Cable Modems Cable Tv Meets The Internet

Cable Modems: Cable Television Meets The Internet Essay, Research Paper

Cable Modems: Cable Television Meets the Internet

John G. Shaw

IS 3348

October 2, 1999

Abstraction

The Telecommunications Act of 1996 opened the manner for overseas telegram Television ( CATV ) companies to go fully fledged telecommunications companies, offering bipartisan voice and information communications services, in add-on to telecasting scheduling. After transition of the Act, the overseas telegram companies were eager to spread out into the new Fieldss of concern that had been opened to them, particularly the quickly turning Internet Service Provider ( ISP ) concern. The biggest hurdle confronting the overseas telegram companies is that overseas telegram telecasting systems were designed for one-way traffic, and must be upgraded into modern bipartisan webs in order to back up advanced communications services. This is an expensive and technically complex project. In add-on, interfaces leting subscriber & # 8217 ; s Personal computers to entree the Internet via the CATV overseas telegram had to be developed. These interface devices are called overseas telegram modems. Cable modems are designed to take advantage of the broadband capableness provided by the overseas telegram Television substructure, enabling peak connexion velocities many times faster than conventional dial-up connexions.

Cable Modems, Cable Television Meets the Internet

Cable modems have merely late been introduced for private commercial usage. Cable modems and the overseas telegram informations webs they are a built-in portion of clasp the promise of supplying a great trade of communications bandwidth for the private user. Greater bandwidth peers greater velocity in the kingdom of the Internet. The Internet has merely been around for private usage for a comparatively short period of clip, however, it has grown rather quickly. It appears that the Internet will go on to turn at a rapid gait. Peoples will get down to utilize the Internet for more and more applications. Networking will finally be a portion of the most infinitesimal parts of our day-to-day lives. New Internet applications will doubtless necessitate greater information velocities, and overseas telegram informations webs are a enormous measure frontward in supplying that velocity. Cable modem engineering is still in its babyhood, but it has already revolutionized Internet & # 8220 ; surfing & # 8221 ; . Cable modems are supplying connexion velocities that people merely dreamed about a short clip ago. However, on a greater graduated table, as more and more people start utilizing overseas telegram modem service, the overseas telegram companies will hold to go on upgrading their webs to maintain up with increased demand. Finally, fiberoptic overseas telegram will make into single places. This discovery development will increase bandwidth by orders of magnitude, and it is overseas telegram modem that has already started this procedure.

Method

& # 8220 ; Cable Modems, Cable Television Meets the Internet & # 8221 ; is an enlightening overview of overseas telegram modems and overseas telegram informations systems. Extensive research was done to look into how overseas telegram modems work, and how overseas telegram modems fit into a overseas telegram information system. The overseas telegram industry was merely allowed to come in the ISP concern less than three old ages ago. Because overseas telegram modems are comparatively new devices, and overseas telegram informations web engineering has advanced quickly, the latest up-to-date beginnings of information had to be used to supply accurate information. Recent magazine articles and Internet sites had the most current information. The information in hardback books was disused and dated. After researching the topic, the consequences of the research were presented in the paper. The mentions used as beginnings of information for the paper are cited.

Consequences

Cable modems are proved engineering. Cable information webs provide enormous velocity every bit good as upgrade potency.

Discussion

The stuff presented here shows that overseas telegram modem engineering is robust and has enormous potency to go on turning. Cable modems are merely another measure to the entire networking of mundane life. This development is still a long manner off. But, it is bound to go on. It will go on earlier, instead than subsequently

Residential Internet use has grown quickly despite the frustratingly slow velocities available through conventional dial-up telephone modem connexions. These voiceband connexions are limited to 56 Kbps or less. Surfboarding the & # 8216 ; Net with a dial-up modem is normally a click-and-wait experience. There is a enormous demand for faster Internet connexions. The Telecommunications Act of 1996 opened the manner for overseas telegram Television ( CATV ) companies to go fully fledged telecommunications companies, offering bipartisan voice and information communications services, in add-on to telecasting scheduling ( Clark, 1999 ) . Cable companies that offer these drawn-out services are known as Multiple Service Operators ( MSO ) . The draw a bead oning Multiple Service Operators realize there is a ample market of Web surfboarders who feel a & # 8220 ; demand for velocity & # 8221 ; , and they want to be the 1s to run into that demand. Cable modems are devices that allow high-velocity entree to the Internet by manner of a overseas telegram telecasting web. Cable modems work much the same manner as traditional dial-up telephone modems, but overseas telegram modems are much more powerful. Alternatively of utilizing telephone lines as the connexion medium to the Internet, overseas telegram modems use the overseas telegram that carries overseas telegram Television scheduling as its connexion medium. Cable modems are designed to take advantage of the broadband capableness provided by the overseas telegram Television substructure, enabling peak connexion velocities many times faster than dial-up connexions. More bandwidth peers more velocity. A overseas telegram modem endorser may see entree velocities from 500 Kbps to 1.5 Mbps or more, depending on the overseas telegram web architecture and traffic burden ( Halfhill, 1996 ) . With their blaze velocity, overseas telegram modems are able to quickly download big sound and picture files, supplying true multimedia capableness. In add-on to rush, overseas telegram modems offer another cardinal benefit: changeless connectivity. Cable modems are on-line every bit shortly as the computing machine is turned on. This is possible because overseas telegram modems use connectionless engineering, much like an office LAN ( Ostergard, 1998 ) . There is no demand to dial in to get down a session, so there are no busy signals and no demand to bind up their telephone line. Besides, with monetary values runing from $ 40 and $ 60 per month, which includes overseas telegram modem lease and limitless Internet entree, overseas telegram modem Internet service is highly cost effectual when compared to other high-velocity informations systems.

