124 School of Doctoral Studies (European Union) Journal Cable Modems and Asymmetric Digital Subscriber Lines (ASDL) Abstract

Transcription

1 124 School of Doctoral Studies (European Union) Journal 2012 Cable Modems and Asymmetric Digital Subscriber Lines (ASDL) Peter M. Ross Candidate to MSc at the SDS of the European Union in Brussels, Belgium Abstract Technologies changes all the time. Those who works on computers knows that all too well. Before they get a computer paid off, it is already out of date. Well it is the same way with the internet. The most common way to get on the internet is dial-up-networking, and we all know how slow that can be sometimes, and how aggravating it can be when we get cut off. But that is quickly changing. Two of the recent technologies in connecting to the internet are cable modems and ASDL lines. Will these two new technologies help with the problems we are now having with the Internet, and is it worth the extra money? Read the rest of the essay, and you decide. Below I have summarized both types, expained the comparisons and differences of the two, discussed the limitations of both technologies, and finally the solutions to those limitations. Summary of the Two Related Technologies Cable Modems So what exactly is a cable modem? A cable modem is a modem that received data through your cable TV company. 1 A cable modem will typically have two connections, one cable wall outlet and the other to a computer (PC) 2 Most cable modems are external devices that connect to the PC through a standard 10 Base-T Ethernet card and twisted-pair wiring. 3 So what are the steps involved in the installment process? Below is a description of that installation process: The home user often has to act as his or her own system integrator. Installation requires careful integration of the telephone company service, the terminal adapter, the computer system, and the software. Service from the cable company will likely result in a technician bringing the modem to your home, installing the modem, installing the necessary software, and when the technician leaves your house, you will be up and operating. This places the installation and activation burden on the cable company rather than on the subscriber. 4 1 (13 Mar. 1999). p Cable Modems Overview, Jan, shtml. (13 Mar. 1999). p.1. 3 Cable Modem Frequently Asked Questions. cmic2.htm. (12 Mar. 1999). p Cablemodem FAQ. (14 Mar. 1999). p 1. So we have been talking about cable modems. But is it really a modem? This paragraph answers that question thoroughly. The fact that the word "modem" is used to describe this device can be a little misleading only in that it conjures up images of a typical telephone dial-up modem. Yes, it is a modem in the true sense of the word - it Modulates and Demodulates signals. But the similarity ends there because cable modems are practically an order of magnitude more complicated than their telephone counterparts. Cable modems can be part modem, part tuner, part encryption/ decryption device, part bridge, part router, part NIC card, part SNMP agent, and part Ethernet hub. Typically, a cable modem sends and receives data in two slightly different fashions. In the downstream direction, the digital data is modulated and then placed on a typical 6 MHz television carrier, somewhere between 42MHz and 750 MHz. There are several modulation schemes, but the two most popular are QPSK (up to ~10 Mbps) and QAM64 (up to ~36 Mbps). This signal can be placed in a 6MHz channel adjacent to TV signals on either side without disturbing the cable television video signals. The upstream channel is more tricky. Typically, in a two-way activated cable network, the upstream (also known as the reverse path) is transmitted between 5 and 40 MHz. This tends to be a noisy environment, with lots of interference from HAM radio, CB radios and impulse noise from home appliances. Additionally, interference is easily introduced in the home, due to loose connectors, or poor cabling. Since cable networks are tree and branch networks, all this noise gets added together as the signals travel upstream, School of Doctoral Studies (European Union) Journal

