In the 80s the Local Area Network (LAN) was adopted to interconnect computers at many corporate, governmental, and educational sites. Now that LANs are commonplace, the Wide Area Network (WAN) is becoming an indispensable link to connect an enterprise across longer distances. Initially WANs carried voiceband traffic—voice calls and voiceband data modem calls. Voiceband data modems were, and still are, the primary method of remotely accessing a corporate LAN, or the Internet. Remote users connected to a distant site via a modem dial-in to log-on as a remote user or to FTP a few files. Using WANs to connect distant LANs was relatively uncommon, since the fastest modems operated at only 14.4 kilobits-per-second (Kbps). Higher speed data services were only available using dedicated private line data services, such as "switched 56K", "T1", and "frame relay". These high-speed data connections were rarely true WAN connections, in other words, they couldn't dial anywhere, instead they were "nailed up" connections that tied together remote corporate LANs. Although ISDN was developed to provide a true switched data connection, it was never widely deployed, or used. This is changing. Today's high-speed data WANs are becoming true switched connections, ISDN is helping, but new services are coming that will provide an order of magnitude increase in data price/performance to the home.

In 1995 the World Wide Web brought graphical, hypertext-linked Internet access to every computer equipped with a modem. Today nearly every PC user wants a higher speed data connection to the Internet, and most users are now looking to the new 56 Kbps modems (ISDN is still not widely available). "Modeming in" from a home office for remote access is now an everyday occurrence for millions of PC users.

So, how will we get more data bandwidth to the home? From the phone company of course. Historically phone companies have relied on voice calls to generate most of their revenue, and have been very cautious to adopt new data services, like ISDN in the 80s. Today however, the phone companies are running additional "plain old telephone lines" (POTS) to homes for the second data line! This costs money, forces area code changes, and overburdens the existing voice switches with voiceband modem data traffic. Add it all up and the phone companies want and need a better data service today. In addition, the Telecommunications Act of 1996 permits competition in the Local Exchange Carriers (LEC) market, in other words, the POTS phone lines to homes and business. These Competitive Local Exchange Carriers, or C-LECs, also see the opportunity to provide new high-speed data services as a large opportunity. All told, broadband data services will be rivaling even the venerable voice services in terms of market size, and certainly are one of the largest telecommunications market opportunities in decades.

Over the next five years the dominant local data services are likely to be based on a few of the data technologies that already exist today—new technology isn't required. The following sections will describe what these technologies are, and what they do for the subscriber and the phone company.

Voiceband modems are the most common type of modem, and by far the most widespread: over 100 million are in daily use, and 95% of Internet access is via voiceband modems. Voiceband modems will remain the primary method of Internet access for many years to come. Voiceband modems connect directly to the central office (CO) voice switch, can dial any number and hence work on any "plain old telephone service" (POTS) line. However, voiceband modems cannot exceed 56 Kbps, they tie up one phone line (costing the subscriber more), and they tie up a port on the CO voice switch. Moreover, users often stay online for hours rather than minutes (voice calls typically last only a few minutes). Thus they cost the CO significantly more than voice calls, they degrade overall performance, and they force the phone companies to upgrade their existing expensive voice switches.

Voiceband modems have existed for almost 30 years, the earliest being the Bell 103 transferring data at 300 bps (bits-per-second), and more recently the V.34 (33.6 kbps or thousand bps). The fastest voiceband modems now available use one of two technologies: K56flex or X2. K56flex, developed by Lucent Technologies and Rockwell, is the most widely supported 56 Kbps modem protocol today, supported by over 700 leading PC, modem, and remote access server manufacturers and Internet Service Providers (ISPs) worldwide. The next voiceband modem technology standard will be V.PCM, which is a version of 56 Kbps modems being standardized by the Telecommunications Industry Association (TIA). V.PCM will provide better interoperability between 56K modems from different vendors, meaning your connection will be faster more often. It's worth noting that 56 Kbps is the fastest speed achievable over a dial-up POTS line. Given the limitations of the voiceband technology, these latest "best of breed" modems will satisfy the demands of many users until higher-speed technology becomes ubiquitous.