Unfortunately for the overseas telegram companies, it is non merely a simple affair of attaching overseas telegram modems to their subscriber & # 8217 ; s Personal computers and allowing them surf off at light velocity. To acquire into the high-velocity Internet Service Provider ( ISP ) concern, a CATV company must construct an expensive and complex IP networking substructure. This web has to be able to back up 1000s of endorsers. Building overseas telegram information web involves turn toing such points as Internet anchor connectivity, routers, waiters, web direction tools, every bit good as security and charge systems ( Salent, 1999 ) . Furthermore, CATV informations systems are comprised of many different engineerings, so criterions regulating overseas telegram modems had to be developed which would let merchandises from different sellers to be interoperable. But, the biggest hurdle confronting the overseas telegram companies is that overseas telegram telecasting systems were designed for one-way traffic, and must be upgraded into modern bipartisan webs in order to back up advanced communications services ( Medin, 1999 ) . This is an expensive and technically complex project.

CATV systems were originally designed to present broadcast telecasting signals to endorsers & # 8217 ; places. In the overseas telegram industry, this is known as downstream traffic. The Head-end is the cardinal distribution point for a CATV system. Video signals are received at the Head-end from orbiters or other beginnings, frequence modulated to the appropriate channels, and so transmitted downstream through the overseas telegram medium into the subscriber & # 8217 ; s places. The subscriber & # 8217 ; s telecasting tuner, or set-top overseas telegram convertor box, demodulates the signal back to a picture image. To see that consumers could obtain overseas telegram service with the same Television sets they use to have over-the-air broadcast Television signals, overseas telegram operators recreate a part of the over-the-air wireless frequence ( RF ) spectrum within a sealed overseas telegram line. The older coax-only overseas telegram systems typically operate with 330 MHz or 450 MHz of capacity ( Ostergard, 1998 ) . While the newer, more expensive intercrossed fiber-optic/coax ( HFC ) systems can run at 750 MHz or more ( Ostergard, 1998 ) . HFC webs combine both fiberoptic and coaxal overseas telegram lines. About half of the overseas telegram endorsers in North America are connected to HFC overseas telegram systems. HFC networks cost much less than a pure fiberoptic web, but provide many of fiber & # 8217 ; s dependability and bandwidth benefits. The fiberoptic part of the HFC web is a star constellation where optical fibre feeder lines run from the overseas telegram head-end to groups of 500 to 2,000 endorsers ( Van Matre, 1999 ) . These groups of endorsers are called overseas telegram nodes or overseas telegram cringles. A trunk-and-branch constellation of coaxal overseas telegram tallies from the optical-fiber feeders to make each endorser.

Because CATV systems were originally designed chiefly to direct signals downstream, merely a little sum of the available bandwidth was allocated for upstream transmittals. There is really small demand for upstream communicating in CATV system that is used entirely for telecasting signal transmittal. The allocated upstream bandwidth is a narrow 5 to 42 MHz set shacking at the lower terminal of the overseas telegram Television RF spectrum ( Barnes, 1997 ) . Downstream overseas telegram Television plan signals begin at 50 MHz, which is the equivalent of channel 2 for over-the-air telecasting signals. Each standard telecasting channel occupies 6 MHz of RF spectrum. So a traditional coaxial overseas telegram system with 400 MHz of downstream bandwidth can transport the equivalent of 60 linear Television channels, and a modern HFC system with 700 MHz of downstream bandwidth has the capacity for 110 channels ( Salent, 1999 ) .

To present bipartisan informations transmittal over a overseas telegram web, one unused 6 MHz telecasting channel, in the 50 & # 8211 ; 750 MHz scope is typically allocated for downstream informations traffic. Another fresh 6 MHz channel, in the 5 & # 8211 ; 42 MHz scope, is used to transport upstream informations. Whenever person chinks on a hyperlink, sends e-mail, or uploads files, they are directing informations upriver. Unfortunately, the upstream set is capable to all kinds of intervention that can falsify informations. This defect makes it near to impossible to utilize a coax-only overseas telegram system for bipartisan high-velocity informations traffic. Coaxial overseas telegram picks up noise from motors, CB wirelesss, microwave ovens, and other contraptions. Ham wireless and Videocassette recorders can interfere enormously with upstream information. Merely CATV systems that have been upgraded to HFC works are capable of high-velocity bipartisan informations transportation. The usage of optical fibre reduces noise and increases the upstream bandwidth, easing upstream informations transmittal. Optical fibre can besides convey signals over much longer distances before necessitating elaboration. To direct the information over the HFC web, optical maser senders convert signals sent from the head-end into optical signals. At each overseas telegram node, a optical maser receiving system reconverts the signals so they can once more be transmitted over tree-and subdivision configured coaxal overseas telegram works, which goes into each single house.

The most of import factor in the deployment of bipartisan overseas telegram informations services is the handiness of high-quality bipartisan HFC works. But upgrading to HFC is really expensive. It costs a overseas telegram company $ 200 & # 8211 ; $ 250 per place to upgrade to HFC works ( Clark, 1999 ) . Some overseas telegram companies that have non upgraded to HFC are offering overseas telegram modems that use the RF coaxial overseas telegram spectrum for fast downstream transmittal and a traditional dial-up modem to manage upstream communications over the public telephone web. However, telephone-return modems do non supply some cardinal benefits available with bipartisan overseas telegram modems, such as ultra-fast upstream velocities, changeless connectivity, and non binding up a endorser & # 8217 ; s telephone line.

The Cable Modem Termination System ( CMTS ) is the cardinal device for linking the overseas telegram Television web to the Internet. The CMTS resides at the overseas telegram head-end. All the traffic to and from the overseas telegram modems in a overseas telegram information web travel through the CMTS. The CMTS connects to an IP router that sends and receives the information from the remainder of the Internet. The CMTS interprets the information it receives from single clients and keeps path of the services offered to each of them. The CMTS besides modulates the informations received from the Internet so that the head-end equipment can direct it to a specific endorser. Some Cable Modem Termination Systems provide the capableness to allow the MSO make different service bundles depending on clients & # 8217 ; bandwidth demands ( Clark, 1999 ) . For illustration, a concern service can be programmed by the CMTS to have, every bit good as transmit, with high bandwidth, while a residential user may be configured by the CMTS to have high bandwidth downstream traffic and limited to low bandwidth upstream traffic.

