CSE 588
Paper 1
New Internet Connection Options For The Home
Exec Summary
Today's modem speeds for consumers is too slow. Near-term options are 56kbps modems, ISDN, cable modems, and ADSL modems, and satellite. 56k and ISDN aren't even in the ballpark bandwidth-wise with the others. Cable modems and ADSL are the two viable long-term mass-market solutions.
Background
Consumers have discovered the Internet in a big way. They have discovered the vast amount of information and entertainment that is available, and they have discovered that when using their modem over standard analog telephone lines, the Internet is very slow. And not just a little bit slow. Too slow. Excruciatingly slow for anything beyond shallow text-only web browsing. Virtually all consumers who connect to the Internet do so via a modem, and modems today are only a single order of magnitude faster than they were ten years ago. With ever increasing CPU speeds and local storage capacity, the Internet connection has become the overwhelming bottleneck for connected consumers.
During the previous ten years, there have been virtually no widely-available cost-effective alternatives to the analog line modem. The next few years, however, promise to provide us with a wider selection of connectivity options, and more importantly, promise to increase bandwidth to the home up to one hundred fold and beyond. All of the options presented here exist, either in the form of "on the shelf, available for purchase today", or "being tested and or rolled out in numerous markets." Future options which do not work today are not considered here, nor are options primarily suited for businesses.
Disclaimer: this topic is very current and wide-reaching. Not surprisingly, there is an astounding amount of information available on-line. I have neither the expertise nor the experience to interpolate or extrapolate to any worthwhile degree from the information available. So rather than do that, I have attempted to filter the volumes of data and opinions into the salient points, and to tie them together cohesively, while letting the sources do most of the talking.
Key Issues
Lehr suggests the following issues be kept in mind when considering connectivity to the home:
1. The outlook of the technology-will it last, will it be out of date in the near future? 
2. The cost of implementation for the user. 
3. The cost of implementation for the companies supporting the user. 
4. Compatibility with existing standards and existing equipment.
5. Ease of use, and installation. 
6. Cost for use (monthly charge, charge per time used).
7. Ability to use the technology at the "advertised" speeds. Will the technology live up to it's high-speed promises?1

56k Analog Modems
Befumo: "Shannon's Law http://it.ucsd.edu/IT/Newsletter/94_december/nushannon.html is a law of physics that governs how fast information can be transferred over twisted-pair copper wire. For years, many have believed that this law limited modem speeds to 33.6-kbits/ second, a speed that modem manufacturers began selling in volume last year. Apparently the consensus that modem speeds stopped at 33.6-kbits was in error. As Dale Wettlaufer  of the Fool's news room likes to say, "Shannon was writing his law for analog, not digital." The technology to push the information coming from the Web to the user at 56-kbits/ second side-steps Shannon's Law by converting the information to a digital format instead of the conventional analog format that had previously been used. The catch? The user has to be on a particularly "clean" phone line, meaning that there cannot be a lot of interference or the modem will have to step down in speed.
Also, you cannot have more than one switch that converts analog to digital in between you and your local phone company, or the higher speed is negated.
Estimates vary on what percentage of the population will be able to enjoy the higher speed, but the consensus seems to hover around 80 to 90 percent."2
Lehr: 56k modems are asymmetric. They can have download speeds of up to 56KB/s, and uploads speeds of 33.6 KB/s. According to U.S. Robotics, who coined their 56KB line as x2 technology:
"x2 technology takes advantage of a special network configuration found when an analog client connects to a digitally connected server. By eliminating the analog-to-digital conversion in the downstream path, x2 can use the practical maximum amount of the available 64 KB/s bandwidth. This technique makes modems with x2 fundamentally different from other high-speed modems. In fact, downloads could more accurately be described as encoded, rather than modulated."
This is the easiest upgrade path, both for end users and service providers. All you do is plug in a faster modem and go, assuming both sides upgrade to compatible modems. Plus, you can go buy a 56k modem today and many ISPs support them.
There are downsides however. There has yet to be an agreement between the major manufacturers on a standard for these modems. The U.S. Telecommunications Industry Association isn't expected to ratify a standard until late this year, meaning that consumers will have to make sure the modems they buy can communicate with modems used by their service provider to attain the high speed.
