Cable Access Beyond the Hype on Residential Broadband Data Services Over Hfc Networks

8/10/2019 Cable Access Beyond the Hype on Residential Broadband Data Services Over Hfc Networks

http://slidepdf.com/reader/full/cable-access-beyond-the-hype-on-residential-broadband-data-services-over-hfc 1/8



IEE E Communications Magazine • November 1996 129

newer, faster, and cheaper alternatives for providing high-speed communications to the millions of residential and smallbusiness customers. Currently, there are three possible trans-port means that can be used to bring high-speed connectivityto customers:• Digital telephone lines• Cable TV (CaTV) systems• Aerial transmission systems

The first alternative takes advantage of the existing point-to-point telephone service, while the other two take ad vantageof broadcast systems for distributing TV programming.

H ighly sophisticated interactive broadba nd services requirethe use of a return path , or upstream channel , for transmissionsfrom a customer s ite. Of the three a lternat ives, the aeria ltransmission systems can currently be used only in a hybrid mode where the return path is based on the use of a voice-grade mod em. Hence, this solution can only be tempora ry andaddresses only a limited spectrum of broadband applications,due to the limitations of the return path and the added com-plexity in system o perat io n, s ince the high-speed servicep r o vider w o u ld h a v e t o u s e , m a n a ge a n d a s so c i a t e da t as t reams tha t a re concurrent ly t r anspor ted over d i f ferentmedia.

Among the remaining two alternatives, digital telephone

service has been evolving for over a decade. The most widelyavailable offering, in relative terms, is the integrated servicesdigital network (ISDN) basic rate service that can provide upto 128 kb/s over current ly deployed unshielded t wisted pa ir(U TP) copper cabling. Technical and logistical prob lems haveprevented this service from becoming as widespread as origi-nally ho ped. E ven if these pro blems ar e resolved, 128 kb/s areno longer sufficient for a full range of broadband services.Thus, telephone operators a re testing new a symmetric com-munication t echnologies that will allow for hundreds of kilo-bits per second transmission speeds on the return path, andseveral mega bits per second speeds on the forward path , ordownstream channel . H owever, we do not envision that t hesesolutions will be mass-marketed to residential customers anytime soon. The technology has not yet sufficiently mat ured

and t he equipment is still too expensive to be a fforda ble toresidential customers.

As CaTV operato rs pursue their quest to increase theirrevenues, they have found tha t their C aTV plants can provideunsurpassed a ggregate band width that can be used for veryhigh-speed data communicat ions . Hence, for the la s t few years, as part of t heir system maintenance and upgrade, theyhave s tarted provis ioning their infras tructure for two-waycommunications. Today about 25 percent of the CaTV sys-tems in the U nited St at es, where Ca TV passes over 90 per-cent of the residences, is two-way-capable, and the rate ofupgrading is rapidly increasing. Two-way-communications-capable Ca TV systems will provide speeds of several t ens ofmegabits per second on the downstream and several megabitsper second on the upstream. At such high speeds, CaTV sys-

tems will be the only systems that can provide a full range ofbroadband services in an integrated manner to residential cus-tomers for the foreseeable future.

With the possibility of high-speed access to residences, theexpectation rises that the C aTV data ca pability, or for tha tmatter even digital telephone data capability, will immediatelyactivate all the desired broadband services, such as the onesmentioned previously, to the home. As we argue lat er in thearticle, this will not be possible overnight. High-speed connec-tivity to the home is merely an enabling technology. It is ahigh-speed communications solution tha t governs only thelast-mile distribution network, sometimes referred to as theaccess network . B ringing a sophisticated broadba nd applica-

tion to the ho me requires an end-to-end solution, one thatincludes the service provider and his equipment, the to talityof intermediate communication networks and their capabili-ties, the access network, and finally the customer home eq uip-ment.

This article is organized as follows. In the following sec-tion, we provide a short overview and a comparison of theCa TV-based and telephony-based last-mile a ccess networks.We then present the spectrum of applications enabled by thehigh-speed CaTV network environment and provide a com-prehensive classification ba sed on the netwo rk characteristics.The req uirements for an end-to-end broadba nd service aredescribed, and it is argued that, in addition to the access net-

work, several a dditional elements are req uired to implementcomplete end-to-end services. We discuss the current situationand d escribe a migration path for delivering the desired ser-vices, that is, the route C aTV operators should follow in orderto provide and guarantee the whole range of broadband ser-vices that C aTV can enable.

THE LAST-M ILE ACCESS NETWORKS

C ustomers are not directly connected to high-speed back-bone networks, but ra ther to “ local” access networks,

which are then connected to regional networks, which arethen connected to national backbone networks. This hierar-chical structure allows for better management of the overallcommunication network, and decreases its operating cost.

Current telephone a ccess networks have a low data speedcapacity (e.g., 28.8 kb/s); hence, t hey present a n ob stacle todelivering high-bandwidth broadband services to customers.

In order to remove this obstacle, better and more efficientaccess networks and technologies need to be introduced. Inthis section, we will describe two such alternatives, one basedon the CaTV distribution network, which is the main focus ofthis article, and one based o n the introduction of digital tele-phone lines.

THE CATV DISTRIBUTION NETWORK

Cable TV was first introduced in the late ‘40s for distributingover-the-air TV broadcasts to (cable) subscribers located toofar from TV stations to receive their transmissions with regu-lar TV antennas. For that reason, CaTV, or CATV, used to

stand for community aerial TV. With the passage of t ime,CaTV penetrated many residential neighborhoods that didnot necessarily have any problem in receiving regular pro-grams over the air. In these neighborhoods, Ca TV broughtbetter picture quality and, more important , a wider selectionof TV channels, some of them not even available over the air.Approximately 60–70 channels can be carried by conventional(analog) C aTV plants.

