CA2173003A1 - Method and apparatus for delivering secured telephony service to a hybrid coaxial cable network - Google Patents
Method and apparatus for delivering secured telephony service to a hybrid coaxial cable networkInfo
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- CA2173003A1 CA2173003A1 CA002173003A CA2173003A CA2173003A1 CA 2173003 A1 CA2173003 A1 CA 2173003A1 CA 002173003 A CA002173003 A CA 002173003A CA 2173003 A CA2173003 A CA 2173003A CA 2173003 A1 CA2173003 A1 CA 2173003A1
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- coaxial cable
- telephony
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- video
- network
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Abstract
A hybrid coaxial cable network employing interdiction to ensure privacy in telephony communications. The video and telephony signals are secured such that telephony and interactive video signals to and from a subscriber do not appear on the network at any other undesired subscriber location. Power is supplied to the subscriber's telephone through the coaxial cable network.
Description
METHOD AND APPARATUS FOR DELIVERlNG SECUR}i:D TELEPHONY
SERVICE IN A HYBRID COAXIA~ CABLE NETWORK
This is a division of copending commonly assigned C~n~ n Patent Application No. 2,141,323 filed May 26, 1994.
Field of the ~vention The invention relates to the field of telecommunications. More particularly the invention relates to the field of multiplex communications. In still greater particularity, the invention relates to the provision of secured telephony in a coaxial cable network. By way of further characterization, but not by way of limitation thereto, the invention uses interdiction to prevent monitoring of a subscriber'stelephone communications by another subscriber on the network, and the inventionalso supplies power to the subscriber's telephone through the coaxial cable network.
D~ lion of the Prior Art Information, and access to it, has received significant attention recently. The building of an "information highway" compared to the national interstate highwaysystem begun in the 1950's has been made a national priority. There are currently three wireline transport elements available for such a highway: (1) fiber optic cable;
(2) coaxial cable; and (3) twisted copper pair cable ("twisted pair"). Presently, twisted pair cable predomin~tes, certainly in the local loop portion of telephone networks. Coaxial cable has been used widely by cable television col--pallies. Both telephone comp~nies and cable companies have made use of fiber optics for main or trunk line signal transport.
Fiber optic cable can carry more information over a greater distance than coaxial cable, while coaxial cable can carry more information over a greater distance than twisted pairs. Rec~llse twisted pair is the predominant local loop technology, at least in the telephone industry, attempts have been made to develop technologies which wiU increase the carrying capacily of copper. In reality, copper wire is a very efficient ll~l~oll means for traditional telephony services.
Within the telephony industry, the terrn "broadband" denotes a very high digital line rate, such as the 156 Megabits per second (Mb/s) optical line rate of new S SONET OC3-level fiber optic systems. The term "baseband" describes the original (unmodulated) form of the electrical or optical signal associated with a single service that is typically presented to the network by a subscriber, and the final form of that signal ~ el~ted from the network to a subscriber. The baseband signal can be either analog or digital in form, and is further characterized as the direct ele.;l.un.agnetic 10 ~.~;,elltation of the base information to be transmitted, with no other carrier or subcarrier energy present. A baseband signal may be carried directly on a tr~ncmicsion line, such as a twisted pair of insul~ed copper wires or an optical fiber.
A baseband signal may also be used to modulate a carrier signal for tr~n.cmi.c.cion on a variety of transmission systems (e.g., radio). In telecommunications, the term 15 "passband" describes the range of frequency ~pe~;lluln which can be passed at low tr~ncmicsion loss through a linear transmission system. Modulated carrier signals p.~sel~led to such a system will be delivered in their original form with minimal loss and distortion, as long as such signals faU within the absolute limits of the passband range of ~ uencies and the dynamic range of signal amplitude for a given linear 20 tr~nsmi~sion system.
An example should help claAfy the relationship b~l~n baseband an passband. The ele~;ll ical signal that is present at a tcl~hone jack during a conversation is the baseband electrical signal leplesellt~lion of the taUker's voice.
This baseb~d signal is typically l~cu~ olled to the telephony swilchh~g office by a twisted pair of insulated copper wires. At the central office, the signal goes through lhe switch and is typically converted to digital form and multiplexed in the time domain for tr~ncmi.csion through baseband digital tr~nsmi.csion systems that carry such signals on copper or fiber optic cables to other localions. The baseband digital S ~ n.c...is.~ion system may carry thousands of individual telephone calls on the same tr~ncmi.ccion line. Even though there are multiple calls in progress on the same tr~ncmi.c.cion line, such a system is still deFmed as "baseband" because there is no modulation of a carrier or subcarrier signal anywhere in the system, and. at any given - instant of time, there is only a single subscriber's signal actually present at a given 10 point on the line. As the original talker's signal reaches the other switching omce involved on the call, it is converted back to the original analog form and put on the copper pair co~le~;led to the far-end telephone set, once again in baseband form.
Passband techniques can also be used to provide telephony services. In cable television systems configured for telel~hony services, the bas~and analog telephone 15 . signal is used to modulate a carrier signal. The modulated carrier signal can be assigned a particular frequency within the passband of the linear tr~n.cmicsion system.
A number of such modulated carrier signals, each ~csigned a different carrier rl~u. n~;y in the passband, can be transmitted all at the same time wilhoul mutual interference. At the far end, a selected modulated carrier signal must be demodulated 20 to remove the carrier signal and recover the baseband signal associated with the service. If the linear tr~n.cmicsion system is ope~ting plul)elly, the derived signal will be delivered to the far-end telephone set, once again in baseband form.
While there is technology that ~u~olls digital line rates on the order of lOOMb/s for short--li.c~nce building twisted-pair wiring, the practical limit for traditional twisted pair copper plant in the loop environ,llelll (from the serving centr~l omce to the ~.Jbsc-il,el-) is on the order of 1.5Mb/s, at a maximum distance of about 12 kilofeet (KF). One emerging technology that is capable of qt1~inin~ this practical limit for twisted pairs is known as High-speed Digital Sul)s~;liber Line (HDSL). A
S similar copper-based technology known as Asymmetric Digital Subsclil)er Line (ADSL) may permit the carriage of a 1.5Mb/s do~llsllealll signal toward the subsc,il~er and an U~ channel of l~e,hdps 16 kilobits per second (Kb/s), all on a single copper pair, to within 18KF from the serving central office. Rather than modify its network to include more fiber and/or coaxial cable. at least one telephone colnpally is deploying ADSL technology (U~4 Today 4129193, Page Bl).
While suited for their intended purpose, these emerging copper-based technologies carry some uncertainties and special restrictions that may reduce their applicability in copper loop plant. At this point, the best-case scenario indicates that such technology could be used only on nonloaded copper loops within 12KF (HDSL) 15 and 18KF (ADSL), I~s~,e-;lively. Thus, this technology would be employable in ~ulJs~n~ially less than 100 percent of the present envil~,n"~el~l. Other limitations (e.g., within-sheath incol--patibility with other services such as ISDN) will likely further reduce the maximum l,enel~tion pel.;enlage.
The maximum practical di~tq-nce that true Broadband rates (e.g., 156Mb/s and 20 higher) can be supported on twisted pair copper plant is on the order of 100 feet.
Given that the emerging HDSL and ADSL copper-based techno10gies provide line rates two orders of magnitude below true brw-clbqn-l rates, and then cover substqnti-q-lly less than 100 percent of the customer base in the best case, copper is clearly not practical as a true bluadband technology solution.
Baseband signal co~nplession techniques offer possibilities for leveragin~ the embedded copper plant for certain speciric services. Baseband co~l,pl~ssion techlli.~.les that COInlJl`t~S a standard movie entertainment television signal with "VCR-quality" into a l.SMb/s channel (including audio) have been demonstrated, as well S as lower-speed devices intended for videoconre~ ci"g and videotelephony applications. The aypa~ t view is that a bearer-channel technology such as ADSL
(described above) and a baseband co"")lt;ssion technology, taken together, could offer a realistic alternative for video services requiring large bandwidth, allowing continued use of the e~i~ling copper plant and obviating the need for fiber-based or other 10 broadband links.
Unrollu~ately, baseband cu"lylt;ssion techniques use a deliberate tradeoff of one or more technical parameters that can reasonably be "sacrificed" as having little or no effect on a given service. For example, low-bit-rate coders for voice and video obtain bandwidth efficiellcies at the e~yense of tr~n~lni~sion delay. A y~ocessin~
15 delay of pelllal~S a half-second through the encoding and decoding ylucess will have little or no effect on one-way broadcast service, but may disturb the natural rhythm of speech in a two-way videotelephony application, making the two-way service awkward to use. Baseband co~np~s~ion techniques are narrowly designed for specific applications (e.g., videotelephony) within generic classes of service (e.g., video), and 20 do not provide cu..,ylele transparency of any basel,and digital signal.
Line coding co.,.~ ssion techniques that may be used to provide ADSL
capabilities offer bandwidth efficiencies in a variety of ways. In one category, Quadrature Alnplilude Modu1ation (QAM) techniques have been used to encode digital information for t~n~mi~sion on microwave radio systems and (more lecenlly) - 2l 73003 channel slots on cable television systems. A 16-state QAM coder offers a 4 bits-per-Hertz (4B/Hz) emciency; a 64-state QAM coder offers a 6 bits-per-Hertz (6B/Hz) efrlciency. This simply means that an input digital signal at the rate of 1.5Mb/s can be 16-state QAM-coded into an analog frequency ~e-;tl~ln~ of about 0.38 MegaHertz S (~Iz), making it possible to be transported on copper wire pairs over longer di.~l~nccs. Similar techniques are also possible on satellite and CATV systems, to provide both digital signal carriage and digital spectrum efficiencies on those media.
In summary, utilizing baseband signal co~p,es~ion techniques results in bandwidth effic;encies which are gained at the penalty of one or more technical 10 parameters. Such a tradeoff may not be possible in the case of a different service on the same medium. In the case of wireline coding teclmiques that deal with the signal after baseband col"pl~ssion, techl-ical complexity and cost gene~lly limit it to 6B/Hz spectrum efficiency. Thus, copper-based systems such as HDSL and ADSL may find limited application in the telephone network. HDSL is actually a pure cost-saving 15 loop alternative to facility arrangements that serve 1.5Mb/s High-Capacity digital service ("HICAP") customers. The cost savings are potentially realized by the ability to use assigned nonloaded pairs in the loop outside plant, rather than designed pairs, as well as going longer distances without outside plant ~eatel~.
ADSL technology could provide early market entry for limited VCR-quality 20 video or other asymmetric 1.5Mb/s applications. Advantages of ADSL include the use of existing copper plant facilities and maximization of network functionality.
Disadvantages include the cost of set-top converters which are not reusable after ADSL is obsoleted. Also, ADSL offers only single channel service. In addition, the service can only reach a limited number of customers and tel~hone service electrical noise can result in video distortion. ADSL is also subject to RF tr~ncmission interference over longer loops.
Fiber optic-based systems are preferable to copper-based networks even with HDSL or ADSL because of their high bit rate transport capability. Information 5 services that require true broadband rates require fiber or coaxial cab~e technology, as a practical matter. Even low-end (i.e., POTS "plain old tcle~hone service") services will reflect a lower per-subsclilJer cost on fiber, compared to present copper-based delivery systems. Specifically, fiber-based systems that provide residence telephony to groups of 4-8 ~ sc.ibel~ with fiber to the curb (F ITC) are expected to 10 achieve cost parity with copper in the near future. However, the cost to replace the existing copper plant in the U.S. with fiber optics is estimated at hundreds of bil~ions of dollars. Thus the length of time required to achieve this conversion could be decades.
