From editor@telecom-digest.org Sat Jan 31 13:57:22 2004 Received: (from ptownson@localhost) by massis.lcs.mit.edu (8.11.6p2/8.11.3) id i0VIvMQ03454; Sat, 31 Jan 2004 13:57:22 -0500 (EST) Date: Sat, 31 Jan 2004 13:57:22 -0500 (EST) From: editor@telecom-digest.org Message-Id: <200401311857.i0VIvMQ03454@massis.lcs.mit.edu> X-Authentication-Warning: massis.lcs.mit.edu: ptownson set sender to editor@telecom-digest.org using -f To: ptownson Approved: patsnewlist Subject: TELECOM Digest V23 #49 TELECOM Digest Sat, 31 Jan 2004 13:55:00 EST Volume 23 : Issue 49 Inside This Issue: Editor: Patrick A. Townson AT&T Wireless Offer Provides Free, Unlimited Mobile-to-Mobile (Solomon) Ads for Gambling Sites Abound Despite Legal Crackdown on Media (Solomon) Comcast Takes on Broadcast TV for Local Ads (Monty Solomon) Hughes Cuts Jobs, Boosts DirecTV Prices (Monty Solomon) The Company They Kept (Monty Solomon) Cell Phone Explosion Burns Man's Buttocks (Monty Solomon) Making the Call / It's Not as if Their Lifelong Ambition (Monty Solomon) Re: VOIP Over Private IP (Bob Snyder) Vonage Router Taken Abroad? (Chas) Re: Some *Good News* About Norvergence! (BMN) Re: Need to Host Child Porn, Illegal Content, Spam? (Fritz Whittington) Re: Treo 600 - Not Turning Off (Gordon S. Hlavenka) Wireless Transmission (Ijaz Ahmed) Optical Fiber (Ijaz Ahmed) All contents here are copyrighted by Patrick Townson and the individual writers/correspondents. Articles may be used in other journals or newsgroups, provided the writer's name and the Digest are included in the fair use quote. By using -any name or email address- included herein for -any- reason other than responding to an article herein, you agree to pay a hundred dollars to the recipients of the email. =========================== Addresses herein are not to be added to any mailing list, nor to be sold or given away without explicit written consent. Chain letters, viruses, porn, spam, and miscellaneous junk is definitely unwelcome. We must fight spam for the same reason we fight crime: not because we are naive enough to believe that we will ever stamp it out, but because we do not want the kind of world that results when no one stands against crime. Geoffrey Welsh =========================== See the bottom of this issue for subscription and archive details and the name of our lawyer; other stuff of interest. ---------------------------------------------------------------------- From: Monty Solomon Subject: AT&T Wireless Offer Provides free, Unlimited Mobile-to-Mobile Date: Fri, 30 Jan 2004 18:54:01 -0500 BASKING RIDGE, N.J.--(BUSINESS WIRE)--Jan. 30, 2004--AT&T Wireless (NYSE:AWE) today announced an offer -- the first of its kind -- that can give new and current customers on qualifying plans the freedom to make unlimited domestic mobile-to-mobile calls at no charge to any of the company's nearly 22 million customers. - http://finance.lycos.com/home/news/story.asp?story=40359863 ------------------------------ Date: Fri, 30 Jan 2004 18:29:16 -0500 From: Monty Solomon Subject: Ads for Gambling Sites Abound Despite Legal Crackdown on Media By Kate Kaye Contributing Writer Who will win the coin toss or be first to challenge a referee call? Better yet, who will win the halftime pay-per-view Lingerie Bowl? No matter who is betting on what this Sunday, odds are that many Super Bowl-related wagers will be placed online. Prominent Web media outlets like MSNBC.com and Lycos could lead the way, despite a government crackdown on media companies that run ads for online gambling sites. http://www.mediapost.com/dtls_dsp_news.cfm?newsID=236319 ------------------------------ Date: Fri, 30 Jan 2004 18:51:34 -0500 From: Monty Solomon Subject: Comcast Takes on Broadcast TV For Local Ads By Michael Learmonth NEW YORK, Feb 2 (Reuters) - Comcast Corp. (NASDAQ:CMCSA), the No. 1 U.S. cable operator, has forged alliances with cable operators around the country in the past year to get a bigger share of the $28 billion local advertising market from broadcasters. The culmination of the effort, to be announced Monday, is called "Comcast Spotlight," the company's $1 billion local advertising sales operation, which will sell time not only on Comcast's systems but on others in 75 markets. The alliances will allow Comcast to sell advertising in regional markets served by rival cable operators, a direct challenge to broadcast TV which has enjoyed a de facto monopoly on local advertising. - http://finance.lycos.com/home/news/story.asp?story=40364114 ------------------------------ Date: Fri, 30 Jan 2004 23:58:19 -0500 From: Monty Solomon