[ Go to Interactive Buyer's Guide: ISDN ]

Cover Story
Rrrrrriiip into the Web!

-- by Cynthia Morgan and Erik Sherman

• Get Fluent in ISDN
• POTS Gets Panned
• Cut the Cord
• What Price ISDN?
• Test-Drive Some TAs
• Quick Route To ISDN Connections

Hook up to the web, and you're a click and a scroll away from just about anything, from news to new cars to cartoons. But without a connection that offers sufficient speed, you might feel you're surfing across a quiet pond: You'll get where you're going sooner or later, but the ride won't be half as much fun.

Right now, the link spanning the desktop and the Web is a lopsided equation. On one side, there's a mile-high dam restraining a flood of technologies-electronic commerce, videoconferencing, interactive gamesmanship and more. At the other side, there's a tiny pipe labeled "modem." There, in a nutshell, is the biggest obstacle to delivering the promise of the Internet: bandwidth.

Desktop communications haven't kept pace with the rapid expansion of PC components such as storage, memory and processor power. Nor have they kept up with the explosive growth in byte-hungry Web applications. Last year, Bill Gates suggested the 28.8Kbps modem would be an Internet staple for the foreseeable future. Yet today you can surf a data pipeline many times that size. All it takes is education, patience and, often, a fat wallet. A more modest expansion, four times faster than a 28.8Kbps modem, can be had for somewhat more than the price of an extra phone line. Your old analog modem-or even your brand new one-simply can't keep up. ISDN keeps the data on the Web and your PC's requests in their digital formats, eliminating the need to convert to analog and providing a significant boost in speed. (See sidebar "POTS Gets Panned.")

The world of digital communication starts with ISDN, which, ironically, began a quarter-century ago as a way to improve voice telephony. Although widely adopted in Europe and Japan, it's had limited success in the U.S. as a high-speed communications medium. Because it runs over the same twisted-pair copper wires analog phones use, it's a good way to deliver up to 128Kbps of uncompressed data streams to residential and small business users. In today's increasingly decentralized business model, it's also an efficient way to connect telecommuters to the home office.

The nice thing about analog communications was its relative simplicity. ISDN will let you shift your communications into high gear, but it's considerably more involved than analog and you'll need to know a lot more to make it work right. (See sidebar "Get Fluent in ISDN" for a glossary of ISDN terms.)

ISDN Checklist, Part I: Preinstallation

For starters, call your phone company, ask for ISDN sales and obtain the following information:

Can ISDN be installed at your location? If not, find out when an upgrade is planned and start looking for alternative high-speed connections (see sidebar "Cut the Cord")

What kind of service is available? ISDN service is available in two forms: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). The BRI service, commonly sold to desktop users, provides three communication channels: two 64Kbps Bearer or B channels to carry data and a third, 16Kbps Delta or D channel, to control the initiation and disconnection of calls. The two B channels can be aggregated, or combined, into a single 128Kbps pipe. PRI bundles 23 B channels and a 64Kbps D channel for transmission rates of 1.544Mbps, the transmission speed of a T1 line.

The phone company often refers to standard BRI ISDN service as 2B+D, Generic Data M, S or Standard. BRI is capable of either voice or data transmission.

How much does it cost? The best plans provide flat-rate, unlimited service for less than $75 a month. But you'll probably have to select a package plan offering a certain number of hours per month. Excess minutes can cost from 2 to 8 cents per channel. Installation and activation charges range from $100 to $250. Ask about special savings options. Now that new technologies are encroaching on ISDN, phone companies often waive part of the installation cost, or offer bulk-rate usage packages. (See sidebar "What Price ISDN?" for a sampling of rates around the country.)

When can it be installed? In some areas, fufilling an ISDN order can take as long as six weeks.

What's the CO switch and which protocols does it use? An AT&T 5ESS switch running National ISDN-1 protocols is ideal. This combination supports most ISDN devices, or terminal adapters (TAs), and usually presents fewer problems with dual-channel aggregation.

Record your connection's Service Profile Identifiers (SPIDs) and Directory Numbers (DNs). You'll need both to configure your TA so it can identify itself to the central office (CO) switch.

Because ISDN BRI's two data channels are assigned separate identifying codes for configuration and dialing in many parts of the U.S., you can use the two channels separately. You can pass data through an ISDN line at 64Kbps and still have a channel free for making voice calls or faxing. You can't plug an analog phone directly into an ISDN jack, but many TAs include one or two analog jacks. And some ISDN TAs, such as the ZyXel Omni TA128 reviewed in this article, can save you money by letting two or more computers share a single TA and ISDN line.

