316,
which supplies the resulting 435.2Mb/s multiplexed digital signal to a
demultiplexer 318. The demultiplexer 318 demultiplexes this digital
signal to produce the 4 video signals, which it supplies with the
corresponding channel identities to the selector 310, and the messa~e
channel or X bits which it supplies to a message channel inkerface
unit 320. The interface unit 320 is coupled to the control unit 312
for bidirectional communications therewith; accordingly, it also
provides an upstream message channel at a bit rate of 2.~6Mb/s via an
electro-optical transmitter 322 and the coupler 314 to the fiber 10.
This upstream message channel is conveniently Manchester encoded in
the interface unit 320, decoding being performed in the unit 228 of
the VSS 2C, and has a similar frame format to that of the downstream
message channel as shown in Fig. 6. These message channels provide
for bidirectional communications between the control units 312 and 224
for the purposes described further below.
Correspondingly, the control unit 312 communicates
bidirectionally, with a control unit in each VPC 40 as described
below, via a serial communications interface unit 324. The ONI 30
further includes, for each ~PC 40, an AMI (alternate mark ;nversion)
encoder 326 and a coaxial cable interface unit 328.
Under the control of the control unit 312 the selector 310,
which supplies the C bits (channel identity bits3 to the control unit
312, supplies to each of its outputs a multiplexed digital signal at a

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bit rate of 217.6Mb/s, comprising the respective selected 2 digital
video channels together with a downstream message channel from the
control unit 312 supplied via the serial communications in~erface unit
32~ to an input of the selector 310. Each such multiplexed signal,
having a frame format as described below with reference to Fig.7, is
encoded by the respective AMI encoder 326 and supplied via the
respective coa~ial cable interface unit 328 to the respective coaxial
cable 48. In the upstream direction, a message channel having a
similar frame format is supplied from the respective cable 48 via the
respective unit 328 to the serial communications interface unit 324
and thence to the control unit 31~.
Referring to Fig. 7, the frame format of each 217.6Mb/s
multiplexed si~nal comprises frames with a period of 3.125us, and
hence comprising 680 bits or 85 bytes, of which a first byte is a
frame byte having the form lOOlOlYl, where Y is a bit of the message
channel. The remaining 84 bytes are video bytes of the 2 selected
video channels, bit interleaved in the same manner as described with
reference to Fig. 6. Thus if the 2 selected channels are the channels
a and b, these bytes have the bit sequence Vb7, Va7, Vb6, Va6, ...VbO,
VaO as illustrated in Fig. S.
The Y bits in a superframe of 256 frames9 and hence in a
superframe period of 800us, form the downstream message channel with a
frame format as shown in Fig. 7. Each message frame comprises 32
bytes consisting sequentially of an initial synchronizing byte
~hexadecimal 69), a mode or M byte, 28 message bytes comprising a
message length byte, a message type byte, and 26 data bytes, and two
cyclic redundancy check ~CRC) bytes.
Thus each 217.6Mb/s downstream signal comprises 2 digital
video signals e~ch hav;ng an average bit rate of 107.52Mb/s9 the Y
bits having a bit rate of 320kb/s, and framing bits at an average bit
rate of 2.24Mb/s. The upstream signal on each cable 48, having as
indicated above a simîlar frame format to that of the Y bits as shown
in F;g. 7, has a bit rate of 160kb/s with a frame period of 1.6ms~ and
is conveniently Manchester encoded as for the upstream message channel
on the fiber 1~. The downstream and upstream signals on each cable
48 are separated in frequency by filters in the coaxial cable
interface unit 328, as they have widely different frequencies.

