United States Patent [191
Bigham et al.
Patent' Number:
Date of Patent:
Aug. 6, 1996
Primary Examiner-Melvin Marcelo
Assistant Examiner—Melissa Kay Carman
Attorney, Agent, or Firm-Lowe, Price, LeBlanc & Becker
[75] Inventors: John A. Bigham, Pottstown, Pa;
Kamran Sistanizadeh, Arlington, Va.;
Dave Little, Columbia, Md.
A video distribution network having an architecture that
distributes video services over a greater serving area. The
broadcast consolidation section receives broadband data
from a plurality of information providers, preferably as
[73] ASSigIICCI Bell Atlantic Network Services, 1110-,
Arlington, Va-
compressed, digital signals using asynchronous transfer
mode (ATM) transport. The broadcast consolidation section
combines the ATM streams from different information pro
[21] Appl. No.: 413,207
[22] Flled‘
Mar‘ 28’ 1995
[51] Int. 01.6 ...................................................... .. H04J 3/24
[52] US. Cl. ........................ .. 370/531; 370/60; 370/601;
ring. The broadcast ring supplies the consolidated broadcast
370/94 1. 348/6. 348/7. 348/12
consolidated broadcast data to MPEG data on an RF carrier,
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and combines the RF signal with other RF signals before
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access node. Each local video access node combines the RF
broadcast data from the corresponding video access node
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with downstream IMTV tra?ic supplied by an ATM back
bone subnetwork. The combined RF signals are output from
the local video access nodes to the access of network
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viders and outputs a consolidated signal onto a transport
servicing these subscribers. ATM demultiplexers in the
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video network hubs and the local video access nodes per
form MPEG processing on received ATM cell streams,
1/199] Johnson a,
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assign identi?cation values, and output on broadband chan
8/1992 Paik er a1, ____ ..
nels or narrowband signaling channels, on the basis of
6/1993 Hearty et al
7/1993 W?chob ------ -.
corresponding VPI/VCI values and downloaded routing
information, resulting in efficient transport of signaling
9/1993 Littoral et a]. .
6/1995 Wunderlich et a1. ................... .. 380/20
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MPEG (moving picture experts group) is a broad generic
standard for digital video program compression. A number
of speci?c compression algorithms satisfy MPEG require
ments. MPEG-2 is a second generation compression stan
dard capable of encoding video program material into a 6
Mbits/sec bit stream and packetizing a number of 6 Mbits/
sec channel streams into a single higher rate signal transport
stream. The conversion of MPEG-2 data into ATM cell
The present invention relates to full service digital broad
band networks offering a full range of digital communica—
tions by transporting compressed, digital information using
format, however, imposes additional overhead requirements
Asynchronous Transfer Mode (ATM) backbone transport
that reduce the information-carrying capacity of the net
and RF distribution over a hybrid-?ber-coax local loop
work. For example, synchronous transmission protocols,
such as SONET, may require a stream of continuous data to
retain synchronization. Thus, an ATM data stream carrying
MPEG video data that is transmitted on a synchronous
carrier may need to be padded with ATM idle cells, or
“dummy cells”, in order to ensure proper synchronization
Distribution of full motion video data has evolved from
early television broadcasting to meet viewer demand.
with the physical layer. Therefore, the network’s informa
tion-carrying e?‘rciency is reduced each time information
data is converted to another layer of transport protocol.
In addition, there has been a growth of VIPs offering
Recently, several different wideband digital distribution net
works have been proposed for offering subscribers an array
of video services; including true Video On Demand service.
The following U.S. Patents disclose representative examples
of such digital video distributions networks: Yurt et al. U.S.
Pat. No. 5,253,275, Yurt et al. U.S. Pat. No. 5,132,992,
Ballantyne et al. U.S. Pat. No. 5,133,079, Tindell et al. U.S.
Pat. No. 5,130,792, Lang U.S. Pat. No. 5,057,932, Lang U.S.
Pat. No. 4,963,995, Cohen U.S. Pat. No. 4,949,187, Baji et
al. U.S. Pat. No. 5,027,400, and Walter U.S. Pat. No.
4,506,387. For example, Litteral et al. U.S. Pat. No. 5,247,
347 discloses a digital video distribution network providing
connected to the PSTN internal switches. Thus, a need exists
for increased bandwidth and ef?cient connectivity tech
niques in the PSTN as competition increases between VIPs
for connectivity to subscribers.
An example of a video network utilizing a Level 1
subscribers with access to multiple Video On Demand
service providers through the public switched telephone
The prior art video networks have not addressed many
problems which arise when the networks must be adapted to
provide end users with equal access to multiple video
information providers. The networks of the prior art also
Gateway is disclosed in commonly-assigned copending
application Ser. No. 08/304,174, ?led Sep. 12, 1994 (attor
ney docket No. 680-093), the disclosure of which is incor
porated herein in its entirety by reference. FIG. 1 corre
typically have not been designed to accommodate a full
range of digital services such as telephone, video, video
on-demand, data services, information services, interactive
services, and other modern digital offerings.
video services to subscribers. The growth in the number of
VIPs offering services will result in capacity problems on the
PSTN connecting the VIP services to their subscribers. In
addition, any one VIP may not fully utilize the physical
connection to the PSTN when providing video services.
Thus, if a plurality of VIPs each use an assigned optical ?ber
at, for example, ?fty percent capacity, the PSTN will be
ine?iciently utilized if the optical ?ber of each VIP is
A disadvantage of systems such as that of Litteral et al.,
sponds generally to FIG. 4 of this commonly-assigned
copending application and discloses a hybrid ?ber-coax
system which provides RF transport of both analog and
digital broadband services. The illustrated network provides
which use the PSTN as a video distribution system is that
broadcast video distribution, archival video services and
they are often bandwidth limited. Because the systems use
interactive multi-media services as well as plain old tele
the PSTN only for connectivity between subscribers and/or
between subscribers and Video Information Providers
(VIPs), there is no capability for dynamic routing of digi
tized video without requiring dedicated leased, wide band
width circuits. Also, point-to-point connectivity makes it
through multiple central o?ices, several different central
o?ices would each have a Loop Transport Interface similar
in structure to the Interface 10 depicted in FIG. 1. In some
respects, each Loop Transport Interface serves as the head
end of an otherwise conventional optical ?ber trunk and
coaxial cable type CATV distribution network.
are now widely available through existing CATV systems.
Attempts have been made to improve the core switching,
multiplexing and transmission technologies for integrated
bandwidth, low delay, packet~like switching and multiplex
In the Loop Transport Interface 10, a laser type optical
transmitter 12 transmits downstream signals through ?bers
14 to optical to electrical nodes referred to as “optical
network units” or ONU’s. The laser operates in a linear
ing. In ATM, usable capacity can be assigned dynamically
(on demand) by allocating bandwidth capacity to supply
?xed-sized information-bearing units called “cells” to point
to-point or multi~point outputs. Each cell contains header
and information ?elds. The ATM standard, CCITT.121/2
speci?es a 53 byte cell which includes a 5 byte header and
a 48 byte payload.
The network of FIG. 1 includes a Loop Transport Inter
face 10 located in a telco central of?ce. In an area serviced
diilicult to offer a wide array of broadcast services such as
digital networks to support voice, data and video services
from VIPs for multiple users. For example, ?ber optic
transmission systems with bandwidths ranging from 155.52
to 2,488.32 Mbps have been considered to improve band
width access. In addition, asynchronous transfer mode
(ATM) has been developed as a technique to provide broad
phone service.
mode in the range of 5—750 MHz. The transmitter 12 is
followed by an optical splitter and can transmit to several
ONU nodes 16. Each ONU 16 performs optical to electrical
conversion on the downstream signals and supplies down
stream RF electrical signals to a coaxial cable distribution
system 18.
