Network providing signals of different formats to a user by multplexing ...

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NETWORK PROVIDING SIGNALS OF ing in backbone networks. In ATM, usable capacity can be

DIFFERENT FORMATS TO A USER BY assigned dynamically (on demand) by allocating bandwidth

MULTPLEXING COMPRESSED capacity to supply fixed-sized information-bearing units

BROADBAND DATA WITH DATA OF A called "cells" to point-to-point or multi-point outputs. Each

DDJFERENT FORMAT INTO MPEG 5 cell contains header and information fields. The ATM

ENCODED DATA STREAM standard, CC1TT.121/2 specifies a 53 byte cell which

includes a 5 byte header and a 48 byte payload.

... However, customer premises equipment such as settop

FIELD OF THE INVENTION boxes generally cannot accept AXM ^ utilize an Mpeg

The present invention relates to digital networks offering 10 (moving picture experts group) standard for digital video

a full range of digital communications by transporting program compression. A number of specific compression

compressed digital information using a compression algo- algorithms satisfy MPEG requirements. MPEG-2 is a sec

rithm. ond generation compression standard capable of encoding

video program material into a 6 Mbits/sec bit stream and

BACKGROUND OF THE RELATED ART 15 packetizing a number of 6 Mbits/sec channel streams into a

Known loop distribution systems (or access subnetworks) sinSle nigher rate sign*1 transport stream. The conversion of

handle upstream and downstream data other than video data MPEG-2 data into ATM cell format, however, imposes

in a manner which is similar to that of a model Ethernet additional overhead requirements that reduce the

LAN. These known loop distribution systems are quite information-carrying capacity of the network. For example,

restrictive in either the manner in which non-video data is 20 synchronous transmission protocols, such as SONET, may

transported or in the type of non-video data which may be require a stream of continuous data to retain synchroniza

transported. As used in this application, the term "data" also tion- an ATM stream carrying MPEG video data

includes control signals associated with a video connection that is transmitted on a synchronous carrier may need to be

or some other non-video application. Padded with ASM idle ^ 01 "dummy cells", in order to

Typically, the downstream "data" is routed on a shared 25 ensure P"*** synchronization with the physical layer, channel or other facility shared among a number of end users FIG. 1 depicts an example of a video network utilizing a using IP packets ("IP" stands for Internet Protocol) and IP hybrid fiber-coax system which provides RF transport of formatting. Each user on the network is assigned an both analog and digital broadband services as well as a "address" and a stream of IP packets containing data is „ variety of data communications. The illustrated network forwarded to a particular user by attaching their address onto provides broadcast video distribution, archival video serthe stream of IP packets. However, the address is not used vices and interactive multi-media services as well as plain to direct the IP packets to particular equipment or to a old telephone service. As discussed below, the data cornparticular physical destination. Rather, the stream of IP munications utilize IP addressing. To facilitate packets is made generally available on the network and users „ understanding, an overview of the network is given followed filter out the stream(s) of IP packets intended for them by bY a discussion of data transport through the network, using hardware or software which looks for their respective The network of FIG. 1 includes a Loop Transport Interaddress, face 10 located in a telco central office. In an area serviced

The upstream "data" is typically routed using time divi- through multiple central offices, several different central sion multiple access (TDMA) which assigns respectively 40 offices would each have a Loop Transport Interface similar different time slots for transmission to different users. Data in structure to the Interface 10 depicted in FIG. 1. In some for each user is sent upstream only during the timeslot respects, each Loop Transport Interface serves as the headassigned for that user. If necessary, packets of information end of an otherwise conventional optical fiber trunk and from a single user can be distributed among successive coaxial cable type CATV distribution network, timeslots assigned to that user. Once all of the upstream data 45 In the Loop Transport Interface 10, a laser type optical gets into the shared channel or other shared facility of the transmitter 12 transmits downstream signals through fibers distribution system, the origin of the packets of information 14 to optical to electrical nodes referred to as "optical can be identified from the time slots in which they are network units" or ONU's. The laser operates in a linear present and the information originating from one user can be mode in the range of 5-750 MHz. The transmitter 12 is reassembled by receiving equipment into its original form. 50 followed by an optical splitter and can transmit to several The reassembled information can be distributed in the same ONU nodes 16. Each ONU 16 performs optical to electrical manner as the downstream data using IP routing. conversion on the downstream signals and supplies down