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Referring to Fig. 4, each VPC 40 comprises a control unit 410
as indicated above, input and display devices 412 connected thereto, a
coaxial cable inter-face unit 414 similar to the unit 328, a clock and
frame recovery, demultiplexer, and serial-to-parallel converter unit
416, a serial communications interface unit ~18, two digital-to-analog
converters (DACs) 420, and a VCR playback switch 422. The DACs 420
are the converse of the ADCs 210, and are preferably as described in
the previously mentioned patent application. The coaxial cable
interface unit 414 supplies the 217.6Mb/s downstream signal to the
unit 4169 which supplies the 2 107.52Mb/s digital video signals one
to each of the DACs 420 for supply respectively to the TV 42 and to
the VCR 44 v;a the playback switch 422, which enables playback of
programs from the VCR to the TV. The unit 416 also supplies the
downstream Y bits or message channel at 320kb/s to the serial
communications interface unit 418 and thence to the control unit 410.
In the upstream direction, the 160kb/s message channel is provided
from the control unit 410 via the serial communications interface unit
418 and the coaxial cable interface unit 414 to the coaxial cable 48.
The input and display devices 412 can comprise conventional
units, such as a 7-segment display unit for displaying selected
channel numbers and other information, and a keyboard and/or an infra-
red remote control device for entering channel selections. These
devices are coupled to the control unit 410 for human selection of
television programs.
From the above description it should be appreciated that
message channel communications are provided in both the downstream and
upstream directions between the control units of each VPC 40 and the
associated ONI 30, and between the control units of each ONI 30 and
the VSS 20. Such communications can be used for program selection and
confirmation in the manner described below, and additionally for
maintenance and administration purposes.
In addition, it should be appreciated that the VSS 20 provides
a 4 from 64 selection of video signals for each ONI 30, and each ONI
30 in turn provides a 2 from 4 selection of these video signals for
each VPC 40. The manner in which such selections are accommodated
using the message channel communications is described below. In this
following description, references are made for convenience to

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11
communications between the VPC and ONI and between the ONI and VSS; it
should be understood that these references actually refer to
communications between the control units of these units.
The 64 video signals can comprise television programs of three
types: broadcast program channels which are available to all
subscribers; pay-per-channel (PPC) program channels which are
available only to those subscribers who pay to receive the particular
program channel; and pay-per-v;ew (PPV) programs for which a
subscriber must enter a predetermined access code to receive the
particular program. To this end, the VSS 20 (or CAT~ equipment with
which the VSS 20 communicates) maintains in memory a subscriber
access record, or provisioning map as referred to above, recording for
each subscriber any PPC channels available to, and PPV access codes
for, that subscriber.
In operation, the VSS maintains for each subscriber a record
of the four channels which are requested by the subscr;ber. For each
subscriber, the ONI polls each VPC periodically for possible messages
which may indicate desired channel selection changes, and may
communicate such changes to the VSS as new channel requests to be
recognized and, if appropriate, acted upon.
Initially, suppose that a subscriber at a VPC requests a new
channel, via the keyboard or infra-red remote control device of that
VPC. the VPC queues this request until it is next polled by the ONI
~via the Y bit message channel), whereupon the VPC submits the channel
request via the upstream message channel to the ONI. If all ~ video
channels a to d available on the fiber 10 are already in use (by other
VPCs of the same subscriber), and none of these is the requested
channel, then the ONI communicates to the VPC via the Y bit channel
that the new channel request is denied, and a corresponding message
3~ is displayed by the VPC on its display device. If, on the other hand,
the requested channel is already being received via the fiber 10 as
one of the channels a to d, then the ONI controls the respective
selector 310 to supply this channel as one of the video channels to
the VPC together with a Y bit message indicating that the request has
been granted, a corresponding message being displayed by the display
device of the VPC.

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12
If neither of the above conditions is fulfilled, i.e. if there
is at least one of the video channels a to d free and the requested
channel is not already being supplied to the ONI via the fiber 10,
then the GNI allocates for the request one of the video channels a to
d which is free, so that subsequent requests do not result in
conflicts, and forwards the request on the upstream message channel
to the VSSt where the request is detected. If the request is for a
broadcast channel, or for a PP~ channel which is available to this
subscriber, then the VSS controls the selector 220 to supply the
requested program channel as the allocated one of the channels a to d
on the fiber 10, and communicates via the X bits a message to the ONI
indicat;ng granting of the request. The ONI controls the respective
selector 310 accordingly to supply the channel to the VPC, with a Y
bit message indicating grant of the request as above. If the request
is for a PPC channel which is not available to the subscriber, the VSS
supplies an X bit denial message to the ONI, and this is forwarded to
the VPC and displayed, the allocated one of the channels a to d
subsequently being freed.
If the request forwarded to the VSS is for a PPV program, a
longer sequence of communications takes place in a similar manner,
involving for example a request from the YSS via the ONI to the VPC
for an access code, return of this code (entered by the subscriber)
from the VPC via the ONI to the VSS with verification of the access
code, supply of the requested program for a timed preview period with
a request to the VSS for confirmation to continue viewing, and either
expiry of this period or confirmation and consequent billing. In each
case, the messages between the VSS and ONI and between the ONI and
VPC are conducted via the message channels as discussed above, using
the X and Y bits in the downstream direction and the corresponding
message bits in the upstream direction. In th;s situation, if the
access code entered by the subscriber is incorrect and is therefore
not verified, the VSS does not supply the requested program whereby
unauthorized viewing of program signals is prevented.
Although a particular embodiment of the invention has been
described in detail, it should be appreciated that numerous
modifications, variations, and adaptations may be made thereto ~ithout
departing from the scope of the invention as defined in the claims.

