Number 203 - April 2000

Connecting to the Internet by Modem, Cable, Satellite, and DSL
by Herbert Wong, Jr., NOCCC Hardware SIG Leader - herbwong@primenet.com - January 2000
The Internet is the driving force behind computer usage for most people. Home computer users generally rely upon modem technology to connect to the Internet. That is slowly changing from V.90 modem technology to high-speed access technology such as cable modem, satellite, and Digital Subscriber Line. (DSL).     Although they are relatively common, high-speed (variously known as broad bandwidth or broadband or high bandwidth} service is not yet available everywhere, even in urban areas such as Orange County, California. Some areas will have cable modem, but satellite and DSL are more commonly available. Except for satellite, all of these technologies depend upon certain minimum downstream (incoming) telephone company line configurations to be present, or else the high speeds may not be available. V.90 Modems     The highest performance modem technology available today is called the V.90 standard. Since its highest theoretical data transmission rate is 56 Kbps (kilobits per second), it is often called 56k. It is based upon V.34 technology for upstream (outgoing) transmissions and a compromise between two competing designs for downstream transmissions. The two designs are the Rockwell/Lucent K56Flex and the U.S. Robotics X2.     Many ISPs (Internet Service Providers) support only the V.90 protocols and are no longer supporting the competing K56Flex and X2 protocols. However, V.90 modems are typically based upon chipsets that also support one of the two precursors, K56Flex or X2.     As a result, it is not uncommon to achieve higher compatibility and performance from a modem that is manufactured using the same chipset that is used in the ISP's modems. When purchasing a modem, it is still best to call your ISP and ask for their recommendation.     V.34 relies upon a strictly analog (continuous waveform) technology for its telephonic communication. The highest data transmission rate is about 33.6 Kbps. This rate can be obtained in either upstream or downstream transmissions. Since the rates are the same, this is called symmetrical.     Just when everyone thought that the V.34 standard was the ultimate in modem technology, the underlying concept of V.90 technology was independently developed by two manufacturers (in K56Flex and X2).     By using digital (discrete value) technology, V.90 is able to have a theoretical downstream transmission rate of 56 Kbps. The upstream data rate is currently restricted to V.34 technology. Since the rates are different, this is called asymmetrical.     Your residential analog telephone is connected to the telephone company's central office (CO) by an analog circuit called the local loop. Your calls are ultimately routed within the telephone company to another central office. The telephone company's internal circuits are almost entirely digital. From that central office, another local loop carries the signal to the destination telephone.     Under ordinary circumstances, your residential analog telephone's analog signal is converted to a digital signal by the central office for the telephone company's internal use. This is called an analog-to-digital conversion (aka. (A to D), (A-D), etc.). The destination's central office may convert that local loop's digital signal to an analog signal for a residential analog telephone. This is called a digital-to-analog conversion (aka. (D to A), (D-A), etc.).     In summary, the standard upstream signal from your telephone is A-D, D-D (digital-to-digital), and D-A. In response, the downstream signal to your telephone is normally the same, which is A-D, D-D, and D-A; this is important, as you will see later. Let's change the scenario slightly.     You call your ISP. The ISP has installed digital lines from their facilities to their central office. Therefore, the final local loop signal from their modem to the central office remains entirely digital (digital to digital).     Because of this, your ISP is now able to send data to you at theoretical rates of up to 56 kilobits per second. Due to existing U.S. laws, Federal Communications Commission (FCC) power restrictions may reduce this rate to 53 kbps; [but] this may soon change. These theoretical rates are determined by Shannon's theorem, which shows that there is a limit for a given signal due to noise.     In summary, the upstream signal to your ISP from your telephone is A-D, D-D, and D-D. In response, the downstream signal from your ISP to your telephone is now D-D, D-D, and D-A.     V.90 is asymmetrical because of problems in making [the] A-D conversions. Within the constraints of the existing telephone system (including sampling rates and frequencies), the data stream will develop inaccuracies when it is converted from an analog-signal to a digital-signal (known as quantization errors) at the higher 56K data rates. Digital-to-analog conversions do not have quantization errors.     