Subject: Hughes Cuts Jobs, Boosts DirecTV Prices By Greg Tarr El Segundo, Calif. - Hughes Electronics said it has begun an 'organizational restructuring' effort, which has reduced certain Hughes Corp. administrative jobs and relocated others to its DirecTV unit. Now under the direction of News Corp., the company said it has 'consolidated several functions that have been based at the company into its DirecTV unit.' As a result of the restructuring, approximately 50 positions have been eliminated at the Hughes corporate office, while approximately 30 other posts were relocated to DirecTV. A Hughes spokesperson said the jobs were primarily administrative support positions. http://www.twice.com/index.asp?layout=story&doc_id=130801 ------------------------------ Date: Sat, 31 Jan 2004 00:25:48 -0500 From: Monty Solomon Subject: The Company They Kept By ROGER LOWENSTEIN In the old days in Coudersport, a tiny Pennsylvania town at the northern edge of Appalachia, if you had trouble with your cable hookup, you simply called John Rigas to come over and fix it. If you needed a loan, or a few bucks for a local charity drive, you darn sure called him too. There didn't seem to be anyone in this town of 2,600 that Rigas wouldn't help, or didn't like, which is maybe why Rigas seemed cut from the same cloth as his idol, the pundit Will Rogers. Rigas's other hero was Sam Walton, and like the folksy Walton, Rigas built his company, Adelphia Communications, from scratch into a giant corporation. This sort of story has become so familiar in recent years that you almost don't have to add the kicker. Yes, it all came tumbling down. Yes, Rigas's company failed, and Rigas himself, along with two of his sons, is sitting in the dock, accused of the worst case of looting of any C.E.O. of the Enron era. The difference is that unlike other supposed villains, Rigas, a 79-year-old son of Greek immigrants, was a genuine business hero, a pioneer in cable television. Many of the current corporate miscreants -- think Dennis Kozlowski of Tyco -- appear to be calculating and utterly unrepentant. Rigas, who has spent much of the past two years in a state of shock, is nothing if not likable. And when he goes on trial this month in Manhattan's federal courthouse, the jurors will confront the improbable: a central figure in a white-collar scandal who is as ordinary as they are. The mystery of how Rigas, a frail, white-haired man who seemingly had neither the motive nor the disposition to commit a fraud, came so undone, has riveted his hometown. Some say the answer lies with his sons, who directed the company's frantic growth in the late 90's; others cite the family's habit of blurring private interests and public ones, which was pretty easy to do in a remote company town like Coudersport. Mystery or not, Rigas's fall says a lot about America's wave of business scandals. The explanation put forth by people from Alan Greenspan on down is that executives got greedy (as if that were something new), but Rigas, who never sold a share of his company's stock, and didn't get stock options either, doesn't quite fit the mold. So what else was it? However badly the Rigases behaved, they were helped along the way by lenders and investment bankers, auditors, lawyers, analysts -- just about anyone whose job it should have been to protect the public. And this is what truly distinguishes the latter stages of the last bull market: not that a handful of executives got greedy but that the safeguards supposedly built into our financial culture stopped functioning. http://www.nytimes.com/2004/02/01/magazine/01RIGAS.html ------------------------------ Date: Sat, 31 Jan 2004 01:34:43 -0500 From: Monty Solomon Subject: Cell Phone Explosion Burns Man's Buttocks KUALA LUMPUR, Malaysia -- A Malaysian man was shaken and scalded Tuesday after his mobile phone exploded beside him while he was sleeping, the national news agency reported. Mohamed Radzuan Yasin said he was recharging his cell phone and placed it on his bed near him before he took a nap. Three hours later, he was jarred awake by what he described as a small explosion. http://www.boston.com/news/odd/articles/2004/01/27/cell_phone_explosion_burns_mans_buttocks/ ------------------------------ Date: Sat, 31 Jan 2004 10:26:16 -0500 From: Monty Solomon Subject: Making the Call It's not as if their lifelong ambition is to irritate us at dinnertime By Wells Tower Sunday, January 25, 2004; Page W12 Washington Post Magazine Sometimes when Darren Dooley's team of telemarketers is not selling as much as it might be, a quick word of encouragement