Historically, CaTV networks were developed as one-waybroadcast systems using the network topology best suited forthis service, the t ree to pology shown in Fig. 1. The systemconsists of a head -end (H /E) station t hat collects the TV pro-grams, usually through satell i te downlinks, and then dis-

Figure 1. A coaxial CaTV network.



IEE E Communications Magazine • November 1996130

tributes them over coaxial cables along t he branches of a tree-like network to customer sites, which are located at the leavesof the tree. The distance between the H/E and a remote cus-tomer can be several tens of kilometers. Hence, to compen-sate for signal att enuation and maintain a good signal quality,

there a re several one-way analog amplifiers (as many a s 30)along the cable fro m the H /E to a customer.

To increase system capacity, reliability, picture quality, andresistance to noise interference, and to decrease maintenancecosts, during the last few years and at an ever-increasing rate,Ca TV o perators have been replacing large sections of t heirall-coaxial plans with fiber. The resulting network is called,appropriately, a hybrid fiber coaxial (HF C) netwo rk.

The CaTV HFC Access Netw ork — In an H FC network, themain coaxial “ tree trunk” from the H /E t o the outskirts of acommunity, spanning on the order of 1000 homes, is replacedwith high-reliability, low-attenuation fiber. This implies that alarge number of the a nalog amplif iers a long the long treetrunk are not needed any more. Hence, the reliability of the

system increases and the quality of the signal improves, sincethere exist fewer active components between the origin (H /E)and the destination (customer site) of the TV signal.

With the introduction of a “cleaner,” more efficient com-munication path also comes the potential for providing two-way dat a services over the H FC network. In order to providethese services, C aTV opera tors need to not o nly upgrade theirnetworks to HF C, but to replace their one-way amplifiers withtwo-way amplifiers to a llow upstream tra nsmissions from acustomer t o the H /E. Although this can happen d uring theinstallation of the fiber for those amplifiers located on it , itmay take some extra time to replace the ones located withinthe customer coaxial neighborhood . Figure 2 shows a two -way-capable HFC network. The fi ber nodes at the boundariesof the fiber and coa xial plant regions convert light to electrical

signals for downstream tra nsmissions (i.e., from t he H /E t osubscribers) and vice versa for the upstream transmissions.Of the bandwidth available today on an HFC network (750

MH z; it will be 1 G H z in future systems), the range between 5MH z and 42 MHz w ill be used fo r upstream t ransmissions,with the range of 54 MH z and a bove for downstream trans-missions. To guarantee compatibility with current systems, thef req uency spect rum between 54 MH z and 450 MHz w i l lremain undisturbed to ca rry current analog a nd digital trans-missions, while the frequencies above 450 MHz will be used toprovide enhanced switched or broadcast data services. Thesefrequency allocations are illustrated in Fig. 3.

B oth the upstream and d ownstream spectra will not be

available all a t once for transmission or reception. Instead,per I EE E 802.14 [6], the upstream spectrum will be dividedinto channels from a f ew hundred kilohertz to approxi-mately 1 MHz wide, while the downstream will be divided into6-MHz channels. With appropriate modulation techniques,tra nsmission rate s of abo ut 2–3 Mb/s are possible perupstream channel, using quaternary phase shift keying(QPSK) modulation, while transmission rates of about 30 Mb/sare possible per dow nstream channel, using 64-qua drat ureamplitude modulation (QAM). H igher speeds are achiev-able with more a dvanced modulation techniques.

Similar to the need for a voice-grade modem for datatran smissions over regular telephone lines, one need s touse a cable modem to t ra nsmit and receive digita l dataover an H FC ne twork. U nderscoring the ever-increasingdesire for H FC-based data services, a recent industry studyprojects an explosive increase of the cable modem marketat about 100 percent or more growth per year for the nextfew years [7].In ord er to achieve the widespread a cceptance enjoyed by

voice-grade mod ems, cable modems and the H FC networkson which they operate must be standa rdized. In other words,the communicat ion protocols that govern the modulat iontechniques, transmission ra tes, sharing of the H FC network

resources, management of the network, and so on must bewell defined so that third-party cable modem manufacturerscan build them and be assured that the modems will operateon a ny (s tandard-compliant) two-way HFC network. Stan-dardization will lower the cost of cable modems to the con-sumers, but, most important, will guarantee interoperability ofthe modems purchased from one’s local electronics store. Itwould be extremely annoying, to say the least, if consumershave to buy new cable mod ems every time they move into new residences served by different cable operators.

The IE EE 802.14 working group (WG ) is working towardsthe development of physical (PH Y) and med ium access con-trol (MAC) layer communication protocols for HFC networks[6, 8].1 It is expected that the first dra ft of the IE EE 802.14standard will be available before the end of this year, with the

basic standard ization process being completed during the firsthalf of 1997.

THE DIGITAL SUBSCRIBER LINE ACCESS NETWORK

The only truly currently available means for two-way commu-nication to the home is via the analog plain old telephone ser-v ice (P OTS). I t s ma in advant age is tha t i t i s prac t ica l lygloba l ly ava i lable , a l low ing anybody wi th a vo ice-grad emodem to (theoretically) exchange digital data with any othervoice-grade modem in the world. POTS systems, though, pro-vide low-band width connection s, currently up t o 28.8 kb/s, andtheore tically no more tha n 34 kb/s.

