There isn’t very much that’s sexy about the communications network known as the Internet backbone. It isn’t run by twentysomething hipsters, it’s rarely the subject of frenzied stock speculations, and its operations are sufficiently arcane as to seem almost unremarkable.

But the backbone, as its name suggests, is critical to everything the Internet does. It’s already become a big business. And it’s now in the midst of an extraordinary building boom that is transforming what was, until just two years ago, a government-run research network into the world’s fastest and most sophisticated communications system.

Already, the U.S. Internet backbone carries 12.75 billion e-mail messages annually, and e-mail represents less than one-tenth of Internet traffic, far less than the graphically rich World Wide Web transmissions, according to Eric Arnum, a contributing editor to the industry newsletter Electronic Mail and Messaging Systems. Increasingly, the Internet will be carrying voice calls and video as well--usurping much of the work once carried out by the traditional long-distance telephone network.

Physically, the backbone is the grid of high-capacity optical fiber lines that carries the bulk of Internet traffic, plus the system of specialized switches and routers that direct the traffic.


Although there are more than 4,000 Internet service providers in the U.S.--companies that link your home or business computer to the Internet--only about a dozen firms form the backbone. These so-called national backbone providers range from two of the biggest and best-known long-distance phone companies--MCI Communications Corp. and Sprint Corp.--to much smaller newcomers such as Digex Inc. of Beltsville, Md., which regard the Internet as their sole business.

The national backbone providers sell hookups to the Internet service providers, which in turn charge access fees to individual users.

AT&T; Corp., the 800-pound gorilla of phone companies, is so far the odd one out. AT&T;'s Worldnet Internet service actually gets its access through the backbone provider BBN Planet, which in turn leases some of its fiber lines from MCI. This puts AT&T; in the odd position of indirectly relying on its fiercest rival for one of its fastest-growing services.

“They’re lying in the weeds, waiting to see if it becomes a really big business,” analyst Ulric Weil of Friedman, Billings, Ramsey & Co. said of AT&T.; “Eventually, they’ll have to be in this business. It isn’t something they can stay aloof from as a fully integrated [telecommunications] company.”


Isolating revenue associated with the backbone is tricky because the biggest players are in so many closely related businesses. Weil and other analysts have estimated total backbone revenues for 1996 at about $750 million.

Cambridge, Mass.-based Forrester Research estimates that annual sales of Internet services will hit $30 billion by 2000, from less than $1.5 billion now. Access fees--to both Internet service providers and the national backbone firms--will account for three-quarters of that revenue, according to Forrester.

That doesn’t include the money to be made supplying equipment to the backbone firms as their never-ending construction project goes forward. Some of the equipment suppliers rank among the new elite of the stock market’s high-tech sector--companies such as Cisco Systems Inc., U.S. Robotics Corp. and Ascend Communications Inc.

With more than a quarter of America’s households and a third of its businesses online by 2000, traffic will be growing even faster than revenues. MCI’s monthly Internet traffic--now about 330 terabytes (330 trillion bytes)--has been tripling yearly for the last three years and should be well into the petabytes (think of a 1 followed by 15 zeros) when the new millennium arrives.

By comparison, the full Encyclopedia Britannica contains about 1 gigabyte (a billion bytes) of information.

Such growth, while invigorating to investors, makes for a volatile and messy environment. The system is becoming so complex that there is only a general consensus on exactly what constitutes the backbone and who its top players are.

Today’s backbone is a commercial descendant of the original Internet framework that the federal government began assembling in the late 1960s to facilitate communication among military and scientific researchers. It evolved into a network linking a handful of university-based supercomputers and began its explosive growth in the mid-1980s when other regional computer networks--most of them university-based--were allowed to connect.

As recently as two years ago, the Internet was still a creature of the federal government, operated under the auspices of the National Science Foundation. But in April 1995, the agency turned over the keys to the private sector.


At that time, there were four major hubs of Internet traffic--in San Francisco, Chicago, New York and Washington. At these so-called national access points, the backbone firms connected with one another in a process they call “peering” to enable customers of one company to communicate with those of another.