The optical transmitter receives and transmits signals
from an RF (radio frequency) combiner 20. The combiner 20
combines levelized RF signals from several sources to
produce the appropriate signal spectrum for driving the
optical transmitter 12. One set of signals supplied to the RF
combiner 20 are group of AM-VSB (amplitude modulated
vestigial sideband) analog television signals 22 from one or
more appropriate sources (not shown). Such signals are
information into one 6 MHZ bandwidth analog channel. As
another example, US. Pat. No. 5,231,494 to Wachob, the
disclosure of which is incorporated herein in its entirety by
reference, teaches quadrature phase shift keyed (QPSK)
modulation of a plurality of video, audio and data signals
essentially “in-the-clear” CATV type broadcast signals
capable of reception by any subscriber’s cable ready tele~
into a single data stream within a standard six MHz channel
allocation for transmission over a CATV type distribution
vision set.
The analog television signals are broadcast from the
optical transmitter 12 through the tree and branch optical
The 6 MHz bandwidth RF signals from the modulators 34
are supplied to the optical transmitter 12 for downstream
transmission together in a combined spectrum with the
and coax distribution network to provide “basic” CATV type
service to all subscribers on the network. In order to obtain
AM-VSB analog television signals 22. The downstream
transport of the digital programming is an RF transmission
essentially the same as for the analog basic service channels,
but each of the channels from the RF modulators 34 contains
4 or 6 digitized and compressed video program channels,
additional network services as discussed below, the sub
scriber may obtain a digital entertainment (DET) 24. A
network interface module in the DET 24 includes a tuner
that permits subscribers to the digital services to receive the
analog broadcast channels through the same equipment used
for the digital services.
The network depicted in FIG. 1 also provides transport for
referred to hereinafter as “slots”. The 6 Mhz digital program
channels are carried through the ?ber and coaxial system in
standard CATV channels not used by the analog basic
digitized and compressed audio/video programming, both
service programming. The ONU 16 is essentially transparent
for certain broadcast services and for interactive services, 20 to both the analog basic service channels and the channels
such as video on demand. The network uses a video com
carrying the digital programming and supplies all of the
pression called Motion Picture Experts Group (MPEG). The
MPEG encoded video is transported to each Loop Transport
signals as a combined broadcast over the coaxial cable
Interface using asynchronous transfer mode (ATM) trans
port and switching.
In the illustrated network, digital broadcast service signals
26 in MPEG encoded form and arranged in ATM cell
packets are applied to an ATM packet demultiplexer 28 in
the Loop Transport Interface 10. These broadcast service
signals 26 originate in one or more broadcast VIP’s ATM
encoders controlled by the VIP servers. The ATM broadcast
network 18.
At the subscriber premises, a network interface module
(NIM) (not shown) couples the set-top device or digital
entertainment terminal (DET) 24 to a drop cable of the
coaxial distribution network 18. In this network con?gura
tion, the NIM includes an analog frequency tuner controlled
by a microprocessor to selectively receive the RF channel
signals, including those channels carrying digital informa
tion. The NIM also includes a QPSK, QAM or VSB
demodulator to demodulate a selected one of the digitized
services carry premium service type programming. For
program signals carried in one of the digital slots within a
certain interactive services which utilize one digitized chan
nel to provide limited downstream transport to a large 35 received 6 MHz channel and performs a forward error
correction function on the demodulated data. A digital
number of subscribers, the ATM broadcast cell stream
signals originate from a server 30. Fully interactive broad
audio/video signal processor within the DET decompresses
band digital signals, in MPEG-ATM format, are also applied
received video signals, generates graphics display informa
tion and performs digital to analog conversion to produce
to the ATM packet demultiplexer 28 from an ATM switch
output signals compatible with a conventional television set
The analog tuner in the NIM tunes in all channel frequen
cies carried by the network, including those used for the
analog broadcast services. The DET 24 includes a bypass
In addition to the analog broadcast signals, the RF com
biner 20 receives a variety of other analog RF signals from 45 switch in the NIM and an analog demodulator to selectively
supply analog signals from the basic service channels
a group of RF digital modulators 34 that output the MPEG
directly to the audio/video output terminals or to the modu
streams from the ATM packet demultiplexer 28 as digital
lator, to provide signals to drive a standard television
broadband information in RF analog format. Each RF modu
lator 34 outputs a 6 MHz bandwidth IF signal which an
upconverter (not shown) tunes to a different RF channel 50
The DET 24 also includes a remote control and/or keypad
having a corresponding carrier frequency. A network data
to receive various selection signals from a user. The DET
processor (NDP) 38 uses the VPI/VCI header from the ATM
relays data signals upstream over a QPSK signaling channel
cells to control the ATM packet demultiplexer 28 to route the
on the coaxial cable to the ONU 16 in response to user inputs
MPEG bit streams to the appropriate digital RF modulator
such as selection of a pay per view event. The actual
34. The NDP 38 provides the control information to the 55 transmission of any such data signals upstream from the
32. The ATM packet demultiplexer 28 terminates all ATM
cell transport through the network, and converts the cell
payload information into a plurality of MPEG-2 format bit
ATM packet demultiplexer 28, for example, by an ethernet
DET 24 occurs in response to a polling of the DET. The
bus 38a. The Ethernet bus 38a is also coupled to the network
controller 36, the ACC 4000D 46, and the video manager 50.
Thus, the video manager 50 and the ACC 4000 46 can
ONU 16 combines upstream data signals from the DET’s
serviced thereby and transmits those signals upstream over
another optical ?ber 42 to an optical receiver 44 in the Loop
Transport Interface 10. Each DET 24 may transmit data on
provide control data for use by the ATM packet demulti
a different carrier frequency or timeslot, in which case the
The RF modulators 34 use 64 QAM (quadrature ampli
tude modulation) or 16 VSB (vestigial sideband) modulation
techniques. The 64 QAM is used to modulate 4 channels of
6 Mbits/s MPEG encoded digital video information into one
6 MHZ bandwidth analog channel. Similarly, l6 VSB modu
lates 6 channels of 6 Mbits/s MPEG encoded digital video
network controller 36 knows which DET sent particular data
based on the received frequency channel. Alternatively, for
interactive services, the DET may transmit a unique identi
?cation code with the upstream message.
In the implementation of the network illustrated in FIG. 1,
an ACC 4000D 46 performs set top management and
speci?c program access control functions. Service pro?les
For archival services and many other interactive services,
for each customer on the network and their DET’s are set up
each VIP has a level 2 gateway and some form of broadband
and stored within the ACC 4000D 46. The ACC 4000D 46
may also provide an interface to appropriate billing systems
(not shown) for some broadcast services, such as pay per
view. For ATM broadcast services, when a subscriber ?rst
signs up, a portfolio of channels subscribed to by that
customer is established in the subscriber’s pro?le data
within the ACC 4000D 46. Based on this pro?le data, the
ACC 4000D 46 downloads a service map into the subscrib
er’s DET 24. The downstream transmission portion of the
information ?le server 403. The ATM switch 32 provides
communications links between the Loop Transport Inter
faces 10 and the level 2 gateways and ?le servers 60.
Customer access to the VIP’s is controlled through one or
possibly more programmed computer or processor elements
performing the processing functions of the Level 1 Gateway
48. A permanent virtual circuit (PVC) controller 57 and a
video manager 50 respond to signals from the Level 1
Gateway to control the point to point routing through the
network provides an out-of-band downstream signalling
channel to the DET’s using intemet protocol (IP) address
ing. For example, for the downloading of the service map
information from the ACC 4000D 46 to each DET 24, the
ACC 4000D 46 outputs the service map information to the
network data processor (NDP) 38 via the Ethernet 38a. The
NDP includes a QPSK modulator for modulating the service
map information onto the out-of-band downstream signaling
channel. The modulated signals are then output to the RF
combiner 20. At the subscriber site, the subscribers’ DET/
NIM would recognize, capture and process the out-of-band
signaling data based on the corresponding IP address. This
downstream signaling channel also carries signals for con
The PVC controller 57 stores data tables de?ning all
possible virtual circuits through the ATM switch 32 and the
?ber ports, RF channels and multiplexed digital channel
slots which may be used to transport each data stream
processed by the ATM packet demultiplexer 28 through the
?ber 14 to the appropriate ONU 16 serving each DET. The
data tables in the PVC controller 57 and the video manager
50 thus de?ne “permanent virtual circuits” between the
VIP’s equipment 403 and the DET’s 24.