will get the crew back on track. Other times, the situation requires what Dooley, who is the night and weekend manager at RDI Marketing in Cincinnati, calls "lighting a fire under their [butts]." It is late morning on a Sunday, and Dooley has just ordered 15 employees to lay down their headsets and report to the training room. They regard him nervously. They can hear the tinder beginning to crackle. "All right, listen up," Dooley says. "Everyone in this room has one thing in common, and one thing only. You're all sitting in there collecting a paycheck and you all have zero sales." The under-performers, mostly high school and college students, have spent the morning trying to persuade people all across America to sign up for new Gold MasterCards. They nibble their lips, fiddle with their cuticles. They look guilty and bored. "I know it's Sunday, but that's no excuse," he says. "I don't care what the situation is. If you call somebody and he's already pissed off, then try to make him happy. There's other people in there who've got four and five sales. They're being assumptive. They're being enthusiastic. If you're not getting sales, it's because you're in there talking and . . . not giving a hundred percent." http://www.washingtonpost.com/wp-dyn/articles/A36801-2004Jan21.html ------------------------------ Subject: Re: VOIP Over Private IP From: Bob Snyder Date: Fri, 30 Jan 2004 14:31:23 -0500 nyukfah@pd.jaring.my (nyuk fah) writes: > My current internet connection is private ip and behind a firewall. > Thus I wonder any solution VOIP over HTTP? Which I can solve the > private IP and firewall limitation? No, not over HTTP, at least if you want decent quality VoIP, since HTTP uses TCP as it's transport. TCP guarantees a complete and in-order data stream, and does this by stopping the flow of data to an application under it gets missing packets resent by not acknowledging them to the sender. Thus, a couple of missing packets could easily cause at least several seconds of no audio, even though the missing packets may only make up a fraction of a second of loss. VoIP usually uses UDP for the audio connection, with H.323 or SIP controlling it. Many firewalls have provisions to be configured to properly NAT H.323, or you could use a gatekeeper routed setup for H.323. SIP has provisions for proxy servers and NAT inside the protocol. You probably want to check your firewall's documentation and see if it supports firewalling/NAT'ing H.323. Bob ------------------------------ From: xarush@omelas.com (Chas) Subject: Vonage Router Taken Abroad? Date: 30 Jan 2004 16:59:07 -0800 Organization: http://groups.google.com I have a Vonage phone and I am really satisfied with the service. I wonder if anyone has any experience taking the router to different countries. I was thinking of sending one to my friend Gustavo in South America. He has a high speed internet connection. Any thoughts? Any Experience? Thanks. Chas [TELECOM Digest Editor's Note: Vonage works anywhere there is high- speed internet. Gustavo will have to have a USA phone number, however. Maybe when you get it for him, have Vonage set it up with a number in the same community yourself, so that your calls to him will always be free even if you use some other hardwired phone (in your town) to call him other than your Vonage line. His calls to you or anywhere else will always be 'free' of course. You are *certain* he has high speed broadband service? Some times people in other countries refer to 'high speed' when they actually mean 56-K dialup. I will help you pay for setting him up: write and ask for an e-coupon for one month of free service. You get the box and pay for the first month's service, then apply the e-coupon I will send on request for the *second* month's service. Actually, you use the link in the e-coupon to open his account in order to get the one month free. Write to me not-for pub and ask for a Vonage account. PAT] ------------------------------ From: BMN Subject: Re: Some *Good News* About Norvergence! Date: Fri, 30 Jan 2004 19:35:01 -0500 Organization: Bell Sympatico Well that's just great, but what happens when you factor in the cost of the matrix box + interest over five years? I would think that would chip away at my real potential saving considerably. On average I can save a client 30% off their telecom expenses without signing any long term contracts or requiring any capex. That's just simple optimization. Also, what happens next time a better deal comes around? The client is stuck! If you consider that next opportunity could save them 20% or more then