It is possible to provide higher transmission speeds overcopper telephone lines by removing the 4-kHz bandwidthrestriction historically imposed to facilitate analog voice com-

munications. Telephone operators have been pursuing thisdirection for the last few yea rs through the introduction ofvarious digital subscriber line (D SL) solutions which allow digita l data t ransmission to/from the customer termina l equip-ment (telephones, computers, etc.).

The best known and most available DSL solution is theISD N service, which can transmit digital data over UTP tele-phone wires o n two 64 kb/s channels, called the B channels,and one 16 kb/s signaling cha nnel, called t he D chann el, infull duplex mode. The two B channels can be used inde pen-

Figu re 2. A two-way-capable CaTV HFC ( access) network .

1 The IEEE 802.14 WG mai ntains a Web page at http://www.walking-

dog.com/catv.html.




dently for voice and/or da ta transmis-sion or can be combined into a single128 kb/s da ta channel.

ISD N offerings are over a decadeold, and they were initially availableto a l imite d number of businesses .Lately, many local exchange carriershave started providing ISD N servicesto res ident ia l cus tomers as wel l .D espite its a pparent superiority overanalog d ata connections, ISD N is not as widespread a s expect-ed due to several technical and logistical problems. A signifi-cant problem is that I SD N cannot co-exist on t he same wireswith analog PO TS: one needs separate l ines for ISD N andPO TS to provide a “ live” PO TS service in case of power f ail-ure. This may lead to installation of a dditional telephone linesin homes; this , in conjunct ion with the l imited number oftechnicians and customer service representa tives awa re ofISDN installations, may lead to a long delay to obtain the ser-vice after one req uests it. Furthermore, the customer needs toserve as his/her own system integra tor a nd proper ly configurethe connection bet ween his/her computer, the IS D N modem ,and the I SD N jack on the wall. Another problem is the cost:an I SD N mode m may cost a nywhere between $300 and $500

[9], well above the cost of regular analog line modems. Pricingpolicies are a n add itional problem, since they are regulated bygovernment directives. In its simplest fo rm, is an I SD N con-nection equivalent to one or two a nalog connections? Cur-rently, different telephone operators use different chargingphilosophies. In a more complicated form, are the chargesgoing to be the same as telephone charges or not?

A significant impediment to the successful deployment ofISD N is its chara cteristic as an end -to-end solution; tha t is, tobenefit from ISD N, both communicating parties and the net-work between must support ISDN.2 ISDN support by the net-work is not as widespread as desired, because upgrading thewhole system to support ISD N connections over the long peri-ods of t ime for which a customer may want to remain con-nected (e .g . , t o an on- l ine da t a serv ice or to h is o f f ice

computer) is extremely expensive to the telephone operator.The telephone system to day ha s been designed around thethree-minute telephone call length. D ata service connectionscan easily run for several hours, thus putting major stress onthe telephone system.

B ecause of the problems mentioned, ISD N services arecurrent ly provided only to a sma ll number of customers ,although this number is constantly increasing. Moreover, theavailability of multimedia applications and digitized videorequiring bandwidth on the order of megabits per second sug-gests that ISD N speeds will not be sufficient for high-speedbroadba nd services to the home.

To address this problem, a new generation of DSL is beingdeveloped, asymmetric DSL (ADSL). Depending on the dis-tance of a customer from the telephone center, speeds from

appro ximately 1.5 Mb/s (with a l ine lengt h of 540 m) toappr oximat ely 9 Mb/s (with a lin e lengt h of 270 m) a re possi-ble fo r “ do wnstre am” tra nsmissions, and 16 kb/s to 640 kb/sfor “ upst ream” t ransmissions. I t i s mpor t an t to note tha tAD SL service can co-exist with P OTS on the same wires, withPOTS service available even when the ADSL modem doesnot operate. D ue to these characteristics, ADSL is a promis-ing high-speed telephone solution, but it is still an immatureand e xpensive technology; AD SL eq uipment is quite expen-

sive, with AD SL mode ms costing at least $1000 each [10]. Inaddition, the charging policies are still an open issue.

Even highe r speeds are possible with very high-speedAD SL (VD SL), bu t , l ike AD SL, th is is s t i ll a t echnologyunder development that cannot easily be marketed to residen-tial users any time soon.

For a n excellent overview of D SL technologies, see [11].

REMARKS

We believe that HFC-based services will cost less than corre-sponding services provided over telephone connections. Thisis because CaTV technology is naturally a share d-mediumtechnology, implying that equipment a t the H /E can be mo reefficiently used by customers. The tree-and-branch topology

of the C aTV system allows for the aggregation of a ll the traf-fic generated by and directed to its customers, who then canbenefit from the same economy of scale that large institutionshave long enjoyed when it comes to da ta networking.

On the o ther hand, telephone connections are point-to-point, which requires equipment to be practically dedicated toeach subscriber. This increases the cost and complexity of pro-viding high-speed services to large co mmunities of residentia lcustomers. A case study has shown that the shared-resourcesapproa ch of Ca TV results in tremendous cost savings overpoint-to-point ISD N connections per normalized peak band-width [12].

Moreover, with the HF C shared-medium approach, it ispossible to be continuously on-line, 24 hours a day, 7 days aweek, without wa sting any network resources, using them only

during periods when one actively receives or transmits infor-mation over the network. With dial-up telephone connections,this cannot easily be done. It will be too costly for a customerto be continuously on-line, and it w ill be too costly for thetelephone operators to engineer the network to operate oversuch long connection times per subscriber.