For a full, broadband interactive session, the subscriber
operates the DET 24 to interact with the Level 1 Gateway 48
and select a VIP. The PVC controller 57 responds to instruc
The microprocessor in the DET 24 controls access to any of
these channels based on the downloaded map information
stored in the system memory. For example, if one subscriber
requests HBO, and that subscriber has paid to subscribe to
HBO, the subscriber’s DET 24 contains map information
instructing it to tune to the RF channel and select and decode
the digital program slot carrying HBO for display on the
subscriber’s television set 40. However, if a requesting
subscriber has not paid for HBO, the downloaded service
map will not provide the requisite data for tuning and
decoding of that channel. If a decryption key is needed, the
Level Gateway 48 instructs the video manager 50 to instruct
the ACC 4000D 46 to transmit the key to subscriber’s DET
The implementation of the network illustrated in FIG. 1
a customer subscribing to each particular provider’s ser
vices. These data tables de?ne the header information and
the switch port to the packet handlers needed to route cells
to the correct Loop Transport Interface. The video manager
50 stores similar data tables identifying the transmission
trolling software downloading and/or selection of certain
channels or frames for decoding in interactive services.
All digital broadcast service signals are broadcast into
each subscribcr’s premises, and each DET 24 includes
means for receiving and decoding each such digital broad
cast service channel, which may include premium channels.
Loop Transport Interface 10 serving each DET terminal of
tions from the Level 1 Gateway by activating the ATM
switch 32 to establish a downstream virtual circuit path
between a port of the VIP’s server and the ATM packet
demultiplexer 28 within the Loop Transport Interface 10
servicing a subscriber requesting a call connection to the
particular VIP. The video manager 50 assigns a particular
one of the digitized video channel slots in a digital program
type RF channel to carry the particular point to point
communication. Speci?cally, the video manager controls the
ATM packet demultiplexer 28 to route MPEG data recov
ered from the ATM cells for the particular point to point
communication to the port for one of the RF modulators 34
so that the modulator will include the MPEG data in the
port for 24 D50 telephone channels. Each subscriber pre
assigned digital channel slot within a particular 6 MHz RF
channel. The video manager 50 also transmits a signal
downstream through the signaling channel to the subscrib
er’s DET 24 instructing the DET to tune to the particular RF
channel and decode MPEG data from the speci?cally
assigned digital channel within that RF channel. Similar
dynamic assignments of RF channels on a CATV system to
mises has telephone interface referred to as a Cable Network
individual terminals for interactive services are disclosed in
Unit (CNU) 52 coupled to the coaxial cable which serves to
couple two-way signals between a twisted wire pair into the
home and the telephone frequency channels on the coaxial
US. Pat. No. 5,220,420 to Hoarty et al. and US. Pat. No.
5,136,411 to Paik et al., the disclosures of which are
also provides telephone service. Between the optical net
work unit and the subscriber premises, the 700-750 MHz
portion of the spectrum on the coaxial cable carries the
telephone signals. This allocated spectrum provides trans
cable 18. Upstream telephone signals are applied from the
optical receiver 44 to a host digital terminal (HDT) 54 which
incorporated herein in the entirety by reference.
Concurrently, the Level 1 Gateway 48 would instruct the
PVC controller 57 to control the ATM switch 32 to establish
an upstream virtual circuit for control signals sent from the
DET 24. In such a case, the upstream signals from the DET
provides an interface to a standard digital telephone switch
56. Downstream telephone signals from the switch 56 pass
through the HDT 54 to the RF combiner 20 for transmission
are passed up through the ?ber-coax network and receiver 44
in the 700-750 MHZ frequency range over the ?ber to the 60 to the network controller 36, and then the VIP’s level 2,
ONU l6 and the coaxial cable distribution system 18.‘
gateway via the ATM switch 32.
Upstream telephone signals are output in the 540 MHz
While the network disclosed in FIG. 1 is able to provide
frequency range of the coaxial cable, which are block
broadcast video and interactive video services to video
converted in the ?ber nodes for transport on an optical ?ber.
subscribers, the overall architecture is limited in that the
The implementation of the network illustrated in FIG. 1 65 loop transport interface 10 is able to service only a limited
also offers access to video information providers (VIP’s) for
number of living units, for example approximately 2.000.
interactive broadband services, such as video on demand.
Thus, if it is desired that full-service digital broadband video
services are to be provided to a greater population, a
data streams, such as ATM cell streams or data signaling
substantial expenditure must be invested to install additional
messages. For example, the ATM packet demultiplexer is
adapted to apply speci?ed PID values to MPEG streams for
loop transport interfaces throughout proposed video service
transmission to either a single VIU or a group of VIU’s,
areas. Since the costs for installing and implementing the
additional loop transport interfaces 10 may be substantial, a
network provider may be hesitant to invest substantial
capital for new equipment necessary for the additional loop
transport interfaces if the new subscribers in the proposed
based on the VPI/VCI value of the incoming ATM cell
stream; thus, the ATM packet demultiplexer is effective for
providing MPEG-encoded data for broadcast or IMTV ses
sions. In addition, the ATM packet demultiplexer is able to
encode non-video data, such as operating system code,
video service areas are willing to pay only a limited amount
of subscriber fees.
encryption keys, or signaling data, into MPEG packets
having a speci?c PID value for a VIU. Since the non-video
data may be supplied to a video end o?ice by an ATM stream
source, such as an ATM backbone subnetwork, the ATM
In addition, the network disclosed in FIG. 1 requires a
substantial amount of control processing and connectivity
with the video information providers and the corresponding
packet demultiplexer is able to receive video and non-video
servers 60. If additional loop transport interfaces 10 are to be
data such as signaling data from a high-bandwidth ATM
added to proposed service areas, the VIPs may be required
to communicate with multiple level 1 gateway controllers 48
from the different service areas, creating additional di?icul
ties in management and service processing for the VIPs.
The network disclosed is FIG. 1 also has limited ?exibil
ity in that the ATM packet demultiplexer 28 recovers MPEG
data having preassigned PID values from the ATM cell
streams. It would be desirable to provide an ATM packet
stream source or a low-bandwidth source. Regardless of the
source, the demultiplexer can selectively output the MPEG
encoded data on either an in-band channel or an out-of-band
channel. Thus, the ATM packet demultiplexer, also referred
to as an MPEG packet router, is able to route any necessary
20 data to a VIU based on a speci?ed connection block descrip
tor and PID value.
The ATM packet demultiplexer of the present invention is
demultiplexer that provides additional ?exibility in MPEG
encoding to enable dynamic MPEG encoding of ATM cell
implemented in a video distribution network having an
architecture that is designed for ?exible implementation,
expandability, and efficient resource management to opti
mize economies of scale. Although the disclosed network
The ATM packet demultiplexer 28 also is limited in that
can be implemented in a small-scale service area, the
the ATM cell streams generally must include MPEG-en
expandability and distributed architecture of the network
coded data streams before transmission through the network.
It would be desirable to provide an arrangement that did not 30 enables signal processing costs to be distributed over a larger
serving area, thereby enabling network providers to provide
necessarily require MPEG-encoded data in the ATM cells
video services at lower costs to subscribers.
transported to the loop transport interface 10, but that was
adapted to accept ATM cells carrying different data formats.
Finally, the network disclosed in FIG. 1 involves IP
addressing using TCPIP protocol; this technique, however,
The network is designed for centralized control of net
work services and interfaces between video information
providers (VIPs) and video information users (VIUs), while
at the same time providing ?exible signaling and transport of
results in additional IP address management at the VIP and
each DET, as well as additional IP processing at the DET. It
control signals and video data. The VIPs are able to com
is anticipated that the increased popularity of Internet will
result in revision in protocol standards to accommodate
municate with the centralized control of the network for VIU
account management, event scheduling, and for tra?ic man
increased IP address lengths, thereby increasing overhead
agement (bandwidth assignments, data transport paths, etc.).
and reducing available bandwidth on the network for data
transmission. Further, the network disclosed in FIG. 1
The network manages both point—to-multipoint (broadcast)
and point-to-point (interactive) sessions with minimal over
head required by the VIP.
requires different data paths for video data and signaling
data, thereby complicating data transport to the DET. It
would be desirable to provide a ?exible, e?icient signaling
communication system that precisely described the e?icient
transport of signaling information to individual DET’s.
data to and from the VIP to a VIU, independent of the data
format or the hardware of the network users. The term
“network users” generally refers to both VIPs and VIUs.