The Integrated Services Digital Network (ISDN) provides stream RF electrical signals to a coaxial cable distribution

users with security and access to a 2B+D channel, in which system 18.

each one of the two "B" channels guarantees 64 kilobits to 55 The optical transmitter receives and transmits signals the user whether they are using it or not However, ISDN and from an RF (radio frequency) combiner 20. The combiner 20 IP are inflexible because they are reliant upon and restricted combines levelized RF signals from several sources to to a specific protocol, such as IP or ISDN. produce the appropriate signal spectrum for driving the Attempts have been made to improve the core switching, optical transmitter 12. One set of signals supplied to the RF multiplexing and transmission technologies for integrated 60 combiner 20 are group of AM-VSB (amplitude modulated digital networks to support voice, data and video services vestigial sideband) analog television signals 22 from one or from VIPs for multiple users. For example, fiber optic more appropriate sources (not shown). Such signals are transmission systems with bandwidths ranging from 155.52 essentially "in-the-clear" CATV type broadcast signals to 2,488.32 Mbps have been considered to improve band- capable of reception by any subscriber's cable ready telewidth access. In addition, asynchronous transfer mode 65 vision set. The analog television signals are broadcast from (ATM) has been developed as a technique to provide broad- the optical transmitter 12 through the tree and branch optical bandwidth, low delay, packet-like switching and multiplex- and coax distribution network to provide "basic" CATV type 3 4

service to all subscribers on the network. In order to obtain transmission together in a combined spectrum with the

additional network services as discussed below, the sub- AM-VSB analog television signals 22. The downstream scriber may obtain a digital entertainment (DET) 24. A transport of the digital prograiriming is an RF transmission network interface module in the DET 24 includes a tuner essentially the same as for the analog basic service channels,

that permits subscribers to the digital services to receive the 5 but each of the channels from the RF modulators 34 contains analog broadcast channels through the same equipment used 4 or 6 digitized and compressed video program channels,

for the digital services. The network depicted in FIG. 1 also referred to hereinafter as "slots". The 6 Mhz digital program

provides transport for digitized and compressed audio/video channels are carried through the fiber and coaxial system in

programming, both for certain broadcast services and for standard CATV channels not used by the analog basic interactive services, such as video on demand. The network service programming. The ONU16 is essentially transparent

uses MPEG encoded video, which is transported to each to both the analog basic service channels and the channels

Loop Transport Interface using asynchronous transfer mode carrying the digital programming and supplies all of the

(ATM) transport and switching. In the illustrated network, signals as a combined broadcast over the coaxial cable digital broadcast service signals 26 in MPEG encoded form network 18

and arranged in ATM cell packets are appliedI toATM M the subscriber premises, a network interface module

packet demultiplexer 28 in the Loop Transport Interface 10. « ( shown) couples the set-top device or digital

These broadcast service signals 26 originate in one or more , _/. t t • , ,vm-~v. » J ui e*.

broadcast VIP's ATM encoders controlled by the VIP serv- entertainment terminal (DET) 24 to a drop cable of the

ers. The ATM broadcast services carry premium service type coa*lal f"***TM .^fT , 1

programming. For certain interactive services which utilize configuration, the NTM includes an analog frequency tuner

one digitized channel to provide limited downstream trans- 20 controlled by a microprocessor to selectively receive the RF

port to a large number of subscribers, the ATM broadcast cell channel signals, including those channels carrying digital

stream signals originate from a server 30. Fully interactive information. The NTM also includes a QPSK, QAM or VSB

broadband digital signals, in MPEG-ATM format, are also demodulator to demodulate a selected one of the digitized

applied to the ATM packet demultiplexer 28 from an ATM program signals carried in one of the digital slots within a

switch 32. The ATM packet demultiplexer 28 tenninates all 25 received 6 MHz channel and performs a forward error