Cable information web architecture is similar to that of an Ethernet Local Area Network ( LAN ) ( Halfhill, 1996 ) . Current overseas telegram modem systems use Ethernet frame format for upstream and downstream transmittals. Basically, the overseas telegram operators are constructing some of the universe & # 8217 ; s largest & # 8220 ; intranets & # 8221 ; . Cable operators are concentrating on supplying high-velocity intranet entree alternatively of consecutive Internet entree because a web connexion is merely every bit fast as its slowest nexus. The head-end at most MSOs normally connect to the Internet via a T1 line, which has a information rate of 1.5 Mbps, significantly slower than a overseas telegram modem, which can theoretically present 30 Mbps ( Brownstein, 1997 ) . But, the Internet is merely every bit fast as the slowest waiter. The benefit of a 1.5 Mbps T1 Internet connexion is lost if a endorser tries to entree content stored on a Web waiter that is connected to the Internet though a 56-Kbps line.

Therefore, the constrictions for Internet traffic in a overseas telegram web system are normally the gateway to the Internet, every bit good as the Internet itself. The overseas telegram companies & # 8217 ; solution to this job is to travel the Internet content closer to the endorser. Many popular Web sites are cached on the overseas telegram operator & # 8217 ; s waiter. So, when a overseas telegram modem endorser goes to entree a popular Web page, he will be routed to the waiter in the head-end at top-speed. If a site International Relations and Security Network & # 8217 ; t cached, nevertheless, the head-end waiter has to travel looking for it out on the engorged Internet, merely as a conventional ISP & # 8217 ; s waiter does. Cable modem endorsers should see high velocities ( multiple MBit/sec ) every bit long as they stay within the local overseas telegram web system. However, informations transfer rates can decelerate down well when the user needs to venture out onto the Internet.

Like LANs, overseas telegram modem systems rely on a shared entree platform ( Ostergard, 1999 ) . All the overseas telegram modem endorsers in a overseas telegram cringle portion available bandwidth to the head-end. Everyone on the local overseas telegram cringle portions the same overseas telegram, which can transport about 30 Mbps entire bandwidth. So as more endorsers hook up overseas telegram modems, more users will be sharing the same sum of bandwidth. Because of this, there are concerns that overseas telegram modem users will see hapless public presentation as the figure of endorsers increase on the web. If congestion does get down to happen due to high use, the overseas telegram operators do hold the capableness to upgrade bandwidth capacity. A overseas telegram operator can easy apportion an extra 6 MHz picture channel for high-velocity informations, duplicating the downstream bandwidth available to users. Another option for adding bandwidth is to subdivide the physical overseas telegram web by running fiberoptic lines deeper into vicinities. This reduces the figure of overseas telegram modems served by each node section, and therefore, increases the sum of bandwidth available to endorsers.

Based on bandwidth entirely, it would look that 200 overseas telegram modem endorsers sharing a 27-Mbps connexion would each acquire about 135 Kbps of throughput, which is non much better than a 128-Kbps ISDN connexion ( Salent, 1999 ) . However, unlike circuit-switched telephone webs where a company is allocated a dedicated connexion, overseas telegram modem users do non busy a fixed sum of bandwidth during their on-line session. Alternatively, they portion the web with other active users and utilize the web & # 8217 ; s resources merely when they really send or receive informations in speedy explosions. So alternatively of 200 overseas telegram online users each being allocated 150 Kbps, each user is able to utilize all the bandwidth available during the short period of clip they need to download their informations packages.

Another constriction in overseas telegram informations networking is the interconnectedness presently being used between the overseas telegram modem connect and the subscriber & # 8217 ; s Personal computer. A splitter is used to divide the coax overseas telegram in the subscriber & # 8217 ; s place into two lines, one for the Television set and another for the overseas telegram modem. Cable modems are external devices that connect to the coax overseas telegram by manner of a standard & # 8220 ; F & # 8221 ; port connection ( Barnes, 1997 ) . Ethernet10Base-T twisted-pair wiring and RJ-45 connections are used to link the overseas telegram modem to the Personal computer. The distorted brace wiring from the overseas telegram modem connects to the RJ-45 doodly-squat of a 10Base-T Ethernet card that has been installed in the subscriber & # 8217 ; s Personal computer. While overseas telegram modems can have informations at velocities up to 30 Mbps, the Personal computer itself is limited by its Ethernet interface. Ethernet theoretically runs at 10 Mbps but is normally much slower, typically a upper limit of 4 Mbps ( Barnes, 1997 ) . Because most place computing machines do non hold an Ethernet card installed, overseas telegram operators must typically put in one when linking a new client for overseas telegram modem service.

Suprisingly, this apparently simple process presents a major constriction in the overseas telegram modem installing procedure. First, the user & # 8217 ; s computing machine must hold an ISA or PCI card slot available in their computing machine for the Ethernet arranger. Besides, the card installing frequently requires configuration work within the operating system scenes to forestall struggles with other hardware devices. Due to the complexness, overseas telegram operators are frequently forced to direct a specialised computing machine technician to manage Ethernet card installings, a procedure that can take more than 20 proceedingss per endorser. Besides, the demand of opening each client & # 8217 ; s Personal computer to put in hardware creates a possible liability for the overseas telegram operator. Eager to avoid the Ethernet card concern, overseas telegram operators have searched for an alternate attack. The solution they have found prevarications is a device nicknamed a & # 8220 ; dongle, & # 8221 ; which is a Universal Serial Bus ( USB ) arranger. USB is a & # 8220 ; plug-and-play & # 8221 ; engineering for linking peripheral devices to computing machines, including modems, keyboards, pressmans and scanners ( Van Matre, 1999 ) . USB ports are external interfaces, so there & # 8217 ; s no demand to open the computing machine to put in a USB device. External Universal Serial Bus ( USB ) modems and internal PCI modem cards are under development.