You may also need a Network Termination-1 device (NT-1) that provides an interface between TA and ISDN lines. Today's TAs usually include NT-1 capability, but you still have some other issues to consider when shopping for a TA.

ISDN Checklist, Part II: Selecting a TA

How will you use your ISDN line? If you intend to add voice or fax capabilities, select a TA that either includes those capabilities or offers an external analog port you can use to attach these devices.

Which drivers come with the TA? Most offer some degree of Windows 95 compatibility, but not all offer Windows 3.x and NT drivers. If you need them, make sure you can get them before you buy.

Internal or external? Internal TAs bypass the comm port speed limitations. They may be your only choice if your computer lacks a PS/2 mouse port and you need the remaining serial port for another device. They're usually less expensive, but they lack the external units' diagnostic LED displays and can't move easily between computers.

Price. Expect to pay between $200 and $400 for a basic ISDN TA with one analog port. Other features, such as the ability to enable two PCs to share a single BRI line, PCMCIA-size units, or automatic switching between ISDN and analog connections, are extra.

ISDN doesn't have a standard audible dial tone, but the time between call initiation and connection is usually a second or two. It's still more costly than a normal-or POTS (plain old telephone service)-line, but prices are dropping fast. The downward slide should continue as competing technologies, such as ADSL and satellite transmissions, come online. Unlike dedicated communications links, which charge you whether you use them or not, ISDN employs a pay-as-you-go plan.

ISDN is not without drawbacks. Although it's generally available throughout the U.S., many local CO switches don't yet support it. And online services and ISPs may offer only a few ISDN ports, leaving you with "Can't Connect" messages during busy periods.

Furthermore, performance advantages are solely for data transmission; fax and voice transmissions won't be affected because of their analog nature. And ISDN can't do much about poor Web performance if it's due to congestion on the Internet or at the ISP connection. Also, if your power goes off, your phone won't work, so don't rely on an ISDN line as the only phone line into your home or business.

Unlike analog calls, ISDN calls are generally billed from the moment of call initiation, not connection, so you'll be charged for unsuccessful call attempts.

Newsgroups are full of horror stories about new ISDN subscribers receiving $500 bills for excess usage. Phone companies (and many ISPs) regard each B channel as a separate line. So a package plan calling for 100 hours of single-channel use gives you just 50 hours if you're aggregating the two B channels through Multilink-Point-to-Point Protocol (MPPP). Under good conditions, an MPPP-enabled TA will automatically aggregate a second-channel call to an available ISDN port once the first connection is successful. The process should be transparent, although in our experience it can require some experimentation. If your ISP charges extra for dual-channel Internet access, consider finding one that doesn't.

Monitor your ISDN usage. Many comm programs do this automatically, and your ISP should have records. If you're primarily connecting to the Internet, check these against your phone bills periodically. Usage monitoring is especially important for network administrators. Many devices send a "keep alive" string to stay connected. Without flat-rate billing, open ISDN links could ring up hundreds or even thousands of dollars in unnecessary charges.

Installation and configuration of an ISDN line can be a nightmare if you don't ask the right questions or order the appropriate services. Although your phone company pays for work done up to the "demarc," (the line of demarcation between its phone lines and the wires inside your house), you may have to pay to bring additional phone lines inside, and that can be expensive. If you already have two phone lines, you're probably better off converting an existing line to ISDN and using one of its channels as your second voice line.

ISDN Checklist, Part III: Installation and Use

On installation day, have your computer, software and TA ready. Discovering problems right away can save you the cost of an additional service call. Once you have a working line (and verified your SPIDs and DNs), follow these few installation pointers.

ISDN doesn't have analog's dial tone, so you may need to deselect any "Wait for dialtone" options you find when you're configuring software.

Select the fastest connection speed, usually 115,200 bits per second (more on this later)

Connections to private ISDN-connected networks may require tweaking before they'll work with MPPP.

You can sometimes force an ISDN/fax modem to make an ISDN connection by selecting "pulse" dialing.

A "busy" signal, common if your ISP has only a few ISDN ports, will appear as a failure to respond.

Connection takes only a few seconds, so if your call appears to be "ringing" continuously, hang up and try again.

ISDN sales reps happily point out you can combine B channels for 128Kbps. Be careful though, because not all ISDN equipment supports channel aggregation. And some versions of the Windows operating system don't fully support MPPP.

Win95 had MPPP support problems early in its history. Microsoft's ISDN Accelerator Pack utility has largely eliminated these problems. You can download the software for free (go to http://www.winmag.com/win95/software.htm and click on Get ISDN), but later versions of the utility require updated TA drivers. Be sure to pick the one that works with your device.