Also, the H FC technology can be gracefully upgraded toprovide even higher ba ndwidth per customer without req uir-ing any change in the customer’s equipment. This can be doneby placing the fiber no des closer and closer to residences, giv-ing rise to fiber to the neighborhood and fi ber to the curb archi-tectures. C ommunities as small a s 10–20 homes can t hus beserviced from each individual fiber node.

Based on the above, although we believe data services toresidential customers will be a vailable via telephone connec-

tions, we do not believe they will represent the bulk of digitalt ransport mechanisms for many years to come. D ue to t helower da ta speeds achievable on them, logistical constraints,and regulatory o bstacles, any da ta offerings over telephonelines appear to be tempora ry solutions, only to b e surpassedby Ca TV of ferings, at least in regions CaTV has penetrated.

APPLICATIONS

I t has become clear that HFC networks with support for digi-tal data transmission provide the only competitive alterna-

tive to telephone networks for communication to the home.H ybrid solutions for the d ownlink, using, for example, over-

Figure 3. Upstream and downstream transmission regions in a two-way HFC network.

2 Moreover, the two par ties must comply to the same standards; for exam-

ple, voice analog-to-digital ( A/D ) encoding in North America is different

from that in Europe!




the-air transmissions such as satellite and microwave, willsoon experience bottlenecks due to the limited voice-gradetelephone connections for the return path.

The main cha racteristic of HF C networks, which differenti-ates them and makes them more attractive than the alterna-tives, is their a bility to provide full-duplex connections withhigher bandwid th to t he home (end user). As such, they canprovide improved services to the end user; especially in com-parison with telephone networks, they provide a dvantages due

to their broadcast nature as well.The netwo rk infrastructure, such as the cable network, is

only one of the significant elements necessary to provide anend-to-end service. There a re o ther req uirements as well(powerful servers, management systems, etc.). In t he follow-ing, we describe several a pplications which are enabled b yHFC networks, assuming that all the remaining service ele-ments are in place. Such applications can be classified in sev-eral wa ys. We consider the more significant para meters ofcable networks for a comprehensive classification:• The existence o f three di f ferent st reams : one dig it a l

upstream and two downstream, one for digital and onefor a nalog tra nsmission

• The broadcast nature of the transmission medium

These characteristics enable a wide spectrum of applica-tions ranging from traditional and conventional television ser-vices to intera ctive multimedia applications. Sophisticatedinteractive applications can be realized due to the ability totransmit audio and video digitally in addition to data. Further-more, in our classification we take into account the real-timeor non-real-time nature of an a pplication.

The classification of the most popular (expected) applica-tions enabled in an H FC environment is shown in Table 1,where the rows of the t able correspond to a ll possible media(data, audio, and video) transmitted over the digital upstreamconnections, while the co lumns represent a ll possible mediadownstream tra nsmissions in either digital or ana log form.

Ea ch cell in the ta ble represents a class of appli-ca t ions which combine the correspondingupstream and downstream transmissions; that is,the entry with data upstream transmission andanalog downstream transmission corresponds toapplications where the client transmits data tothe H /E (e.g. , a m ovie req uest), and the H /Etransmits the movie on one of t he analog chan-nels, such as in a pay-per-view application.

Clearly, ea ch class can include several applica-tions, which can be classified in ca tegories usingthe two remaining parameters: broadcasting andreal-time transmission . B ased on these criteria ,four different categories of applications emergebased on the broa dcasting (or non-broadcasting)and real-time (or non-real-time) nature of theapplication. As the table indicates, there existclasses, and categories within classes, where nomeaningful applications exist (or, at lea st, are notcurrently foreseeable).

NON-REAL-TIME APPLICATIONS

A large set of non-real-time applications can berealized over HFC networks. Assuming a dat a

upstream conne ction fro m the user to the H /E,for example, one can envision applications wherevar ious media a r e del ivered to the end-userthrough the do wnstream connection.

Ful l-duplex dig i t a l da t a communica t ionbetween the user and the H/E allows access to all

resources available through the global network. Internetaccess is probably the most important application — the usercan access all available resources on the I nternet a nd use itsservices. This, in add ition to access to o ther net works, willenable end users to request data on demand, ranging frombrowsing shopping catalogs a nd thea ter schedules to news,weather forecasts, and banking. Currently, this class of appli-cations is the most expected, beca use it will capitalize on avast amount of already available information content. Exam-

ples of this application class include the following:Remote educati on , which ba sically consists of tapping into

the vast resources available on digital libraries aroundthe world that contain multimedia information and tuto-rial presentations on a vast array of topics. The popularWeb surf ing can be considered as a form of remote learn-ing, if there exists a pa rticular ed ucational ob jective forthe search, or a form of entertainment otherwise.

Home office , where a person’s office is their own home, a ndbusiness is conducted entirely from home, and connec-tion to clients is made through telephones and computers.

Electronic commerce , which represents a vast array of mon-etary and, in general, financial transactions that can takeplace electronica lly via interco nnected co mputers. Thevirtual mall and remote shoppi ng are simple examples of

electronic commerce, where people can (Web) browsethrough the pages of e-mail cata logs, request ad ditionalinformation for selected items, and purchase them on-line. Clearly, in parallel to interactive applications, non-interactive versions of them will also be available, whereusers will request and download data on demand for sub-sequent browsing, study, or use: catalogs, news, books,announcements, software delivery, catalog ordering, andso on.In a ddition to the abo ve applications, Internet access also

provides a significantly strong enabling technology for telecom- mut ing , where users can t a p in to their o f f ice computerresources using a high-speed connection from home (signifi-

Table 1. The HFC appli cations spectrum .