Thus, the use of the ATM packet demultiplexer of the
A principal object of the present invention is to provide a
seamless, smooth approach for connecting a video informa
tion user (VIU) to the video information provider (VIP) of
their choice, in a multiple provider environment. The con
The ATM packet demultiplexer, as used in the network of
the present invention also is adapted to transport broadband
present invention enables the disclosed network to accom
modate different access technologies and hardware speci?
cations that may be used by the video information providers,
as well as the video information users. In addition, the
nection to the VIP of choice must be provided in a non 55
discriminatory manner that enables the user to easily access
network is adapted to transport broadband data that may be
types other than video; thus, the network is adapted to
transport any type of data that satis?es the interface require
that particular provider. The network must have the capa
bility to selectively connect the VIU to broadcast services
ments of the network, thereby enabling transport of inter
and to IMTV services.
example, Internet. As such, the network of the present
Another objective is to provide an improved distributed
active multimedia services from sources such as, for
invention provides network interfaces designed to serve as
network architecture that distributes video services over a
generic interfaces, thereby providing maximum ?exibility
greater serving area, while at the same time maintaining
?exibility for VIPs to provide broadcast IMTV and point
to-point video services and that maximizes use of shared
for the network users.
The network of the present invention has a distributed
architecture to service a number of local serving areas with
network resources.
65 a minimum of hardware or signal processing. According to
The present invention includes an ATM packet demulti
a preferred embodiment of the present invention, the net
plexer for providing ?exible MPEG addressing of incoming
work includes a broadcast consolidation section, a broadcast
ring, a plurality of video network hubs, a plurality of video
FIG. 3 is a block diagram of the video network hub shown
in FIG. 2 according to the preferred embodiment of the
present invention.
FIG. 4 is a block diagram of the video end offices shown
in FIG. 2 according to the preferred embodiment of the
end offices, and an ATM backbone subnetwork. These
components of the network provide an architecture that
provides both distributed services and ?exibility for provid
ing service as well as expandability.
present invention.
The network broadcast consolidation section serves as a
network interface for broadcast video information providers.
The network interface is adapted to accept baseband analog
video as well as digital video. The broadcast consolidation
section combines the broadcast data from the VIPs and
outputs the consolidated broadcast data on a unidirectional
broadcast ring. The broadcast ring supplies the consolidated
broadcast data to a plurality of video network hubs (VNH)
coupled to the broadcast ring, also referred to as video
access nodes (VAN).
Each of the video network hubs serviced by the broadcast
ring downloads the consolidated broadcast data from the
broadcast ring, converts the consolidated broadcast data to
MPEG data on an RF carrier, and combines the RF signal
with other RF signals (such as over-the-air broadcast signals
or public access channel TV) before transmission by optical
?ber. Each video network hub outputs the combined RF
signals to a corresponding plurality of video end offices, also
FIG. Sis a block diagram of the access subnetwork shown
in FIG. 2 according to the preferred embodiment of the
present invention.
FIG. 6 is a block diagram of the ATM backbone network
and the control systems for the full service network shown
in FIG. 2.
FIG. 7 is a block diagram of the ATM packet demulti
plexer shown in FIG. 4 according to the preferred embodi
ment of the present invention.
FIG. 8 is a block diagram of the digital entertainment
terminal (DET) shown in FIG. 5.
FIG. 9 is a detailed block diagram of the network interface
module (NIM) shown in FIG. 8.
referred to as local video access nodes (LVAN). The video
end offices receive the combined RF signals from the
corresponding video network hub, combine the received RF
signals with point~to-point downstream tra?ic from the ATM
backbone subnetwork, and output the combined RF signals
ture of a full service network. As discussed in detail below,
the disclosed ATM packet demultiplexer, also referred to as
an MPEG router, provides ?exibility in the addressing of
video information users serviced by the network. To better
to the access subnetwork servicing the subscribers, such as
a hybrid-?ber-coax loop distribution system.
understand the operation of the ATM packet demultiplexer,
it is helpful ?rst to place that demultiplexer in context. The
preferred network architecture therefore is discussed ?rst.
The network includes an ATM backbone subnetwork
designed to provide transport for all control and signaling
trallic throughout the network, as well as transport for any
data for point-to-point communications from an appropriate
source to the video end oflice serving a subscriber requesting
a session with the particular source. Thus, not only does the
The present invention is directed to the use of an ATM
packet demultiplexer within a distributed network architec~
ATM backbone subnetwork provide signaling information
between the Level 1 gateway, the network control center and
the corresponding video network hubs and video end offices,
FIG. 2 discloses a distributed network architecture for a
broadband data full service network according to a preferred
embodiment of the present invention. The disclosed network
is arranged to centralize signal processing tasks within a
LATA in order to minimize hardware. At the same time, the
disclosed network provides maximum flexibility by provid
but it also provides the point of interconnection for VIPs for
ing communications to local access nodes, each serving a
IMTV sessions with VIUs.
Thus, the present invention provides a broadband data
network that provides centralized control and signal pro
local loop of subscribers.
cessing with distributed data transport to provide broadband
data services to a greater number of subscribers at a greater
backbone subnetwork 106, a level 1 gateway 108, a video
data control center 110, and a plurality of video end offices
or local video access nodes (LVANs) 112. According to the
level of efficiency for both VIPs and VIUs.
Additional objects, advantages and novel features of the
invention will be set forth in part in the description which
follows, and in part will become apparent to those skilled in
the art upon examination of the following or may be learned
preferred embodiment, each of the video network hubs 104
will serve a corresponding plurality of up to six (6) LVANs
112. In addition, the preferred embodiment will provide up
to sixteen (16) VNH’s 104 serviced by the ring 102.
by practice of the invention. The objects and advantages of
the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out
in the appended claims.
The broadcast consolidation section 100 serves as the
Reference is made to the attached drawings, whereby
elements having the same reference numeral designations
represent like elements throughout.
The network disclosed in FIG. 2 includes a broadcast
consolidation section (BCS) 100, a broadcast ring 102, a
plurality of video network hubs (VNH) or video access
nodes 104 coupled to the broadcast ring 102, an ATM
FIG. 1 is a block diagram of a proposed architecture for
broadcast head-end and network interface (NI) for broadcast
VIPs 114 and 116. The broadcast consolidation section 100
is adapted to receive broadcast video data in any format that
may be convenient for the VIP. Speci?cally, the broadcast
consolidation section 100 includes a digital encoder 118 to
convert baseband analog video signals, for example from
VIP 116, into a digitally-compressed DS-3 signal stream.
Alternatively, the digital encoder 118 could be replaced with
a video dial tone network.
an MPEG-2 encoder to provide compressed MPEG-2 pack
FIG. 2 is a block diagram of a distributed network
architecture for a broadband data full service network
ets at a D86 rate.
according to a preferred embodiment of the present inven
The broadcast consolidation section 100 also includes an
ATM cell multiplexer 120, also referred to as an ATM edge
device, which performs policing and rate conversion of
incoming ATM streams. The ATM edge device 120 performs
policing of ATM cell streams by monitoring the data rate of
incoming data streams from VIPs. For example, if the VIP
stream before transport to the ATM edge multiplexer 120.
The ATM streams may be output at a 45 Mbits/sec (DS-3)
rate for carrying up to six (6) MPEG-encoded programs, or
on an optical ?ber at 155 Mbits/sec (QC-3) for carrying up
114 has subscribed by contract to transmit a data stream at
3 Mbit/s to the network, the ATM edge device 120 will
prohibit or drop ATM cells that are transmitted above the
to twenty (20) MPEG-encoded programs.