One possible alternative to fiber or copper networks is a hybrid network which 15 utilizes existing facilities and employs fiber optics, coaxial cable and copper wiring.
Such a network would allow the delivery of many advanced services and yet be more cost emcient to allow earlier conversion to a broadband network with significant fiber optic capability included. At least one co...pany has amlou,~ced plans for such a hybrid nGlwOIk (Denver Post, 4124193 Page Cl).
20In general, hybrid net~ro-ks combine a tele~hony nelwo,k and a video n~lwolk. One drawback of such a netwo-k is some duplication of equi~,l..enl required to ll~lsl)o-l the s~a~te signals. That is, if, for exarnple, the telephony services could be sent over the video netw~-h, then a s.ll~5t;l..lial portion of the cost and complexity of the hybrid l~elwolk could be elimin~ted. However, in~order to send telephony and video signals over the same transport medium, the unique characteristics of each signal must be addressed. For video signals this is not as difficult as some of the issues ~u~luuilding transport of telephony signals. That is, video signals are generally sent in one direction, from the provider to the subscriber, 5 while telephûny requires two-way transport. ~s video evolves into interactive video, however, two-way video signal transport issues will also beco~,.e significant.
Telephony, in addition to requiring two-way communication, has two other requi.~.ne..ls not necessarily addressed by video networks: powel~lg and privacy of conln~n~ication. In video networks the power to operate the subscriber television set, 10 for example, is provided by the subscriber. That is, the subscriber plugs his or her television andlor video cassette r~ol-ler into an electrical outlet which provides power in the s~ sc,iber location. In the event of a power outage, for whatever reason, the user is unable to view the television unless he or she has a backup source of power (i.e., battery or generator). Few people have such backup power. In 15 telephony, on the other hand, subscribers expect phone service whether or not elecl-i-;ily is available. The following paragraphs discuss a history of power in the telephony network.
Telephones on the early manual networks had their own battery boxes which contained dry cells. These IJatl~lies were used to power the carbon granule 20 mi.;~pholles. In addition, a hand crank generator in the phone supplied the needed sign~ting to call others on the same line, or the opel~tor. These two power sources within the tcl~hone allowed a user to originate a call and to talk to other users.
Neither of these sources were dependent upon household power, allowing calls to be placed even before rural electrification.
When aulo...atic switching was introduced into the network, the battery box was replaced with a common battery located at the switchJ including a common ringing voltage source. The central of~lce switch also needed power to operate and make con,le~lions b~lweell users. Supplying power to each telephone allowed current S flow and the timed in~ uplion of that current (dial pulses) to signal the switch of the user's intentions. In addition, the busy state current could be used by the telephone to power the carbon miclupllolle.
Because of the need to protect tl-e switch and the telephone connections from service interruptions, the power plant at the central office was backed up with large 10 wet cell batteries. These batteries in turn were often backed up with motor-generator sets. Several different voltages are used witlun the network, but the primary supply is -48 volt direct current (vdc) and ~:105 volts at 20 Hz.
Over time as the telephone network grew in size and service penetration approached 100 percent, service availability (reliability) became one of the most 15 hn~Jol~l~ obligations of the nel-volk. For a time the telephones in users' homes belonged to the network and were maintained by the network owner. In the past 20 years the ownel~ ) of the telephone has changed again and carbon microphones aren't used anymore. However, the new electronic telephones with their silicon chips still rely on the network to supply power for cal~ supervision and even for memory 20 backup.
Service availability is a responsibility shared by the network and the user.
The nel~olk is ,~ onsible for m~in~ining the switch and connecling trunks as well as testing and m~inl~ining the individual lines to each user. The user also contributes to service availability by keeping the telephone on-hook when it is not needed, by maintaining premises wiring and terminal equipment in good repair, and by limiting the total quantity of equipment comle~;led to one line.
~ inill~ the batlefies in the telephone's battery box was difficult. Thus network power is l"t;~.dble. First of all, the financial cost associated with placing S the terminal power back in the terminal equipment would be huge. The supply and ltell~ce of the needed batteries would either be folgollell (li`ke those in smoke detectors) or would be elimin~ted. Both of these results would limit the user's service availability. The second reason that power will likely remain in the network is due to the regulatory bodies who are concellled with "life-line" services. This relates to 10 phone service being perceived as a necessity as pointed out above. Basic telephone service is expected to be available to everyone at a reasonable cost 24 hours a day.
There are a few excel)lions. Some services are powel~d by the user today.
As more services are introduced in the future, the user equi~ tnl associated with these new services may also be non-network powered. One good example is 15 Integrated Services Digital Network (ISDN) services, whether Basic or Primary Rate Interfaces. With ISDN, the network powers its portion of the circuit and tlle user powers the terminal e4ui~ e-ll. Most data services also fall into this category.
Power can only be provided over a fiber optic network with great difficulty and e~,ellse. As discussed above, power can and is easily provided over a copper-20 based n~lwlJlk. There are video systems today which uti~ize cable phone systems inwhich tel~holly is provided over a video nelwork system. However, such systems require power supplied by the subsclil)el, usual~y in the form of AC power and (in some cases) l,allc,ies at the ~.lbs~;libel- premises. In addition, adaptive hardware in the form of converter boxes are needed to utilize the phone system.
Safeguarding privacy of communications is a fundamental rule in the telephone industry. This is required by law and violators are subject,to heavy penalties.
Telephone subscribers have the expectation that their usage and their communications will be kept confidential. The requirement for privacy extends to the identity of the 5 parties to the communications, and even to the fact that the communications took place. Traditional loop plant architecture provides each subscliber a dedicated tr~nsmi~sion path all the way back to the switching central omce. Except for the deliberate case of multiparty service, the physical "star" topology ensures that every subscliber~s communication is not available to others who are not a party to the 10 com--.unicdtions. Referring to Fig. 1. a star type nelwo.k architecture is shown. A
star a chil~t~ ; is a physical point-to-multipoint arrangement. There are two types of star a~ il~lures. In Fig. lA a private line type of star is shown. That is each of lines 1, 2, 3, ...(n) is separate and distinct and provides a dedicated transmission path to the central office. In Fig. lB a party line type of star is shown. In this case 15 each of the parties commonly connecled in this --allller may listen to any of the others. There is no privacy. Such party line configurations, once common for cost reasons, are gradually being elimin~ed as networks are mode..~ed.
Cable television systems are configured in a broadcast bus architecture, and all services carried on such systems are inhel~,nlly available to all subs.;libcl~
20 conlle~tcd to the bus, including telephone channels carried in the passband. A logical bus type of ar~t~il~;lul~ is illustrated in Fig. 2A. In a bus al~ il~lult; all users share common bandwidth as in a party line star architecture. Generally, cable co.~-l,a~ues e.--~loy a "tree-and-branch" style bus architecture (Fig. 2B). This is essenlially a logical bus on a tree and branch physical structure. Similarly, a party line architecture (Fig. lB) is eSSGnl-allY a logical bus on a physical star. In any event, the bus style architecture used by cable companies, while sufficient for delivery of video services, does not ensure privacy of communications for telephony or interactive video services. While encryption techniques can be used to mitigate the potential 5 problem, they add cost and are not foolproof. As interactive services that use voice-1~ slJvnse units flourish, more mass-market customers will routinely ~e touchtoning such information as credit card numbers and PIN authorizations. Any bus-based a.~;hil~;l~J.e that provides telephony or interactive video services capability must incolpo.~l~ means to ensure privacy of communications.
Finally it is necessary to provide some means to segregate selvices (commonly ter ned "grooming" in the telephone industry) provided by the central office into two basic categories: "switched services" (e.g. POTS) that terminate on the line side of the central omce switching machine; and "special services" (e.g.
burglar alarm, plogl~n channel services, etc.) that terminate on otber equipment in 15 the central omce. The se~;legation into these two categories is accomplished in modern telephone networks by the use of equipment that provides for Time Slot Inte..;llange (TSI) of digital signals.
Modern digital switches recognize only signals which are tr~n.cmitted in discrete digital rate and format. That is, the switch views the transmitted/received 20 signal in 64 Kb/s incl~nellls. In order to make the signal intelligible to the switch, it must be ~1. senled in this basic format. For POTS, the switch expects to "see" a digital signal with a specific line code, line rate, ones density, frame format, and signqling bit convention, with other bits used for mu-law voice coding of the taL~cer's voice. Special services signals are not usually in a form recognizable by the switch.
Conventional n~lwolk~ use pulse code modulation techniques to convert from analog to digital and vice versa and then use time division multiplexing to order to sequence (package) a number of services in a common bit stream for tr~ncmicsion. Time division multiplexing divides the time during which each message is transmitted along S the data linlc into discrete time intervals. Each port on the multiplexer is then sequenlially sampled for the time interval and that data sample is transmitted s~ue"lially or serially with a number of other data samples from other ports. A
demultiplexer at the receiving end of the tr~nsmi.csion then recombines the serially transmitted data into the port co~spol~ding to the signal origin. While suited for its 10 intended purpose, this type of tr~n.cmicsion technique l~uhes e~yen~ e time slot h~ ;hal)ge.~ to reorder the time slots to separate switched services from special services. In addition, the TSI technique is not transparent to all of the bits. That is, the ability to ~elro~m certain functions such as cyclic r~undancy check code (CRC6) on an end-to-end basis is lost with the TSI technique.
15Summary of the Il,~ ~,lic~
The invention is a nel~olk for providing video and telephony services to a subscliber. The network i"co,~uo.~tes fiber optic cable, coaxial cable, and twisted pair copper wiring. The network provides power for the telephony services from a nel~o,k location through coaxial and copper wiring to the ~ul,sc,il)el. Power can be 20 provided over coaxial cable relatively easily. Thus, in the hybrid network power for the telephony portion of the service is provided through the network from the point - at which coaxial cable and copper are used. Interdiction devices are used to selectively transmit video signals to a subsc,iber location.
The invention relies on the use of fiber/coax passband infrastructure as the basic bearer channel for all services in the residential mass market served by the nelwolk. The selective delivering device would be physically located in place of a curbside Optical Network Unit (ONIJ), and subsumes all of the basic telephony 5 rL"~ 5 ("talk" battery, ringing, testing, etc.). The selective delivery device O~)G.~leS as the source/sink element for baseband telephony, is ~o-lve,t;d over the coaxial cable plant from the optical node typically serving up to 400 subscribers, and provides co~ ,lete transparency for the entire two-way passband spectrum into 4-8 homes, except for the channel slots used to transport telephony services. In one 10 embodiment the actual link to the home consists of a twin-coaxial-cable "drop" that derives the tip/ring RJ-I I interface from the center conductors of the coaxial cable pair at a Network Interface (NI). compatible with all existing inside telephony wire arrangell,e"ls. The other output of the NI is a standard F-fitting CATV conneclur, co---patilJle with the existing coaxial cable inside wire. The t;u~l,side device also 15 houses the passband interdiction device. In the ~,er~ d embodiment~ the NI at the residence includes only passive filters and no active electronics.