2 2012 Peter M. Ross 125 combining and increasing. Due to this problem, most manufacturers will be using QPSK or a similar modulation scheme in the upstream direction, because QPSK is more robust scheme than higher order modulation techniques in a noisy environment. The drawback is that QPSK is "slower" than QAM. 5 To find out the performance, benefits, and limits please read about them in their perspective places. Asymmetric Digital Subscriber Lines So what are ADSL Lines, and how do they work? First of all, ADSL was originally designed so you still can use it as a regular phone line when the power goes out, which would be a big improvement over BRI ISDN. 6 ADSL is the technology telephone companies are using to offer faster data access over copper phone lines. 7 ADSL Lines works by installing a box that splits the existing phone line. 8 moving internet data more quickly than it does downstream 9 So what is the magic that causes ASDL lines to work this way? Well, ASDL takes advantage of the portion of the bandwidth not used for voice calls. Essentially, it splits the 1 MHZ bandwidth into three information channels: One high-speed downstream channel, one mediumspeed duplex (upstream/downstream) channel, and one conventional voice channel. (Down stream refers to data transmitted from the telephone network to customers to the network). 10 To find out the benefits and limitations of ASDL lines please read about them in their perspective places. 5 Cablemodem FAQ. (14 Mar. 1999). p Kegal, Dan. Dan Kegal ADSL Page about ADSL. (14 Mar. 1999). p Cisc s ADSL Line Attacks Telco Marcket. 2 June, wysiwyg://85/ ww4.zdnet.com/intweek/stories/news/0,4164,320874,00. html. (11 Mar. 1999). p Directions Fall ADSL versus Cable Modems. (14 Mar. 1999). p More on ADSL. html. (12 Mar. 1999). p Analog Devices ADSL (Asymmetric Digital Subscriber Line) Technology. html. (14 Mar. 1999) p Compare and Contrast the Two Related Technologies pertaining to Cost and Performance Cost of Cable Modems and Asymmetric Digital Subscriber Lines So are these two technologies expensive? I guess that depends on your meaning of expensive. The cost of cable modems depends on the way it is purchased. Most users rent the modems from the cable company for just a few dollars, just as they rent their cable boxes. An Ethernet Card is required for a cost of $50.00 or so, and most companies have an installation charge of fifty to one hundred dollars. 11 That was the hardware price. So how much is the monthly charge for the Internet? Well, most cable providers charge $30-50 per month for service, in addition to cable TV fees. In most cases, you do not have to subscribe to cable TV to get cable modem service. 12 The installation and activation fee for ASDL lines are $99.95, and for the equipment it is $ After that the service will range from $49.95 to $ Performance of Cable Modems and Asymmetric Digital Subscriber Lines To talk about the performance of cable modems and ASDL lines we first need to discuss how they connect. With Cable Modems, there are several methods for computer connection, but it appears that Ethernet 10Base-T is emerging as the most predominant method. 14 ADSL modem connects to a standard analog phone line. 15 Next we need to discuss how fast each one is. Claimed speeds (for cable modems) are up from 5 to 30 Mbps (5,000k to 30,000K) for downloading, and 64k to 768 K four uploading 16 However, this is not true with many of the subscribers. Your cable modem will connect to your 11 (13 Mar. 1999). p (13 Mar. 1999) p Fast Access. (12 Mar. 1999). p Cable Modems Overview, Jan, shtml. (13 Mar. 1999). p More on ADSL. html. (12 Mar. 1999). P (13 Mar. 1999) p. 2 Ross P. M. - Cable Modems and Asymmetric Digital Subscriber Lines (ASDL)

3 126 School of Doctoral Studies (European Union) Journal 2012 computer through a 10BaseT Ethernet Card. The maximum bandwidth for that card is 10Mbps, and few people get more than 4 Mbps. 17 That is still fast!!! At least faster than today s on-line services. It s speed can go up to 1000 times faster than today s fastest modems. In 1.2 seconds, a user can download data that today takes 20 minutes to transfer. 18 Just imagine, that means that would save you 19 minutes and almost 59 seconds. You wouldn t even the miss the time it takes to download. ADSL lines are about as fast as cable modems ADSL achieve download speeds of up to 9Mbps and upload speeds of up to 1.5Mbps over regular analog phone lines. It does this by taking advantage of unused frequencies on existing phone lines, which means you can still use the same line for telephone calls. 19 Lets see how this compares with a conventional modem. Data speeds from home computers to the internet will range from 160 kilobits a second, and downstream speeds to the Internet will be one four megabits a second. The most conventional modems operate at 28.8 kilobits a second. 20 This amazing speed allows subscribers to do many things at once. For example, ADSL preserves lifeline services (i.e., the voice network that people depend upon for day-to-day communications and emergency situations). This three-channel approach allows subscribers to send an , download a video for viewing, and talk on the telephone all at the same time. Telecommuters can access their corporate local area network, and simultaneously video conference with a customer. In fact, using ADSL s full capability provides enough bandwidth for running four channels of MPEG compressed video with no interruption to normal telephone service. 