~L3(:~2~i~4

In particular, the numbers, formats and frequencies of particular
signals and units may all be varied to suit desired circumstances.
Furthermore, although the described embodiment of the
;nvent;on uses dig;tal transmission of video signals from the VSS via
each ONI to each VPC, this need not be the case and analog
transmission may instead be used partly or entirely. For example, the
video signals may be transm;tted d;g;tally from the VSS to each ONI,
where the selected v;deo signals may be converted back into analog
form for transmission to each VPC, for example as an r.f. modulated
signal distributed via coaxial cable or other wiring.





A single figure which represents the drawing illustrating the invention.

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Admin Status

Title Date
Forecasted Issue Date 1992-06-02
(22) Filed 1989-05-03
(45) Issued 1992-06-02
Lapsed 2009-06-02
Correction of Expired 2012-12-05

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Filing $0.00 1989-05-03
Registration of Documents $0.00 1991-06-28
Registration of Documents $0.00 1991-06-28
Maintenance Fee - Patent - Old Act 2 1994-06-02 $100.00 1994-05-18
Maintenance Fee - Patent - Old Act 3 1995-06-02 $100.00 1995-05-17
Maintenance Fee - Patent - Old Act 4 1996-06-03 $100.00 1996-05-01
Maintenance Fee - Patent - Old Act 5 1997-06-02 $150.00 1997-04-30
Maintenance Fee - Patent - Old Act 6 1998-06-02 $150.00 1998-05-06
Maintenance Fee - Patent - Old Act 7 1999-06-02 $150.00 1999-04-29
Maintenance Fee - Patent - Old Act 8 2000-06-02 $150.00 2000-05-11
Maintenance Fee - Patent - Old Act 9 2001-06-04 $150.00 2001-05-24
Maintenance Fee - Patent - Old Act 10 2002-06-03 $200.00 2002-05-30
Maintenance Fee - Patent - Old Act 11 2003-06-02 $200.00 2003-05-21
Maintenance Fee - Patent - Old Act 12 2004-06-02 $250.00 2004-05-25
Maintenance Fee - Patent - Old Act 13 2005-06-02 $250.00 2005-05-24
Maintenance Fee - Patent - Old Act 14 2006-06-02 $250.00 2006-05-25
Maintenance Fee - Patent - Old Act 15 2007-06-04 $450.00 2007-05-18
Current owners on record shown in alphabetical order.
Current Owners on Record
NORTEL NETWORKS LIMITED
Past owners on record shown in alphabetical order.
Past Owners on Record
BELL-NORTHERN RESEARCH LTD.
DITTBURNER, ROBERT CARSON
GRAVES, ALAN FRANK
HAGGLUND, BARRY BENJAMIN
NORTEL NETWORKS CORPORATION
NORTHERN TELECOM LIMITED
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.

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Document
Description
Date
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Number of pages Size of Image (KB)
Description 1993-10-31 13 643
Representative Drawing 2000-12-19 1 16
Drawings 1993-10-31 5 107
Claims 1993-10-31 3 91
Abstract 1993-10-31 1 22
Cover Page 1993-10-31 1 16
Fees 1998-05-06 1 34
Fees 2000-05-11 1 32
Fees 2001-05-24 1 39
Fees 1997-04-30 1 32
Fees 1996-05-01 1 35
Fees 1995-05-17 1 27
Fees 1994-05-18 2 79