The invention addresses the issue of communications privacy by permanently interdicting all of the telephony channels in the passband for both directions of tr~ncmission. The interdiction is accomplished external to the premises of all 20 subsclibel~ so served. No modulated telephony signal ever a~ in recoverable form on the coaxial cable drop, ensul~lg complete privacy of con~lnunicd~ions. This interdiction can be acco---plislled by several means. One method involves the pe~ anenl insertion of a truly random jamming signal in the part of the passband that contains the telephony passband channels hl the direction of tr~ncrnicsion toward the -customer. An alternative method involves the use of a negative trap (e.g. band-stop filters) that prevents any of the telephony passband channels from reaching the drop cable toward the ~I~bsclibel. In the set of passband frequencies f~r the upstream direction of tr~n.~mi.~sion (toward the central office), an isolation amplifler and S suitable directional coupler arrangement prevents any individual subscliber from monitoring the upstream telephony channels of other tel~hony subsclib~ .~ on the bus. Convenlional j~mming or negative trap techniques in the upstream direction of tr~nsmi.ssion are not ay~"lJy~iate, since there are other applications that originate from the subsclibel premises that use a portion of the upstream frequencies. This requires 10 tr~nsmi.ssion transparency from the. subscfilJer toward the network. A preferred embodiment of the invention uses a modified interdiction device external to subscfibels' premises to accomplish this function.
Nonswitched telephony special services (burglar alarms, etc.) must be sorted from ordinary switched telephony services. In the preferred embodiment, the present 15 invention performs this function by frequency assignment at the remote telephony channel modulators and demodulators. This is accomplished by remotely setting both transmit and receive fi~uencies of the individual channels from the central office.
At the central office, the blocks of switched services of modulated telephony channels in the passband are converted to/from the framed digital format required by the 20 telephone switch, and the blocks of nonswitched special services are converted to the framed digital format and bypass the switch, or are further ll~ls~,olled to other locations. Thus, use of the Time Slot Interchange (TSI) technique with its assorted lilllilalions and high cost equipment is elimin~ted.
Brief D~ tion of the Drawin~.c Fig. I illustrates a "star" type network a.chi~ with a private line architecture (Fig. IA) and a party line architecture (Fig. IB);
Fig. 2 illustrates a "bus" type architecture with a traditional bus-(Fig. 2A) and 5 a cable type bus (Fig. 2B);
Fig. 3 illustrates a broadband hybrid fiber/coaxial cable network arcllitecture;
Fig. 4 illustrates an alternate hybrid fiber/coaxial cable network architecture;
Fig. 5 illustrates a preferred embodiment of the invention for a hybrid fiber/coaxial cable network architecture;
Fig. 6 is a schematic illustrating a baseband below passband curb unit;
Fig. 7 is a sche,llatic illustrating the interdiction device to ensure privacy protection for the preferred embodiment;
Fig. 8 is a sclle..,atic illustrating a network interface for the preferred embodilne,ll, and Fig. 9 is a more detailed drawing illustrating the combiner and splitter unit;
and Fig. 10 illustrates network line cards.
D~3_. ;IJl;on of the Preferred Embodiment Like reference numerals will denote like structure throughout the dcsc,i,~lion 20 of the various figures. Referring to Fig. 3, a broadband hybrid fiber/coaxial cable network architecture is shown. A digital switch 11 and a video tr~nsmi.~sion device 12 includi~g RP modulators 9 and electric/optical converters 10 are shown in a cent~l omce I3. Digital telephony signals are carried over DS1 lines 6 through SONEI multiplexer 19 to a fiber optic cable 14. This architecture l~lt;s~ s a fiber -to the curb (I;~ITC) type of architecture with a video remote ~ ;",oll overlay. That is, fiber optic cables 14 carry digital telephony signals (SONET OC3) from the central office through a remote digital terminal 18 to an optical network unit 15 (ONU). ONU 15 may include a video interdiction device 16 or interdiction device 5 16 could be separately located as shown in Fig. 3. The analog video signals (AM-FDM) from a number of video information providers 23 are carried through fiber optic cable 14 to one or more re~note nodes which may include an analog passband video receiver 17 which includes optical/electrical converters where the analog optic signals are converted to analog electrical signals on a coaxial cable 24.
A power supply cable 20 which may be a 22 gauge electrical cable supplies power directly from power source 32 in central omce 13 to optical nc;twolk unit 15.
From optical network unit 15 telephony services may be provided to subscriber premises 21 over a conventional twisted copper pair line 22 to a telephone 27.
Typically an ONU serves up to eight subscriber locations. Video services from a 15 number of video information providers 23, such as satellite systems or video storage/retrieval equipment, or other suppliers are provided to subscriber premises 21 through coaxial cable 24. A video set-top converter 25 may or may not be ilcid to descramble these vide~ signals to a television 26.
The network depicted in Fig. 3 avoids several problems as~oci,lled with the 20 delivery of telephony and video signals to the home. That is, since the signals are carried on separate transport systems, each of the signals may be treated separately.
- For example, telephone 27 in subsclil,er premises 21 may be pGw~"~d from central office 13 as is done in conventional telephony. Pow~ g of the set-top converter 25 and television 26 may be done from subscriber premises 21. In addition, privacy issues with respect to telephony services over copper wire 22 are maintained as in a convenlional telephony nelwcjlh. As is known in the art~ more than one ONU could be coln-ecled to terminal 18. Similarly, more than one interdiction tap 16 could be collllecled to receiver 17. The drawbacks with the network shown in Fig. 3 include 5 complexity and cost. That is, fiber optic cable 14. power cable 20, and coaxial cable 24 must be laid from each cent~l office 13 to each optical network unit 15 or ~.lbsclil,er premises 21. In addition, additional equipn~ent such as remote digital terminals 18 are r~ui-ed to emciently transport the optical signals.
Referring to Fig. 4, an alternate hybrid fiber coax network is illustrated. As with Fig. 3. central office 13 includes telephone switch 11 and video transmission equipment 12 from which a system manager 28 controls various ancinary functions of video services supplied from providers 23. As with the architecture in Fig. 3, telephony signals and video signals are carried from central omce 13 on fiber optic cable 14 through the feeder portion of the outside plant 29. The telephony signals are 15 passed through remote digital te-l--illals 18 and supplied through fiber optic cable 14 to optical network unit 15. The video signals are tran~olled to video receiver 17 where they are converted from optical to electrical signals on coaxial cable 24. The video signals are then supplied to interdiction device 16 at the location of the optical nelwvlk unit 15. In this embodiment ONU 15 and interdiction device 16 are 20 col-ne~ed and preferably co-located. The major difference belw~en Fig. 4 and Fig.
SERVICE IN A HYBRID COAXIA~ CABLE NETWORK
This is a division of copending commonly assigned C~n~ n Patent Application No. 2,141,323 filed May 26, 1994.
Field of the ~vention The invention relates to the field of telecommunications. More particularly the invention relates to the field of multiplex communications. In still greater particularity, the invention relates to the provision of secured telephony in a coaxial cable network. By way of further characterization, but not by way of limitation thereto, the invention uses interdiction to prevent monitoring of a subscriber'stelephone communications by another subscriber on the network, and the inventionalso supplies power to the subscriber's telephone through the coaxial cable network.
D~ lion of the Prior Art Information, and access to it, has received significant attention recently. The building of an "information highway" compared to the national interstate highwaysystem begun in the 1950's has been made a national priority. There are currently three wireline transport elements available for such a highway: (1) fiber optic cable;
(2) coaxial cable; and (3) twisted copper pair cable ("twisted pair"). Presently, twisted pair cable predomin~tes, certainly in the local loop portion of telephone networks. Coaxial cable has been used widely by cable television col--pallies. Both telephone comp~nies and cable companies have made use of fiber optics for main or trunk line signal transport.
Fiber optic cable can carry more information over a greater distance than coaxial cable, while coaxial cable can carry more information over a greater distance than twisted pairs. Rec~llse twisted pair is the predominant local loop technology, at least in the telephone industry, attempts have been made to develop technologies which wiU increase the carrying capacily of copper. In reality, copper wire is a very efficient ll~l~oll means for traditional telephony services.
Within the telephony industry, the terrn "broadband" denotes a very high digital line rate, such as the 156 Megabits per second (Mb/s) optical line rate of new S SONET OC3-level fiber optic systems. The term "baseband" describes the original (unmodulated) form of the electrical or optical signal associated with a single service that is typically presented to the network by a subscriber, and the final form of that signal ~ el~ted from the network to a subscriber. The baseband signal can be either analog or digital in form, and is further characterized as the direct ele.;l.un.agnetic 10 ~.~;,elltation of the base information to be transmitted, with no other carrier or subcarrier energy present. A baseband signal may be carried directly on a tr~ncmicsion line, such as a twisted pair of insul~ed copper wires or an optical fiber.
A baseband signal may also be used to modulate a carrier signal for tr~n.cmi.c.cion on a variety of transmission systems (e.g., radio). In telecommunications, the term 15 "passband" describes the range of frequency ~pe~;lluln which can be passed at low tr~ncmicsion loss through a linear transmission system. Modulated carrier signals p.~sel~led to such a system will be delivered in their original form with minimal loss and distortion, as long as such signals faU within the absolute limits of the passband range of ~ uencies and the dynamic range of signal amplitude for a given linear 20 tr~nsmi~sion system.
An example should help claAfy the relationship b~l~n baseband an passband. The ele~;ll ical signal that is present at a tcl~hone jack during a conversation is the baseband electrical signal leplesellt~lion of the taUker's voice.
This baseb~d signal is typically l~cu~ olled to the telephony swilchh~g office by a twisted pair of insulated copper wires. At the central office, the signal goes through lhe switch and is typically converted to digital form and multiplexed in the time domain for tr~ncmi.csion through baseband digital tr~nsmi.csion systems that carry such signals on copper or fiber optic cables to other localions. The baseband digital S ~ n.c...is.~ion system may carry thousands of individual telephone calls on the same tr~ncmi.ccion line. Even though there are multiple calls in progress on the same tr~ncmi.c.cion line, such a system is still deFmed as "baseband" because there is no modulation of a carrier or subcarrier signal anywhere in the system, and. at any given - instant of time, there is only a single subscriber's signal actually present at a given 10 point on the line. As the original talker's signal reaches the other switching omce involved on the call, it is converted back to the original analog form and put on the copper pair co~le~;led to the far-end telephone set, once again in baseband form.
Passband techniques can also be used to provide telephony services. In cable television systems configured for telel~hony services, the bas~and analog telephone 15 . signal is used to modulate a carrier signal. The modulated carrier signal can be assigned a particular frequency within the passband of the linear tr~n.cmicsion system.
A number of such modulated carrier signals, each ~csigned a different carrier rl~u. n~;y in the passband, can be transmitted all at the same time wilhoul mutual interference. At the far end, a selected modulated carrier signal must be demodulated 20 to remove the carrier signal and recover the baseband signal associated with the service. If the linear tr~n.cmicsion system is ope~ting plul)elly, the derived signal will be delivered to the far-end telephone set, once again in baseband form.
While there is technology that ~u~olls digital line rates on the order of lOOMb/s for short--li.c~nce building twisted-pair wiring, the practical limit for traditional twisted pair copper plant in the loop environ,llelll (from the serving centr~l omce to the ~.Jbsc-il,el-) is on the order of 1.5Mb/s, at a maximum distance of about 12 kilofeet (KF). One emerging technology that is capable of qt1~inin~ this practical limit for twisted pairs is known as High-speed Digital Sul)s~;liber Line (HDSL). A
S similar copper-based technology known as Asymmetric Digital Subsclil)er Line (ADSL) may permit the carriage of a 1.5Mb/s do~llsllealll signal toward the subsc,il~er and an U~ channel of l~e,hdps 16 kilobits per second (Kb/s), all on a single copper pair, to within 18KF from the serving central office. Rather than modify its network to include more fiber and/or coaxial cable. at least one telephone colnpally is deploying ADSL technology (U~4 Today 4129193, Page Bl).