21 Some more performance benefits of cable modems are that they do not tie up the phone line, lines are always open (no dialing in, no busy signals), and multiple users (including full cable TV) on a single coax connection. 22 With cable modems, you may also have access to streaming audio and video server, local content (community information and services), access to CD-ROM servers, and a wide variety of other service offerings. New service ideas are being born daily. 23 One other performance benefit of ASDL lines is that homes with a single phone line will be able to make voice calls while connected to the Internet 24 Just think, your family will not get mad for tying up the phone lines. Some other performance benefits are that no dial up process or waiting, runs over a dedicated twisted pair copper line, finally the network is monitored 24 hours/day, 7 day/ week. 25 So how does ADSL cram so much data through a pair of cables? Well, twisted pair copper wire will actually support over 1 megahertz of frequency bandwidth, although long telephone lines may attenuate signals at one MHz by as much as 90 db. One MHz is the upper edge of the band by ADSL. Advanced digital signal processing and creative algorithms provide ADSL with the horsepower to utilize the large dynamic ranges, separate channels, and maintain low noise figures. 26 Here are some very convenient benefits of ASDL Lines. Unlike cable modems, ADSL is easy to install. It uses existing copper twistedpair telephone lines from a local exchange carrier (central office) to the subscriber s home or office. Little or no rewiring is necessary. ADSL is cost-effective. It requires 17 Cable Modems, Jan, wysiwyg://156/ Modems/ (13 Mar. 1999) p Cable Modems Overview, Jan, whatis.shtml. (13 Mar. 1999). p More on ADSL. adsl.html. (12 Mar. 1999). P More on ADSL. adsl.html. (12 Mar. 1999). P Analog Devices ADSL (Asymmetric Digital Subscriber Line) Technology. back_adsl/index.html. (14 Mar. 1999) p Advantages, Jan, shtml. (13 Mar. 1999). p Cable Modem Frequently Asked questions (FAQs). cabledatacomnews.comcmic2.htm. (12 Mar. 1999). p More on ADSL. adsl.html. (12 Mar. 1999). p Dedicated Access. info_dsl.html. (12 Mar. 1999). p Wong, Kevin B. Look Out ISDN, Here Comes ADSL. interworks.org/conference/works97/sessions/sno14/paper.html. (14 Mar 1999). p. 6. School of Doctoral Studies (European Union) Journal

4 2012 Peter M. Ross 127 no major upgrades in the existing telephone network infrastructure. ADSL is viable. Issues that have lowed the deployment of high-speed fiber networks to the home (e.g., prohibitive cost and installation) do not apply. ADSL works with existing POTS (plain-old telephone service). High- Speed data transport can occur simult aneously with voice calls and fax transmissions. 27 Finally, the beauty of ADSL is that you won t have to install and/or purchase new telephone lines. 28 ADSL lines are not only beneficial to homes and businesses but also to schools. Here is what ADSL lines can do for education. Asymmetric digital subscriber line (ADSL) technology offers schools a faster on-ramp to the Information Superhighway - at a cost within reach. With ADSL, students spend less time waiting and more time learning.adsl offers schools a fast and cost-effective on-ramp to the Information Superhighway. Once there, the learning possibilities are endless... Using ADSL technology, schools can connect to and from: the Internet other schools, community colleges and universities local and national libraries homes of teachers and other students district offices 29 There are many other establishments that ASDL can help with their speed. However if it was up cable modems, it would be just like a network server. While no one is on it it is pretty quick, but once there is a lot of people on it, it gets slower. So what is the major difference in ASDL lines and cable modems? Well, I am going to summarize what I have already said plus add some more differences. ADSL provides a dedicated service over a single telephone line; cable modems offer a dedicated service over a shared media. While cable modems have greater downstream bandwidth capabilities (up to 30 mbps), that bandwidth is shared among all users on a line, and will therefore vary, perhaps dramatically, as more users in a neighborhood get online at the same time. Cable modem upstream traffic will in many cases be slower than ADSL, either because the particular cable modem is inherently slower, or because of the rate reductions caused by contention for upstream bandwidth slots. The big difference between ADSL and cable modems, however, is the number of lines available to each. There are no morethan 12 million homes passed today that can support two-way cable modem transmissions, and while the figure also grows steadily, it will not catch up with telephone lines for many years. Additionally, many of the older cable networks are not capable of offering a return channel; consequently, such networks will need significant upgrading before they can offier high bandwidth services. 