Dat a In t ern et Ao D(real-t im e) VoD(real-t im e) Pay-p er-viewE-m ail M usic dow nload N ear Vo D Tim e-b asedDo D Aud io p review (real-t im e) su b scr ip t ionSof tw are V ideo dow n load

d o w n lo ad Vid eo p reviewMul i-par ty

gam es (real-t ime)

Au d io Telep h on e Asym m et ricVo ice m ail co n f eren cing

Vid eo Asym et ric Vid eoco n f er en ci ng co n f er en ci n g

Video mai l

No Upst ream Data Aud io V ideo Subscr ip t ionsu b sc ri p t i on su b sc ri p t io n su b sc ri p t io n Br o ad c ast

Dat a b r o ad c ast ( re al -t im e ) ( re al -t im e )TV sch ed ule rad io st at io n V id eo b ro ad castV id eo -g am e A ud io b ro ad cast

d o wn lo a d

Dod: Data on demandAoD: Aud io on demandVoD: Video on demand

Downstream

Upst ream Digital Analog

(Digital) Data Audio Video Video




cantly higher than what is conventionally available), and thusbe as productive as in the office environment, but from thecomfort of their home. Co nsidering the emerging policiesagainst massive commuting for many categories of workers,this technology may become a significant fa ctor in this trendbecoming more widely acceptable and successful.

Tradi t iona l e-mai l servi ces wil l prov ide a s ign i f ican timprovement in interpersonal communication, allowing usersto exchange text messages at a significantly lower cost thancurrent voice connections. Clearly, these applications will beuseful for business as well as nonbusiness purposes.

D owns t ream d el ivery o f d ig i t ized a udio and /or v ideoenables another popula r ca tegory o f appl ica t ions . I t w i l lbecome fea sible to deliver to users non-real-time audio orvideo on demand to their systems for later playback. In thisfashion, users can initiate playback sessions at their leisure forspeeches, music, video /aud io previews, an d so on. I t is impor-tant t hat t his class of applications can be used for mail ser-vices as well , where users will be able t o exchange a udio(voice) an d/or video ma il messages.

Audio or video information in the digital upstream channelis meaningful only in the context of a conferencing or mailapplication. This is indicated in Table 1 with the applicationclasses shown in the second and third rows. We have not rea l-

ly considered voice as an upstream traff ic type with data asdownstream, s ince this basically implies voice commandthrough speech recognition, which in essence is covered bydata transmission on the upstream.

Many of the above applications can be classified under ageneral category, distributi on services , where content like soft-ware, bo oks, music, and video movies or programs can be dis-tr ibuted electronically from centra l repositories to users’computers.

When no upstream connection is utilized, a large numberof applications emerge, similar to the subscription applications

available tod ay through ana log channel TV. Subscript ionapplications for a digital downstream channel transferringdata, audio, or video are similar to program subscriptions inthe case of a nalog do wnstream transmission. So d ata subscrip-

tion as well as real-time audio and video subscription applica-tions emerge. Similarly, a large number o f a pplications will bedeveloped that relate to broadcasting data, audio, or video.

REAL-TIME APPLICATIONS

R eal-time applications require media to be delivered to theuser in an isochronous fashion. The high band width of H FCnetworks enables such applications, which in a ddition t o inter-active applications will provide the end user with the ability todo business and bring improved entertainment to the home.

U sing a full-duplex data connection to the H /E, one canbring multimedia applications to the end user, who will beable to bro wse and request delivery of video, audio, and da tafrom d igital libraries and repositories. Such applications willprovide a new means of remote trainin g and education in the

home, school, or workplace. Entertainment is also a vast areaof applications in this class, since it becomes feasible to pro-vide mul tipl ayer digital games , where several players may besimultaneously act ive on t he same game board, or s imilarapplications. Such services can also take advantage of thebroadcast na ture of the network, allowing multiple users toview the common information simultaneously.

When the downstream connection delivers digitized audioor video, it becomes feasible to deliver real-time audio-on-demand (AoD) or video-on-demand (VoD) services to theuser (audio /video strea ming). A customer will be ab le to ha ve,for e xample, real-time music delivered a nd pla yed on his/herstation on a dema nd basis. Personalized radi o or TV stations

will deliver to users the desired series of songs or programs(or simply the desired type of audio or video content). In thecase of video, which will be compressed to a dapt to the low bandwidth available for digital downstream connections, sev-eral real-time schemes may emerge: VoD, near VoD (NVoD),video previews, “personalized” video programs, and so on.The ab ility to deliver dig ital a udio/video to t he end user willbe significant to the advertising industry, since it will becomefeasible to provide audio and video previews to a large bodyof potential customers (either in real time or non-real-time).The broa dcasting nature of the medium will enable efficientand cost-effective delivery of such services.

Co-existence of the digital upstream connections with theana log downstream will enable applicat ions that combine(synchronize) these connections. An immedia tely available setof services is the body of applications where currently tele-phone o rders a re ma de f or TV services, such a s pay-per-view and time-based subscription (i.e., subscription to channels forcertain time windo ws). The digital upstream can be effectivelyused to deliver to the H /E a ll informat ion currently providedby telephone.