On top of the lack of a standard, U.S. Robotics also announced recently that the 56KB modems are limited to a download speed of 53 KB/s. U.S. Robotics says Federal Communications Commission regulations "limit the signal level" that digitally connected server equipment can transmit, effectively limiting download speed. So even though the technology is capable, the Federal Regulations don't allow data to move that fast over the POTS (Plain Old Telephone Service).3
ISDN
Microsoft: ISDN stands for Integrated Services Digital Network - the name for digital telephone service that works over existing copper telephone wiring. There are several types of ISDN service, but the most appropriate type for individual computer users is the ISDN Basic Rate Interface (BRI). 
Basic Rate ISDN divides the telephone line into 3 digital channels: 2 "B" channels and one "D" channel, each of which can be used simultaneously. The B channels are used to transmit data, at rates of 64k or 56k (depending on your telephone company). The D channel does the administrative work, such as setting up and tearing down the call and communicating with the telephone network. With two B channels, you can make two calls simultaneously.
Most of the world's existing telephone network is already digital. The only part that typically isn't digital is the section that runs from the local exchange to your house or office. ISDN makes that final leg of the network digital.4
Lehr: ISDN is a connection that is offered through several phone companies, and has proven to be a good source of home connectivity. The downsides of ISDN are the cost and the difficulty of setting up the hardware. Along with the hardware costs of purchasing an ISDN modem, the installation cost and the usage costs can be extremely overwhelming. Modems can cost up to five hundred dollars, and installation can also run a few hundred dollars. Various pricing models exist, such as monthly fees around forty dollars for thirty hours, and unlimited usage for around seventy-five dollars. For most consumers, this is prohibitively expensive. Overall it seems to be an overwhelming inconvenience for a staggering cost, and a slightly improved connection.5
Broadband Modems
Halfhill: Broadband modems superficially resemble analog modems. They interface your computer to an external network and communicate with a compatible modem at the other end of the line by converting digital data into modulated RF signals. Likewise, they receive modulated RF signals and convert them back into digital data. These basic functions are common to all modems (see diagram on next page).

What makes broadband modems so much faster is that they exploit a much wider swath of spectral bandwidth. Analog modems are limited to only 3.3-kHz POTS. By comparison, cable modems use the bandwidth of an analog TV channel, which is 6 MHz wide for NTSC and 8 MHz for PAL. Wider frequency exploitation translates into theoretical speeds of 8.448 Mbps and 30 Mbps for ADSL and cable modems, respectively. 
These sky-high speeds would quickly overwhelm a computer's serial port. Consequently, most broadband modems require a 10Base-T Ethernet port. This also makes it easier to hook up a broadband modem, because it doesn't need special protocols or drivers -- any standard Ethernet stack will do. From the computer's point of view, it's on an Ethernet LAN, not a special network. 
The network interface card (NIC) sends Ethernet packets to the modem. The modem modulates the data and transmits it over the phone line or coaxial cable to the receiving modem at the other end of the connection. In the opposite direction, your modem converts the RF signals it receives back into Ethernet packets before sending them to the Ethernet card in your computer.6
Lehr: The two primary contenders in the broadband modem arena are cable modems, and ADSL modems, described in the next sections.
Cable Modems
Lehr: At first glance, cable modem technology seems to be the best technology offered when compared to prices. Many cable television companies have tested in small areas, and some are actually offering service now. The outlook over the next few years seems great for cable modem technology. Download speeds are blisteringly fast, and connection times can be as long as you want for rates as low as thirty dollars a month. Cable modems are asynchronous, but the upload speed is still estimated at a whopping 2 MB/s, so for most users, it is as much as they would need. 
The benefits of cable modems far outweigh the disadvantages right now. Fast connections, great throughput, cheap Internet access. It seems to have home connectivity completely under wraps. However, cable modem technology may not hold up for long. The way the cable modem network topology is set up is that each neighborhood is set up as a LAN, sharing a connection that is split multiple times into each and every household. Right now, with only a few users taking advantage of this service, connections are always speedy, but in the future, when every household is actively using cable modems, the network could get seriously bottlenecked. Who would have thought you might need to bang on your apartment floor yelling, "Stop DOWNLOADING!"? 