These peering arrangements--I’ll carry your traffic if you’ll carry mine--are generally 1-to-1 deals with no money changing hands. But according to Jack Rickard, editor and publisher of Boardwatch magazine, which covers the Internet, the big players are picky about whom they accept as partners, which can make it tough for new firms to enter.

An even bigger obstacle is the amount of capital it takes to compete.

“There will be some kind of a shakeout at the backbone level,” said Vinton G. “Vint” Cerf, an MCI senior vice president who helped develop the dominant networking language of the Internet. The competitive struggle will determine “who’s capable of continuing to invest in capacity,” Cerf said.

MCI is near completion of a $60-million upgrade of its own piece of the backbone. Sprint says it has invested $100 million over the last 18 months in a similar effort.

Other backbone providers that are pouring in capital include UUnet, a unit of Worldcom Inc.; Cable & Wireless’s CWIX system; IBM’s Global Network; BBN Planet Inc.; PSInet Inc.; ANS, a unit of America Online Inc.; and Digex, which went public with a $45-million stock offering in October.

The big phone companies own most of the high-speed fiber lines used in the backbone, and they lease these lines to other backbone firms. All the backbone providers are investing in routers and switching systems.

In addition to the four original national access points, new hubs have sprung up in Los Angeles, San Jose, Seattle, Houston and elsewhere. As more backbone firms interconnect with one another at the new exchange points, the distinction between the new hubs and the original four is becoming of mainly historical significance, experts say.


Backbone firms also are continually adding their own private “nodes” or “points of presence,” along the backbone, where they peer with one or two other backbone firms and establish connections with regional Internet service providers. Sprint and MCI, for instance, have more than a dozen such hubs apiece in major metropolitan areas.

In this fashion, the backbone keeps expanding, and definitions get muddier.

Because the backbone’s highest-capacity fiber lines, or “pipes,” can handle more traffic than the fastest router, the routers--electronic post offices that sort e-mail and other data flowing through the Internet--can become bottlenecks. But the smaller pipes can also get clogged when too much information is pumped through them.

The backbone companies are continually monitoring their systems, trying to figure ways to shift traffic away from pressure points and avoid having information “packets” needlessly bounced like pinballs from router to router, causing delays and lost data.

However, today’s most notorious Internet traffic jam--the one bedeviling America Online--has nothing to do with the backbone, experts say.

The gridlock at AOL is concentrated at the banks of modems that receive phone calls directly from the service’s dial-up customers. After AOL pumped up demand by offering unlimited Internet access for a flat monthly fee, the company discovered it didn’t have enough modems to handle all the incoming calls, and users started getting busy signals.

Thomas S. Mulligan is a staff writer in The Times’ New York bureau. He can be reached via e-mail at


The Internet Backbone

At the core of the sprawling Internet computer network is a system of high-speed data-transmission lines and specialized computers that is known as the Internet backbone.

While there are thousands of Internet service providers, or companies that offer to link home or business computers to the Net, only about a dozen major firms form the backbone.These companies provide hookups to the Internet service providers, which in turn connect the individual users. Backbone operations were turned over to the private sector by the National Science Foundation in 1995 and are now among the most reliable revenue generators in the Internet world. The map shows some of the major transmission lines of the backbone and indicates the major hubs where the lines converge.

How Fast Is Fast?


TYPE SPEED APPROX. TIME TO TRANSMIT 680 MB Standard modem 28.8 Kbps 53 hours, 43 minutes, 53 seconds 2-channel ISDN 128 Kbps 12 hours, 5 minutes, 34 seconds T1/DS-1* 1.544 Mbps 58 minutes, 43 seconds T3/DS-3 44.736 Mbps 2 minutes, 2 seconds OC-3** 155.52 Mbps 34.95 seconds OC-12 622.08 Mbps 8.77 seconds


* A DS-1 line is a digital version of a T1 line.

** OC-3 is the same as three T3 lines. OC-12 is equivalent to 12 T3/DS-3 lines

-Source: Internet World Note: Some network links have been made faster since this map was created.