Once MPPP does work, there's still no guarantee you'll have 128Kbps. Modern computers are distressingly antique when it comes to serial comm ports, and can't handle that speed. The problem is the port's Universal Asynchronous Receiver/Transmitter (UART), which initiates data transmission and collects it upon receipt from the serial port. In early PCs, UARTs limited transmission rates to a mere 19.2Kbps under ideal conditions. Today's UARTs have boosted that limit to 115.2Kbps. The process can create a bottleneck in a high-speed data transmission, causing data overruns and retry errors that dramatically reduce performance.

Your PC most likely has an 8250, 16450 or a 16550AN UART; the 16550AN provides the 115.2Kbps performance. To check, go to Control Panel/Modems in Win95 or NT 4.0, click on the Diagnostics tab, select your modem from the list and choose More Info. Your UART will be listed under Port Information. In Win3.x, check the Microsoft Diagnostics (MSD) utility (the info will be listed in the COM section). If yours isn't a 16550, you may want to contact your manufacturer for an upgrade, or consider installing an internal TA or a serial port card with built-in 16550.

If you're still using Windows 3.1x with a 16550, you'll need to upgrade your communications drivers, because they don't fully support the faster UART. CyberCom's CyberDrive (available at ftp://ftp.malch.com) is a good freeware substitute.

Need more than 115.2Kbps? A faster CPU and more memory will provide improvements-albeit marginal ones-because the faster data is read (that is, removed) from the serial port, the sooner new information can be received. You can also eliminate the UART bottleneck by using an internal ISDN adapter to bypass the serial port. Such a card combines the buffering memory usually found on modern communications devices with its own traffic-management chip, often a 16550. The problem with installing this card is you lose the external TA's diagnostic LED display, which can be a great help during installation. Plus, installing an internal card may not even be an option if you're out of expansion slots.

Several companies sell high-speed serial ports that overcome the 115.2 limitation by adding extra buffering to the chip. This boosts transmission throughput up as high as 300Kbps under ideal conditions. An even better solution to serial-bandwidth problems is the Universal Serial Bus (USB) that's just now appearing in desktop PCs. A new Plug-and-Play standard, USB offers data-transfer rates as high as 12Mbps. That's more than enough bandwidth for any reasonable desktop connection.

Relay Races

ISDN and dial-up phones are circuit-switched technologies, meaning when a call is initiated, the network establishes a fixed path between transmitting and recipient devices for communication, then destroys the path when the call terminates. Packet-switched technologies, such as frame relay, break data into chunks, or packets, and send each out across the network along whichever route presents itself. A frame relay link can operate between 56Kbps and 1.544Mbps (the speed of a T1 line) or higher, but tends to have longer latency, or periods of delay caused by variations in the different paths data packets take.

Customers generally select frame relay connections by estimating their data traffic loads and buying enough bandwidth to move that amount at the speed they want. This is referred to as a Committed Information Rate (CIR). If there's excess data, the network considers it "discardable." When the network is congested, it drops the excess data. It then has to be retransmitted, which slows throughput considerably. To combat this, many network administrators add ISDN lines to handle data overflow during heavy traffic periods.

Depending on the CIR, frame relay costs can range from a few hundred to a few thousand dollars per month. Frame relay still relies on the public network. A private dedicated or leased line can offer anywhere from 9.6Kbps to 2.5Gbps (known as Sonet) bandwidth and costs considerably more. But it eliminates the problem of network congestion by establishing a permanent, private link between transmission points. Analysts estimate there are 750,000 T1 lines currently installed in the U.S., and a similar number of E1s (the Euro-Japanese equivalents) installed overseas.

You can also lease fractional T1 (FT1) service, where you buy as many 64Kbps channels (up to 23) as you need, and expand as your business grows. But leased lines require significant networking or telephone equipment to manage them, and at T1 or higher the lines may require expert fine-tuning to achieve optimal throughput. These costs can easily exceed the actual cost of leasing the connection.

Mightier Modems

If its cost and complexity put ISDN on the back burner for you, emerging modem technologies may be more appealing.

Recently, the modem industry announced a new technique to push analog modems past current transmission rate limits by placing digital data right on an analog line. The technology takes advantage of the public telephone network's mostly digital composition and can reach speeds of 56Kbps-about twice the speed of a 28.8Kbps modem (see this month's Newstrends section). Further, it works with standard analog lines, and you can install it in relatively new modems with only a firmware upgrade. Most major modem and network communications manufacturers have announced plans to support the standard, and the first modems using 56Kbps should hit retail shelves early this year.