Cable modems receive informations much faster than they can direct it. Cable modem makers have designed their modems to utilize less than a full 6 MHz bearer channel for upstream traffic. Typically 2 MHz broad sets are used for upstream information traffic. Cable Television webs transfer informations utilizing sophisticated digital transition strategies which greatly increase the sum of informations that can be sent. 64-state quadrature amplitude transition ( 64 QAM ) is digital transition technique used for directing informations downstream over a coaxial-only overseas telegram web. A individual downstream 6 MHz telecasting channel may back up up to 27 Mbps of downstream informations throughput from the overseas telegram head-end utilizing 64 QAM transmittal engineering. HFC webs are able to implement 256 QAM, which supports 36 Mbps of downstream informations throughput. However, 64QAM and 256 QAM are susceptible to interfering signals, doing them unable to back up noisy upstream transmittals. Quadrature Phase-Shift Keying ( QPSK ) is a digital frequence transition technique used for directing informations upriver over coaxal overseas telegram webs. QPSK is suited for directing informations upriver over a overseas telegram information web because it is reasonably immune to resound. Depending on the sum of overseas telegram RF spectrum allocated, upstream channels may present 500 Kbps to 10 Mbps, utilizing 16 QAM or QPSK transition techniques, with 16QAM being the fastest transportation method of the two ( Salent, 1999 ) .

Upstream overseas telegram modem traffic is ever sent in explosions. Each modem transmits upstream explosions in clip slots. These clip slots can be designated as reserved, contention, or runing slots. As the name implies, a reserved slot is a clip slot that is reserved to a peculiar overseas telegram modem. No other overseas telegram modem is allowed to convey in this reserved clip slot. The CMTS allocates the reserved clip slots to the assorted overseas telegram modems under its control through a bandwidth allotment algorithm. Reserved slots are usually used for longer informations transmittals ( Ostergard, 1998 ) .

Contention clip slots are unfastened for all overseas telegram modems to convey in. If two overseas telegram modems attempt to reassign at the same time in the same contention slot, their packages collide and the information is lost. The CMTS detects the hit and signals that no information was received, which makes the each overseas telegram modems attempt to retransmit the informations after waiting a random length of clip.

Ranging is the procedure of automatically seting transmit degrees and clip beginnings of single overseas telegram modems. Ranging is performed to see that explosions coming from different modems line up in the right clip slots and are received at the same power degree at the CMTS. A unvarying power degree for explosions making the CMTS facilitates hit sensing. If two overseas telegram modems transmit at the same clip, but one is much weaker than the other one, the CMTS will merely observe the strong signal and presume that no hit took topographic point. If the two clashing upstream signals are the same strength, they will both be detected by the CMTS as garbled. The CMTS will so cognize that a hit took topographic point and will teach the overseas telegram modems to retransmit their packages ( Ostergard, 1998 ) .

Ranging slots are besides used to counterbalance for the differences in physical distance between the CMTS and each of the overseas telegram modems. The big geographic range of a overseas telegram information web poses particular jobs as a consequence of the transmittal hold between users near to head-end versus users at a distance from overseas telegram head-end. To counterbalance for overseas telegram losingss and hold as a consequence of distance, the CMTS performs runing, which allows each overseas telegram modem to measure its clip hold in conveying to the head-end. Large CATV webs can see long holds in the msec scope. The runing protocol compensates for these holds by traveling the & # 8220 ; clock & # 8221 ; of each overseas telegram modem frontward or backward to do up for they delay. Ranging is performed sporadically by the CMTS for each overseas telegram modem under its control. Three back-to-back clip slots are set aside for runing. The CMTS commands the overseas telegram modem to convey in the 2nd clip slot. The CMTS so measures the transmittal clip and gives the overseas telegram modem a little positive or negative rectification value for its local clock. The two clip slots on either side of the 2nd clip slot are required to see that other traffic does non interfere with the runing explosion ( Ostergard, 1998 ) .

The overseas telegram modem itself is comprised of the undermentioned major constituents ; the Tuner, the Demodulator, the Burst Modulator, the Media Access Control ( MAC ) Mechanism, the Interface, and the Central Processing Unit ( CPU ) . External overseas telegram modems have an on-board CPU to manage direction processing. Internal overseas telegram modems are being developed that will utilize the PC & # 8217 ; s CPU much like the manner internal dial-up modems do. The overseas telegram modem & # 8217 ; s tuner connects straight into the CATV mercantile establishment. For bipartisan informations transportation, a tuner must hold a bipartisan diplexer to interrupt out the upstream and downstream traffic ( Ostergard, 1999 ) .

The Cable Modem & # 8217 ; s Demodulator receives the downstream IF signal from the tuner and, as the name implies, demodulates it. The Demodulator is composed of an A/D convertor, a QAM64/256 detector, MPEG frame synchronism, and Reed Solomon mistake rectification. Downstream information is framed harmonizing to the MPEG-TS ( transport watercourse ) specification. The frame format for this specification is a 188/204 byte block, with a individual fixed sync byte in forepart of each block. The Reed-Solomon mistake rectification algorithm reduces the block size from 204 bytes to 188 bytes, which leaves 187 bytes for MPEG heading and warhead ( Ostergard, 1998 ) .

The upstream information traffic is modulated by the overseas telegram modem & # 8217 ; s Burst Modulator. The Burst Modulator feeds the overseas telegram modem & # 8217 ; s Tuner, performs Reed Solomon encryption of each downstream explosion, performs QPSK or QAM16 transition on the designated upstream frequence, and D/A transition. The Burst Modulator & # 8217 ; s end product signal is fed through a variable end product amplifier, so the signal degree can be adjusted to counterbalance for overseas telegram loss ( Ostergard, 1998 ) .