As mentioned previously, audio or video information in thedigital upstream channel is meaningful only in the context of aconferencing or mail a pplication. The real-time applications

with audio and video upstream envisioned for the near futureare the confe rencing applications. Asymmetric conferencingaccommodates the ca ses where, for example, only one of twoconferring parties has the support for video conferencing,while the other only has a udio conferencing. Asymmetric con-ferencing applications allow for interoperability of audio a ndvideo conference systems. The broadcasting characteristic ofthe medium enables multiparty conferencing easily.

Over H FC networks, PO TS-like telephony is also expectedto be provided. Although we do not expect that HFC telepho-ny will ever replace regular POTS as the main means for resi-dential voice communications, the a bility to add dynamically asecond (or third, et c.) “ telephone line” for services like fa xingor da ta/teleconf erencing over the same medium is quit eappealing. We expect that the HFC networks will provide a

“ virtual copper wire” conduit to PO TS providers. This willsave money for both the customer and the POTS providers,who will not have to la y and ma intain extra telephone lines.

The last row of the applications in Table 1 corresponds tocases where no upstream informa t ion is necessary for theapplication implementation. Ana log downstream, for example,corresponds to the conventional CaTV environment, whereno upstream channel exists; so applications such as broadcastTV and premium channel subscription fall in this category.

Similar to subscription in the case of analog downstreamtransmission, one can easily envision subscription applicationsin the case of a digital downstream channel transferring data,audio or video. Furthermore, as far as data are concerned,one can easily deliver applications such as TV program sched-ules and information, video-game d ownload, and news distri-

bution as part of data broadcasting applications.

FULL SERVICE REQUIREMENTS

C urrent C aTV systems are ba sically isolated islands thatconsist of a n H /E and the residential community that the

particular H /E serves. The only info rmat ion currently carriedby traditiona l Ca TV is TV programming in one-way broadca stmode. On occasion, low-rate digital data can be transmittedduring the vertical retrace interval. Since this feature results intoo low da ta ra tes (< 16 kb/s) for broadband and even formost narrowband applications, it is given no further consider-ation in t his article.




Hence, most of the services discussed in the previous sec-tion cannot be provided automatically just because the CaTVoperato r has simply enabled tw o-way communications on itsaccess network. As Ca TV opera tors upgrade t he access net-work side of th eir plants, they must do so on the “ other side”as well. They need to provide the means through which theservice providers can a ccess the high-speed H FC access net-works and ma ke their services available to the Ca TV cus-tomers, as shown in Fig. 4.

In a C aTV tree-and-branch netwo rk, the H/E , which islocated at the root of the tree, is the natural choice for con-necting servers. Thus, we believe tha t in “ first-generation”

two-way H FC systems we will see service providers beingdirectly connecte d to t he H /E, by eithe r being physicallyloca ted a t , or c lose to , the H /E, or b eing connectedthrough permanent leased high-speed telephone connec-tions. This service provision model has been adoptedtoda y by the majority of the two-way H FC tr ia ls [13].Therefore, t he H /E needs to be eq uipped with the neces-sary high-speed interconne ction de vices, for example,high-speed fiber distributed data interface (FDDI) LANsif the service providers are lo cated at or nea r the H /Esite, or ISD N, T1, and T3 telephone equipment fo r con-nection to remote service providers over leased lines, asshown in Fig. 5.

Without a doubt the most popular service, at least atthe out set , w i l l be In t ernet a ccess. This is the mos t

requested service, and given the f act tha t ma ny serviceproviders can a lso carry their services over the I nternet,an I nternet connectivity of the highest quality will be anabsolute necessity from da y one of H FC system opera-tion. This implies that the CaTV operators must carefullychoose a highly reliable Internet service provider (ISP)which not only provides excellent customer service 24hours a day, 7 days a week, but is willing, if it has notdone so a lready, to support high-speed connect ivitybetween the H /E a nd the ISP locat ion, and o f coursebetween the ISP and the I nternet itself. This means thathigh-speed telephone connections must be establishedbetween t he IS P and the H /E. Alternatively, high-speed

H FC, o r microwave connections in case the H/E and t he ISPare in line of sight of each other, could be installed, bypassingthe telephone network entirely. The CaTV operators maychoose to be ISPs themselves.

When it comes to Inter net a ccess, the H /E ca n act a s arouter and an int elli gent hub to direct traffic to and from thecustomer and the Internet. On the other hand, through simplestatistica l analysis of the custome r traf fic, the H/E ca n alsoserve as a local cache . I t can e f f ic ien t ly and in te l l igent lyprefetch from the Internet a plethora of popular pieces ofdata, and make them available to the customers as soon asthey are requested. The Web itself can assist in that. Thereexist a plethora of Web search engines that can help ea silylocate a nd prefetch important pieces of informat ion. As amatter of fact, there even exist top-100 Web page collectionscovering a wide range o f topics.

As the number of service providers and their off eringsincreases, and customers diversify their interests, providingdirect connections to certain service providers or cachinginformation locally may become irrelevant. In this case, it willbe better to leave it to the customer to select and access thepar ticula r services he/she desires. Most pro ba bly, these new services and service providers are not going to be locatedwithin or near each community served by a CaTV system, but

rather a nywhere on the globe. Therefore, the network archi-tecture will have to be enhanced and gradually migrate fromlocal directly a tta ched service providers to service providersconnected at t he customers’ will to the H /E o ver switchedhigh-speed broadband networks, as shown in Fig. 6. This willrequire the H /E t o further upgrad e its interconnection equip-ment and be able to support switched broa dband tra ffic over,for example, asynchronous transfer mode (ATM), which is thenetwork of choice for broa dband communications.