Go back to the last summary (two paragraphs above). See figure 4a. Just kidding, there are no figures here. As you can see, the downstream signal from your ISP does not have any analog-to-digital conversions. The upstream path does have analog-to-digital conversions.     One final problem can arise to prevent 56Kb data rates. The local loop from your telephone to the central office might have an unexpected analog-to-digital conversion in it. The signal from the local central office to your telephone might be D-A, A-D, and D-A instead of just D-A. Satellite     The next step up the ladder to broadband (high speed) communication is to use a satellite dish for downstream reception. This service is good for geographical areas that do not have the newer infrastructure required for cable modem or DSL service.     Satellite service requires a standard modem (V.34 is sufficient) and telephone line for upstream communications. A satellite dish must be mounted outside with an unobstructed, line of sight view of the correct geosynchronous satellite (located somewhere to the south).     Upstream data rates are up to 33.6 kilobits per second (as in V.34). Satellite downstream data rates are up to 400-500 kilobits per second.     Satellite expenses are much greater than other competing technologies, so service contracts are more expensive. Monthly contracts (as of January 8, 2000) with the satellite service company (most likely Hughes Network Systems) vary from 25 on-line hours for $30, 100 hrs for $50, and 200 hrs for $130 including ISP services. Additional hours are $2 per hour.     Rumor has it that there is a restriction on the quantity of data that one can download from the satellite. I read one message that claimed that excessive downloading caused a restricting filter to be implemented on the account. As a result, the writer's downstream performance was inferior to his prior 28 kilobits per second modem rates!     In summary, a satellite dish is a good way of communicating if: you have a dedicated telephone line to use (like a traditional modem), you are not connected for very many hours, you don't download significant amounts of data, and you don't want to use remote locations (since you must have a satellite dish).	Cable Access     Cable television service was designed as a downstream transmission medium. Television signals are sent over a very broadband, shielded copper cable (sometimes optical fiber cable) to a television receiver. With a few modifications, a little bit of bandwidth was diverted for computer users to connect to the Internet.     A cable must be brought to your residence. A splitter physically divides the signal into television and data segments (cables). The television portion is optionally connected in the traditional fashion. The Internet access cable is connected to a box called a cable modem.     A short run of network cable (like Category-5 twisted pair) connects the box to a 10-megabit per second Ethernet card that is installed in your PC.     Supposedly, there are cable access boxes that use USB (universal serial bus) instead of Ethernet to attach to the PC. That isn't such a good idea at this time. USB supports a theoretical maximum of 12.5 megabits per second. That wouldn't leave much USB resources for other peripherals. There is no guarantee that such a USB configuration will work (at the maximum of its capacity). In addition, there is no surcharge to use an Ethernet cable box as compared to an Ethernet printer, scanner, etc.     One obvious characteristic of cable access is that you are now on a network. Your data packets are circulating through the neighborhood. A simple packet sniffer can expose your data. Anyone who has unrestricted file and printer sharing enabled on their system is subject to file and printer sharing!     Cable access is always connected. There is no dial-up, negotiation, username, password, etc. As a result, you must take a few precautions to prevent unwanted utilization of your system's resources. There are bad people out there and you should explore safeguards like hardware or software firewalls. At the least, disable file and printer sharing if they are not needed. That is beyond the scope of this article. [See Beginner's Section of this issue - TOGGLE ed]     It would be reasonable to expect that as many as 500-2,000 people would be sharing your cable segment. If a few of them are working on mirroring the Internet onto their PCs, your bandwidth (performance) can be seriously impacted.     Since downstream rates are affected by so many factors, it is hard to give an accurate number that you could expect to obtain. Expect a minimum of at least a few hundred kilobits per second. Many users can obtain over one megabit per second at times.     