While suited for their intended purpose, these emerging copper-based technologies carry some uncertainties and special restrictions that may reduce their applicability in copper loop plant. At this point, the best-case scenario indicates that such technology could be used only on nonloaded copper loops within 12KF (HDSL) 15 and 18KF (ADSL), I~s~,e-;lively. Thus, this technology would be employable in ~ulJs~n~ially less than 100 percent of the present envil~,n"~el~l. Other limitations (e.g., within-sheath incol--patibility with other services such as ISDN) will likely further reduce the maximum l,enel~tion pel.;enlage.
The maximum practical di~tq-nce that true Broadband rates (e.g., 156Mb/s and 20 higher) can be supported on twisted pair copper plant is on the order of 100 feet.
Given that the emerging HDSL and ADSL copper-based techno10gies provide line rates two orders of magnitude below true brw-clbqn-l rates, and then cover substqnti-q-lly less than 100 percent of the customer base in the best case, copper is clearly not practical as a true bluadband technology solution.
Baseband signal co~nplession techniques offer possibilities for leveragin~ the embedded copper plant for certain speciric services. Baseband co~l,pl~ssion techlli.~.les that COInlJl`t~S a standard movie entertainment television signal with "VCR-quality" into a l.SMb/s channel (including audio) have been demonstrated, as well S as lower-speed devices intended for videoconre~ ci"g and videotelephony applications. The aypa~ t view is that a bearer-channel technology such as ADSL
(described above) and a baseband co"")lt;ssion technology, taken together, could offer a realistic alternative for video services requiring large bandwidth, allowing continued use of the e~i~ling copper plant and obviating the need for fiber-based or other 10 broadband links.
Unrollu~ately, baseband cu"lylt;ssion techniques use a deliberate tradeoff of one or more technical parameters that can reasonably be "sacrificed" as having little or no effect on a given service. For example, low-bit-rate coders for voice and video obtain bandwidth efficiellcies at the e~yense of tr~n~lni~sion delay. A y~ocessin~
15 delay of pelllal~S a half-second through the encoding and decoding ylucess will have little or no effect on one-way broadcast service, but may disturb the natural rhythm of speech in a two-way videotelephony application, making the two-way service awkward to use. Baseband co~np~s~ion techniques are narrowly designed for specific applications (e.g., videotelephony) within generic classes of service (e.g., video), and 20 do not provide cu..,ylele transparency of any basel,and digital signal.
Line coding co.,.~ ssion techniques that may be used to provide ADSL
capabilities offer bandwidth efficiencies in a variety of ways. In one category, Quadrature Alnplilude Modu1ation (QAM) techniques have been used to encode digital information for t~n~mi~sion on microwave radio systems and (more lecenlly) - 2l 73003 channel slots on cable television systems. A 16-state QAM coder offers a 4 bits-per-Hertz (4B/Hz) emciency; a 64-state QAM coder offers a 6 bits-per-Hertz (6B/Hz) efrlciency. This simply means that an input digital signal at the rate of 1.5Mb/s can be 16-state QAM-coded into an analog frequency ~e-;tl~ln~ of about 0.38 MegaHertz S (~Iz), making it possible to be transported on copper wire pairs over longer di.~l~nccs. Similar techniques are also possible on satellite and CATV systems, to provide both digital signal carriage and digital spectrum efficiencies on those media.
In summary, utilizing baseband signal co~p,es~ion techniques results in bandwidth effic;encies which are gained at the penalty of one or more technical 10 parameters. Such a tradeoff may not be possible in the case of a different service on the same medium. In the case of wireline coding teclmiques that deal with the signal after baseband col"pl~ssion, techl-ical complexity and cost gene~lly limit it to 6B/Hz spectrum efficiency. Thus, copper-based systems such as HDSL and ADSL may find limited application in the telephone network. HDSL is actually a pure cost-saving 15 loop alternative to facility arrangements that serve 1.5Mb/s High-Capacity digital service ("HICAP") customers. The cost savings are potentially realized by the ability to use assigned nonloaded pairs in the loop outside plant, rather than designed pairs, as well as going longer distances without outside plant ~eatel~.
ADSL technology could provide early market entry for limited VCR-quality 20 video or other asymmetric 1.5Mb/s applications. Advantages of ADSL include the use of existing copper plant facilities and maximization of network functionality.
Disadvantages include the cost of set-top converters which are not reusable after ADSL is obsoleted. Also, ADSL offers only single channel service. In addition, the service can only reach a limited number of customers and tel~hone service electrical noise can result in video distortion. ADSL is also subject to RF tr~ncmission interference over longer loops.
Fiber optic-based systems are preferable to copper-based networks even with HDSL or ADSL because of their high bit rate transport capability. Information 5 services that require true broadband rates require fiber or coaxial cab~e technology, as a practical matter. Even low-end (i.e., POTS "plain old tcle~hone service") services will reflect a lower per-subsclilJer cost on fiber, compared to present copper-based delivery systems. Specifically, fiber-based systems that provide residence telephony to groups of 4-8 ~ sc.ibel~ with fiber to the curb (F ITC) are expected to 10 achieve cost parity with copper in the near future. However, the cost to replace the existing copper plant in the U.S. with fiber optics is estimated at hundreds of bil~ions of dollars. Thus the length of time required to achieve this conversion could be decades.
One possible alternative to fiber or copper networks is a hybrid network which 15 utilizes existing facilities and employs fiber optics, coaxial cable and copper wiring.
Such a network would allow the delivery of many advanced services and yet be more cost emcient to allow earlier conversion to a broadband network with significant fiber optic capability included. At least one co...pany has amlou,~ced plans for such a hybrid nGlwOIk (Denver Post, 4124193 Page Cl).
20In general, hybrid net~ro-ks combine a tele~hony nelwo,k and a video n~lwolk. One drawback of such a netwo-k is some duplication of equi~,l..enl required to ll~lsl)o-l the s~a~te signals. That is, if, for exarnple, the telephony services could be sent over the video netw~-h, then a s.ll~5t;l..lial portion of the cost and complexity of the hybrid l~elwolk could be elimin~ted. However, in~order to send telephony and video signals over the same transport medium, the unique characteristics of each signal must be addressed. For video signals this is not as difficult as some of the issues ~u~luuilding transport of telephony signals. That is, video signals are generally sent in one direction, from the provider to the subscriber, 5 while telephûny requires two-way transport. ~s video evolves into interactive video, however, two-way video signal transport issues will also beco~,.e significant.
Telephony, in addition to requiring two-way communication, has two other requi.~.ne..ls not necessarily addressed by video networks: powel~lg and privacy of conln~n~ication. In video networks the power to operate the subscriber television set, 10 for example, is provided by the subscriber. That is, the subscriber plugs his or her television andlor video cassette r~ol-ler into an electrical outlet which provides power in the s~ sc,iber location. In the event of a power outage, for whatever reason, the user is unable to view the television unless he or she has a backup source of power (i.e., battery or generator). Few people have such backup power. In 15 telephony, on the other hand, subscribers expect phone service whether or not elecl-i-;ily is available. The following paragraphs discuss a history of power in the telephony network.
Telephones on the early manual networks had their own battery boxes which contained dry cells. These IJatl~lies were used to power the carbon granule 20 mi.;~pholles. In addition, a hand crank generator in the phone supplied the needed sign~ting to call others on the same line, or the opel~tor. These two power sources within the tcl~hone allowed a user to originate a call and to talk to other users.
Neither of these sources were dependent upon household power, allowing calls to be placed even before rural electrification.
When aulo...atic switching was introduced into the network, the battery box was replaced with a common battery located at the switchJ including a common ringing voltage source. The central of~lce switch also needed power to operate and make con,le~lions b~lweell users. Supplying power to each telephone allowed current S flow and the timed in~ uplion of that current (dial pulses) to signal the switch of the user's intentions. In addition, the busy state current could be used by the telephone to power the carbon miclupllolle.
Because of the need to protect tl-e switch and the telephone connections from service interruptions, the power plant at the central office was backed up with large 10 wet cell batteries. These batteries in turn were often backed up with motor-generator sets. Several different voltages are used witlun the network, but the primary supply is -48 volt direct current (vdc) and ~:105 volts at 20 Hz.
Over time as the telephone network grew in size and service penetration approached 100 percent, service availability (reliability) became one of the most 15 hn~Jol~l~ obligations of the nel-volk. For a time the telephones in users' homes belonged to the network and were maintained by the network owner. In the past 20 years the ownel~ ) of the telephone has changed again and carbon microphones aren't used anymore. However, the new electronic telephones with their silicon chips still rely on the network to supply power for cal~ supervision and even for memory 20 backup.
Service availability is a responsibility shared by the network and the user.
The nel~olk is ,~ onsible for m~in~ining the switch and connecling trunks as well as testing and m~inl~ining the individual lines to each user. The user also contributes to service availability by keeping the telephone on-hook when it is not needed, by maintaining premises wiring and terminal equipment in good repair, and by limiting the total quantity of equipment comle~;led to one line.
~ inill~ the batlefies in the telephone's battery box was difficult. Thus network power is l"t;~.dble. First of all, the financial cost associated with placing S the terminal power back in the terminal equipment would be huge. The supply and ltell~ce of the needed batteries would either be folgollell (li`ke those in smoke detectors) or would be elimin~ted. Both of these results would limit the user's service availability. The second reason that power will likely remain in the network is due to the regulatory bodies who are concellled with "life-line" services. This relates to 10 phone service being perceived as a necessity as pointed out above. Basic telephone service is expected to be available to everyone at a reasonable cost 24 hours a day.
There are a few excel)lions. Some services are powel~d by the user today.
As more services are introduced in the future, the user equi~ tnl associated with these new services may also be non-network powered. One good example is 15 Integrated Services Digital Network (ISDN) services, whether Basic or Primary Rate Interfaces. With ISDN, the network powers its portion of the circuit and tlle user powers the terminal e4ui~ e-ll. Most data services also fall into this category.
Power can only be provided over a fiber optic network with great difficulty and e~,ellse. As discussed above, power can and is easily provided over a copper-20 based n~lwlJlk. There are video systems today which uti~ize cable phone systems inwhich tel~holly is provided over a video nelwork system. However, such systems require power supplied by the subsclil)el, usual~y in the form of AC power and (in some cases) l,allc,ies at the ~.lbs~;libel- premises. In addition, adaptive hardware in the form of converter boxes are needed to utilize the phone system.
Safeguarding privacy of communications is a fundamental rule in the telephone industry. This is required by law and violators are subject,to heavy penalties.
Telephone subscribers have the expectation that their usage and their communications will be kept confidential. The requirement for privacy extends to the identity of the 5 parties to the communications, and even to the fact that the communications took place. Traditional loop plant architecture provides each subscliber a dedicated tr~nsmi~sion path all the way back to the switching central omce. Except for the deliberate case of multiparty service, the physical "star" topology ensures that every subscliber~s communication is not available to others who are not a party to the 10 com--.unicdtions. Referring to Fig. 1. a star type nelwo.k architecture is shown. A
star a chil~t~ ; is a physical point-to-multipoint arrangement. There are two types of star a~ il~lures. In Fig. lA a private line type of star is shown. That is each of lines 1, 2, 3, ...(n) is separate and distinct and provides a dedicated transmission path to the central office. In Fig. lB a party line type of star is shown. In this case 15 each of the parties commonly connecled in this --allller may listen to any of the others. There is no privacy. Such party line configurations, once common for cost reasons, are gradually being elimin~ed as networks are mode..~ed.