We need to remark here that the IEEE 802.14 MAC willcarry ATM cells as one of its payload types. Moreover, theresident ia l broadba nd (R BB ) group of the ATM Forum isworking on d efining ATM services over 802.14-compliantHFC networks.

I t should be emphasized that an H FC network provides

Figu re 4. Preparing a CaTV system to provide data-over-cable services.

Figu re 5. “Fi rst-generation” networks with data-over-cable services.

Figu re 6. Full -connectivity end-to-end high-bandwidth solution .




only an eff icient interconnection means for d elivering a widerange of broadband applications to end-users. Yet, servicesmay not be eff ect ively provided even with the end -to-endhigh-speed connectivity. All the information and intelligencenecessa ry to bui ld a n appl ica t ion is loca ted a t a serv iceprovider site. Thus, the service providers too may ha ve toupgrade their infrastructure to be a ble to provide interactivebroadband services to individual customers.

Contrary to broadcast services, which will continue to beprominent among Ca TV users, who ta ke advantage of thesimplicity of the one-size-fits-all approach, the interactive dataservices discussed in the previous section re quire that serviceproviders address the needs of their customers. Interactive dataservices require highly intelligent computer and communicationsystems that will be able to adjust on-the-fly to the requestsreceived f rom a diverse collection o f individuals. Therefore,we foresee that the development of “personalized” interactiveservices will also spur plenty of activity in the areas of:• Specialized server architectures for supporting large stor-

age and powerf ul high-speed input/output (I/O) subsys-tems

• High-speed interconnection networks between the servercomponents and servers, in general

• Sophisticated management and control systems

In the end, it all boils down to the fact that, to provide aservice to a customer that requires high bandwidth a nd low response t imes, the h igh bandwidt h has to be ava i lablethroughout the path from the server site to the customer, andboth the server and t he customer must have the a ppropriateequipment to support the requested service.

CONCLUDING REMARKS

I n this article, we have discussed issues pertaining to bringingdigital services to residential customers. We have identified

two major players in this area: the telephone and CaTV ser-vice providers. This article ha s been fo cused on the Ca TVsolution.

As cable operators upgrade their all-coaxial networks to

HFC networks, they also modify them to enable two-way datatransport. Cable systems with an abundance of excess band-width are hence getting ready to t ransport digital data at tensof mega bits per second. At such high speeds a new b reed ofda t a serv ices could be po ss ible , which wi l l supplementenhanced versions of already existing ones. In this article, wehave highlighted several such applications. To provide theseapplications, one needs to e stablish an end-to-end (i.e. fromthe da ta server locat ion to the customer) high-speed datatransfer infrastructure. We have presented possible solutionsand migration paths with which this can be a chieved.

We have a lso discussed the possibility of high-speed da tacommunications over telephone lines. The big plus for thisapproach is that t he ana log telephone service and copper tele-phone wires are practically ubiquitous. On the o ther hand, t he

big plus for the CaTV approach is that it can provide unprece-dented data speeds to customers. We believe that the latterwill be the decisive fa ctor in choosing Ca TV over telephonedata services whenever the option is available.

REFERENCES

[1 ] IEEE Communications Magazine , Special Issue on Digi tal Video Commu-nicat ions and Video on Demand , vol . 32, no. 5, May 1994.

[2 ] IEEE Communications Magazine , Special Issue on Reshaping Communi-cations through Technology Convergence, vol . 33, no. 4, Apr. 1995.

[3 ] IEEE Commu nicat ions M agaz ine , Special Issue on Access to BroadbandServices, vol . 33, no. 8, Aug. 1995.

[4 ] IEEE Netw ork , Special Issue on Digi tal Interactive Broadband Video DialTone Networks, vol . 9, no. 5, Sept./Oct. 1995.

[5] IEEE Spectrum , Special Report on Digi tal TV, vol . 32, no. 4, Apr. 1995.[6] J. W. Eng an d J. F. M ol lenauer, “ IEEE Project 80 2.14: Stand ards for Digi-

ta l Convergen ce,” IEEE Comm un. M ag. , vo l . 33 , no . 5 , M ay 1995 , pp .20–23.

[7] Dataqu est Int eract i ve, “ Internet Sur fers to Fuel Cable Mo dem M arket , ”at URL ht tp: / /ww w.dataqu est .com/

[ 8 ] C . B i sd i k i an e t a l . , “ M LAP: A M AC Leve l Access P r o toco l f o r t he H F C802 .14 N e tw or k , ” IEEE Com mu n. M ag. , vo l . 34 , no . 3 , M ar . 1996 , pp .114–21.

[9] J . Gar tner , “ ISDN: Internet A ccess for th e M asses,” at URL ht t p: / / tech-web.cmp.com/products / i sdn.

[ 1 0 ] D a n K e g e l ’ s A D SL p a g e , a t U RL “ h t t p : / / a l u m n i . c a l t e c h . e d u / dank/ isdn/ads l .htm l ”

[11] ADSL Forum, at URL http://www.sbexpos.com/adsl /home_page.html[12] S. E. Gi l le t t , “ Connect ing Hom es to t he Internet : An Engineer ing Cost

M odel o f Cable vs. ISDN,” M IT Lab. fo r Comp . Sci ., Tech. Rep. 65 4, June1 9 9 5 ; s ee a l s o a t U RL h t t p : / / r p c p . m i t . e d u / Pu b s / g i l l et t _ c o n n e c t i n g _ home/abst rac t .htm l .