the NorVergence solution again becomes uncompetitive. It's not like you can go to Norvergence and renegotiate your rates now is it? Moreover the more clients they get the more minutes they buy, the better the deal for NorVergence, but do they pass on the saving to their clients? Regardless of what happens in the telecom sector you are stuck paying X $ until the end of the lease. By the way, then what? What happens at the end of the lease? Is there an equipment buyout? Will Norvergence try and re-sign you for another 60 months? -- yikes! --> If I save $$ in my first two years with them but is costs me $$$ over the next 3 years plus I end up paying $10000 for a $2000 channel bank, I am sorry but their deal just plain sucks. What is truly unfortunate is that these people got sucked in and they have no clue. And I can assure you that I am not a disgruntled ex employee of NorVergence. If any of you manage a telecom dept or a clients, just do quarterly reviews on your service or better yet hire a consultant to do it for you. Keep yourself optimized and on track with the latest products and services. If NorVergence offered 12 month terms, I might be compelled to review their offering. Things change too quickly to be locking yourself or a client into a 60 month term. It's just irresponsible. (IMHO) Brett (flame suit, ON!) TELECOM Digest Editor wrote in message news:telecom23.48.1@telecom-digest.org: > Lord knows we have had enough bad news about the Norvergence people here > in recent weeks, lawsuits, complaints from people who say they were > defrauded, lured into seemingly endless deals with finance companies, > disgruntled employees, etc. [TELECOM Digest Editor's Note: And it is that finance company with no outs allowed which is the hard pill to swallow, isn't it? So much of what Norvergence says is purely an applications problem, Maybe it will work out well for some customers, or maybe not others. Now if Norvergence offered an 'early buy out' option, where the customer and the company both made some compromises, that would work better for a lot of guys. The VP of Telecom (or whatever his/her title is) gets pissed, comes into work and says 'get that junk out of here'. So Norvergence and the telecom manager make an arrangement fair to both and Norvergence aids in an orderly transition to the system the Telecom people want. That would be a little easier to deal with. PAT] ------------------------------ From: Fritz Whittington Subject: Re: Need to Host Child Porn, Illegal Content, or Spam Server? Date: Sat, 31 Jan 2004 02:08:58 GMT Organization: AT&T Worldnet On or about 2004-01-30 11:30, Matt Simpson whipped out a trusty #2 pencil and scribbled: > Lisa Minter wrote in message > news:: >> I got this spam in email today. My question is, why don't police or >> FBI nip this in the bud, stop it before it even gets started? > Maybe because it's the police or FBI sending it out as a sting > operation, trying to catch people stupid enough to respond to > something that's so blatant about being illegal. Could be. I don't read much Russian, but I think this may be a "joe job". The site seems to be pretty legitimate, at first glance. The odd thing is, the spam email seems to originate from somewhere in China. Not to mention that I really can't see a Russian company co-operating with the FBI ... Fritz Whittington I know how men in exile feed on dreams of hope (Aeschylus, Agamemnon) ------------------------------ Date: Sat, 31 Jan 2004 00:36:35 -0600 From: Gordon S. Hlavenka Reply-To: nospam@crashelectronics.com Organization: Crash Electronics Subject: Re: Treo 600 - Not Turning Off Jeff wrote: > Ever since I got my Treo 600, it has not been able to turn itself off > when it is charging. Even though, I have the setting "turn off after 1 > minute", it stays on all night when I have it plugged in and charging! Perhaps the Treo is using its microprocessor to monitor the charging process. I know the HP100LX and 200LX work like this; even pressing the Power button won't turn them off when they're plugged in with battery charging enabled. > ... will this hurt the Treo if the screen stays on overnight when > charging? Probably not. The backlight probably has a lifespan, so if it's on all the time that could cause problems. But the LCD doesn't care. Gordon S. Hlavenka http://www.crashelectronics.com "If we imagined he could _find_ the car, we could pretend it might be fixed." - Calvin ------------------------------ From: Ijaz Ahmed Subject: Wireless Transmission Date: Sat, 31 Jan 2004 03:10:32 +0500 Hi! I am Ijaz Ahmed from Pakistan . Here are my