Cable television systems are configured in a broadcast bus architecture, and all services carried on such systems are inhel~,nlly available to all subs.;libcl~
20 conlle~tcd to the bus, including telephone channels carried in the passband. A logical bus type of ar~t~il~;lul~ is illustrated in Fig. 2A. In a bus al~ il~lult; all users share common bandwidth as in a party line star architecture. Generally, cable co.~-l,a~ues e.--~loy a "tree-and-branch" style bus architecture (Fig. 2B). This is essenlially a logical bus on a tree and branch physical structure. Similarly, a party line architecture (Fig. lB) is eSSGnl-allY a logical bus on a physical star. In any event, the bus style architecture used by cable companies, while sufficient for delivery of video services, does not ensure privacy of communications for telephony or interactive video services. While encryption techniques can be used to mitigate the potential 5 problem, they add cost and are not foolproof. As interactive services that use voice-1~ slJvnse units flourish, more mass-market customers will routinely ~e touchtoning such information as credit card numbers and PIN authorizations. Any bus-based a.~;hil~;l~J.e that provides telephony or interactive video services capability must incolpo.~l~ means to ensure privacy of communications.
Finally it is necessary to provide some means to segregate selvices (commonly ter ned "grooming" in the telephone industry) provided by the central office into two basic categories: "switched services" (e.g. POTS) that terminate on the line side of the central omce switching machine; and "special services" (e.g.
burglar alarm, plogl~n channel services, etc.) that terminate on otber equipment in 15 the central omce. The se~;legation into these two categories is accomplished in modern telephone networks by the use of equipment that provides for Time Slot Inte..;llange (TSI) of digital signals.
Modern digital switches recognize only signals which are tr~n.cmitted in discrete digital rate and format. That is, the switch views the transmitted/received 20 signal in 64 Kb/s incl~nellls. In order to make the signal intelligible to the switch, it must be ~1. senled in this basic format. For POTS, the switch expects to "see" a digital signal with a specific line code, line rate, ones density, frame format, and signqling bit convention, with other bits used for mu-law voice coding of the taL~cer's voice. Special services signals are not usually in a form recognizable by the switch.
Conventional n~lwolk~ use pulse code modulation techniques to convert from analog to digital and vice versa and then use time division multiplexing to order to sequence (package) a number of services in a common bit stream for tr~ncmicsion. Time division multiplexing divides the time during which each message is transmitted along S the data linlc into discrete time intervals. Each port on the multiplexer is then sequenlially sampled for the time interval and that data sample is transmitted s~ue"lially or serially with a number of other data samples from other ports. A
demultiplexer at the receiving end of the tr~nsmi.csion then recombines the serially transmitted data into the port co~spol~ding to the signal origin. While suited for its 10 intended purpose, this type of tr~n.cmicsion technique l~uhes e~yen~ e time slot h~ ;hal)ge.~ to reorder the time slots to separate switched services from special services. In addition, the TSI technique is not transparent to all of the bits. That is, the ability to ~elro~m certain functions such as cyclic r~undancy check code (CRC6) on an end-to-end basis is lost with the TSI technique.
15Summary of the Il,~ ~,lic~
The invention is a nel~olk for providing video and telephony services to a subscliber. The network i"co,~uo.~tes fiber optic cable, coaxial cable, and twisted pair copper wiring. The network provides power for the telephony services from a nel~o,k location through coaxial and copper wiring to the ~ul,sc,il)el. Power can be 20 provided over coaxial cable relatively easily. Thus, in the hybrid network power for the telephony portion of the service is provided through the network from the point - at which coaxial cable and copper are used. Interdiction devices are used to selectively transmit video signals to a subsc,iber location.
The invention relies on the use of fiber/coax passband infrastructure as the basic bearer channel for all services in the residential mass market served by the nelwolk. The selective delivering device would be physically located in place of a curbside Optical Network Unit (ONIJ), and subsumes all of the basic telephony 5 rL"~ 5 ("talk" battery, ringing, testing, etc.). The selective delivery device O~)G.~leS as the source/sink element for baseband telephony, is ~o-lve,t;d over the coaxial cable plant from the optical node typically serving up to 400 subscribers, and provides co~ ,lete transparency for the entire two-way passband spectrum into 4-8 homes, except for the channel slots used to transport telephony services. In one 10 embodiment the actual link to the home consists of a twin-coaxial-cable "drop" that derives the tip/ring RJ-I I interface from the center conductors of the coaxial cable pair at a Network Interface (NI). compatible with all existing inside telephony wire arrangell,e"ls. The other output of the NI is a standard F-fitting CATV conneclur, co---patilJle with the existing coaxial cable inside wire. The t;u~l,side device also 15 houses the passband interdiction device. In the ~,er~ d embodiment~ the NI at the residence includes only passive filters and no active electronics.
The invention addresses the issue of communications privacy by permanently interdicting all of the telephony channels in the passband for both directions of tr~ncmission. The interdiction is accomplished external to the premises of all 20 subsclibel~ so served. No modulated telephony signal ever a~ in recoverable form on the coaxial cable drop, ensul~lg complete privacy of con~lnunicd~ions. This interdiction can be acco---plislled by several means. One method involves the pe~ anenl insertion of a truly random jamming signal in the part of the passband that contains the telephony passband channels hl the direction of tr~ncrnicsion toward the -customer. An alternative method involves the use of a negative trap (e.g. band-stop filters) that prevents any of the telephony passband channels from reaching the drop cable toward the ~I~bsclibel. In the set of passband frequencies f~r the upstream direction of tr~n.~mi.~sion (toward the central office), an isolation amplifler and S suitable directional coupler arrangement prevents any individual subscliber from monitoring the upstream telephony channels of other tel~hony subsclib~ .~ on the bus. Convenlional j~mming or negative trap techniques in the upstream direction of tr~nsmi.ssion are not ay~"lJy~iate, since there are other applications that originate from the subsclibel premises that use a portion of the upstream frequencies. This requires 10 tr~nsmi.ssion transparency from the. subscfilJer toward the network. A preferred embodiment of the invention uses a modified interdiction device external to subscfibels' premises to accomplish this function.
Nonswitched telephony special services (burglar alarms, etc.) must be sorted from ordinary switched telephony services. In the preferred embodiment, the present 15 invention performs this function by frequency assignment at the remote telephony channel modulators and demodulators. This is accomplished by remotely setting both transmit and receive fi~uencies of the individual channels from the central office.
At the central office, the blocks of switched services of modulated telephony channels in the passband are converted to/from the framed digital format required by the 20 telephone switch, and the blocks of nonswitched special services are converted to the framed digital format and bypass the switch, or are further ll~ls~,olled to other locations. Thus, use of the Time Slot Interchange (TSI) technique with its assorted lilllilalions and high cost equipment is elimin~ted.
Brief D~ tion of the Drawin~.c Fig. I illustrates a "star" type network a.chi~ with a private line architecture (Fig. IA) and a party line architecture (Fig. IB);
Fig. 2 illustrates a "bus" type architecture with a traditional bus-(Fig. 2A) and 5 a cable type bus (Fig. 2B);
Fig. 3 illustrates a broadband hybrid fiber/coaxial cable network arcllitecture;
Fig. 4 illustrates an alternate hybrid fiber/coaxial cable network architecture;
Fig. 5 illustrates a preferred embodiment of the invention for a hybrid fiber/coaxial cable network architecture;
Fig. 6 is a schematic illustrating a baseband below passband curb unit;
Fig. 7 is a sche,llatic illustrating the interdiction device to ensure privacy protection for the preferred embodiment;
Fig. 8 is a sclle..,atic illustrating a network interface for the preferred embodilne,ll, and Fig. 9 is a more detailed drawing illustrating the combiner and splitter unit;
and Fig. 10 illustrates network line cards.
D~3_. ;IJl;on of the Preferred Embodiment Like reference numerals will denote like structure throughout the dcsc,i,~lion 20 of the various figures. Referring to Fig. 3, a broadband hybrid fiber/coaxial cable network architecture is shown. A digital switch 11 and a video tr~nsmi.~sion device 12 includi~g RP modulators 9 and electric/optical converters 10 are shown in a cent~l omce I3. Digital telephony signals are carried over DS1 lines 6 through SONEI multiplexer 19 to a fiber optic cable 14. This architecture l~lt;s~ s a fiber -to the curb (I;~ITC) type of architecture with a video remote ~ ;",oll overlay. That is, fiber optic cables 14 carry digital telephony signals (SONET OC3) from the central office through a remote digital terminal 18 to an optical network unit 15 (ONU). ONU 15 may include a video interdiction device 16 or interdiction device 5 16 could be separately located as shown in Fig. 3. The analog video signals (AM-FDM) from a number of video information providers 23 are carried through fiber optic cable 14 to one or more re~note nodes which may include an analog passband video receiver 17 which includes optical/electrical converters where the analog optic signals are converted to analog electrical signals on a coaxial cable 24.
A power supply cable 20 which may be a 22 gauge electrical cable supplies power directly from power source 32 in central omce 13 to optical nc;twolk unit 15.
From optical network unit 15 telephony services may be provided to subscriber premises 21 over a conventional twisted copper pair line 22 to a telephone 27.
Typically an ONU serves up to eight subscriber locations. Video services from a 15 number of video information providers 23, such as satellite systems or video storage/retrieval equipment, or other suppliers are provided to subscriber premises 21 through coaxial cable 24. A video set-top converter 25 may or may not be ilcid to descramble these vide~ signals to a television 26.
The network depicted in Fig. 3 avoids several problems as~oci,lled with the 20 delivery of telephony and video signals to the home. That is, since the signals are carried on separate transport systems, each of the signals may be treated separately.
- For example, telephone 27 in subsclil,er premises 21 may be pGw~"~d from central office 13 as is done in conventional telephony. Pow~ g of the set-top converter 25 and television 26 may be done from subscriber premises 21. In addition, privacy issues with respect to telephony services over copper wire 22 are maintained as in a convenlional telephony nelwcjlh. As is known in the art~ more than one ONU could be coln-ecled to terminal 18. Similarly, more than one interdiction tap 16 could be collllecled to receiver 17. The drawbacks with the network shown in Fig. 3 include 5 complexity and cost. That is, fiber optic cable 14. power cable 20, and coaxial cable 24 must be laid from each cent~l office 13 to each optical network unit 15 or ~.lbsclil,er premises 21. In addition, additional equipn~ent such as remote digital terminals 18 are r~ui-ed to emciently transport the optical signals.
Referring to Fig. 4, an alternate hybrid fiber coax network is illustrated. As with Fig. 3. central office 13 includes telephone switch 11 and video transmission equipment 12 from which a system manager 28 controls various ancinary functions of video services supplied from providers 23. As with the architecture in Fig. 3, telephony signals and video signals are carried from central omce 13 on fiber optic cable 14 through the feeder portion of the outside plant 29. The telephony signals are 15 passed through remote digital te-l--illals 18 and supplied through fiber optic cable 14 to optical network unit 15. The video signals are tran~olled to video receiver 17 where they are converted from optical to electrical signals on coaxial cable 24. The video signals are then supplied to interdiction device 16 at the location of the optical nelwvlk unit 15. In this embodiment ONU 15 and interdiction device 16 are 20 col-ne~ed and preferably co-located. The major difference belw~en Fig. 4 and Fig.
3 is that power may be supplied through coaxial cable 24 by a power supply 32 which may include an electrical coluleclion to the electrical utility and backup batteries.
Thus, power supply cable 20 in Fig. 3 is elimin~te~l The eliminq~ion of power supply cable 20 I~,resenls a significant cost savings over the alcl~ urt; of Fig. 3. As with Fig. 3~ the video signals through coaxialcable 24 are supplied to customer premises 21 through interdiction unit 16 contained in optical network unit 15. Power is now supplied to telephone 27 from power supply 32 through coaxial cable 24 and ONU IS. Coaxial cable 24 from interdiction device 16 to ~;USlUlllel premises 21 supplies only video signals to television 26 and does not supply power. As with Fig. 3, a video set-top converter 25 may or may not be included in the system. Fig. 4 ~ sents a sub~lal,lial improvement over the n~lwo-k shown in Fig. 3 in that the elimin~q~tion of power supply cable 20 results in significant cost savings and simplifies the alchil~tu~e.