Both the up

watercourse and downstream traffic travels through the overseas telegram modem’s Media Access Control mechanism. The MAC mechanism’s maps are reasonably complex. The MAC mechanism’s chief intent is to implement MAC protocols under the way of the CMTS. MAC protocols are used to time-share the overseas telegram media among the assorted overseas telegram modems in a overseas telegram information web. The MAC procedures can be implemented in hardware, or a combination of package and hardware. Both the CMTS and the MAC mechanism implement MAC protocols to execute runing processs to counterbalance for overseas telegram media holds and line losingss. The CMTS besides interfaces with the MAC mechanism in each overseas telegram modem to delegate upstream frequences and upstream clip slots. The CMTS controls informations traffic on the overseas telegram web through the usage of a particular control channel. When the overseas telegram modem is turned on, it scans all its assigned channels to turn up the control channel, which can be identified by its alone heading signal. The CMTS control channel tells each subscriber’s overseas telegram modem when it can convey, on which frequence set, and for how long. The information that passes through the MAC mechanism goes into the computing machine interface of the overseas telegram modem, which is 10Base-T Ethernet for the bulk of current overseas telegram modems ( Ostergard, 1998 ) .

A overseas telegram information system is comprised of many different engineerings and criterions. The first coevals of overseas telegram modems used assorted proprietary protocols that made it impossible for the CATV web operators to utilize multiple sellers overseas telegram modems on the same system. Cable operators have long believed success in the high-velocity information concern would necessitate that overseas telegram modems be interoperable, low-priced and sold at retail like telephone modems and informations web interface cards. This manner, MSOs could avoid the capital load associated with buying overseas telegram modems and renting them back to endorsers, and consumers would be able to take merchandises from a assortment of makers.

The Institute of Electronic and Electrical Engineering & # 8217 ; s ( IEEE ) 802.14 Cable Television Media Access Control ( MAC ) and Physical ( PHY ) Protocol Working Group was formed in May 1994 by a figure of sellers to develop international criterions for informations communications over overseas telegram. The original end was to subject a overseas telegram modem MAC and PHY criterion to the IEEE in December 1995, but the bringing day of the month slipped to late 1997 ( Van Matre, 1999 ) .

The overseas telegram operators were dying to acquire into the high-velocity information concern every bit shortly as possible, and became impatient waiting IEEE 802.14. So, the overseas telegram operators combined their buying power to jumpstart the criterions procedure. In January 1996, overseas telegram operators Comcast, Cox, TCI, and Time Warner, runing under a limited partnership dubbed Multimedia Cable Network System Partners Ltd. ( MCNS ) , issued a petition for proposals ( RFP ) to retain a undertaking direction company to research and print a set of interface specifications for high-speed overseas telegram informations services by the terminal of the 1996 ( Van Matre, 1999 ) .

MCNS released its Data Over Cable System Interface Specification ( DOCSIS ) for overseas telegram modem merchandises to sellers in March 1997. Afterwards, IEEE released its criterion, but by that clip, the overseas telegram operators had already wed themselves to the MCNS DOCSIS criterion. To day of the month, more than 20 sellers have announced programs to construct merchandises based on the MCNS DOCSIS criterion. The overseas telegram companies MediaOne ( once Continental Cablevision ) , Rogers Cablesystems, and CableLabs, besides signed on to the DOCSIS RFP. Together, this alliance represents the bulk of the North American overseas telegram industry, functioning 85 % of U.S. overseas telegram endorsers and 70 % of Canadian endorsers. Even though DOCSIS is the dominant US overseas telegram informations web criterion, it has yet to be officially certified by any independent criterions organic structure. The DOCSIS demands are now managed by CableLabs. A CableLabs enfranchisement plan administers vendor equipment conformity to the DOCSIS demands and interoperability trials. Standardized DOCSIS overseas telegram modems started transporting in limited measures in the 3rd and 4th quarters of 1998 with wider handiness expected in the first one-fourth of 1999. No major sellers are presently constructing modems based on the initial IEEE criterion ( Van Matre, 1999 ) .

The differing overseas telegram modem specifications advocated by IEEE 802.14 and MCNS reflect the precedences of each organisation. IEEE 802.14 is a vendor-driven group, and has focused on a making a future-proof criterion based on weapons-grade engineering. The MSO members of MCNS, on the other manus, are far more concerned with minimising merchandise costs and were in an utmost haste to acquire into the high-velocity information market. To accomplish its aims, MCNS sought to minimise proficient complexness and develop a engineering solution that was equal for its members & # 8217 ; demands ( Van Matre, 1999 ) .

Under the MCNS DOCSIS specifications, to enable crystalline transportation of Internet Protocol messages across a overseas telegram system, three of the protocol beds of the International Organization for Standardization & # 8217 ; s ( ISO ) 7 Layer Open System Interconnect ( OSI ) Reference Model are used. These three beds are the Network Layer, Data Link Layer and the Physical Layer. The maps of each bed are described below ( Salent,1999 ) .

Network Layer The Network Layer uses the Internet Protocol ( IP ) , which enables IP traffic to be seamlessly delivered over the overseas telegram modem platform to end-users.

Data Link Layer The Data Link Layer is comprised of three sublayers: a Logical Link Control ( LLC ) Sublayer, which conforms to Ethernet criterions, a Link-Security Sublayer that supports the basic demands of privateness, mandate, and hallmark, and a Media Access Control Sublayer, suited for overseas telegram system operation, that supports variable-length protocol informations units ( PDU ) .

Physical Layer The Physical Layer which defines the upstream and downstream transition format. There is minimum matching between physical and higher beds which accommodates the incorporation of future physical bed engineerings.