Asynchronous transfer mode or “ATM” transport is an
subscribed bit rate; in this case, a 6 Mbit/s stream would be
advanced, high-speed packet switching technology. In ATM,
rejected as an unauthorized rate.
information is organized into cells having a ?xed length and
format. Each cell includes a header, primarily for identifying
In order to maximize the data-carrying capacity of the
ATM streams supplied to the ATM edge multiplexer 120, the
cells relating to the same virtual connection, and an infor
VIP 144 and the VIP 116 will preferably supply digital video
signals in compressed MPEG-2 format that are transported
mation ?eld or “payload”. According to the preferred
embodiment, a 53 byte ATM cell includes a cell header
in ATM cells.
consisting of 5 bytes and a payload consisting of 48 bytes of
The MPEG-2 standard, recognized in the art, provides a
standardized format for packetizing the compressed audio
and video information and for transporting other data. Under
the MPEG-2 standard, incoming individual video signals
payload data. The ATM cell header information includes a
virtual path identi?er/virtual channel identi?er (VPI/VCI) to
identify the particular communication each cell relates to.
For example, the virtual path identi?er (VPI) may be used to
identify a speci?c VIP 114 or 116, and the virtual channel
identi?er (VCI) may be used to identify a speci?c output
and related audio signals are encoded and packetized into
respective Video and Audio Packetized Elementary Streams
(PBS). The video and audio PES’s from one or more sources
port of that VIP. In such a case, for example, VIP 114 could
be assigned a VPI value of “65”, and VIP 116 could be
assigned a VPI value of “66”. Thus, the VPI/VCI value of
the ATM cell header could be used to identify the source of
of video programming may be combined into a transport
stream for transmission or storage.
Each frame of compressed program information (audio,
video or data) is broken down into a series of transport
packets. Although video frames can vary in length, the
transport packets have a ?xed 188 byte size. Thus, different
frames are broken down into different numbers of MPEG
ticular sender is not necessarily periodic. Each device using
transport packets. For example, for a 6 Mbits/sec encoding
system, a group of frames consisting of a total of 15 frames
for one-half second of video breaks down into approxi
the ATM stream.
In ATM, transfer is asynchronous in the sense that the
recurrence of cells that contain information from any par
the ATM network submits a cell for transfer when they have
a cell to send, not when they have an assigned or available
transmission time slot. However, the ATM cells may ride in
mately 4000 transport packets.
the payload of a high-speed time division multiplexed
Transport stream packets consist of a 4 byte header
section, an optional adaptation ?eld and a payload section.
The header information includes, inter alia, a synchroniza
tion byte, a variety of different ?ags used in reconstruction
media, such as a SONET optical ?ber. ATM allows any
arbitrary information transfer rate up to the maximum sup
of the video frames, and a thirteen bit program identi?cation
(PID) number. PID value 0 is reserved as an indication that
ported by the network, simply by transmitting cells more
often as more bandwidth is needed.
During the ATM conversion process, the individual pro
grams from the MPEG packets are broken into cell payloads
the packet includes program association table data. PID
value 1 is reserved for identi?cation of packets containing
conditional access data, such as encryption information.
Other program identi?cation numbers are utilized to identify
transport packets with the program source from which they
and VPI/VCI header information is added to map the pro- ,
also include a program clock reference (PCR) value within
grams into ATM virtual circuits in the corresponding output
cell stream. As noted above, each MPEG packet consists of
188 bytes, whereas each ATM cell includes 48 bytes of
payload data. The preferred mapping scheme uses two
different adaptations. The ?rst adaptation maps one 188 byte
MPEG packet into ?ve ATM 48 byte cell payloads. The
second adaptation maps two 188 byte MPEG packets into
the optional adaptation ?eld. For example, the PCR may be
present in only 10 out of every 4000 video transport packets.
eight ATM 48 byte cells payloads.
MPEG packets of 188 bytes map efliciently into ATM
Periodically, the transport packet for each program will
MPEG-encoded packets can be output in a variety of data
rates. For example, the MPEG-2 compression standard is
able to encode a video program to a 6 Mbits/sec bit stream,
cells if pairs of packets are mapped into 8 cells. However, a
delay is imposed on mapping of a ?rst cell while waiting for
the second cell in the pair. To minimize jitter during decod
ing, the packets carrying the PCR need to be encoded and
and packetize up to four (4) 6 Mbits/sec bit streams into a
single 27 Mbits/sec stream. For other lower-rate data
transported quickly. To avoid delaying ?rst packets contain
streams carrying text or signaling information, up to eight
ing a PCR while processing a second packet, the ATM
(8) 3 Mbits/sec bit streams can be packetized into a single 27 55 multiplexer 215 maps ?rst packets containing a PCR imme
Mbits/sec stream, and up to sixteen (16) 1.5 Mbits/sec bit
diately, using the ?ve cell adaptation procedure. As noted
streams can be packetized into a single 27 Mbits/sec stream.
above, the PCR is typically present in only 10 out of every
Alternatively, six (6) analog audio-video program signals
can be processed in parallel to provide six (6) 6.312 Mbits/
sec MPEG-2 packets that can be output on a single 45.736 60
Mbits/sec DS-3 bit stream. In addition, a synchronous
optical ?ber such as SONET at 155 Mbits/sec (QC-3) can
carry twenty (20) 6 Mbits/sec MPEG streams.
Thus, each of the VIPs 114 and 116 are preferably able to
compress up to six (6) NTSC analog audio/video program
signals in parallel into an MPEG-2 format. The resulting six
(6) MPEG-2 packet streams are combined into an ATM
4000 packets. Also, at least some of those 10 packets likely
will arrive as the second packet of a pair. Consequently, only
a very small number of packets are mapped using the less
e?icient 5-cell adaptation.
As noted above, each cell of a particular stream will have
a header which contains a virtual path identi?er/virtual
circuit identi?er (VPI/VCI) to identify the virtual circuit that
the cells pertain to. All MPEG packets for a given program,
whether video, audio or data, will be mapped into ATM cells
having the same VPI/VCI. Conversely, cells having a given
VPI/VCI will contain data corresponding to only one iden
ti?ed program. Thus, each ATM cell carrying video infor
programs at 6 Mbits/sec. Thus, the ATM edge processor is
able to fully load the downstream optical ?bers 121 thereby
to fully load the capacity of the network. A more detailed
description of the ATM cell multiplexer 120 is found in
mation for a speci?ed program from a video information
provider can be identi?ed on the basis of its corresponding
copending and commonly-assigned application Ser. No.
08/380,744, ?led Jan. 31, 1995 (attorney docket No. 680
109), the disclosure of which is incorporated in its entirety
by reference.
According to the preferred embodiment, the digital
As noted above, the VIP 114 and/or VIP 116 may transmit
the ATM cells on a SONET optical ?ber at an OC-3 rate, or
may transmit the ATM cells at a DS-3 rate. The transmission
of ATM cells in an asynchronous DS-3 signal may require a
common clock reference in order to ensure frame alignment.
encoder 118 outputs a digitally encoded data stream in DS-3
In a particular aspect of the present invention, the network
interface 100 receives the DS-3 signal carrying six MPEG2
format (45 MB/s), and the ATM edge multiplexer 120
outputs an ATM stream in OC-3c format (155.5 MB/s), to a
channels in ATM cell format from the ATM VIPs in accor
SONET multiplexer 122. The SONET multiplexer 122
multiplexes the D83 and OC-3 signals from the digital
encoder 118 and the ATM edge multiplexer 120 and outputs
dance with a physical layer convergence protocol (PLCP).