While the architecture of Fig. 4 is an improvement on that of Fig. 3! it would be even more significant if the telephony signals and the video signals could becarried on a con~l-.on l[~ oll system thus eliminq~ing the duplication of fiber optic cables shown in both Fig. 3 and Fig. 4. By carrying the video and telephony signals IS over a common integral network transmission system however other issues are raised. Chief among these issues is a privacy issue. That is if the telephony and video signals were both sent to the subscriber premises 21 over the same line it may be possible for a subscriber to tap into the telephony signals of all neighbors co-~ne led to the coaxial cable bus. This would be done by tuning and demodulating from the myriad of carrier channels on the coaxial cable in the lel~bolly signalrange. It would be relatively easy for one minimqlly skilled in elecllullics to devise means which could tune in on these telephony channels carried in the sl,e~tlu~
This is possible be~use the other telephony signals in the example would also em~n~t~ from the remote optical node 17. With one coaxial cable system carrying all of these signals a subscriber is able to access the signals of these other subscribers.
Referring to Fig. 5, the preferred embodiment of a fiber/coax transport a~chile~ is shown in which the telephony and video signals are transported through 5 a common integral nelwolk. That is, central office 13 includes telephony switch 11 and video tr~ncmi~sion eyui~,mellt 12 as shown in Figs. 3 and 4. Alternative video suppliers 23 could supply video signals to video tr~n~mi.ssion equipment 12.
Telephony signals from switch 11 and from special services eyuip.llelll 33 are supplied to a digital conversion RF modulator/demodulator unit 34. The telepilony 10 signals must be modulated to be transported on the analog passband fiber optic cable 14. The video signals from video transmission equipment 12 are com~ined with thetelephony signals in a combiner ll~u~scei~er unit 35. These optical signals are sent (and received) on fiber optic cable 14 to/from an optical node 17 which includes an optical/electrical conversion unit as shown in Figs. 3 and 4. The remote digital15 terrninal 1~ as shown in Fig. 4 is elimin~t~ because the distribution function it performs is no longer neede(l. Power plant 32 is co-located with optical node 17.
By elimin~ion of remote digital terminal 18 and the associaled fibers in the main fiber optic cable, significant cost savings are achieved by this a,~:hil~tule over that shown in Fig. 4. It is the elimin~ion of remote digital terrninal 18 on the ONU 15 20 which ~ises the privacy issue. The combined telephony and video signals fr~m opffcal node 17 along with the power supply from power plant 32 are calTied on coaxial cable 24 to a selective delivery means which may include a Baseband Below Passband (BBP) device 37. Device 37 includes many of the functions performed by optical netwolk unit 15 in Figs. 3 and 4 with significant additions and modiflcations.
Telephony and video signals are supplied to telephone 27 and television 26 on subscriber premises 21 through a network interface 43.
Rer~ lling to Fig. 7, BBP unit 37 is shown in greater detail. BBP device 37 includes an interdiction device 16 also used for telephony, a modulator/demodulator S unit 39, and a power converter unit 41. Interdiction device 16 is a modification of the shndard inlGldiclion device known in the art and used in video networks. That is, a device such as an eight-port interdiction unit available from Scientific Atlanta Corporation (Model No. 9508-021) may be so modifed. The standard interdiction device uses a j~mming oscillator 49 to jam certain channels and transmit only those which are made available to the subs~;-il er. Alle~natively. a negative trap (consisting of band-stop filters) could be used in place of oscillator 49 as an interdiction device to ~ttenn~e the nondelivered channels below the noise floor. Interdiction device 16 is modified in the preferred embodiment by including isolation amplifiers 47 andforward coupler 48 in the ulJsll~nl direction of tr~ncmi~sion such that only thebaseband telephony signal to and from the subscriber to be served is available at a given subscriber location. That is, the standard interdiction device is modified so that all of the downstream telephony channels are interdicted and each upstream 5-30 MHz port is isolated. Thus, a subsc~iber is prevented from tuning into telephonecalls of other ;)llbsclil)cl~ on the nel~olk.
Referring to Figs. 5, 6, and 7, the privacy p,~ lion a~o-ded by the present invention is illustrated. Central office 13 sends video and telephony signals - "do~4.. sl,~", to subsc.il,e- s premises 21 and receives signals associated with video as well as telephony signals sent up~lr~ from subse,ibe, s premises 21. The al-;hit~:tu.~ is esse.ltially a "bus type architecture (see Fig. 2). Thus, absent any , p.~aulions, each subs~ er could monitor the video and/or telephony signals from other sul~5~ )el~i on the bus. For downstream video this is not a problem. The cable television co--~pany today uses this type of system and the only concelll is to interdict (jam or trap) selected premium channels which the subscriber has not paid for.
S However, if inle.a~;live video and/or telephony are added, privacy becomes i~npo- lant.
In order to ensure privacy in this type of network, in addition to inlerdiclion device 16 and modulator/demodulator device 39, additional protection is needed.
Unless modified, interdiction device 16 ensures that only selected dow~.sll~am video channels are delivered to subsc.iber premises 21. Modulator/demodulator device 39 10 ensures that only selected telephony channels are delivered to and from subscriber premises over the telephone line. However, for interactive video and To prevent the selective tuning to other subsclilJe-~ telephone clld ~nels through the illle/acli~e video line 24 conlle~led to F-ftting c~nlleclor 46. additional interdiction is needed. In the p-t;rt;ll~d embodiment, isolation arnplifier 47 and forward coupler 48 are added to a 15 modified jamming oscillator 49 in interdiction device 16.
Amplifier 47 and coupler 48 may optionally be combined with bandpass filters (not shown) as is known in the art to selectively transmit a subset of upstream signals.
As disl;uss~ above the 5-30 MHz bandwidth is used for telephone and interactive signals as;,ociated with video communications. There are three usable 6 MHz 20 chal~lels in this bandwidth from approximately 8-26 MHz. Since each 6 MHz channel can carry over 400 individual telephony channels, only two channels would generally be needed for telephony in the preferred embodiment. The other 6 MHz cl~ el is available for interactive control/request signals assocldled with video services. Amp 47 and coupler 48 (optionally with selective filters) selectively t~nsmit only the interactive signals associated with video channels in the upstream direction. All of the channels used for telephony are eliminated in the downstream direction by interdiction device 16. Thus, there is no way for any particular sul~sc~ibel- to listen to the telephony channels of another subscriber in either direction 5 of tr~n~mi.csion. Privacy is thus assured.
Referring to Figs. 5 and 6, modulator/demodulator device 39, which may be a cable telephony device such as "CablePhone~" which is commercially available from Jerrold, Inc., demodulates the telephony signal from coaxial cable 24 and may send the demodulated telephony signal through standard copper tip and ring wires 42 10 directly to telephone 27. Modulator/demodulator unit 39 also receives the baseband tcl~pllolly signals from telephone 27 in subscriber premises 21 and modulates that signal onto coaxial cable 24. Optionally, modulator/demodulator unit 39 could send the baseband telephony signal to combiner 44 to be combined with passband signals such as video onto coaxial cable 24. BBP device 37 also includes a power converter 41 which supplies -48 volt DC power, :~ 105 volt AC ringing power, and other converted power for the modulator/demodulator unit 39 to power the telephone 27 as in a standard telephony network.
Referring to Figs. 5, 6 and 7, telephone 27 and television 26 on subscriber premises 21 receive the video and telephony signals through a nelwûlk interface 43.
20 In the embodiment shown in Fig. 5, the video signals from interdiction device 16 and the lel~holly signals from modulator/demodulator device 39 are combined in a combiner unit 44 (Fig. 6) and tben sent over dual coaxial cable drops to a splitter.
Referring to Fig. 8, splittèr 36, 38 is contained in the network interface unit 43. That is, passive ele~;tlunics are also included in network interface 43. The network interface unit 43 includes a high pass filter 36 with DC blocking to provide RF
transparency for all passband frequencies and to block all telephony signals. A low pass filter 38 with DC transparency removes RF passband energy and passes all telephony signals. A twin carbon block pruleclur unit 50 is also included as is known 5 in the art. A standard RJ-l I telephony conlle~;tor 45, and an F-fitting conlleclor 46 which is standard in the video cable TV network are included. Because the conlle~;lors 45 and 46 are standard, the subscriber premises would not have to be rewired or locally powered to deliver services from this network. While the embodiment shown is the preferred embodiment, it is also possible to connect the 10 coaxial cable from modified interdiction device 16 directly to the network interface F-fitting 46 and the copper wire 42 from modulator/demodulator device 39 directly to the RJ-II conlleclor on network interface 43. In either event, the modulated tcl~hon.y signals which would otherwise be carried onto coaxial cable 24 along with the video signals are eliminated at interdiction device 16 such that only the 15 demodulated telephony signal from demodulator device 39 is available to a particular subscriber. Thus, any possibility of a subscriber eavesdropping on telephone calls from other subscribers is elimin~ed. If more than one coaxial cable bearing video services is supplied to network interface 43, a P-Intrinsic-Negative (PIN) diode switch or other devices known in the art, for example, could be used to allow the subsclil)er 20 to select which set of services he or she would prefer at any particular tirne.
The BBP unit 37 enables the network archilectu~e shown in Fig. 5 to provide the best features of the two basic wire line apprûaches tû residential access arul~ tur~ (baseband FTTC and passband cable television) and solves for the - s~ e problems ûf each approach at a cost significantly less than u~ili7ing both types of network as shown in Figs. 3 and 4. The network architecture disclosed in Fig. 5 provides a true broadband network that subsumes all existing services and all future services for tel~hony and video services at a cost substantially less than other types of hybAd networks.
Referring to Fig. 9, a more detailed description of the combiner 44 and splitter36, 38 is shown. As previously described, combiner 44 is contained in BBP unit 37.
Combiner 44 preferably includes commercially available L-Section f~ters 52 shownschematically. These filters are contained in RF-shielded enclosures 53 providing greater than 65 dB of isolation between each of coaxial cables 24 over the passband.
The splitter includes commercially available high pass filters 36 and low-pass flters 38 contained in n~twolk interface 43. As with the combiner. the filters are contained in RF-shielded enclosures 53 providing more than 65 dB of isolation between coaxcables 24 which are connected to F-ftting 46.
The present invention uses frequency division rather than Time Slot I1llel~;1lange (TSI) techniques to map the signals for tr~ncmi.csion. By so doing, the cost associated with TSI equipment and the nonenablement of certain functions such as monitoring signal degradation (C~C6) is removed. Although TSI could be employed in the network of the present invention, frequency assignment techniques are preferred because the signals are already in the fi~uencr domain for tr~ issiu.~. The present invention uses a linear ch~nnel whicll simull~.eously tl~ the signals parallel in time rather than in series in time. There is no mutual hllelrt;~e,lce among the simultaneously l-ans~n~ d signals in the linear challllel because they are tr~nsmitted at different frequencies.