At the physical bed, which defines transition formats for digital signals, the IEEE and MCNS specifications are similar. The 802.14 specification supports the International Telecommunications Union & # 8217 ; s ( ITU ) J.83 Annex A, B and C criterions for 64/256 QAM transition, supplying a maximal 36 Mbps of downstream throughput per 6 MHz telecasting channel. The Annex A execution of 64/256 QAM is the European DVB/DAVIC criterion, Annex B is the North American criterion supported by MCNS, while Annex C is the Nipponese specification. The proposed 802.14 upstream transition criterion is based on QPSK and 16QAM, virtually the same as MCNS ( Van Matre, 1999 ) .

The MAC sublayer provides the general demands for many overseas telegram modem endorsers to portion a individual upstream informations channel for transmittal to the web. These demands include hit sensing and retransmission, timing and synchronism, bandwidth allotment to overseas telegram modems at the control of CMTS, mistake sensing, mistake handling, and mistake recovery, every bit good as processs for registering new overseas telegram modems.

For the MAC sublayer, 802.14 specified Asynchronous Transfer Mode ( ATM ) as its default solution from the head-end to the overseas telegram modem. MCNS went a different path, utilizing a strategy based on variable-length packages that favors the bringing of Internet Protocol ( IP ) traffic. Although the MCNS MAC is based on packages and the IEEE specifies fixed ATM cells, both overseas telegram modem solutions specify a 10Base-T Ethernet connexion from the overseas telegram modem to the Personal computer ( Van Matre, 1999 ) .

IEEE 802.14 commission members say they chose ATM because it best provides the quality of service ( QoS ) warrants required for incorporate bringing of picture, voice, and informations traffic to overseas telegram modem units. The group saw ATM as a long-run solution that would supply the flexibleness to present more than merely Internet entree.

Initially, overseas telegram operators were entirely focused on presenting high-velocity Internet services to consumers and believed ATM would add unneeded complexness and cost to overseas telegram modem systems. By back uping a variable-length package execution, MCNS members plan to capitalise on the favourable pricing associated with Ethernet and IP networking engineering. However, QoS warrants were added under DOCSIS version 1.1 ( Van Matre, 1999 ) ..

The Link-Security Sublayer insures the privateness of overseas telegram modem user informations by coding link-layer informations between overseas telegram modems and CMTS. Security is a major concern with overseas telegram modems because the entire bandwidth is shared by all overseas telegram modems in a local cringle. This means all downstream informations is received by all the overseas telegram modems in a cringle. Each overseas telegram modem uses the Ethernet frame format to filtrate out the informations it needs from the downstream of informations. The CMTS encrypts the warhead informations of link-layer frames transmitted on the overseas telegram web. The Security Association ( SA ) assigns a set of security parametric quantities including identifying informations to a overseas telegram modem. All of the upstream transmittals from a overseas telegram modem travel across a individual upstream informations channel and are received by the CMTS. In the downstream informations channel, the CMTS must choose allow the appropriate SA parametric quantities based on the finish reference of the mark overseas telegram modem. Baseline privateness employs the informations encoding criterion ( DES ) block cypher for encoding of user informations. The encoding can be integrated straight within the MAC hardware and package interface.

Cable modem engineering offers enormous advantages. A overseas telegram modem user can acquire the public presentation of a T-1 line at a fraction of the cost. Current overseas telegram modem service connexion velocities are much greater than that of a dial-up ISP at approximately the same monetary value. Dial-up ISPs offer 56 Kbps connexions for around $ 20 per month. Emerald Coast Cable Television, the MSO for the Fort Walton Beach, Florida country presently charges $ 30 a month for limitless Internet entree with a overseas telegram modem. A overseas telegram modem offers velocities between 500 Kbps to 1.5 Mbps. Even the low terminal of this scope is an order of magnitude faster than a 56 Kbps connexion. Cable modems presently retail for about $ 300, but the monetary values are forecast to drop quickly. Emerald Coast Cable Television charges $ 15 a month to lease a overseas telegram modem.

In add-on to their blaze velocity, another advantage of overseas telegram modems is changeless connectivity. Cable modems are on-line every bit shortly as the computing machine is turned on. The overseas telegram modem user does non hold to dial-in to get down an on-line session. There are no busy signals and tied up telephone lines like there are with dial-up modems. Another advantage of overseas telegram modem engineering is that it has enormous upgrade capacity. Twisted brace telephone lines have already used up a ample part of their built-in bandwidth capacity ( Halfhill, 1996 ) . On the other manus, MSOs have already created a enormous sum of shared bandwidth with their ascents to HFC webs. Furthermore, as the figure of overseas telegram modem users grows, and excessively many users try to portion the available bandwidth, the overseas telegram operators have the capableness to add more. Many MSOs have six optical fibres in their overseas telegram packages and are merely presently utilizing two of them. The MSOs could & # 8220 ; light up & # 8221 ; these fresh fibres and greatly increase the sum of bandwidth to be shared. Another option is to apportion extra 6 MHz channels for high-velocity informations. Still, another option for adding bandwidth is to subdivide the physical overseas telegram web by running fiberoptic lines deeper into vicinities. This reduces the figure of overseas telegram modems served by each node section, and therefore, increases the sum of bandwidth available to endorsers ( Medin, 1999 ) .

Another advantage of overseas telegram modems is that they are non the traffic constrictions on a overseas telegram information web. The overseas telegram modems have enormous throughput capacity. It is the other constituents of the overseas telegram web and the Internet itself that slow traffic down. Some of the points that slow down a overseas telegram information web are the 1.5 Mbps T-1 overseas telegram Internet connexion, the Ethernet Personal computer interface card, current Personal computer engineering, and plain old Internet congestion. But all these points are being upgraded to let ultra-fast informations traffic. The Internet is traveling through turning strivings and there is still a batch of turning to make ( Medin, 1999 ) .