30 Analyze the Limitations of the Two Technologies From what you have read, you have found out that both cable modems and ASDL lines have a good performance record and has many benefits that the regular phone line don t have. However, like anything else, they both have their limitations. Limitations of Cable Modems One limitation of cable modems is that the local cable utility must offer this service; you can t just plug a modem into your cable TV cable. 31 Another limitation is the way that information is sent. Some cable companies offer two-way cable modem service: you send and receive data through the cable modem. Unfortunately many cable networks are one-way. To access the internet through a one-way cable system you have to dial in with a regular modem and phone line. Uploads go through the regular modem, while downloads go through the cable modem. Since most internet surfing 27 Analog Devices ADSL (Asymmetric Digital Subscriber Line) Technology. html. (14 Mar. 1999) p Directions Fall ADSL versus Cable Modems. (14 Mar. 1999). p ADSL Application Notes Frequently Asked Questions.24, June (14 Mar. 1999). p (13 Mar. 1999). p. 1 (14 Mar. 1999). p. 1 Ross P. M. - Cable Modems and Asymmetric Digital Subscriber Lines (ASDL)

5 128 School of Doctoral Studies (European Union) Journal 2012 involves downloading information to your computer the speed hit isn t that big, but it is inconvenient. 32 Speed is also a consideration. Under most circumstances speed can range from 4Mbps to 30 Mbps. However, being on a cable modem will be like being on an office LAN. Early in the morning before everyone goes to work, the network at the office is nice and speedy. When other people show up and start printing and accessing the file server, the network slows down. Exactly the same thing will happen with cable modems if the networks aren t upgraded to keep up with the subscriber use. 33 Even though cable modems have been around for a while the Availability is very limited. The Gartner Group predicts 1 to 2% of internet access will be through cable modems in the year 2000, though Jupiter Communications puts the number at 7% 34 Another limitation is the hook-up. The cable modem installation process can be difficult and time-consuming, slowing the pace of subscriber growth. 35 Here is an explaination of the hook up: First, here are the things you need. 1 LanCity Cable Modem Connecting the Cable Modem Please READ ALL DIRECTIONS CAREFULLY as you install your cable modem. Disconnect any cable that is currently plugged directly into your CABLE TV WALL OUTLET in your room. Note: If you don't have anything connected to your cable TV jack, go to the next step. Connect the SHORT COAXIAL CABLE provided by the manager's office to the jack labeled IN on the THREE WAY COAXIALCABLE coupler that is also provided. Connect the other end of the SHORT COAXIAL CABLE to the CABLE TV WALL OUTLET in your room. You should now have one end of the SHORT COAXIAL CABLE plugged in to the CABLE TV WALL OUTLET in your room, and the other end of the SHORT COAXIALCABLE plugged in to the IN jack on the THREE WAY COAXIALCABLE coupler. Take the end of the cable that you originally had connected to the CABLE TV WALL OUTLET in your room and connect it tothe jack labeled OUT on the THREE WAY COAXIALCABLE Coupler. Note: If you didn't have anything connected to your cable TV jack (see step 1), go to the next step. Connect the LONG COAXIAL CABLE provided by the manager's office to the jack labeled TAP on the THREE WAY COAXIALCABLE coupler. Connect the other end of the LONG COAXIAL CABLE to the jack labeled CABLE on the LanCity CABLE MODEM. Connect the SMALL ROUND POWER PLUG at the end of the cable attached to the POWER SUPPLY TRANSFORMER to the jack labeled POWER on your LanCity CABLE MODEM. Connect the STANDARD COMPUTER POWER CABLE to the POWER SUPPLY TRANSFORMER if this hasn't been done by the manager's office already. Plug the POWER CABLEinto a POWER OUTLETin your room. Connect your RJ-45 ETHERNETCABLEto the ETHERNETCARDyou installed in your computer. Connect the other end of your RJ-45 ETHERNET CABLE to the jack labeled DATA on your LanCity cable modem. 32 (13 Mar. 1999). p (13 Mar. 1999). p (13 Mar. 1999). p Cable Modem FAQ, Feb, (13 Mar. 1999). p. 5. School of Doctoral Studies (European Union) Journal