Currently companies such as Highway 1, offer home Internet connections via your cable box, which includes all the services of a regular ISP for fifty dollars monthly in addition to your normal cable bill. This price is all inclusive, covering everything from web access, to email, newsgroups, and chat. Highway 1 boasts speeds of 1500 KB/s download and 300 KB/s uploads. This is considerably slower than what cable modems are capable of, but is also a good speculation to make, expecting that network activity is going to lower their performance. 
Cable modems are relatively easy to install, and like any good service provider, most companies will come out and do it all for you for a fee. However, the user does have to buy some additional hardware. An Ethernet card is required for this type of Internet connection. On most cable modem setups, the modem is installed and acts as a router for your house or apartment. From it, you can run network cable to computers within your home. Most cable companies allow the cable modem to be rented. At Highway 1, the cable modem lease is included in the rate previously cited. The cost to the cable companies is also minimal. The existing cable television installation is all that is really required, except a few extra adapters and wires within the home.7
Ankhoa: Widespread penetration of cable modems is questionable. First, phone companies' national household telephone line penetration is more than 90%, while CATV companies' embedded coaxial cable plant represents at best about 60% of the residential market nationally. Secondly, only about 5-40% (depending on the source) of CATV companies' cable facilities have been upgraded to two-way digital transmission capability. Trapped by financial shortfalls, most CATV companies will need to pursuit the popular partnering strategy to bail them out. Notwithstanding the traditional poor service image, CATV customers may have to face with service congestion and connectivity problems due to the shared network nature of the Cable modem network. Unless, a CATV company limits the number of subscribers per each node in its Cable modem network to reduce packet collisions and errors, and even at a slightly higher rated bandwidth (maximum 10 Mbps) than that of ADSL modems (maximum 8 Mbps), CATV companies will suffer a shared bandwidth vs. dedicated bandwidth and security issues.8
ADSL
Lynch: Trusty old copper-its ubiquity in the local telco infrastructure makes it an ideal candidate for pushing higher data rates to customers. But just how much can providers squeeze out of those twisted pairs? With voice-grade modems, filters at the edge of the core network limit voice-grade bandwidth to 3.3 kHz. Today that roughly translates to a top rate of about 33.6 kbit/s. Remove those filters, and bandwidth can increase into the megahertz realm, possibly yielding tens of Mbit/s for data traffic. 
The one factor that constrains data rates over copper wire pairs is attenuation, which increases with line length and frequency. The ADSL Forum says the practical limits on data rates in one direction over 24-gauge copper wire range from 1.544 Mbit/s at 18,000 feet to 51.840 Mbit/s at 1,000 feet. By adding DSL modems to copper pairs, these data rates can be achieved. A variety of flavors of DSL exist, but the ones that achieve the highest data rates are asymmetric: ADSL (asymmetric DSL) and VDSL (very high data rate DSL). At least 80 percent of all telephone service subscribers are within 18,000 feet of a central office. Those customers will be able to get at least 1.5 Mbit/s downstream (from the network to the user) and anywhere from 16 to 640 kbit/s upstream over ADSL-equipped copper lines. At shorter lengths, ADSL can offer up to 9 Mbit/s downstream. 
ADSL uses frequency multiplexing, with one frequency band for regular phone service, another for upstream data, and a third for downstream data, explains Bob Olshansky, manager for advanced service platforms at GTE Labs (Waltham, Mass.). Each of those bands uses efficient digital transmission techniques, such as quadrature amplitude modulation (QAM), to modulate a carrier with many different levels to get thousands of bits on a single frequency, he says.9
Motorola: At the core of ADSL is Discrete Multitone (DMT) line coding. The US standards body, ANSI (American National Standards Institute) T1 Committee, chose DMT over CAP (Carrierless Amplitude/Phase Modulation) and QAM (Quadrature Amplitude/Phase Modulation) because of the technology's robustness over long distances. In tests performed at Bellcore, DMT was also proven to have better noise immunity and greater flexibility in the date rates than its two challengers.
DMT utilizes the spectrum between 26 kHz and 1.1 Mhz for broadband data and the spectrum from 0 to 4 kHz for POTS. The spectrum above 26 kHz is further divided into 249 discrete channels, as shown on the following page.

DMT's most significant advantage is its ability to dynamically adapt to the line conditions to attain the maximum throughput per channel, ref. figure 2. A DMT transceiver has sometimes been called "The Optimized Transceiver" for this reason.