Do not expect to obtain 30-megabits per second as some cable-industry web sites promise. The cable access box and the Ethernet card are both designed for 10-megabits per second. It would be unreasonable to expect these components to deliver three times greater than their designed performance. xDSL     DSL is the reason why I don't think we will see modem standards beyond V.90. DSL connects to your existing telephone line just like a modem (well, sort of, but not really). The minimum performance for DSL is four to five times higher than a V.90 modem.     The many variations of DSL (ADSL, SDSL, VDSL, IDSL, MSDSL, RADSL, etc.) give it the generic name xDSL.     SDSL (Symmetrical DSL) is a particular HDSL (High Bit Rate DSL) variant that uses a single twisted-pair of wires to obtain T1 or E1 line speeds. SDSL is also a generic name for DSL service that has identical (guaranteed) upstream and downstream data rates. The same applies to ADSL (Asymmetrical DSL), there is particular DSL configuration and there is a generic meaning (upstream and downstream rates are different).     The common configuration for DSL (typically ADSL) requires a splitter to be installed at the telephone line's entry point into the residence. The normal voice telephone line is unchanged. The data line goes to a DSL box that is connected to a 10-megabit Ethernet adapter in the computer.     Different configurations of DSL do not require the use of a signal splitter. However, some variants will not provide the same performance as the splitter configuration. Obviously, a splitter and additional data line require the services of a qualified technician. A splitterless configuration could be a do-it-yourself project; as easy as installing a printer.     Conceptually, the DSL service operates invisibly to the voice telephone service (which is below the splitter's low-pass filter at approximately 4-kilohertz). Some DSL variants operate by allocating and deallocating (as line conditions vary) additional 4-kilohertz bands that are each capable of providing 64 kilobits per second (don't quote me on that one).     After you have DSL service installed and it is working correctly, you can expect to see a wide range of performance. Distance (i.e., wire length) from the central office is critical; as is line condition. Under optimal conditions, the best data rate (theoretically around 8.5 megabits per second) is seen at a distance of less than 5,000 feet. The minimum DSL rate (300-500 kilobits per second) occurs at about 15,000-18,000 feet. At greater distances, your request for DSL may likely be rejected.     Practically speaking, you might see a maximum downstream data rate of about 1.5 megabits per second and upstream data rates of 768 kilobits per second. It will vary quite a bit from installation to installation.     You're ready to sign up for DSL service. You can pay for any number of combinations of upstream/downstream data rates. Both asymmetrical and symmetrical data rates are available.     What do you select? Get the cheapest service available. Currently, most DSL providers are happy just to get it installed and working. You will get the highest data rates that are physically possible for your installation. There are no restrictions.     But then again, it is possible for the DSL provider to restrict your gigabytes of download per month or to throttle back your data rates to lower rates. Of course, doing these things is bad for business and will not excite new potential customers in a competitive and growing industry.     The biggest caveat to DSL is that you must sign up for a one- to three-year contract. New legislation may allow third party DSL providers to reduce service charges by about $20 per month! That could mean $240-$720 over the life of a contract. I expect the rate changes to take effect the day after I sign up for DSL.     When signing up for DSL services, look for free installation and DSL hardware. Look for a service contract of one year or less. Don't forget to add in the cost of ISP services. And, don't forget security; as with cable access, you are always online.     North Orange County Computer Club's Links Page at http://www.noccc.org with all of the following and hundreds more.     Cable Modem Help - Cable modem help and FAQ at http://www.cablemodemhelp.com.     DSL Reports - A great place to find and search for information about DSL service providers, pricing, service, etc. at http://www.dslreports.com.     Find out if high speed Internet access is available to you! Lists providers, speeds, prices, etc. at http://www.getspeed.com.     DirecPC - Hughes Network Systems (HNS) DirecPC satellite Internet access at http://www.direcpc.com.     The DSL Sourcebook - 2nd Edition - A technical but comprehensible online book about Digital Subscriber Line. You must read this if you want to understand the technology at http://www.paradyne.com/sourcebook_offer/sb_html.html.     You can find the latest version of this article on my web page at http://www.primenet.com/~herbwong/articles/ connectingtotheinternet.html.     You can contact me at herbwong@primenet.com.
Number 203 - April 2000