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Windows on the Web
The 56K Modem Myth
Don't let misinformation about 56K technology trip you up.

-- by Cynthia Morgan

They're everything you've been promised and less. At least 3Kb per second less, and that's on a good day. On a bad day, you may not see much difference between a 56K modem and your good old-fashioned 33.6Kbps modem.

The truth is 56K modems are not yet "up to speed." A number of factors are hindering the technology's performance, not the least of which is the industry itself, currently embroiled in a 56K standards war. So before you hotfoot it to your local computer store, know what the technology can and cannot do.

For starters, "56K" is a misnomer. Inventors named the technique for market familiarity-56Kbps is a common digital communications speed throughout the world. But a 56K modem's ISP-to-user connection, for example, maxes out at about 53Kbps. (Even if a 56K modem could hit its full 56Kbps stride, the U.S. Federal Communications Commission restricts the power load on public phone lines to about 53Kbps.)

Speeds of 53Kbps are reached only under ideal conditions. Preliminary trials show everyday speeds hover in the 45Kbps-to-50Kbps range.

On the bright side, if you're using one of these modems primarily for Web surfing, you could enjoy a substantial speed difference over a 33.6Kbps modem. Speeds for other tasks vary.

Before it becomes a routine mode of Internet transportation, 56K faces some difficult battles with interoperability standards, aging phone lines and outdated equipment. Most of those issues will be resolved by the end of the year, but Internet usage charges may increase when ISPs pass on the cost of upgrading high-speed lines and network equipment.

To understand what causes a 56K modem's limitations, you need to know what's behind analog modem technology. A modem modulates (translates) outgoing digital computer signals into audible analog tones, then sends those tones over the phone network. At the receiving end, a modem demodulates (reconstructs) incoming analog tones into digital signals. During the conversion process, any interference from nearby electrical devices, flaws in the line or other connection problems can introduce errors into the signal. The receiving modem rejects any error-filled signals, forcing the data to be resent and lowering overall throughput. The faster the transmission speed, the more likely you are to encounter errors.

The ISP you use for your Internet connection, however, most likely uses digital lines, which don't need analog conversions and can therefore operate at higher speeds. Because the phone company's lines are also generally digital in nature, the only real analog bottleneck will be at your "local loop," the segment between your modem and the telephone company's switching system.

Older modems perform the analog/digital conversions at both ends of the link, whether they're needed or not. But 56K modems take advantage of the digital connection and will not perform analog/digital conversions from the ISP to the user (downstream), when conditions permit. That dramatically reduces errors in the overall transmission and permits downstream transmission speeds between 55Kbps and 58Kbps.

As with any modem technology, actual throughput depends on line quality and the presence of "quantization noise." If an ISP's digital connection back to the telephone company switch isn't "clean"-that is, free of interruptions, enhancements or impairments that can force an analog-to-digital conversion between the ISP and the user-transmission speeds will drop to or below a standard modem's rates. And older, poor-quality lines can slow 56K transmission speed down even more, according to the modem manufacturers.

A 56K modem will also fall back to 33.6Kbps if it's routed through a private branch exchange (PBX), because all but the most modern PBX systems resort to analog conversions. This is liable to scare large corporations away from using 56K technology.

Worse, the phone networks in older, heavily-populated areas were sometimes designed with equipment that performs as many as six A/D conversions in the local loop. And some T1 lines, the less-expensive types generally preferred by ISPs, aren't compatible with 56K technology.

You're also likely to hit a 33.6Kbps speed bump when you take your 56K PCMCIA card on the road, because hotels generally route guests' phone lines through a PBX. Your data won't fare any better internationally, because signals moving through undersea cables must undergo a different conversion process. In addition, two 56K modems can communicate with each other only at standard analog modem speeds of 33.6Kbps.

And that's not all. Unlike older modem technology, 56K is asymmetrical-that is, the extra speed is available only when data is moving downstream. Data travels at standard analog modem speeds when it moves upstream (out of your computer), because your connection via POTS is still analog and requires an analog-to-digital conversion to move data through your local loop.

This may change in the future, although just when is unclear; 56K developer Lucent Technologies has demonstrated symmetrical connections of 40Kbps to 45Kbps in the lab. But the company has no plans to incorporate it into this generation of modems. For now, 56K won't be of much use in applications requiring symmetrical transmission, such as videoconferencing and the back-and-forth file transfer common to telecommuters.

As if that weren't enough, the modem industry is duking it out over standards, and consumers will have to roll with the punches. For now, 56K modems and network equipment are available in two incompatible versions: the x2 standard from U.S. Robotics, and K56flex, a joint effort of modem chipset manufacturers Lucent and Rockwell. The technologies are the same, but implementations such as the encoding schemes used in translating digital signals to analog make them incompatible. So if you opted for an x2 modem and your ISP has K56flex network equipment, you won't get 56K.