ATM cell transport through the network, and converts the correction function on the demodulated data. A digital

cell payload information into a plurality of MPEG-2 format audio/video signal processor within the DET decompresses

bit streams. received video signals, generates graphics display informa

In addition to the analog broadcast signals, the RF com- tion and performs digital to analog conversion to produce

biner 20 receives a variety of other analog RF signals from 30 output signals compatible with a conventional television set

a group of RF digital modulators 34 that output the MPEG 40.

streams from the ATM packet demultiplexer 28 as digital The analog tuner in the NTM tunes in all channel frequen

broadband information in RF analog format Each RFmodu- cies carried by the network, including those used for the

lator 34 outputs a 6 MHz bandwidth IF signal which an analog broadcast services. The DET 24 includes a bypass

upconverter (not shown) tunes to a different RF channel 35 switch in the NIM and an analog demodulator to selectively

having a corresponding carrier frequency. A controller iden- supply analog signals from the basic service channels

tified as the video manager SO provides instructions to the directly to the audio/video output terminals or to the

ATM demultiplexer 28 to use the VPI/VCI header from the modulator, to provide signals to drive a standard television

ATM cells to route the MPEG bit streams to the appropriate receiver.

digital RF modulator 34. The video manager 50 provides the 40 The DET 24 also includes a remote control and/or keypad

control information to the ATM packet demultiplexer 28, for t0 receiVe various selection signals from a user. The DET

example, by an ethernet bus 38a. The Ethernet bus 38a is relays data signals upstream over a QPSK signaling channel

also coupled to the network controller 36, the ACC 4000D on me coaxial cable to the ONU 16 in response to user inputs

46, and the network data processor (NDP) 38. Thus, the such 35 selection of a pay per view event The actual

video manager 50 and the ACC 4000 46 can provide control 45 transmission of any such data signals upstream from the

data for use by the ATM packet demultiplexer. The NDP 38 det 24 occurs in response to a polling of the DET. The

transmits downstream signaling and/or data via QPSK ONU 16 combines upstream data signals from the DET's

modulated out-of-band signaling channels. The network serviced thereby and transmits those signals upstream over

controller 36 receives and processes upstream signaling another optical fiber 42 to an optical receiver 44 in the Loop

and/or data transmissions through upstream QPSK modu- 50 Transport Interface 10. Each DET 24 may. transmit data on

lated out-of-band signaling channels. a different carrier frequency or timeslot, in which case the

The RF modulators 34 use 64 QAM (quadrature ampli- network controller 36 knows which DET sent particular data

rude modulation) or 16 VSB (vestigial sideband) modulation based on the received frequency channel. Alternatively, for

techniques. The 64 QAM is used to modulate 4 channels of interactive services, the DET may transmit a unique identi

6 Mbits/s MPEG encoded digital video information into one 55 fication code with the upstream message.

6 MHz bandwidth analog channel. Similarly, 16 VSB modu- ^ the implementation of the network illustrated in FIG. 1,

lates 6 channels of 6 Mbits/s MPEG encoded digital video an ACC 4000D 46 performs set top management and

information into one 6 MHz bandwidth analog channel. specific program access control functions. Service profiles

As another example, U.S. Pat. No. 5231,494 to Wachob, for each customer on the network and their DET's are set up

the disclosure of which is incorporated herein in its entirety 60 and stored within the ACC 4000D 46. The ACC 4000D 46

by reference, teaches quadrature phase shift keyed (QPSK) may also provide an interface to appropriate billing systems

modulation of a plurality of video, audio and data signals (not shown) for some broadcast services, such as pay per

into a single data stream within a standard six MHz channel view. For ATM broadcast services, when a subscriber first

allocation for transmission over a CATV type distribution signs up, a portfolio of channels subscribed to by that

network. 65 customer is established in the subscriber's profile data

The 6 MHz bandwidth RF signals from the modulators 34 within the ACC 4000D 46. Based on this profile data, the

are supplied to the optical transmitter 12 for downstream ACC 4000D 46 downloads a service map into the subscrib