Cable modem engineering does hold some disadvantages. Cable information webs are still in their babyhood and are traveling to see some turning strivings as the remainder of the Internet is upgraded to manage more traffic. Most of the disadvantages of overseas telegram informations systems the consequence of bequest issues within the CATV systems. However, the overseas telegram companies were cognizant of these disadvantages before they got into the concern, and they know how to get the better of the jobs. The solutions to the most of the jobs of overseas telegram informations webs are known. But, it will take a great trade of money to implement these solutions. The MSOs have invested already invested one million millions in making overseas telegram informations webs, and they are willing to put more to stay competitory with the telephone industry.

The biggest bequest issue induced job confronting overseas telegram modem engineering is that CATV systems were originally designed to transport Television programming from the overseas telegram operator to the subscriber & # 8217 ; s place. The CATV systems were ne’er intended to be used for bipartisan or point-to-point communications. The MSOs have the capableness to upgrade their systems to present bipartisan informations communications by exchanging to HFC works, but there are no easy solutions to the point-to-point communicating quandary. The tree and subdivision constellation of a CATV system is non contributing to point-to-point communicating. There was no demand for sophisticated exchanging systems, like those used in a telephone system, when the CATV systems were first developed. Unfortunately for the MSOs, a shift web is indispensable for point-to-point communicating.

Another disadvantage of overseas telegram informations systems is slow upstream communicating. But, fortuitously for the MSOs, the high-velocity telephone informations engineerings besides have this job. The root of the job is that CATV systems were chiefly designed for downstream bringing of Television scheduling. So, the bulk of the coaxal overseas telegram bandwidth of a CATV system was dedicated to downstream traffic. There was really small bandwidth set aside for upstream traffic. To farther complicate affairs, the overseas telegram modem makers are doing their merchandises use much narrower bandwidth, 2 MHz, for upstream communicating.

The issue of shared bandwidth is besides a disadvantage for the overseas telegram informations systems. If the MSOs do non upgrade capacity as more people sign up, overseas telegram modem entree velocities may go slower. Upgrading capacity is a reasonably straightforward exercising for the MSOs. It is merely a inquiry of if the MSO & # 8217 ; s are willing to put the money to do the ascents. Another shared bandwidth issue is security. All the downstream traffic in a overseas telegram information web goes to all the overseas telegram modems in the web and all the upstream bandwidth is shared by all the overseas telegram modems in a local cringle. IP and web protocols are used to do certain traffic is unafraid and routed decently. Many of the non-standardized first coevals overseas telegram modems did non hold encoding capablenesss, so users were able to entree other user & # 8217 ; s traffic. Second coevals modems and CMTS equipment are built harmonizing to the DOCSIS specification, which contains security and information encoding demands. Still another disadvantage of utilizing a overseas telegram modem is that the user does non hold a pick of ISPs. The lone ISP available to a overseas telegram modem user is the local overseas telegram company. This is because overseas telegram Television lines do non hold & # 8216 ; common-carrier & # 8217 ; position as do phone lines. However, there are some attempts underway to alter this.

The recommended application for overseas telegram modems is for private, non commercial usage. Because of the shared bandwidth issue, most MSOs will non let a endorser to host a waiter with their overseas telegram modem. A overseas telegram modem endorser who tried to host a waiter would utilize a great trade of the shared bandwidth, which would be damaging to the other endorsers on the cringle. But, for a private user, overseas telegram modem systems decidedly offer the most bandwidth for the money. There are about 75 million overseas telegram Television endorsers in North America ( Medin, 1999 ) . As of August 1999, overseas telegram operators were offering bipartisan high-velocity Internet service to about half of these clients ( Medin, 1999 ) . More than one million of these endorsers have signed up for overseas telegram modem service.

The future chances of the overseas telegram modem are first-class. The current overseas telegram modem engineering is stable and betterments are being developed at a rapid gait. Soon there will be internal overseas telegram modems on the market that will non necessitate the Ethernet interface. There is enormous upgrade capacity available to the MSOs and it appears that the MSOs are willing to do the capital investings required to do the ascents. The MSOs have already moved the fiberoptic overseas telegram stopping point to the end-users. It remains to be seen if the MSOs will travel the fiberoptic overseas telegram all the manner to the end-user. The coax part of the HFC web that goes the & # 8220 ; concluding stat mi & # 8221 ; to the place is restricting factor to wide bandwidth. Peoples are calculating that the house of tomorrow will be wholly networked. A great trade of bandwidth, more than there is available now, it traveling to be needed to carry through this. Right now, there is guess that as more and more people start utilizing broadband entree, there will come a point where there are so many high-velocity users that the Internet & # 8217 ; s anchor will be & # 8220 ; broken & # 8221 ; . But, this will non go on if anchor capacity is upgraded. If the Internet anchor is non upgraded, upgrading the overseas telegram informations webs will be like constructing a new ace fast off-ramp to the main road. Cable modem users will be able to acquire on the Internet main road much faster. But, they will happen a traffic jam on the main road when they get at that place. Fortunately, the costs associated with upgrading the Internet anchor will be little in comparing to the cost of make overing other parts of the Internet to better public presentation. Besides, there is the issue of overseas telegram modems altering Internet use forms. As webs perform better, people are traveling to demand more and more out of them. To utilize the overused main road analogy, current Internet traffic is composed by and large of little autos ( e-mail ) and some trucks ( artworks ) and merely seldom a convoy of trucks ( big audio/video files or plans ) . Traffic flows swimmingly most of the clip. However, if the composing of Internet traffic displacements to a great extent towards sound and picture files, it would intend more and more truck convoys will be on the main road, taking up whole lanes and cut downing the infinite available for other traffic. The future looks bright for overseas telegram modems, but the powers that be must see the Internet can manage the increased traffic that will ensue from the growing of overseas telegram informations webs.