6 2012 Peter M. Ross short coaxial cable 1 long coaxial cable 1 three way coaxial cable coupler 1 three prong standard computer power cable (for connecting to the LanCity power supply transformer) 1 power supply transformer (for connecting to the LanCity Cable Modem) Note: You need to purchase an ethernet card and RJ-45 Cable before setting up your cable modem. The ethernet card must also be installed in your computer. Configuring your ethernet card to access the network You will need the appropriate documentation for your computer's operating system in order to properly configure your ethernet card and LanCity cable modem to access the Residence Hall network. The documentation is available online at the Student Network Service web site, at or you can purchase a copy of the documentation at any Student Network Service center on campus. For locations and hours of operation, please visit the Student Network Service web site. The following operating systems are Supported: Apple Macintosh and higher. edu/service/sns/macintosh.html Microsoft Windows for Workgroups msu.edu/service/sns/windows.html Microsoft Windows 95 sns/windows.html Microsoft Windows NT 4.0 Workstation msu.edu/service/sns/windows.html Troubleshooting Your Cable Modem If you are unable to get a connection after you have installed your ethernet card, properly connected your cable modem, configured your operating system to recognize your ethernet card, and registered your computer with the DHCP server, please call a consultant at If you have worked with a consultant and you are still unable to access the network, please bring your cable modem and cables to the manager's office to have it tested and swapped if needed Setting up your cable company. 5 Nov cable.html. (14 Mar. 1999). p Now you have read how hard it is too set up a cable modem. You know how something that can be very inconvenient. Well, there are also two other very inconvenient disadvantages. They are loss of security since cable TV is not a secure network, and not all websites are accessible. 37 Why is security a problem? Well, because cable networks are shared resources, much like networks in offices and business places, it's possible that someone might try to access your information while it's in transit. If this happens, they might be able to reconstruct it and read messages or intercept personal data. 38 The last limitation that I found was that you don t have a choice of ISPs. Cable TV lines do not have common carrier status as do phone lines. 39 A customer only has one company to choose from instead of the many servers we have to choose from on dial-up networking. Limitations of Asymmetric Digital Subscriber Lines One of the limitations of ASDL lines is that of distance. ADSL s effectiveness drops off the further a customer is from a phone company switching office. Those nearest switching offices can expect top speed, while those four km away likely won t see speeds over one megabit a second. 40 Suggestions and Solutions to Overcome Limitations of the Two Related Technologies Suggestions and Solutions to the Limitations of Cable Modems The reason that you can only receive this from the cable is the fact that you have to rent the cable modem. The service also has to come from because of the fact that television is also involved. A solution to this could be that if the other internet companies somehow could be television capable and be able to rent out or sell the modems. 37 Directions Fall ADSL versus Cable Modems. (14 Mar. 1999). p Cable Modems. (14 Mar. 1999). p Comparing Cable to DSL. (13 Mar. 1999). p More on ADSL. html. (13 Mar. 1999). p. 1. Ross P. M. - Cable Modems and Asymmetric Digital Subscriber Lines (ASDL)

7 130 School of Doctoral Studies (European Union) Journal 2012 Computer retailers could also sell the modems. The solution to the way that information is sent is to offer more two way cable modems. This way both speeds can be as fast. Also, you would not need your phone to upload. A solution to speed problem is that if congestion does begin to occur due to high usage, cable operators have the flexibility to allocate additional bandwidth for data services. A cable operator can simply allocate an additional 6 MHz video channel for high-speed data, doubling the down stream bandwidth available to users. Another option for adding bandwidth is to subdivide the physical cable network by running fiber-optic lines deeper into neighborhood. This reduces the number of homes served by each network segment, and thus, increases the amount of bandwidth available to users. 