The figure below gives a graphical representation of how DMT adapts to line conditions. The first of the three graphs represents a theoretical maximum transmission, fully loaded with 15 bits per channel prior to transmission. The second graph depicts the signal-to-noise results that the DMT transceiver computes based on an analysis of the line condition during initialization. The transceiver then maps the actual bits per channel to be transmitted based on the results shown in graph 2. The outcome is shown in the third graph.

The dip in the middle of graph 2, represents a noise source such as HDSL interference and/or an AM radio station. In the most severe case, a DMT-based ADSL transceiver has the ability to completely block out a sub-channel if it becomes too noisy. The DMT transceiver continues to adapt to the line conditions during all subsequent transmissions. Therefore, a DMT transceiver will achieve the highest throughput possible on any given telephone line.
ADSL employs embedded digital signal processing techniques to implement the DMT coding technique, and various communications functions. In addition, forward error correction allows the receiver to identify and correct errors that occur during transmission. The combination of Reed Solomon forward error correction, trellis encoding, echo cancellation, and MPEG compression results in rates that enable high quality, full motion video transmission over the standard telephone line.10
King: In its new life, ADSL could undermine ISDN as an Internet access option, just as that technology is gaining mainstream acceptance with users. Despite growing demand for ISDN, some U.S. telephone companies remain ambivalent about the service--as evidenced by their problems in forging a pricing strategy for ISDN (see "ISDN Takes a Hike"). Some of that ambivalence stems from the high cost to deploy ISDN. To make a central office ISDN-ready, telcos need a software upgrade to their digital switch; that upgrade can cost anywhere from $200,000 to $500,000, depending on the size of the switch, says Karen FitzGerald, director of business development for Bell Communications Research (Bellcore, Morristown, N.J.). ISDN line cards cost about $125 to $400 each. And if customers are more than about 18,000 feet away from a central office, the telco has to recondition the loops and install repeaters (which cost $2,000 each) to reach those users.
In contrast, digital subscriber line technologies don't require upgrades to the central office switch. "ADSL builds on the existing data networking infrastructure," says Bob Olshansky, manager for advanced service platforms at GTE Laboratories (Waltham, Mass.). "Except for the modems and line cards, everything else is off the shelf. You don't have to invent new technologies and it can be installed line by line." In February, GTE Telephone Operations began an ADSL trial for Internet access in Irving, Texas.
For data services, ADSL requires a line card at the central office and a modem at the customer site. The modem and line card create three information channels; a downstream channel that offers from 1.5 Mbit/s to 6.1 Mbit/s, and upstream channel the delivers from 16 kbit/s to 640 kbit/s, and a voice channel. At the central office, the line card splits the voice from the data, forwarding the voice channel to the central office switch. For Internet access, the data goes into an Ethernet switch and then to a router and over a T1 connection to the Internet service provider Right now, carriers can expect to spend anywhere from $2,000 to $3,000 per line for ADSL. But depending on volume, that could drop to as low as $500 to $1,000 by the beginning of next year, says Rob Faw, president of Westell International Inc. (Tampa, Fla.), a maker of ADSL modems.11
While rates have not been determined, any ADSL-based services offered would be priced to be extremely competitive with, if not less expensive than, cable modems. Being competitive against cable modems make ADSL a tremendous technology. If ISDN pricing stays at a per usage price structure, ADSL is sure to win the high bandwidth battle. Having this dedicated connectivity at your fingertips, and having it on existing phone lines is awesome, and it would also allow for every home to have this type of connection without having to share bandwidth.
Satellite
Bernier: Not much is happening with broadband satellite services today. But in the next few years there will be at least five global satellite networks offering fixed broadband services. 
The satellite groups claim that satellites can cost-effectively deliver blanket coverage to provide broadband services in areas outside metropolitan regions, where other carriers are less likely to focus their early efforts. 
"SpaceWay's role is to provide a wireless complement to the terrestrial network," said Ed Fitzpatrick, a vice president at Hughes Communications in charge of SpaceWay. Fitzpatrick said the high-speed ADSL services the telephone companies are testing and the cable modem services that cable TV companies are beginning to offer will be rolled out on a spotty basis. SpaceWay, which will have two geostationary satellites above North America and Asia, where service will launch first, as well as above Europe and Latin America later, will be able to reach those consumers and businesses that don't have access to ADSL, cable modems or direct fiber connections. 