The hereafter holds a batch of competition for the overseas telegram modem industry. There are other high-velocity informations engineerings on the skyline which are traveling to be in ferocious competition with overseas telegram informations webs. Right now, overseas telegram modems offer the simplest, fastest and cheapest broadband entree. But this could easy alter in the hereafter. The phone companies are looking to give the overseas telegram companies some more competition in the high-velocity Internet entree market. Asynchronous Digital Subscriber Lines ( ADSL ) are merely get downing to come on line. ADSL velocity should be comparable to overseas telegram modems. However, velocity will depend on the user & # 8217 ; s distance to the following telephone company switch. A possible ADSL client can no be any farther from 15,000 pess from the switch if 26-gauge twisted-pair wire is used. However, this distance increases to 18,000 pess if 24-gauge wire is used ( Clark, 1999 ) . With ADSL, the closer 1 is to the telephone company switch, the higher the connexion velocity. Like a traditional dial-up modem, ADSL will supply the user with a dedicated, ever on, line to his ISP. Because there is a dedicated connexion, there will non be any shared bandwidth concerns like there are for overseas telegram modems. ADSL uses filters to divide the bing Cu phone line into three separate frequence channels. A 0- to 4-KHz set carries the traditional parallel telephone signal and a higher frequence set is used for upstream information transportations at rates up to 640 Kbps. The remainder of the set is used to convey informations downstream, either from the Internet or as video-on-demand, at velocities of up to 8 Mbps. ADSL is likely to be more expensive than overseas telegram informations entree and it is excessively early to find how fast ADSL will be in the existent universe ( Clark, 1999 )

Another beginning of competition for the MSOs is a satellite-based, high-velocity Internet service called DirecPC, which is available through Hughes Network Systems ( Clark, 1999 ) . For $ 499, U.S. clients can buy a kit that includes a orbiter having dish, a Personal computer interface card, and package. This monetary value does non installation. With this service, upstream transmittals are sent via dial-up connexions to the ISP. The upstream information petitions go to the DirecPC orbiter web operations centre, which broadcasts the requested informations down to the users from a Galaxy IV Satellite at rates up to 400 Kbps. This service starts at $ 9.95 per month, but goes up to $ 129.95 per month for the premium bundle. With the basic $ 9.95 rate, the user will besides be charged 60 cents for each M of information downloaded from the orbiter ( Clark, 1999 ) .

Another hereafter beginning of competition for overseas telegram modems is wireless overseas telegram. Wireless overseas telegram sounds like an oxymoron, but wireless overseas telegram Television is already an established concern. Wireless overseas telegram plants by utilizing a orbiter system to air multichannel Television scheduling to places equipped with dish aerials that operate in the 2- to 2.6-GHz scope ( Clark, 1999 ) . The system can besides be used to convey informations every bit good. The downstream informations from the orbiter is received by the dish, which passes the information through coaxial overseas telegram to a particular modem that converts the signal into IP data the computing machine can computing machine understand. This procedure works for downstream informations, but upstream informations transmittal involves utilizing a standard parallel telephone line. The industry is working to set up a wireless upstream way, but a feasible solution is at least two old ages off ( Clark 1999 ) .

Cable modems are the moving ridge of the hereafter. Of all the current broadband engineerings, overseas telegram modems offer the most benefits. Cable modems are simple to run, make non necessitate a great trade of immaterial hardware, offer the fastest connexion velocities, and are the least expensive of all the options. There are some disadvantages to overseas telegram modems and overseas telegram informations systems, but there are solutions to these disadvantages. Merely as computing machines have already done, networking will go a big portion of mundane life. Better networking means holding more velocity, and holding more velocity takes holding more bandwidth, and overseas telegram informations webs provide that bandwidth. As more people begin to utilize overseas telegram modems, the MSOs will hold to upgrade the capacity of the system. This means they will hold increase the fiberoptic parts of the HFC webs. As the fiberoptic parts of the MSO & # 8217 ; s HFC webs grow larger, fiberoptic overseas telegram will acquire closer and closer to the place. Cable modems are the forerunner of things to come because they will drive the demand for fiberoptic to the place. Fiber-optic to the place is merely a affair of clip, and when this happens the Internet will go even bigger than anyone has imagined.

Mentions

Barnes, B. , Feinberg, B. ( 1997 ) . Cable modems burn up the wires. C/Net. [ No folio ] Retrieved September 16, 1999 from the World Wide Web: //http: //www.cnet.com/Content/Features/Techno/Cablemodems/index.html

Brownstein, M. ( 1997, October ) . Batter up for broadband. Byte. [ No folio ] . Retrived September 16, 1999 from the World Wide Web: //http: //www.byte.com/art/9710/sec5/art5

Clark, D. D. ( 1999, October ) . High-speed information races place. Scientific American, 94-99.

Halfhill, T. R. ( 1996, September ) . Interrupt the bandwidth barrier. Byte. [ No folio ] . Retrived September 16, 1999 from the World Wide Web: //http: //www.byte.com/art/960910/sec6/art1

Medin, M. , Rolls, J. ( 1999, October ) . The cyberspace via overseas telegram. Scientific American,

100-101

Ostergard, R.V. ( 1998 ) . ABC of overseas telegram modems. Cablemodems.org. [ No folio ] . Retrieved September 7, 1999 from the World Wide Web: // hypertext transfer protocol: //www.cablemodems.org/tutorial/01.htm

Salent, M.D. ( 1999 ) Cable modem proficient tutorial. Cable Modem Information Network. [ No folio ] . Retrieved September 20, 1999 from the World Wide Web: // hypertext transfer protocol: //www.cablemodem.net/tt/primer.html

Van Matre, D.L. ( 1999 ) Overview of overseas telegram modem engineering and services. Cable Data Communications. [ No folio ] . Retrieved September 20, 1999 from the World Wide Web: //http: //www.cabledatacom.com/cmic/mic1.html