research articles about Wireless Transmission Please post them in the Digest For the benefit Of Telecomm readers. Thanks! Ijaz WIRELESS TRANSMISSION For unguided media, transmission and reception are achieved by means of an antenna. For transmission, the antenna radiates electromagnetic energy into the medium (usually air), and for reception, the antenna picks up electromagnetic waves from the surrounding medium. There are basically two types of configurations for wireless transmission: directional and omnidirectional. For the directional configuration, the transmitting antenna puts out a focused electromagnetic beam; the transmitting and receiving antennas must therefore be carefully aligned. In the omnidirectional case, the transmitted signal spreads out in all directions and can be received by many antennas. In general, the higher the frequency of a signal, the more it is possible to focus it into a directional beam. Three general ranges of frequencies are of interest in our discussion of wireless transmission. Frequencies in the range of about 2 GHz (gigahertz = 109 Hz) to 40 GHz are referred to as microwave frequencies. At these frequencies, highly directional beams are possible, and microwave is quite suitable for point-to-point transmission. Microwave is also used for satellite communications. Frequencies in the range 30 MHz to 1 GHz are suitable for omnidirectional applications. We refer to this range as the broadcast radio range. Another important frequency range, for local applications, is the infrared portion of the spectrum. This covers, roughly, from 3 X 10 n to 2 X 10M Hz. Infrared is useful to local point-to-point and multipoint applications within confined areas such as a single room. Terrestrial Microwave Physical Description The most common type of microwave antenna is the parabolic dish. The antenna is fixed rigidly and focuses a narrow beam to achieve line of-sight transmission to the receiving antenna. Microwave antennas are usually located at substantial heights above ground level in order to extend the range between antennas and to be able to transmit over intervening obstacles. To achieve long-distance transmission, a series of microwave relay towers is used, and point-to-point microwave links are strung together over the desired distance. Applications The primary use for terrestrial microwave systems is in long-haul telecommunications service, as an alternative to coaxial cable or optical fiber. The microwave facility requires far fewer amplifiers or repeaters than coaxial cable requires over the same distance, but necessitates line-of-sight transmission. Microwave is commonly used for both voice and television transmission. Another increasingly common use of microwave is for short point-to- point links between buildings. This can be used for closed-circuit TV or as a data link between local-area networks. Short-haul microwave can also be used for "bypass"applications. A business can establish a microwave link to a long-distance telecommunications facility in the same city, bypassing the local telephone company. Transmission Characteristics Microwave transmission covers a substantial portion of the electro- magnetic spectrum. Common frequencies used for transmission are in the range 2 to 40 GHz. The higher the frequency used, the higher the potential bandwidth and therefore the higher the potential data rate. As with any transmission system, a main source of loss is attenuation. This loss is proportionally less than with twisted pair or coaxial cable, allowing repeaters or amplifiers to be placed farther apart for microwave systems-10 to 100 km is typical. Attenuation is increased with rainfall. The effects of rainfall become especially noticeable above 10 GHz. Another source of impairment is interference. With the growing popularity of microwave, transmission areas overlap and interference is always a danger. Thus, the assignment of frequency bands is strictly regulated. Satellite Microwave Physical Description A communication satellite is, in effect, a microwave relay station. It is used to link two or more ground-based microwave transmitter/receivers, known as earth stations or ground stations. The satellite receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink). A single orbiting satellite will operate on a number of frequency bands, called transponder channels or simply transponders. Two common configurations for satellite communication are generally used In the first, the satellite is used to provide a point-to-point link between two distant ground-based antennas. In the second, the