[13 ] T. S. Perry, “ The Tr ials and Travai ls of Int eractive TV,” IEEE Spectrum ,vo l . 33, no. 4, Apr . l 1996, pp. 23–28.

BIOGRAPHIES

CHATSCHIK BISDIKIAN [SM] received the Diplom a in electr ical engin eer ing fromthe School of Engineer ing of the Ar is tote l ian Univers i ty of Thessalonik i inGreece, in 1983, an d t he M .Sc. and Ph.D. degrees, bot h in e lec t r i ca l engi -n e e r in g , f r o m t h e U n i v e r si t y o f C o n n e c t i c u t , St o r r s , in 1 9 8 5 a n d 1 9 8 8 ,

respectively. Since 1989 he has been a research staff member with the IBMT . J. Wat son R esear ch C en te r , Yo r k t ow n H e i gh ts , N ew Yor k . H i s cu r r en tr esear ch i n te r est s a r e m u l t i m ed i a and b r oad band com m un i ca t i ons , H FCn e t w o r k s an d c a b l e m o d e m s , m o d e l i n g a n d p e r f o r m a n c e ev a lu a t i o n o fh igh-speed networks , computer sys tem model l ing and analys is , and queu-i ng and p r obab i l i t y t heor y and t he i r app l ica t ion t o com p ute r com m un i ca -t i on ne tw or ks . H e has pub l i shed ove r 60 techn i ca l paper s on th ese ando the r r e l a ted a r eas , and he ho l ds a pa ten t on s l o t r euse fo r s l o t t ed busnetw orks . Dr. B isdik ian is a 1995 f inal i st f or th e Eta Kappa Nu Outs tandingYoung Electr ical Engineers Award, has served as a member of the Editor ialBoar d o f t he Telecommunicat ion Systems Journal , and h as se r ved o n t heprogram committees and chaired sessions for many conferences.

KIYOSHI M ARUYAM A received th e M.S. and Ph.D. degrees in com pu ter sciencef r om th e U n i ve r si t y o f I l l i no i s , U r bana- Cham pa i gn , I l l i no i s , i n 1970 and1972, respectively. Since 1972 he has been a research staff member at IBMT. J. Wat son Research Center . He has cond ucted research in t he f ie ld s ofpat tern recogni t ion, p ic ture p rocess ing, p aralle l process ing, d ata com mu ni -ca t i on ( SN A) , and vo i ce com m un i cat i on . H e has he l d num er ous m anage-

ment pos i t ions in IBM Research. From 1986 to 1 988 h e was on assignmentto Rolm, respons ib le for th e netw ork archi tec tures in Rolm ATSL and beinginvolved in ISDN D-channel han dl ing , ISDN f ram e re lay ing, an d Rolm PBXfo l l ow - ons . F r om 1989 to 1992 , he w as on ass i gnm ent w i t h As i a Pac i f i cGroup an d IBM Japan as d i rector o f te lecomm unicat ion s sys tems. He w asr espons i b l e f o r deve l opm ent and m ar ke t i ng o f t e l ecom m un i ca t i ons andne tw o r k ing p r oduc ts in t ha t r eg i on . A f te r h i s r etu r n f r om the assi gnm ent ,he became senior technical consul tant in the area of comp uter sc iences atI BM Re se a r ch a n d t h e n m a n a g e d t h e C o n su m e r P r o d u c t s g r o u p , w h i c hexplored mul t imedia and speech technologies . He is cur rent ly manager ofResident ia l Broadband Netw orks , conduct ing research o n res ident ia l gate-ways and ho me netw orks.

D A V I D SE ID M A N [ M ‘ 8 8 ] i s a n a d v i s o r y e n g i n e e r a t t h e I B M T. J. W a t s o nResearch Center in the M ul t im edia Com mu nicat ions System s depar t men t .He received a Ph.D. in e lec t r i ca l engineer ing f rom Columbia Univers i ty in1994 . Fo r t he pas t n i n e year s, he has condu c ted r esear ch i n h i gh - speedcommunicat ions networks , focus ing on FDDI, MPEG, and mul t imedia sys-tems. H is research interes ts inc lude interconnect ion networks , WDM, and

computer archi tecture. His e-mai l address is [email protected].

D IMITRIOS N. SERPANOS [SM ] r ece i ved th e D i p l om a i n com put e r eng i neeri ngand informat ion sc iences f rom the Univers i ty of Pat ras in Greece in 1985,and the M.A. and Ph.D. degrees in computer sc ience f rom Pr inceton Uni -ve r si t y i n 1 988 and 199 0 , r espec t i ve l y . D r . Se r pano s i s a r esear ch s ta f fm emb er at IBM T. J. Wat son Research Center since 1990 . He is current ly am em b er o f t he I n te r act i ve M ed i a So l u t i ons depar tm en t w or k i ng on m u l t i -med ia systems and residential netw orks. His research interests include h igh-s p e e d n e t w o r k s a n d c o m m u n i c a t i o n s y st e m s , p a r a l l e l a n d d i s t r i b u t e dcomput ing, computer archi tec ture, and VLSI . Dr . Serpanos holds two U.S.patent s and h as publ i shed several technical papers and invent ion s. He is amember of the New York Academy of Sciences, the ACM, and the TechnicalChamber of Greece.

Cable Access Beyond the Hype on Residential Broadband Data Services Over Hfc Networks

Documents

Transcript of Cable Access Beyond the Hype on Residential Broadband Data Services Over Hfc Networks