New technologies allowing satellites to support higher payloads and the ability to put digital signal processors on satellites to route traffic to enable satellite services like SpaceWay, offer relatively low-cost broadband services, he said. SpaceWay should be able to offer high-speed services for between $30 and $40 a month, Fitzpatrick said. 
Promised data rates for most of these satellite networks are typically as high as 2 megabits per second on the upstream path and 6 Mbps on the downstream. The companies expect customer equipment, including antennae and PC interface devices, to be at or below $1,000 per subscriber, with numbers varying depending on the satellite company.12
Halfhill: Another alternative is DirecPC, from Hughes Network Systems-a close cousin of DirecTV. The PC version transmits data from a geosynchronous communications satellite directly to a 24-inch dish antenna connected to your PC. The result is a highly asymmetrical network: 400 Kbps downstream. A standard analog modem carries upstream messages, so the maximum speed is 33.6 Kbps. The speeds are well short of what cable modems and ADSL offer.13
Conclusions
What's the best alternative for each consumer depends on their needs, their location, and their urgency. As slow as 28.8kbps is, it might be worth sticking with for a little while longer if you have the patience. If you need more bandwidth today, 56k modems are very cheap, and you get another 20kbps or so in the downlink. I would say you'd have to have a pretty strong argument for needing that extra 20kbps (if you can even realize that extra throughput on your phone line) before I would suggest going that route.
ISDN is the obvious choice if you need substantially higher bandwidth today, but again, it's not really that much higher bandwidth compared with what's to come with the broadband modems. That means that its effective life if procured today would be very short, like two years at the maximum. Couple that with ISDN's still high cost for hardware, installation, and line charges, and it's clear that ISDN should be avoided by all but the most urgently needy consumers.
Satellite services will be a boon for consumers who don't live in metropolitan areas (hence no broadband modems), and are willing to pay a little more for broadband-level service. But the price will limit its penetration to those who cannot receive wired service.
Both wired broadband modems appear viable, but ADSL more so than cable modems in the long run. Since both use 10BaseT and existing wiring to the home, consumers won't have to commit to one or the other. Just pick whichever is available first and/or offers the most attractive pricing. If cable modems get too bogged down by too many users on the same LAN, you can always switch to ADSL for a reasonably low-cost transition (price of ADSL modem, presumably a couple hundred dollars). It's not critical that one technology dominate and become a standard, but it wouldn't surprise me if market forces took over and one got squeezed out, leaving a single champion broadband modem technology. 
1 Lehr, Christopher John. High Bandwidth at Home: Now or Never? http://www.servtech.com/public/clawz/hiband/. 4 May 1997.
2 Befumo, Randy. "The Motley Fool." EE Times. 9 December  1996.  http://techweb.cmp.com/eet/fool/fool21.html . 4 May 1997.
3 Ibid 1
4 What is ISDN?. http://www.microsoft.com/windows/getisdn/whatis1.htm#isdn. 4 May 1997.
5 Ibid 1
6 Halfhill , Tom R. "Break the Bandwidth Barrier." BYTE. September 1996. http://www.byte.com/art/9609/sec6/art1.htm#096cse1. 4 May 1997.
7 Ibid 1
8 Ankhoa, Albert. ADSL vs. Cable Modem. http://www.primenet.com/~ankhoa/adslcmod.htm. 4 May 1997.
9 Lynch, Karen; Rubin, Paul; King, Rachael; and McGinity, Meg. Infinite Possibilities. http://www.teledotcom.com/0497/features/tdc0497intro.html. 4 May 1997.
10 Motorola's CopperGold Transceiver Delivers: More, Better, Faster. http://www.mot.com/SPS/MCTG/MDAD/adsl/adsl_whitepaper.html. 4 May 1997.
11 King, Rachael. ADSL, Take Two. http://www.teledotcom.com/0496/headend/tdc0496headendadsl.html. 4 May 1997.
12 Bernier, Paula. "What's Up With Broadband Satellite Services?." Inter@ctive Week. 23 October 1996. http://www.zdnet.com/intweek/daily/961023b.html. 4 May 1997.
13 Ibid 6