U.S. Robotics' position as manufacturer of x2 chipsets, end-user modems and ISPs' network equipment enables the company to ensure compatibility at both ends of the connection. By contrast, Lucent and Rockwell supply K56flex chips to dozens of modem manufacturers and network equipment makers, but have far less control over the compatibility of the final products. U.S. Robotics' x2 products, which arrived last spring, took an early lead when compatibility problems delayed the debut of K56flex.

But x2 may not enjoy this lead much longer. For one thing, K56flex supporter 3Com has announced a merger with x2's U.S. Robotics, providing 3Com with a controlling interest in further x2 developments.

And although some modem manufacturers, such as Hayes, are hedging their bets by selling modems from both camps until a single standard emerges, some very big names in the modem business, including Boca, Diamond, Microcom, Zoom, Multi-Tech and Xircom, have come down on the side of K56flex, as have some PC manufacturers, such as Compaq. K56flex has also captured the lion's share of support from network equipment manufacturers, such as Cisco, 3Com and Ascend, whose products encompass more than 90 percent of the plumbing in U.S. Internet connections. That's likely to have a strong influence on which 56K technologies ISPs support for the next year or so.

Nevertheless, 56K compatibility won't really matter in the long run, if Dataquest analyst Lisa Pelgrim's predictions are correct. North America's Telecommunications Industry Association (TIA) will decide upon the first real standard by the end of this year; it will be neither x2 nor K56flex, but rather a compromise between the two, according to Pelgrim. The worldwide standard will come some months later, when the International Telecommunications Union (ITU) reaches a final decision on 56K. Because North America accounts for some 60 percent of worldwide modem sales, the TIA standard is likely to have a strong influence on the ITU standards.

Most modem and network equipment manufacturers have pledged to support whichever standard emerges. Desktop modem manufacturers will supply inexpensive software upgrades or hardware trade-ins. The transition is likely to take longer at the ISP level, where network equipment upgrades can cost thousands of dollars and require extensive compatibility testing. In some cases, the ISP may need to upgrade to more expensive types of high-speed connections to enable 56K transmissions.

If your ISP doesn't offer a local link to a 56K-compatible port, you could wind up with a fast modem and nowhere to call, or be forced to connect to faster ports via long-distance toll calls. So until the standard is settled, it's vital to know which version-x2 or K56flex-your ISP will support before you invest in 56K. Many ISP networks already advertise support of one or both standards.

What they may not mention, however, is the extent of their support for either technology. America Online has announced its support for both standards, but by press time only six of its access numbers actually offered x2 support, and no K56flex support was available. AOL says it will offer K56flex service in 175 of its 540 cities by year's end.

If your ISP will offer local 56K support, a 56K modem is a good idea, and you'll be pleasantly surprised to discover little or no price premium for new modems with 56K capabilities. But be sure to choose one that supports upgrades through software. Less-expensive brands-especially with Rockwell K56flex chipsets-may require costlier firmware upgrades or replacements.

The debut of 56K modems probably isn't the earthshaker it appears at first glance. Still, as an alternative to expensive-and sometimes difficult-to-maintain-ISDN connections, it's the best way yet to break the 33.6Kbps barrier.

Five 56K Buying Tips

Do your homework first to get the most out of the newest modem technology.

  • Make sure your available phone lines don't connect through a PBX or other device that's incompatible with 56K. U.S. Robotics' x2 Line Test is one way to find out. Your local phone company is another.

  • x2 LineTest. This US Robotics BBS can determine if your own phone lines will support the fastest x2 transmission speeds. To use it you'll need a V.34-capable modem and any standard communications package (the HyperTerm utility that comes with Windows 95 is fine). Connect by using your modem to dial 1-888-877-9248 (toll-free). Type the words Line Test when prompted for your name. This will start the test. Because phone line quality can vary from call to call, USR recommends you try several connections to get an overall picture of your setup's x2 compatibility.

  • Ask your online service provider or ISP which 56K modems it will support, if there will be an extra charge for these connections (there shouldn't be) and when the new service will come online.

  • Ask your provider what percentage of its network will be converted to support a 56K connection. If the provider will offer 56K support on only a few local access ports, consider changing providers or hold off on 56K purchases.

  • Before buying a new modem, check with your old modem's manufacturer to see if it can be upgraded to 56K. Newer models probably can be.

  • If you're buying a new modem, choose one that can be flash (software) upgraded when standards change.

Six 56K Shortcomings

    What connections don't support 56K acceleration?

  • upstream (user to ISP) transmissions

  • modem-to-modem connections

  • overseas connections

  • hotel/office connections through a PBX

  • connections made between incompatible 56K devices

  • connections made through older phone equipment

Windows Magazine, July 1997, page 227.

[ Go to July 1997 Table of Contents ]