Figure 1:  Local access with voiceband modem

The best-known form of digital telecommunications, Integrated Services Digital Network (ISDN) is a digital network providing voice and data communications at rates of up to 1.544 (T1 rates in the U.S.) or 2.048 Mbps (E1 rates in Europe) for Primary Rate Interface (PRI) service (actually slightly less since one 64 Kbps channel is used for signaling). Many corporate users rely on T1/E1/PRI service for Internet connectivity to link their distant enterprise locations. Individuals in many areas can order Basic Rate Interface (BRI) ISDN, which provides two 64 Kbps B channels (for data or voice) and one 16 Kbps D channel (for signaling: who's calling, number dialed, and so on). BRI modems use the existing POTS lines to the phone company, but the CO must have ISDN line cards installed, instead of typical POTS line cards, a substantial expense for the phone company. Two B channels can be combined into one 128 Kbps data channel via the BONDING technique (defined by the Bandwidth ON Demand Interoperability Group), yielding a high-speed data pipe for select customers. BRI can operate only up to 18,000 feet (3 miles) from the CO, limiting deployment in a service area.

Two interface techniques are used at the subscribers' location: the Universal (U) and the Subscriber/Termination (S/T). The U interface plugs directly to the phone line. The S/T interface requires a separate Network Termination (NT-1) unit to connect to the U interface at the phone line, but it allows up to eight BRI devices to share the line. Setting up a BRI channel can be complex, since there are so many options to select and configure. BRI is in many cases the best data access available at moderate cost. Although BRI has been available for over a decade, there are fewer than one million subscribers in the U.S. so far. Even with the demand for Internet bandwidth, phone companies have been slow to deploy BRI since it ties up their voice switches with lengthy data calls. Nonetheless, as the cost comes down, and as setup becomes more standardized, ISDN will gain more users.

Figure 2:  Local access with ISDN modem

The newest and most promising digital advance, Digital Subscriber Line (DSL) modems provide a quantum leap over ISDN or voiceband modem data bandwidth. Asymmetric DSL (ADSL), the leading contender, delivers up to 9 megabits-per-second (Mbps) downstream (to the subscriber) and up to 1 Mbps upstream (to the network). ADSL modems save the phone companies money because they combine voice and broadband data on each existing phone line. Within five years, a significant portion of U.S. households will have high-speed data connections to the Internet via ADSL modems. Following are the significant features of ADSL:

• A single local loop (the wires that transmit to the local CO) can provide both voice and data. Life-Line voice is retained—the phone will work in a power outage, but the data connection will be down. Thus only one local loop per subscriber is required.
  
  
• Data is modulated at higher frequencies (up to 1 MHz) than voice signals, and can be passed over 18,000 foot local loops to the subscriber. Typical ADSL will be "rate adaptive", meaning that the fastest connections depend on the quality and length of the local loop.
  
  
• A splitter at both ends separates the voice (below 4000 Hz) from the higher frequency data: voice and data to and from the user pass over the single POTS line to the CO, where voice is sent to the CO voice switch and data is sent to the network via ATM. Thus, phone companies don't need to install more local loops, don't have to buy more voice switches, and won't have degraded service due to data traffic through their voice switches. Subscribers get better data service, even if they're online all the time.

Figure 3:  Local access with xDSL modem

Of all xDSL forms, ADSL is the most significant for mass deployment because voice and data coexist on the same local loop. Ironically, ADSL was first developed for digital video to the home, but video alone did not drive up demand as the Internet has. However, when ADSL is available, there will be virtually unlimited video sources available to the subscriber.

Table 1:  Available types of xDSL technology

As for cable modems, satellite modems, and wireless modems, these are "broadcast" technologies. Broadcasting data to thousands of subscribers does not scale for mass deployment as well as the voiceband/ISDN/ADSL "point-to-point" modems. For example, cable and satellite modems can send hundreds of megabits downstream (to subscribers), but this high-speed bandwidth gets divided by the total number of active subscribers, often hundreds or thousands, reducing the effective bandwidth to as low as the existing voiceband modems. In addition, the upstream connection to the network is difficult to provide; only 7% of the existing cable TV networks can support upstream data; and satellite transponders are costly. Wireless offers portability but is limited to voiceband, or lower, speeds due to the limited radio frequency bandwidth.

The universal need for faster access promises to drive further technological innovations. More people are using 28.8 and 33.6 Kbps modems today. The 56 Kbps limit for voiceband modems has spurred designs that exploit the analog channel to its fullest. The K56flex technology, for example, offers higher data speeds over ordinary telephone lines, so users don't have to pay extra setup or monthly costs for special lines, and telephone companies don't have to add new equipment. ISPs benefit as they can now deliver the Web pages and files that their users need at near-ISDN speeds and at nearly twice the rate of the prevailing 28.8 standard. A few corporations require costly technologies like ISDN for their telecommunications and remote access needs. Meanwhile the vast majority of users, including most businesses, will continue to use the cheapest and easiest to install choice, voiceband modems, and their fastest incarnation, the new 56 Kbps models, while the phone companies begin deployment of ADSL.