The PLCP is a framing structure used to ensure that ATM
the consolidated broadcast data onto the unidirectional opti
cells are aligned with respect to a corresponding video
cal ?ber broadcast ring 102 operating at an 0048 format
frame, even though there may exist drifting of a start and end
(2488.3 MB/s). In other words, the SONET multiplexer 122
of a typical DS-3 frame. Speci?cally, the PLCP references a
may receive a plurality of 003 optical ?bers 121, either
DS-3 header and identi?es the location of each ATM cell
with respect to the DS-3 header. Since the DS-3 frame 20 from the ATM edge multiplexer 120 or a plurality of such
multiplexers. In addition, the SONET multiplexer 121 may
contains a maximum of twelve ATM cells, the PLCP notes
receive a plurality of DS-3 signals from a corresponding
the location of each of the cells 1-12 with respect to the
plurality of encoders such as digital encoder 118. The
DS-3 header. Therefore, even though there may be DS-3
SONET multiplexer 122 buffers the OC-3 and DS-3 input
frame drifting, the PLCP ensures alignment, from a cell
signals and multiplexes the input signals together at a rate of
perspective, between the cell layer and the DS-3 frame so
2488.3 Mbits/sec. An exemplary SONET multiplexer is the
that each of the twelve ATM cells within each DS-3 frame
can be located.
FT-2000, manufactured by AT&T.
The ATM edge multiplexer 120 acts as a groomer for
multiple VIP terminations to prevent extraneous data from
using network resources. The ATM streams from the VIPs
114 and 116 may arrive in either DS-3 format or via optical
?ber in OC-3 format. The ATM edge device 226 provides a
The broadcast ring 102 is arranged as a drop~and—continue
(D/C) SONET transport to service, for example, up to
sixteen (16) VNH’s 104. Although the broadcast ring 102
preferably has one OC-48 ?ber, the broadcast ring 102 may
grooming function, whereby ATM cells are analyzed, on a
cell-by-cell basis, to determine if they should be transmitted
on the network. Speci?cally, ATM cell headers that do not
be modi?ed to include 2 or more OC-48 ?bers for additional
have valid data are dropped from the ATM stream. Each
valid ATM cell is mapped on the basis of its corresponding
VPI/VCI header either to a valid OC-3 output port of the
ATM edge device 120, or possibly to a null port. In addition,
the ATM edge device 120 maps the ATM idle bits containing
tra?ic, or for bidirectional traffic around the ring for redun
dancy. As discussed below in detail with respect to FIG. 3,
each VNH 104 receives the broadcast ATM streams from the
broadcast ring 102, converts the ATM streams to MPEG-2
streams that are transmitted on an RF carrier, and adds local
broadcast information (e.g., over-the-air access, public
access channel) before transport to the LVAN 112 as RF
signals, preferably by optical ?bers.
no information that are present in the ATM stream from the
Each LVAN 112 receives the consolidated broadcast data
VIPs to a null port, thereby rejecting the received ATM idle
The ATM cell mapping, also referred to as cell translation,‘
from the corresponding VNH 104. The LVAN 112 combines
the received RF signals from the VNH 104 with any data
transmitted by the ATM backbone subnetwork 106
enables DS-3 ATM cell streams that are transmitted at 45 addressed to a subscriber served by the LVAN 112. The
less-than-full capacity to be mapped onto at least one 0030
resulting RF signal is transmitted via a local loop distribu
stream operating at full capacity. This is particularly effec
tive when, for example, optical ?bers used by the VIPs 114
or 116 to transport DS-3 ATM streams using optical ?bers
will not be operated at capacity, especially when VIPs using
the optical ?bers have varying bandwidth requirements over
tion network 124 to a customer premises 126. As discussed
below with reference to FIG. 5, the local loop distribution
124 is preferably arranged as a hybrid ?ber-coax distribution
subscriber site includes a network interface device (NID) for
splitting the RF signal, a network interface module (NIM)
time. For example, a VIP providing business news may
require more bandwidth for daytime news programming,
whereas a VIP providing entertainment programming may
require more bandwidth during evenings and weekends. The
ATM edge processor 120 processes all incoming DS—3 bit
for decoding encrypted data from the network and routing
MPEG data streams, and a digital entertainment terminal
NIM. Additional details regarding the NIM and the DET are
discussed below with reference to FIGS. 5, 8 and 9.
As shown in FIG. 2, each LVAN 112 has access to the
ATM backbone subnetwork 106 in order to send and receive
network signaling information to and from the level 1
gateway 108 and/or the video data control center 110. For
example, a video information user (VIU) who wishes service
(DET) for decoding the MPEG data streams passed by the
streams received thereby, and maps the DS-3 bit streams into
at least one condensed, or combined bit stream for trans
mission through the network. Speci?cally, the incoming
DS-3 and 003 streams are supplied to corresponding
first-in-?rst-out (FIFO) input buffers internal to the ATM
edge device 120 to supply the ATM cells to an internal
multiplexer on a cell-by-cell basis. The internal multiplexer
outputs the translated cells preferably to CO3 output buffers
for synchronous transmission on optical ?bers 121. Since
the ATM cells are output at a rate of 155 MHz (QC-3), each
of the optical ?bers 121 carry up to twenty (20) MPEG
system, although an ADSL system or a ?ber~to-the-curb
system may be substituted. In addition, the equipment at the
on the network via one of the LVAN’s 112 may request the
service either by calling a network business o?ice by tele~
phone or by requesting a level 1 gateway session from his or
her customer premises 126 in order to perform online
registration. As discussed in detail below, the ATM back
bone subnetwork 106 provides signaling information
between the LVAN 112 serving the VIU, the level 1 gateway
through the network accordingly. At least some of this stored
data is accessible to the subscriber through a direct interac
tion with the level 1 gateway 108. For example, the user can
identify certain service providers to the level 1 gateway 108
108 and the video data control center 110 in order to activate
the VIU on the network, or to update the services available
to the VIU.
The ATM backbone subnetwork 106 also is adapted to
communicate with the VIPs 114 and 116 in order to perform
account management between the VIPs, the level 1 gateway
108 and the video data control center 110. For example, the
VIP 114 may supply a request to the level 1 gateway 108 for
and de?ne an authorization code or identi?cation number
which must be input before the network should provide a
session with the user’s equipment 126 and the identi?ed
a desired bandwidth in order to broadcast a pay-per-view
event at a predetermined time. The level 1 gateway 108 and
Many of the functions of the level 1 gateway 108 relate
principally to set up, monitoring and billing for point-to
point type interactive sessions. As noted above, however, a
number of the Gateway functions also apply to broadcast
services. For example, the interaction with the level 1
gateway 108 can be used to advance order upcoming broad
cast pay per view events. At the time for the event to begin,
the VIP 114 will determine the appropriate VPl/VCI header
to be loaded onto the ATM stream to be supplied to the ATM
the level 1 gateway 108 will transmit appropriate notice to
the ordering subscriber’s terminal. In response, the terminal
may display the notice to the subscriber or the terminal may
edge multiplexer 120 of the broadcast consolidation section
100. The level 1 gateway 108 will inform the video data
control center 110 of the scheduled event, as well as the
automatically turn on and/or tune to the appropriate com
VPI/VCI of the video data stream. The level 1 gateway 108
munication link through the broadcast network to obtain the
will also communicate with the VIPs 114 and/or 116 via the
ordered event. The interactive features of the level 1 gate
ATM backbone subnetwork 106 in order to maintain up-to
way 108 also permit subscribers to specify limitations they
wish to place on their broadcast services, e.g. total number
date lists of authorized VIUs to receive thev selected VIP
of hours of usage within some de?ned interval and/or time
of day/week of permitted usage. The level 1 gateway 108
Finally, as discussed in detail below with respect to FIG.