Another new technology, which Motorola is marketing to OEMs, will enable you to upgrade to 56Kbps via software. The so-called 28.8 soft modem, dubbed the SM34DFV, has a minimal hardware interface; it uses the CPU for modem controller and data pump functions. A free upgrade to 33.6Kbps should be available early this year, and upgrades to 56Kbps are expected to follow.

But the 56Kbps technique has drawbacks, so don't expect it to replace 33.6 modems any time soon. To work, one side of the transmission must be digitally connected to the phone company's CO switch, modems on both sides must support the new technology, and the lines between must be extremely clean. Data is transmitted asymmetrically; while the digitally connected side can operate in the "downstream" direction at 56Kbps, tests so far show the reverse or "upstream" transmissions from the user's PC are limited to about 30Kbps.

The lack of a 56Kbps interoperability standard is a more pressing concern. Rockwell, Motorola and Texas Instruments all announced plans to build chips using the technique, but no ITU standard (like the V.34 for 28.8Kbps) exists yet for 56Kbps datacom. Without one, modems from two different companies may have trouble talking to each other. In any case, the Rockwell technique barely boosts analog datacomm to the speed of the slowest digital lines.

Where Do We Go from Here?

New technologies on the horizon have the potential to boost consumer-grade bandwidth for much lower cost. Cable modems, for example, will deliver between 4Mbps and 10Mbps, probably via an Ethernet-style interface. That's almost 350 times faster than current 28.8 modems. The cable company sells the service, along with Internet access and interactive television, and includes the cost of configuring the equipment in your home as part of the price. Cable companies say they'll eventually deliver the service for about the price of a cable-TV subscription.

Cable modem trials are already under way in a few dozen U.S. and Canadian locations, but not all of them have been successful. Most older cable networks will require complete rewiring before they'll accept the new devices. Significant questions remain about the ability of diverse-and often divided-cable companies to manage an interconnected network reliably.

The phone companies' answer to the intrusion of cable guys onto their turf is Asymmetrical Digital Subscriber Line (ADSL). This technology uses the twisted-pair copper wires of your current phone line to provide broadband transmission rates in the 64Kbps to 52Mbps range. Because ADSL operates on higher frequencies than voice, you can continue to use the same line for voice transmissions while sending wicked-fast databursts via ADSL. Transmission rates depend on your distance from the transmission point, the quality of the wire and how much you want to pay. And, unlike ISDN, ADSL works even during power outages.

ADSL offers roughly 10 times the bandwidth in the downstream direction than in the upstream direction. A 6.2Mbps ADSL connection downstream, for instance, could send about 640Kbps upstream to the ISP. A 1.5Mbps downstream transmission gives you 64Kbps upstream. That makes it ideal for browsing graphics-rich Web content, but not for uploading large files. It's also less useful for applications requiring symmetric transmission, such as videoconferencing.

Nearly every Baby Bell has ADSL tests under way or planned. Bell Atlantic's Fairfax, Va., test, for instance, has been so successful the company has extended it to participants until it can put an actual program in place. Primarily used to provide interactive-video content at 6Mbps downstream and 64Kbps upstream, the service costs customers a flat rate of $7.95 a month plus per-use fees of anywhere from 49 cents for a 20-minute children's program to $4.49 for a two-hour movie. Most analysts say start-up Net-access ADSL rates will initially run about $50 to $100 a month for the average consumer.

But ADSL is only the beginning. Other xDSL technologies are coming. High Bit Rate DSL (HDSL) can deliver up to 2Mbps very cost-effectively, and is already competing in the T1 leased-line arena. Symmetric DSL (SDSL) attempts to equalize transmission speeds in both directions, and Very High Rate DSL (VDSL) theoretically supports transmission speeds up to 52Mbps. Rate Adaptive DSL (RADSL) technology analyzes line conditions and data load, then adjusts transmission speeds in both directions for optimal transport.

Don't hold your breath for xDSL technology, however. Several issues have to be resolved before it can be widely adopted. One such issue is what to do about long distance calls-an ADSL connection's range is limited to about 8 miles. Equipment remains expensive-as much as $2,500 for the linking device-and you'll need one at each end. And the biggest issue of all is what to do about an already-cramped Internet when video-sized transmissions become commonplace.

The bottom line? If you're frequently online, and are willing to expend time and effort to install and configure it, ISDN can offer some real advantages. If you're in no rush, a couple years' wait could extend your bandwidth options immensely.

[ Go to Interactive Buyer's Guide: ISDN ]

Copyright © 1997 CMP Media Inc.

(From Windows Magazine, January 1997, page 196.)