R~relling to Fig. 10, frequency division signal tr~nsmi.s.sion is acco.l.~ulished by remotely setting the specific transmit and receive frequency pairs for each channel card 51 in BBP device 37. Thus, seg~galion of switched services and special services into respective portions of contiguous s~e~tllll-- is accomplished at the 5 location nearest the user of the services. At central office 13 the RF modulated channels are converted to/from 64 kilobit per second (64 Kb/s) channels that aregrouped logelller in blocks of 24, then formatted into a standard framed DSI signal for termination on the digital switch 11. DSI signals colnl~osed of only specialservices are routed to other terminal equipment, or tr~n.cmi.ccion equipment for10 carriage to other locations. Tbis approach allows the bulk conversion of groups of modulated carrier signals to/from DSI digital signals, obviating the need for either Time Slot Interchange or individual carrier frequency translation ahead of bulk A/D
conversion at central omce 13. Another advantage of the approach is having "universal" channel cards 51 within a given type of service that can be installed in 15 . any slot in any BBP device 37. Thus, spare/replacement inventories of each are kept to a minilnulll. The frequency pairs associated with each card are set and controlled remotely, prererably in central omce 13, such that the users may not alter the cards.
Each subscriber is assigned a unique transmit and receive rl~uellcy pair for tel~hony and special services. The assigned rl~ ;y pair is controlled from 20 central omce 13. Thus contiguous frequency ~ssi~nment to card 51 in BBP device 37 is achieved. This permits g~vu~Jhlg of nonswitched special services that will not terminate on the digital switch. Time slot hlle~hange seg-e~dtion of special andtelephony services at central office 13 is eliminated Since an optical node 19 could serve as many as 50 BBP curb devices 37, the rl~uel)cy division lechlli4ue allows . 21 73003 for assignnlent Or any available frequellcy pair to any service channel card 51 at tlle B13P device 37, regardless Or physic.ll location of the BBP device 37.
There are several signirlcallt bener;ts of the new BBP element. Tlle rlrst is the elimillation or the baseband fiber-to-tlle-curb (FI~C) portion of prevk~usly known 5 hybri(l networks. This is made possible by lhe incorporation of the telephony services in tlle passband portion of the network, greatly simplifyillg the overall complexity Or the outside plant portion of the architecture. The telephony services are provided by a cable telephony method wllicll employs signal modulatioll with some important difrerences. Since talk battery and ringing voltage are powered from the network, 10 local (inside home) powering problems are eliminated. sillce the passband freqllencies that carry telephony services are blocked beyond the selective delivery device, it is not possible to monitor other telepholle subscribers' communicatiolls from a given residence. Thus, the privacy issues associated with telephony services previously provided througll hybrid video-type networks are elimhlated.
While the invention has been disclosed Witll respect to a prererred embodimellt, changes and modifications may be made which are within the intended scope Or the invention as defined by lhe appended claims.
Thus, power supply cable 20 in Fig. 3 is elimin~te~l The eliminq~ion of power supply cable 20 I~,resenls a significant cost savings over the alcl~ urt; of Fig. 3. As with Fig. 3~ the video signals through coaxialcable 24 are supplied to customer premises 21 through interdiction unit 16 contained in optical network unit 15. Power is now supplied to telephone 27 from power supply 32 through coaxial cable 24 and ONU IS. Coaxial cable 24 from interdiction device 16 to ~;USlUlllel premises 21 supplies only video signals to television 26 and does not supply power. As with Fig. 3, a video set-top converter 25 may or may not be included in the system. Fig. 4 ~ sents a sub~lal,lial improvement over the n~lwo-k shown in Fig. 3 in that the elimin~q~tion of power supply cable 20 results in significant cost savings and simplifies the alchil~tu~e.
While the architecture of Fig. 4 is an improvement on that of Fig. 3! it would be even more significant if the telephony signals and the video signals could becarried on a con~l-.on l[~ oll system thus eliminq~ing the duplication of fiber optic cables shown in both Fig. 3 and Fig. 4. By carrying the video and telephony signals IS over a common integral network transmission system however other issues are raised. Chief among these issues is a privacy issue. That is if the telephony and video signals were both sent to the subscriber premises 21 over the same line it may be possible for a subscriber to tap into the telephony signals of all neighbors co-~ne led to the coaxial cable bus. This would be done by tuning and demodulating from the myriad of carrier channels on the coaxial cable in the lel~bolly signalrange. It would be relatively easy for one minimqlly skilled in elecllullics to devise means which could tune in on these telephony channels carried in the sl,e~tlu~
This is possible be~use the other telephony signals in the example would also em~n~t~ from the remote optical node 17. With one coaxial cable system carrying all of these signals a subscriber is able to access the signals of these other subscribers.
Referring to Fig. 5, the preferred embodiment of a fiber/coax transport a~chile~ is shown in which the telephony and video signals are transported through 5 a common integral nelwolk. That is, central office 13 includes telephony switch 11 and video tr~ncmi~sion eyui~,mellt 12 as shown in Figs. 3 and 4. Alternative video suppliers 23 could supply video signals to video tr~n~mi.ssion equipment 12.
Telephony signals from switch 11 and from special services eyuip.llelll 33 are supplied to a digital conversion RF modulator/demodulator unit 34. The telepilony 10 signals must be modulated to be transported on the analog passband fiber optic cable 14. The video signals from video transmission equipment 12 are com~ined with thetelephony signals in a combiner ll~u~scei~er unit 35. These optical signals are sent (and received) on fiber optic cable 14 to/from an optical node 17 which includes an optical/electrical conversion unit as shown in Figs. 3 and 4. The remote digital15 terrninal 1~ as shown in Fig. 4 is elimin~t~ because the distribution function it performs is no longer neede(l. Power plant 32 is co-located with optical node 17.
By elimin~ion of remote digital terminal 18 and the associaled fibers in the main fiber optic cable, significant cost savings are achieved by this a,~:hil~tule over that shown in Fig. 4. It is the elimin~ion of remote digital terrninal 18 on the ONU 15 20 which ~ises the privacy issue. The combined telephony and video signals fr~m opffcal node 17 along with the power supply from power plant 32 are calTied on coaxial cable 24 to a selective delivery means which may include a Baseband Below Passband (BBP) device 37. Device 37 includes many of the functions performed by optical netwolk unit 15 in Figs. 3 and 4 with significant additions and modiflcations.
Telephony and video signals are supplied to telephone 27 and television 26 on subscriber premises 21 through a network interface 43.
Rer~ lling to Fig. 7, BBP unit 37 is shown in greater detail. BBP device 37 includes an interdiction device 16 also used for telephony, a modulator/demodulator S unit 39, and a power converter unit 41. Interdiction device 16 is a modification of the shndard inlGldiclion device known in the art and used in video networks. That is, a device such as an eight-port interdiction unit available from Scientific Atlanta Corporation (Model No. 9508-021) may be so modifed. The standard interdiction device uses a j~mming oscillator 49 to jam certain channels and transmit only those which are made available to the subs~;-il er. Alle~natively. a negative trap (consisting of band-stop filters) could be used in place of oscillator 49 as an interdiction device to ~ttenn~e the nondelivered channels below the noise floor. Interdiction device 16 is modified in the preferred embodiment by including isolation amplifiers 47 andforward coupler 48 in the ulJsll~nl direction of tr~ncmi~sion such that only thebaseband telephony signal to and from the subscriber to be served is available at a given subscriber location. That is, the standard interdiction device is modified so that all of the downstream telephony channels are interdicted and each upstream 5-30 MHz port is isolated. Thus, a subsc~iber is prevented from tuning into telephonecalls of other ;)llbsclil)cl~ on the nel~olk.
Referring to Figs. 5, 6, and 7, the privacy p,~ lion a~o-ded by the present invention is illustrated. Central office 13 sends video and telephony signals - "do~4.. sl,~", to subsc.il,e- s premises 21 and receives signals associated with video as well as telephony signals sent up~lr~ from subse,ibe, s premises 21. The al-;hit~:tu.~ is esse.ltially a "bus type architecture (see Fig. 2). Thus, absent any , p.~aulions, each subs~ er could monitor the video and/or telephony signals from other sul~5~ )el~i on the bus. For downstream video this is not a problem. The cable television co--~pany today uses this type of system and the only concelll is to interdict (jam or trap) selected premium channels which the subscriber has not paid for.
S However, if inle.a~;live video and/or telephony are added, privacy becomes i~npo- lant.
In order to ensure privacy in this type of network, in addition to inlerdiclion device 16 and modulator/demodulator device 39, additional protection is needed.
Unless modified, interdiction device 16 ensures that only selected dow~.sll~am video channels are delivered to subsc.iber premises 21. Modulator/demodulator device 39 10 ensures that only selected telephony channels are delivered to and from subscriber premises over the telephone line. However, for interactive video and To prevent the selective tuning to other subsclilJe-~ telephone clld ~nels through the illle/acli~e video line 24 conlle~led to F-ftting c~nlleclor 46. additional interdiction is needed. In the p-t;rt;ll~d embodiment, isolation arnplifier 47 and forward coupler 48 are added to a 15 modified jamming oscillator 49 in interdiction device 16.
Amplifier 47 and coupler 48 may optionally be combined with bandpass filters (not shown) as is known in the art to selectively transmit a subset of upstream signals.
As disl;uss~ above the 5-30 MHz bandwidth is used for telephone and interactive signals as;,ociated with video communications. There are three usable 6 MHz 20 chal~lels in this bandwidth from approximately 8-26 MHz. Since each 6 MHz channel can carry over 400 individual telephony channels, only two channels would generally be needed for telephony in the preferred embodiment. The other 6 MHz cl~ el is available for interactive control/request signals assocldled with video services. Amp 47 and coupler 48 (optionally with selective filters) selectively t~nsmit only the interactive signals associated with video channels in the upstream direction. All of the channels used for telephony are eliminated in the downstream direction by interdiction device 16. Thus, there is no way for any particular sul~sc~ibel- to listen to the telephony channels of another subscriber in either direction 5 of tr~n~mi.csion. Privacy is thus assured.
Referring to Figs. 5 and 6, modulator/demodulator device 39, which may be a cable telephony device such as "CablePhone~" which is commercially available from Jerrold, Inc., demodulates the telephony signal from coaxial cable 24 and may send the demodulated telephony signal through standard copper tip and ring wires 42 10 directly to telephone 27. Modulator/demodulator unit 39 also receives the baseband tcl~pllolly signals from telephone 27 in subscriber premises 21 and modulates that signal onto coaxial cable 24. Optionally, modulator/demodulator unit 39 could send the baseband telephony signal to combiner 44 to be combined with passband signals such as video onto coaxial cable 24. BBP device 37 also includes a power converter 41 which supplies -48 volt DC power, :~ 105 volt AC ringing power, and other converted power for the modulator/demodulator unit 39 to power the telephone 27 as in a standard telephony network.
Referring to Figs. 5, 6 and 7, telephone 27 and television 26 on subscriber premises 21 receive the video and telephony signals through a nelwûlk interface 43.
20 In the embodiment shown in Fig. 5, the video signals from interdiction device 16 and the lel~holly signals from modulator/demodulator device 39 are combined in a combiner unit 44 (Fig. 6) and tben sent over dual coaxial cable drops to a splitter.
Referring to Fig. 8, splittèr 36, 38 is contained in the network interface unit 43. That is, passive ele~;tlunics are also included in network interface 43. The network interface unit 43 includes a high pass filter 36 with DC blocking to provide RF
transparency for all passband frequencies and to block all telephony signals. A low pass filter 38 with DC transparency removes RF passband energy and passes all telephony signals. A twin carbon block pruleclur unit 50 is also included as is known 5 in the art. A standard RJ-l I telephony conlle~;tor 45, and an F-fitting conlleclor 46 which is standard in the video cable TV network are included. Because the conlle~;lors 45 and 46 are standard, the subscriber premises would not have to be rewired or locally powered to deliver services from this network. While the embodiment shown is the preferred embodiment, it is also possible to connect the 10 coaxial cable from modified interdiction device 16 directly to the network interface F-fitting 46 and the copper wire 42 from modulator/demodulator device 39 directly to the RJ-II conlleclor on network interface 43. In either event, the modulated tcl~hon.y signals which would otherwise be carried onto coaxial cable 24 along with the video signals are eliminated at interdiction device 16 such that only the 15 demodulated telephony signal from demodulator device 39 is available to a particular subscriber. Thus, any possibility of a subscriber eavesdropping on telephone calls from other subscribers is elimin~ed. If more than one coaxial cable bearing video services is supplied to network interface 43, a P-Intrinsic-Negative (PIN) diode switch or other devices known in the art, for example, could be used to allow the subsclil)er 20 to select which set of services he or she would prefer at any particular tirne.