6, the VIP 116 may conduct an interactive (IMTV) session 25 will then control the broadcast network and/or the subscrib
er’s terminal in accord with the limits de?ned by the
with a VIU via the ATM backbone subnetwork 106 and the
LVAN 112 servicing the speci?c VIU. Although not shown
The level 1 gateway 108 comprises a series of application
in FIG. 2, the VIP 116 can conduct IMTV sessions with a
modules. A service data module maintains service data ?les
VIU using a level 2 gateway and an IMTV server internal to
the VIP 116. The Level 2 gateway communicates with the 30 relating to information service providers offering services
through the broadband communication network. This mod
level 1 gateway 108 of the network as well as the network’s
ule also maintains data ?les regarding information users
business service center, to receive and process requests for
subscribing to service through the broadband communica
IMTV sessions that include routing information. The IMTV
tion network. A service control module interacts with users
server outputs broadband data for the VIU as an ATM cell
35 through terminals coupled to the broadband communication
stream to the ATM backbone subnetwork 106.
system. In response to selection information from the users
Communication between the network and the VIP 116, as
well as between the network and the VIU, is performed via
the level 1 gateway 108. From the VIU perspective, a user
will communicate with the network via the level 1 gateway
108 in order to select the VIP 116 for an IMTV session. In
a network providing access to multiple IMTV service pro
viders, the user wishing to establish an IMTV session
identi?es the provider of choice to the level 1 gateway 108
by inputting control signals to the user’s DET, which sup
plies the appropriate signals upstream from the customer
premises 126 to the level 1 gateway 108 via the correspond
ing LVAN 112 and the ATM backbone subnetwork 106. In
response, the level 1 gateway 108 controls the broadband
routing functionality of the network to establish a down
stream broadband communication link and a two-way com
terminals, the service control module uses the data ?les
maintained by the service data module, to generate requests
to established broadband communication sessions. A con
munication signaling link between the provider and the user.
The level 1 gateway 108 receives noti?cation of the status
of broadband communications links as they are being set up
and during ongoing communications through those links.
The level 1 gateway 108 therefore can inform a subscriber
when a requested session can not be set up with a selected
for broadband communication sessions between selected
providers and selecting users terminals. A session manage
ment module is responsive to the requests for broadband
communication sessions, for identifying end to end commu
nication connectivity needed for each requested broadband
communication session. The session management module
generates requests for the identi?ed end to end communi
cation connectivity and collects usage information relating
nection management module in turn is responsive to the
instructions from the session management module. The
connection management module identi?es entry and exit
points through subsections of the broadband communication
network for the communication connectivity needed for
each requested broadband session. This module also inter
acts with a control element of each subsection of the network
to obtain communications connectivity through each sub
section, to establish the end to end communication connec
tivity for each requested session. The connection manage
ment module also provides con?rmation of establishment of
service provider, i.e. because the provider’s server ports are
each requested broadband communication session to the
all busy or because the subscriber is not registered with the
particular provider or due to some technical problem. The 60 session management module.
These and other features of the level 1 gateway 108 are
.level 1 gateway 108 also recognizes when an established
described in further detail in connection with FIG. 6.
link develops a fault or is interrupted and can stop accumu
lating usage or billing data regarding that link. The level 1
FIG. 3 is a block diagram of the network showing in detail
gateway 108 can also notify the subscriber and/or the service
a VNH 104 in accordance with the preferred embodiment of
provider of the failure.
65 the present invention.
The level 1 gateway 108 will also store various informa
As shown in FIG. 3, each VNH 104, also referred to as a
tion relating to each subscriber’ s services and control service
broadcast headend node, comprises a SONET multiplexer
130 that receives the OC-48 signal from the broadcast ring
102. The SONET multiplexer 130 is a drop-and-continue
A ?ber optic receiver 138 converts the optical signal from
the PAC Broadcast Source 135 to a baseband analog PAC
(D/C) multiplexer that “drops" the OC-48 signal from the
broadcast ring 102 for local processing, and outputs the
video signal that is supplied to a modulator 136' for mixing
to a speci?ed 6 MHZ channel.
OC-48 signal to “continue” on the broadcast ring 102. The
SONET multiplexer 130 converts the OC-48 signal to obtain
the OC-3 ATM stream and the digitally-encoded (DS-3)
The analog portion of the VNH 104 also includes a
plurality of antennas 140 that receive Over-the-Air (OTA)
broadcast signals at VHF and UHF frequencies. The OTA
signals are supplied to an analog signal processor 142, which
performs signal conditioning and modulates the OTA signals
baseband video signal output by the ATM edge multiplexer
120 and the digital encoder 118, respectively, as shown in
FIG. 2.
The structure of ATM cells is generally recognized in the
art. The ATM cell includes a header section and a payload
section. In addition, the ATM cell may include additional
television channels 4, 7 and 9 to 24, 27, and 29, respectively,
in order to avoid interference with the PAC or VIP analog
video channels. The VNH 104 may also include another
antenna 140' that receives FM radio signals and supplies the
FM signals to an FM radio signal processor 143. The signal
processor 143 outputs the FM radio signal within a speci?ed
overhead sections that provide additional vendor-proprietary
features, such as priority level assignments, or forward error
correction. The ?rst byte of the header section includes a
4-bit GFC word which provides access control. The ?rst
byte of the header section also includes the lower four bits
of an 8-bit virtual-path identi?er (VPI). The second byte of
the header section includes the upper four bits of the VPI and
the ?rst four hits of a 16-bit virtual circuit identi?er (VCI).
The third byte includes the next eight bits of the VCI. The
fourth byte of the header section includes: the last four bits
of the VCI; a 3-bit payload type (PT); and a cell loss priority
(CLP) bit. The ?fth byte of the header section 410 includes
RF band, preferably the FM radio band, to the RF combiner
Thus, the video signals output by the modulator 136 and
the analog signal processor 142 are analog RF video signals
at different 6 MHZ RF channel frequencies, as well as the
FM signals output by the signal processor 143. The analog
signals output from the FM radio signal processor 143, the
modulator 136 and the analog signal processor 142 go to an
RF combiner 144. The RF combiner 144 is a passive
combiner which combines the VIP, PAC and OTA analog
an 8-bit header error check (HEC) word. The CLP bit is used
to manage tra?ic of ATM cells: in the event of network
congestion, cells with CLT set to 1, indicating a lower
video signals into a single video signal having a plurality of
6 MHZ channels. Thus, the VIP analog video signals, the
PAC analog video signals and the OTA analog video signals
priority, are dropped before cells with CLT set to 0.
The speci?c format of the ATM cell is described, for
example, in the ATM User Network Interface Speci?cation,
can be received and viewed using a conventional television
set, without the need for a digital entertainment terminal.
Version 3.0, published by The ATM Forum, Mountain View,
Calif., also published by Prentice Hall, the disclosure of
which is incorporated in its entirety by reference. According
to the ATM User Network Interface Speci?cation, the values
0-18 for the VCI are reserved; therefore, any ATM cell
having valid data must have a VCI value greater than “18”.
Thus, prior to transmission on the network, the ATM edge
multiplexer 120 identi?es ATM cells that do not have VCI
to speci?ed 6 MHZ bandwidth RF channels. For example,
the analog signal processor 142 may modulate the OTA
Thus, these analog video signals could make up a basic
video service analogous to the type offered by contemporary
cable-TV companies. The RF combiner 144, however,
enables passive combining of different baseband analog
video signals, as opposed to known cable-TV systems,
which require a rewire of modulators whenever a change
was made in channel allocation. Thus, changes in the
values greater than “18” as idle cells that do not carry valid
channel allocation in the disclosed embodiment can be made
merely by reprogramming the modulator 136 and the analog
Referring to FIG. 3, the SONET multiplexer 130 extracts
the ATM cells by analyzing the input stream in S-byte
signal processor 142. As discussed below, the RF combiner
144 is also adapted to combine RF signals carrying the
compressed digital video signals from the VIP.
The digital portion of the VNH 104 receives the com
pressed VIP digital video signals from the recovered OC-3
ATM stream output from the SONET multiplexer 130. The
OC~3 ATM stream is output from the SONET multiplexer
130 to one of several ATM packet demultiplexers (APD) 134
(only one shown for convenience). The APD 134 performs
increments in order to check the header/error/check (HEC)
sequence for valid ATM data; the SONET multiplexer 130
veri?es the HEC sequence, extracts the 53-byte ATM cell
and supplies the ATM cells to an ATM packet demultiplexer
(APD) 134. As discussed in detail below, the APD 134 is
adapted to receive a plurality of ATM cell streams and
recover the MPEG encoded video information from the
ATM cell streams. Although FIG. 3 shows only one ATM
ATM processing by recovering the original MPEG-2 packets
packet demultiplexer 134, in the preferred embodiment the
VNH 104 includes a plurality of the demultiplexers.