satellite provides communications between one ground-based transmitter and a number of ground-based receivers. For a communication satellite to function effectively, it is generally required that it remain stationary with respect to its position over the earth. Otherwise, it would not be within the line of sight of its earth stations at all times. Applications The communication satellite is a technological revolution as important as fiber optics. Among the most important applications for satellites: 1. Television distribution 2. Long-distance telephone transmission 3. Private business networks Because of their broadcast nature, satellites are well suited to television distribution and are being used extensively for this purpose throughout the world. In its traditional use, a network provides programming from a central location. Programs are transmitted to the satellite and then broadcast down to a number of stations, which then distribute the programs to individual viewers. A more recent application of satellite technology to television distribution is direct broadcast satellite (DBS), in which satellite video signals are transmitted directly to the home user. Satellite transmission is also used for point-to-point trunks between telephone exchange offices in public telephone networks. It is the useful medium forhigh-usage international trunks and is competitive with terrestrial systems for many long-distance intranational links, particularly in remote and undeveloped areas. Finally, there are a number of business data applications for satellite. The satellite provider can divide the total capacity into a number of channels and lease these channels to individual business users. A user equipped with the antennas at a number of sites can use a satellite channel for a private network. Traditionally, such applications have been quite expensive and limited to larger organizations with high-volume requirements. Today, the very small aperture terminal (VSAT) system, which provides a low-cost alternative is also in use . A number of subscriber stations are equipped with low-cost VSAT antennas. Using some discipline, these stations share a satellite transmission capacity for transmission to a hub station. The hub station can exchange messages with each of the subscribers and can relay messages between subscribers. Transmission Characteristics The optimum frequency range for satellite transmission is in the range 1 to 10 GHz. Below 1 GHz, there is significant noise from natural sources, including galactic, solar, and atmospheric noise, and human made interference from various electronic devices. Above 10 GHz, the signal is severely attenuated by atmospheric absorption and precipitation. Most satellites providing point-to-point service today use a frequency band width in the range 5.925 to 6.425 GHz for transmission from earth to satellite (uplink) and a bandwidth in the range 4.7 to 4.2 GHz for transmission from satellite to earth (downlink). This combination is referred to as the 4/6-GHz band, or C band. Note that the uplink and downlink frequencies differ. For continuous operation without interference, a satellite cannot transmit and receive on the same frequency. Thus, signals received from a ground station on one frequency must be transmitted back on another. Several properties of satellite communication should be noted. First, because of the long distances involved, there is a propagation delay of about 0.25 sec from transmission from one earth station to reception by another earth station. This delay is noticeable in ordinary telephone conversations. It also introduces problems in the areas of error control and flow control . Second, satellite microwave is inherently a broadcast facility. Many stations can transmit to the satellite, and a transmission from a satellite can be received by many stations. ------------------------------ From: Ijaz Ahmed Subject: Optical Fiber Date: Sat, 31 Jan 2004 03:13:51 +0500 OPTICAL FIBER Physical Description An optical fiber is a thin, flexible medium capable of conducting an optical ray. Various glasses and plastics can be used to make optical fibers. The lowest losses have been obtained using fibers of ultrapure fused silica. Ultrapure fiber is difficult to manufacture; higher-loss multi component glass fibers are more economical and still provide good performance. Plastic fiber is even less costly and can be used for short-haul links, for which moderately high losses are acceptable. An optical fiber has a cylindrical shape and consists of three concentric sections . The two innermost