The BBP unit 37 enables the network archilectu~e shown in Fig. 5 to provide the best features of the two basic wire line apprûaches tû residential access arul~ tur~ (baseband FTTC and passband cable television) and solves for the - s~ e problems ûf each approach at a cost significantly less than u~ili7ing both types of network as shown in Figs. 3 and 4. The network architecture disclosed in Fig. 5 provides a true broadband network that subsumes all existing services and all future services for tel~hony and video services at a cost substantially less than other types of hybAd networks.
Referring to Fig. 9, a more detailed description of the combiner 44 and splitter36, 38 is shown. As previously described, combiner 44 is contained in BBP unit 37.
Combiner 44 preferably includes commercially available L-Section f~ters 52 shownschematically. These filters are contained in RF-shielded enclosures 53 providing greater than 65 dB of isolation between each of coaxial cables 24 over the passband.
The splitter includes commercially available high pass filters 36 and low-pass flters 38 contained in n~twolk interface 43. As with the combiner. the filters are contained in RF-shielded enclosures 53 providing more than 65 dB of isolation between coaxcables 24 which are connected to F-ftting 46.
The present invention uses frequency division rather than Time Slot I1llel~;1lange (TSI) techniques to map the signals for tr~ncmi.csion. By so doing, the cost associated with TSI equipment and the nonenablement of certain functions such as monitoring signal degradation (C~C6) is removed. Although TSI could be employed in the network of the present invention, frequency assignment techniques are preferred because the signals are already in the fi~uencr domain for tr~ issiu.~. The present invention uses a linear ch~nnel whicll simull~.eously tl~ the signals parallel in time rather than in series in time. There is no mutual hllelrt;~e,lce among the simultaneously l-ans~n~ d signals in the linear challllel because they are tr~nsmitted at different frequencies.
R~relling to Fig. 10, frequency division signal tr~nsmi.s.sion is acco.l.~ulished by remotely setting the specific transmit and receive frequency pairs for each channel card 51 in BBP device 37. Thus, seg~galion of switched services and special services into respective portions of contiguous s~e~tllll-- is accomplished at the 5 location nearest the user of the services. At central office 13 the RF modulated channels are converted to/from 64 kilobit per second (64 Kb/s) channels that aregrouped logelller in blocks of 24, then formatted into a standard framed DSI signal for termination on the digital switch 11. DSI signals colnl~osed of only specialservices are routed to other terminal equipment, or tr~n.cmi.ccion equipment for10 carriage to other locations. Tbis approach allows the bulk conversion of groups of modulated carrier signals to/from DSI digital signals, obviating the need for either Time Slot Interchange or individual carrier frequency translation ahead of bulk A/D
conversion at central omce 13. Another advantage of the approach is having "universal" channel cards 51 within a given type of service that can be installed in 15 . any slot in any BBP device 37. Thus, spare/replacement inventories of each are kept to a minilnulll. The frequency pairs associated with each card are set and controlled remotely, prererably in central omce 13, such that the users may not alter the cards.
Each subscriber is assigned a unique transmit and receive rl~uellcy pair for tel~hony and special services. The assigned rl~ ;y pair is controlled from 20 central omce 13. Thus contiguous frequency ~ssi~nment to card 51 in BBP device 37 is achieved. This permits g~vu~Jhlg of nonswitched special services that will not terminate on the digital switch. Time slot hlle~hange seg-e~dtion of special andtelephony services at central office 13 is eliminated Since an optical node 19 could serve as many as 50 BBP curb devices 37, the rl~uel)cy division lechlli4ue allows . 21 73003 for assignnlent Or any available frequellcy pair to any service channel card 51 at tlle B13P device 37, regardless Or physic.ll location of the BBP device 37.
There are several signirlcallt bener;ts of the new BBP element. Tlle rlrst is the elimillation or the baseband fiber-to-tlle-curb (FI~C) portion of prevk~usly known 5 hybri(l networks. This is made possible by lhe incorporation of the telephony services in tlle passband portion of the network, greatly simplifyillg the overall complexity Or the outside plant portion of the architecture. The telephony services are provided by a cable telephony method wllicll employs signal modulatioll with some important difrerences. Since talk battery and ringing voltage are powered from the network, 10 local (inside home) powering problems are eliminated. sillce the passband freqllencies that carry telephony services are blocked beyond the selective delivery device, it is not possible to monitor other telepholle subscribers' communicatiolls from a given residence. Thus, the privacy issues associated with telephony services previously provided througll hybrid video-type networks are elimhlated.
While the invention has been disclosed Witll respect to a prererred embodimellt, changes and modifications may be made which are within the intended scope Or the invention as defined by lhe appended claims.
Claims (4)
1. A system for providing telephony services to a subscriber location comprising:
a network including a fiber optic system and a coaxial cable system connected to said fiber optic system;
means, operatively associaed with said network, for selectively delivering secured telephony signals to and from said subscriber location; and means, operatively associated with said coaxial cable system, for supplying power to a subscriber telephone through said coaxial cable system.
a network including a fiber optic system and a coaxial cable system connected to said fiber optic system;
means, operatively associaed with said network, for selectively delivering secured telephony signals to and from said subscriber location; and means, operatively associated with said coaxial cable system, for supplying power to a subscriber telephone through said coaxial cable system.
2. A method for supplying telephony services to a subscriber location comprising:
transporting telephony signals over a network including a coaxial cable system;
selectively transmitting said telephony signals on said coaxial cable system; and supplying power to a telephone at said subscriber location through said coaxial cable system;
whereby said signals are selectively transmitted to and from said subscriber location such that said signals are secured and cannot be monitored from other subscriber locations.
transporting telephony signals over a network including a coaxial cable system;
selectively transmitting said telephony signals on said coaxial cable system; and supplying power to a telephone at said subscriber location through said coaxial cable system;
whereby said signals are selectively transmitted to and from said subscriber location such that said signals are secured and cannot be monitored from other subscriber locations.
3. A system for providing video and telephony services to a subscriber comprising:
means for providing modulated telephony signals to and from a combined network transmission system, said combined network transmission system including a fiber optic transmission system and a network coaxial cable system;
means, operatively associated with said combined network transmission system, for supplying video signals on said combined network transmission system;
means, operatively. associated width said fiber optic transmission system, for converting said telephony and video optical signals on said fiber optic transmission system to telephony electrical signals and video electrical signals on said network coaxial cable system, and for simultaneously converting said video and said telephony electrical signals on said network coaxial cable system to video and telephony optical signals on said fiber optic transmission system;
means, operatively associated with said combined network transmission system, for selectively delivering said video signals;
means, operatively associated with said network coaxial cable system for providing demodulated telephony signals;
means, operatively associated with said selectively delivering means and said providing means, for combining said selectively delivered video signals and said demodulated telephony signals onto a coaxial cable system of said subscriber;
means, operatively associated with said subscriber coaxial cable system for separating said demodulated telephony signals from said selectively delivered video signals;
means, operatively associated with said network coaxial cable system for furnishing power; and means, operatively associated with said network coaxial cable system for transforming said power.
means for providing modulated telephony signals to and from a combined network transmission system, said combined network transmission system including a fiber optic transmission system and a network coaxial cable system;
means, operatively associated with said combined network transmission system, for supplying video signals on said combined network transmission system;
means, operatively. associated width said fiber optic transmission system, for converting said telephony and video optical signals on said fiber optic transmission system to telephony electrical signals and video electrical signals on said network coaxial cable system, and for simultaneously converting said video and said telephony electrical signals on said network coaxial cable system to video and telephony optical signals on said fiber optic transmission system;
means, operatively associated with said combined network transmission system, for selectively delivering said video signals;
means, operatively associated with said network coaxial cable system for providing demodulated telephony signals;
means, operatively associated with said selectively delivering means and said providing means, for combining said selectively delivered video signals and said demodulated telephony signals onto a coaxial cable system of said subscriber;
means, operatively associated with said subscriber coaxial cable system for separating said demodulated telephony signals from said selectively delivered video signals;
means, operatively associated with said network coaxial cable system for furnishing power; and means, operatively associated with said network coaxial cable system for transforming said power.
4. A video and telephony netwolk including a plurality of telephones operatively connected thereto comprising:
a fiber optic transmission system;
a coaxial cable transmission system connected to said fiber optic transmission system;
a telephone switching system associated with said fiber optic transmision system;
a video provisioning system associated with said fiber optic transmission system;
an interdiction unit operatively associated with said coaxial cable system;
a modulator/demodulator operatively associated with said coaxial cable system;
whereby telephony signals and video signals on said coaxial cable system are interdicted such that only selected telephony signals are transmitted to and from said telephones;
said network further comprising:
means, operatively associated with said coaxial cable system, for combining an interdicted video signal and a demodulated telephony signal on a subscriber coaxial cable system;
means, operatively associated with said subscriber coaxial cable system, for separating said interdicted video signal from said demodulated telephony signal; and means, operatively associated with said coaxial cable system, for supplying power to said telephones.
a fiber optic transmission system;
a coaxial cable transmission system connected to said fiber optic transmission system;
a telephone switching system associated with said fiber optic transmision system;
a video provisioning system associated with said fiber optic transmission system;
an interdiction unit operatively associated with said coaxial cable system;
a modulator/demodulator operatively associated with said coaxial cable system;
whereby telephony signals and video signals on said coaxial cable system are interdicted such that only selected telephony signals are transmitted to and from said telephones;
said network further comprising:
means, operatively associated with said coaxial cable system, for combining an interdicted video signal and a demodulated telephony signal on a subscriber coaxial cable system;
means, operatively associated with said subscriber coaxial cable system, for separating said interdicted video signal from said demodulated telephony signal; and means, operatively associated with said coaxial cable system, for supplying power to said telephones.
Applications Claiming Priority (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US6922793A | 1993-05-28 | 1993-05-28 | |
| US6923393A | 1993-05-28 | 1993-05-28 | |
| US08/068,455 US5440335A (en) | 1993-05-28 | 1993-05-28 | Method and apparatus for delivering passband and telephony signals in a coaxial cable network |
| US069,233 | 1993-05-28 | ||
| US068,455 | 1993-05-28 | ||
| US069,227 | 1993-05-28 | ||
| CA002141323A CA2141323A1 (en) | 1993-05-28 | 1994-05-26 | Method and apparatus for delivering secured telephony service in a hybrid coaxial cable network |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002141323A Division CA2141323A1 (en) | 1993-05-28 | 1994-05-26 | Method and apparatus for delivering secured telephony service in a hybrid coaxial cable network |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2173003A1 true CA2173003A1 (en) | 1994-11-29 |
Family
ID=27427200
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002173003A Abandoned CA2173003A1 (en) | 1993-05-28 | 1994-05-26 | Method and apparatus for delivering secured telephony service to a hybrid coaxial cable network |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2173003A1 (en) |
-
1994
- 1994-05-26 CA CA002173003A patent/CA2173003A1/en not_active Abandoned
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