The VNH 104 includes an analog portion that receives
analog baseband video signals from the VIPs, from a Public
Access Channel (PAC) broadcast source 135, and from
on the basis of the VPI/VCI headers of the incoming ATM
streams. The MPEG packets can be output from the APD
134 without further processing if the VIPs follow a prede
termined provisioning, whereby the PID values for prede
termined data streams remain constant. Alternatively, the
Over-the-Air (OTA). Speci?cally, the SONET multiplexer
APD 134 performs MPEG routing, whereby the recon
130 outputs the DS-3 encoded baseband video signal to a
structed MPEG packets are assigned a new PID value based
on the VPI/VCI value of the ATM stream that carried the
MPEG packets. This mapping of a new PID value in
response to the VPI/VCI of the ATM stream is based upon
a translation table loaded into the ATM packet demultiplexer
DS-3 analog decoder 132, which converts the DS-3 signal
back to the VIP analog baseband video signal. The VIP
analog baseband video signal is output from the analog
decoder 132 to a modulator 136, which includes a tuner to
mix the VIP baseband video signal from the analog decoder
134 via a signaling path 146 (Ethernet or the like), discussed
132 onto a speci?c 6 MHz bandwidth RF channel. The PAC
in detail below. The translation table, also referred to as
Broadcast Source 135 provides public access channel (PAC)
programming related to community activities as a PAC
baseband analog video signal, preferably via an optical ?ber.
MPEG routing information, is supplied from a video man
ager in the video data center 110 (discussed in detail with
respect to FIG. 6).
The MPEG routing also includes outputting the MPEG
packets in accordance with the loaded translation table and
the VPI/VCI of the corresponding ATM cell stream. Spe
ci?cally, the reconstructed MPEG packets are routed from
FIG. 4 discloses one of the network local video access
nodes (LVAN) 112 according to a preferred embodiment of
the present invention. The disclosed LVAN 112 is one of a
plurality of LVANs that is distributed throughout the net
the ATM packet demultiplexer 134 onto one of ?ve 27 MB/s
digital signal paths that serve as inputs to a corresponding
In early implementation stages, however, it is anticipated
modulator/multiplexer 150. The modulator/multiplexer 150
that the ?rst deployed LVAN 112 may be collocated with the
is a Quadrature Amplitude Modulator (QAM) operating at
64 QAM, whereby media access control (MAC) is per
formed to ensure proper timing of the resulting time-division
multiple access (TDMA) signal. Thus, each of the ?ve 27
MB/s digital signals are 64 QAM modulated and multi
plexed into an IF signal, which is upconverted into a speci?c
6 MHZ channel. The QAM/Multiplexer/Upconverter 150
work service area in order to provide service to customers.
VNH 104 in order to service a limited service area. Later
As shown in FIG. 4, the LVAN 112, also referred to as a
video central office or video end o?iee, includes an optical
to-electrical (O/E) receiver 160 that converts the optical RF
signal from the optical ?ber 156 to an electrical RF signal.
The RF signal output from the O/E receiver 160 is supplied
to an equalization ampli?er 162 for signal conditioning
before RF combination by a series of multiple RF combiners
outputs the 6 MHZ channels to the RF combiner 144 for
combining with the other 6 MHZ RF signals. The RF
combiner 144 thereafter outputs the combined RF signals to
multiple lightwave transmitters 154, which output the com
164, similar to the RF combiners 144 shown in FIG. 3. The
combined RF signal is output from the RF combiners 164
bined RF signals on an optical ?ber 156 for transmission to
the local video access nodes 112.
and reconverted to optical signals by the electrical-to-optical
(E/O) transmitters 166. The E/O transmitter 166 supplies the
optical signal to the local loop distribution via optical ?bers
If desired, the LVAN 112 may also combine the RF signal
Although the disclosed network is designed to transport
digital broadband data for high data-rate applications such as
video, the APD 134 of the present invention enables the
network to transport low data-rate information to be broad
cast from an information provider to the VIUs. For example,
an information provider may wish to periodically broadcast
deployed LVANs 112 will be located remotely from the
VNH 104.
application software or signaling information on a low-rate
channel. In such a case, the ATM packet demultiplexer 134
will determine from the VPI/VCl that the data recovered
from the ATM cell stream is a low—rate data signal; conse
quently, the ATM packet demultiplexer 134 will output the
low-rate data signal in MPEG format to a QPSK modulator
152, which modulates the low-rate data signal for RF
transmission after passing through the RF combiner 144.
The low data rate transmission may carry text or signaling
information from a VIP in some way relating to one or more 35
services offered by that VIP. A more detailed description of
from the VNH 104 with a local PAC broadcast signal
supplied by a local PAC source 135. In such a case, the local
PAC broadcast signal is received by a ?ber optic receiver
138, which supplies the conditioned local PAC broadcast
signal to the modulator 136 for conversion to an RF signal
at an available 6 MHZ channel before combining by the RF
combiner 164.
According to the present invention, the LVAN 112
includes an ATM packet demultiplexer that enables MPEG
routing of data received via the ATM subnetwork 172,
including interactive video data, signaling data, or software
the operations of the ATM packet demultiplexer is disclosed
data. The structure of the APD 174 is identical to that of the
APD 134 in FIG. 3. As described in detail below, the ATM
with respect to FIG. 7 below.
packet demultiplexer performs MPEG processing ‘on data
recovered from the ATM cell streams and outputs the
recovered data as data packet streams MPEG-2 format.
The signaling path 146 coupled to the components of the
VNH 104 is preferably an Ethernet communication path, for
example a IO-Base T LAN. Although not shown, the Eth
Thus, the ATM packet demultiplexer provides an “any~data”
signals to each of the components of the VNH 104. The
transport feature, whereby the LVAN 112 is able to transport
any-format data received from the ATM subnetwork 172.
Ethernet signaling path 146 communicates with the video
Thus, the LVAN 112 provides any-data tra?ic between the
ernet signaling path 146 provides signaling and control
data control center 110 via the ATM backbone subnetwork 45 VIU and the network, such as signaling traffic and broad
106 in order to provide the operating status of each of the
band traftic for interactive multimedia television (IMTV)
components of the VNH 104. Speci?cally, the Ethernet
sessions. Speci?cally, the LVAN 112 includes a SONET
signaling path 146 provides upstream signaling data to an
ATM router 148, which packets the Ethernet signals in ATM
format, provides a VPI/VCI header corresponding to the
intemet protocol (IP) address of the intended destination of
the Ethernet signal, and outputs the ATM stream onto the
ATM backbone subnetwork 106. The ATM backbone sub
multiplexer 170 that receives optical signals carrying ATM
streams from the ATM backbone subnetwork 106 via a
network 106 routes the ATM stream from the ATM router
148 of the VNH 104 to a corresponding ATM multiplexer at
the video data control center 110. Preferably, the ATM
backbone subnetwork 106 routes ATM streams between the
VNH 104 and the video data control center 110 along
dedicated virtual paths. The ATM multiplexer at the video
data control center 110 receives the ATM stream, reas
sembles the Ethernet signals, and outputs the Ethernet
signals on its local Ethernet bus with an IP address desti
nation corresponding to the VPI/VCI of the ATM stream.
The ATM virtual circuit to the video data control center 110
is a two-way circuit and carries instructions from the video
data control center 110 back to the components of the VNH
unidirectional OC-48c optical ?ber 172. The SONET mul
tiplexer 170 converts the OC-48 signal into OC-3 signals
carrying ATM streams. The ATM cells transport IMTV
traffic and VIU signaling tra?ic from the VIPs and the
network, respectively. Each OC-3 signal is input to an APD
174, which repackets the ATM cells into recovered data, and
performs MPEG processing and assigns a PID value based
on the VPI/VCI value of the received ATM cells and routing
information from the video manager of the video data center.
The video manager supplies the routing information includ
ing the translation table to the APD 174 via the ATM
subnetwork 106 and the Ethernet data network 200. If the
recovered data is broadband data that is already in MPEG-2
format, the APD 174 merely veri?es the appropriate PID
value for the MPEG packet stream. The APD 174 preferably
is identical to the ATM packet demultiplexer 134 in the VNH
104, although the latter primarily performs MPEG routing
for broadcast video data.
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