are two types of glass with different indexes of refraction. The center one is called the core, and the next layer the cladding. These two sections of glass are covered by a protective and light absorbing jacket. Optical fibers are grouped together into optical cables. Applications One of the most significant technological breakthroughs in data transmission has been the development of practical fiber optic communications systems. Optical fiber already enjoys considerable use in long-distance telecommunications, and its use in military applications is growing. The continuing improvements in performance and decline in prices, together with the inherent advantages of optical fiber, have made it increasingly attractive for local-area networking. The following characteristics distinguish optical fiber from twisted pair or coaxial cable: Greater capacity. The potential bandwidth, and hence data rate, of optical fiber is immense; data rates of 2 Gbps over tens of kilometers have been demonstrated. Compare this to the practical maximum of hundreds of Mbps over about 1 km for coaxial cable and just a few Mbps over 1 km or up to 100 Mbps over a few tens of meters for twisted pair. Smaller size and lighter weight. Optical fibers are considerably thinner than coaxial cable or bundled twisted-pair cable-at least an order of magnitude thinner for comparable information transmission capacity. For cramped conduits in buildings and underground along public rights of-way, the advantage of small size is considerable. The corresponding reduction in weight reduces structural support requirements. Lower attenuation. Attenuation is significantly lower for optical fiber than for coaxial cable or twisted pair and is constant over a wide range of frequencies. Electromagnetic isolation. Optical fiber systems are not affected by external electromagnetic fields. Thus, the system is not vulnerable to interference, impulse noise, or crosstalk. By the same token, fibers do not radiate energy, causing little interference with other equip- ment and providing a high degree of security from eavesdropping. In addition, fiber is inherently difficult to tap. Greater repeater spacing. Fewer repeaters means lower cost and fewer sources of error. From this point of view the performance of optical fiber systems has been steadily improving. Five basic categories of application have become important for optical fiber: 1. Long-haul trunks 2. Metropolitan trunks 3. Rural exchange trunks 4. Subscriber loops 5. Local-area networks Long-haul fiber transmission is becoming increasingly common in the telephone network. Long-haul routes average about 900 miles in length and offer high capacity (typically, 20,000 to 60,000 voice channels). These systems compete economically with microwave and have so under priced coaxial cable in many developed countries that coaxial cable is rapidly being phased out of the telephone network in such countries. Metropolitan trunking circuits have an average length of 7.8 miles and may have as many as 100,000 voice channels in a trunk group. Most facilities are installed in underground conduits and are repeaterless, joining telephone exchanges in a metropolitan or city area. Included in this category are routes that link long-haul microwave facilities that terminate at a city perimeter to the main telephone exchange building downtown. Rural exchange trunks have circuit lengths ranging from 25 to 100 miles and link towns and villages. In the network , they often connect the exchanges of different telephone companies. Most of these systems have fewer than 5000 voice channels. The technology used in these applications competes with microwave facilities. Subscriber loop circuits are fibers that run directly from the central exchange to a subscriber. These facilities are beginning to displace twisted pair and coaxial cable links as the telephone networks evolve into full-service networks capable of handling not only voice and data but also image and video. The initial penetration of optical fiber in this application is for the business subscriber, but fiber transmission into the home will soon begin to appear. A final important application of optical fiber is for local-area networks. Recently, standards have been developed and products introduced for optical fiber networks that have a total capacity of 100 Mbps and can support hundreds or even thousands of stations in a large office building or a complex of buildings. The advantages of optical fiber over twisted pair and coaxial cable become more compelling as the demand for all types of information (voice, data, image, video) increases. TRANSMISSION CHARACTERISTICS Optical fiber systems operate in the range of about 1014 to 1015 Hz; this covers portions of the infrared and visible spectrums. The principle of optical fiber transmission is as follows. Light from a source enters the cylindrical glass or plastic core. Rays at shallow angles are reflected and propagated along the fiber; other rays are absorbed by the surrounding material. This form of propagation is called multimode, referring to the variety of angles that will reflect. When the fiber core radius is reduced, fewer angles will reflect. By reducing the radius of the core to the order of a wavelength, only a single angle or mode can pass: the axial ray. This single-mode propagation provides superior performance, for the following reason. With multimode transmission, multiple propagation paths exist, each with a different path length and hence time to traverse the fiber. This causes signal elements to spread out in time, which limits the rate at which data can be accurately received. Because there is a single transmission path with single-mode transmission, such distortion cannot occur. Finally, by varying the index of refraction of the core, a third type of transmission, known as multimode graded index, is possible. This type is intermediate between the other two in characteristics. The variable refraction has the effect of focusing the rays more efficiently than ordinary multimode, also known as multimode step index. Two different types of light source are used in fiber optic systems: the light emitting diode (LED) and the injection laser diode (ILD). Both are semiconductor devices that emit a beam of light when a voltage is applied. The LED is less costly, operates over a greater temperature range, and has a longer operational life. The ILD, which operates on the laser principle, is more efficient and can sustain greater data rates. There is a relationship among the wavelength employed, the type of transmission, and the achievable data rate. Both single mode and multimode can support several different wavelengths of light and can employ laser or LED light source. In optical fiber, light propagates best in three distinct wavelength "windows," centered on 850, 1300, and 1550 nanometers (nm). These are all in the infrared portion of the frequency spectrum, below the visible-light portion, which is 400 to 700 nm. The loss is lower at higher wavelengths, allowing greater data rates over longer distances . Most local applications today use 850-nm LED light sources. Although this combination is relatively inexpensive, it is generally limited to data rates under 100 Mbps and distances of a few kilometers. To achieve higher data rates and longer distances, a 1300-nm LED or laser source is needed. The highest data rates and longest distances require 1500-nm laser sources. [TELECOM Digest Editor's Note: My thanks to Ijaz Ahmed for sharing his writing on radio waves and fiber optics with us. Those of you in our readership who are familiar with these topics may want to critique the papers presented above and possibly begin a discussion with Ijaz on any errors, etc. PAT] ------------------------------ TELECOM Digest is an electronic journal devoted mostly but not exclusively to telecommunications topics. It is circulated anywhere there is email, in addition to various telecom forums on a variety of networks such as Compuserve and America On Line, Yahoo Groups, and other forums. It is also gatewayed to Usenet where it appears as the moderated newsgroup 'comp.dcom.telecom'. TELECOM Digest is a not-for-profit, mostly non-commercial educational service offered to the Internet by Patrick Townson. All the contents of the Digest are compilation-copyrighted. You may reprint articles in some other media on an occasional basis, but please attribute my work and that of the original author. Contact information: Patrick Townson/TELECOM Digest Post Office Box 50 Independence, KS 67301 Phone: 620-330-6774 Fax 1: 775-255-9970 Fax 2: 530-309-7234 Fax 3: 208-692-5145 Email: editor@telecom-digest.org Subscribe: telecom-subscribe@telecom-digest.org Unsubscribe:telecom-unsubscribe@telecom-digest.org This Digest is the oldest continuing e-journal about telecomm- unications on the Internet, having been founded in August, 1981 and published continuously since then. Our archives are available for your review/research. We believe we are the second oldest e-zine/ mailing list on the internet in any category! 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End of TELECOM Digest V23 #49