41 There are companies doing their best to provide a solution to the time to install. The solution they have provided is that of the Universal Serial Bus (USB)...With USB, the complexity of installation is reduced: No need to open the computer Hot plug and play eliminates the need to reboot. Reduced installation time allows for rapid deployment of cable modems. 42 A solution to the website problem would be more servers allowers cable modems to acess their sites. A solution to the security problem is as follows: Some cable modems are being designed to include encryption and decryption capability. When they encrypt data, cable modems encode or scramble your information. This makes it more difficult for hackers to acquire your data. The way it works is when you send data across the Internet, your modem encrypts it, and the cable modem at the head-end of the cable network decrypts it, then sends it across the Internet. Similarly, when data is sent to you, it's encrypted by the head-end cable modem, then decrypted by your modem. Encryption of data by cable modems is not to be confused with encryption used by Netscape Navigator and Microsoft Internet Explorer. Cable modems only encrypt data along the cable network - data sent across the Internet is not encrypted. Navigator and Internet Explorer can encrypt data across the Internet, but only when you are connected to a secure server. 43 A solution to the choice of ISP s is hard to find because usually there is only one cable company per county, and people are limited to just that one. A solution could be allowing customers to choose which cable company they want to go to. Suggestions and Solutions to the Limitations of Asymmetric Digital Subscriber Lines A solution to the distance could be that phone company could start establishing more switching offices to make it more convient for its customers. Look at all the benefits you can get with cable modems and ASDL lines. Before we were just happy to have something new to play with or get recent information, other than going to the library all the time. Now, however our lives are getting even more faster then what they were before. That means we cannot wait on the Internet to do its thing. So the faster we can get it going, the better it is for us. Cable modems are cheaper than ASDL lines, but they have more limitations. Even with the limitations, cable modems are still reliable and faster than what we are used. Even though both services have limitations, all in all, most of the subscribers are happy with which ever service they have, and are amazed by the speed. 44 It does however seem that ASDL lines are better for those establishment that has to be networked, like education facilities. So since, the farther away people are from phone companies, the slower their service, maybe Cable modems are better for homes. However, whatever service a person may choose would be a blessing in disquise. References ADSL Application Notes. < education_app.html.> (14 Mar. 1999). Advantages. Jan < com/advantages.shtml> (13 Mar. 1999) Analog Devices ADSL (Asymmetric Digital Subscriber Line) Technology. 41 Overview of Cable Modem Technology and Services. com/cmic1.htm (12 Mar. 1999). p Cable Modem FAQ, Feb, (13 Mar. 1999). p Cable Modems. (14 Mar. 1999). p (13 Mar. 1999). p. 1 School of Doctoral Studies (European Union) Journal

8 2012 Peter M. Ross 131 < products/ back_adsl/index.html.> (14 Mar. 1999) p. 2. Cable Modems. < howmodem.htm.> (14 Mar. 1999). Cable Modems <wysiwyg://156/ com/links/cable_modems/> (13 Mar. 1999). Cable Modem Frequently Asked Questions (FAQs). < (12 Mar. 1999). Cable Modem FAQ. < cablemod.html.> (13 Mar. 1999). Cable Modems Overview. Jan < cablemodems.com/whatis.shtml.> (13 Mar. 1999). Cisc s ADSL Line Attacks Telco Market. 2 June, 1998.<wysiwyg://85/ intweek/stories/news/0,4164,320874,00. html.> 11 Mar. 1999). Comparing Cable to DSL. < cablemodemhelp.com/compare.htm.>(13 Mar. 1999). Fast Access. < adsl/comparison.html.>(12 Mar. 1999) Dedicated Access. < dedicated_access/info_dsl.html.(12 Mar. 1999). Directions Fall ADSL versus Cable Modems.< dir98fal.html.> (14 Mar. 1999). Frequently Asked Questions. < (14 Mar. 1999). Kegal, Dan. Dan Kegal ADSL Page about ADSL. < html.> (14 Mar. 1999). More on ADSL. < business/bizznet/bizznews/adsl.html> (12 Mar. 1999). Overview of Cable Modem Technology and Services. < htm.> (12 Mar. 1999). Setting up your cable company. 5 Nov (14 Mar. 1999). p Wong, Kevin B. Look Out ISDN, Here Comes ADSL. sessions/sno14/paper.html. (14 Mar 1999). Ross P. M. - Cable Modems and Asymmetric Digital Subscriber Lines (ASDL)