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Sending the letter "l" across a computer network might not seem like a big deal. But in October 1969, it represented the first communication sent from one computer to another over a telephone line--in this case from the University of California at Los Angeles to the Stanford Research Institute, which would become the precursor to the Internet, the U.S. Department of Defense's Advanced Research Projects Agency Network (ARPANET).
The world's first packet of data, representing the first letter of "log-in," was followed, in time, by trillions of packets over what has evolved into today's network backbones--the huge rivers of optical fiber spanning the continent and bursting with bandwidth that keeps Internet data flowing.
In 2000, the scope of the engineering and technology that has been invested into today's Internet backbones is staggering. It's all been driven by the demands of broadband service providers. In a relatively short time, backbones have been built to carry live streaming video, hefty MP3 files, and billions of email messages and Web pages.
"This whole system has evolved organically for 30 years," says Justin Aborn, assistant chief technology officer for Genuity Inc., which supplies AOL with much of its backbone capacity needs.
Along the way, networks have achieved incredible speeds. For example, Cable & Wireless posts a "current network times" metric on its Web site. It recently proclaimed the round trip data transfer time from San Francisco to Boston took all of 77 milliseconds.
Like most large Internet backbone providers, Cable & Wireless is experiencing tremendous growth in network traffic flow. "We're growing at 200 percent to 300 percent per year," says Chad Couser, public relations manager.
Today's Internet backbones are a collection of optical fiber, high-speed routers, laser transmitters and receivers, Dense Wave Division Multiplexers (DWDM) and demultiplexers, and sophisticated switches that keep the Internet voice, video and data bloodstream coursing across the globe.
The major, or so-called "Tier 1" backbone providers, are generally considered to include UUNet; Sprint Corp.; AT&T Corp.; Genuity Inc., which has built upon the pioneering BBN backbone; Cable & Wireless, which bought MCI's Internet backbone in 1998; Broadwing, formed by the union of Cincinnati Bell and IXC Communications, and several others, including Qwest Communications, Level 3 Communications Inc., Williams Communications and Enron Broadband Services Inc.
What actually constitutes a Tier 1 network backbone is a subject of some debate. Gordon Cook, editor and publisher of the independent Cook Report, defines a Tier 1 backbone this way: if a provider doesn't have to pay any other provider for transit of its traffic, peering excluded.
In other words, UUNet and Sprint are big enough to allow each other's traffic on their respective networks as "peers." Only the most advanced networks have this type of arrangement. Because, as Cook points out, "nobody reaches the entire Internet," the top providers have an interest in letting other traffic on their networks, as long as reciprocal capacity is available.
Core Internet traffic is generally exchanged at the dozen or so worldwide network access points (NAPs). Internet service providers (ISPs) connect directly to backbone networks, or to larger ISPs with direct connections.
Although "peering" is unregulated and highly contentious--the peering agreements between providers are generally kept private--it works to the degree that it makes the Internet functional. "We all realize we depend on each other and we work hard at working well together," Aborn says.
Things are changing, however.
"Many providers are moving away from the NAPs, which are historically known congestion points, to private peering in multiple locations," says Jason P. Gardiner, supervisor of data operations for Sprintlink Internetworking Services. "The backbones are becoming much more complex."
While defining total traffic on backbones is impossible, Cook says that between 30 percent and 40 percent of Internet traffic is carried by UUNet. Sprint, he estimates, is 7 percent and 10 percent behind UUNet.
Most Tier 1 providers maintain networks capable of OC-12--622 megabits per second (Mbs)--speeds or better between major regional points on their networks. Tier 1 providers also maintain 24/7/365 network operations centers for customers, have multiple points of presence (POPs) in major regional centers, and employ some type of redundancy scheme to compensate for a network outage.
Yet at least one engineer questions the usefulness of the word "backbone." "Backbone is probably a term we ought to retire," says Mike O'Dell, senior vice president and chief scientist for UUNet.
With high-speed fiber optics running closer to the end user via the metropolitan and access portion of networks, the old metaphor of interconnections between a spine with branching ribs is no longer universally applicable. The difference between the core network and regional, or metropolitan networks, is beginning to blur. Some consider today's Internet networks to have evolved into a large fishing net, with connected circles of fiber.
O'Dell has a more abstract, and simple, definition: "By backbone, we mean everything that isn't customer touched."
UUNet's network, according to O'Dell, is not homogeneous with consistent bandwidth rates throughout. "We grow the network all the time," O'Dell says, who described an ongoing upgrade of the network's routers and switches. The maximum amount of trunking capacity at this time between regional nodes is OC-192 (10 gigabits per second), while the vast majority of regional links are OC-48, or 2.5 gigabits.
In addition to different bandwidths running at different points in the network, different protocols transport the traffic. For the most part, UUNet's OC-48 links run a hybrid Asynchronous Transfer Mode (ATM), while faster links run MultiProtocol Label Switching (MPLS).
The challenge, according to O'Dell, lies in developing large-scale system-level engineering to compensate for the fact that fiber and capacity isn't always where it's needed.
Competitively maintaining and running a backbone is not merely a matter of providing the raw capacity and dedicated Internet connections to handle ever-growing demands for bandwidth. "The value of a network is based on the content of the network, and the people connected to the network," says Couser, who pointed out that Cable & Wireless hosts the Web sites for Barnes & Noble, The Gap, Staples and The Weather Channel, among others.
Sprint, according to Gardiner, "is the only Tier 1 provider that has native multicasting deployed across its entire backbone."
Genuity provides America Online with more than a third of its dial-up infrastructure, Aborn says. Genuity boasts a rich Internet heritage, tracing its roots back to Bolt Bernack and Newman Inc. (BBN), which contributed several key technologies to ARPANET and became a prominent backbone provider in the Internet's early days. BBN was acquired by GTE and integrated into its Internet group before being renamed and spun out as a condition of GTE's acquisition by Bell Atlantic, which created Verizon.
Genuity provides Web hosting, virtual private network, managed firewall and remote dial-up services to enterprises, Aborn says. The company's new Black Rocket suite of services, which includes Web hosting and applications pre-integrated into the network, are deliverable within 10 days.
Providing voice services over Internet Protocol (IP) networks is another service backbone operators are aggressively pursuing. Genuity, for example, announced in August it was capable of handling 80,000 simultaneous VoIP calls and is building capacity to support greater numbers of calls. Likewise, Cable & Wireless announced last month it was embarking on a global VoIP initiative aimed at business users.
The coming tsunami
The increasing numbers of broadband users will continue to challenge network engineers to keep Internet traffic moving, raising demands for larger and quicker backbones.
"Between four and five years, we need to grow a million-fold," O'Dell says. Aggregate capacity for UUNet's inter-regional trunks in that time frame will support petabit (10 to the 15th power) per second speeds, he says. O'Dell is hoping to place 100 gigabits on a lambda, or DWDM wavelength, and 100 lambdas on a fiber--all on a 100-fiber pair trunk between regions.
"To get here, there's got to be a lot of evolution in the technologies for doing optical stuff," O'Dell says.
Consequently, the industry will be working with many of the top optical networking vendors to push the envelope for speed and capacity while keeping the network elements, such as laser regeneration boxes, or amplifiers, at a minimum.
Broadwing announced a major step in this direction when it signed a deal to use new Corvis Corp. optical switch technology on its network. Broadwing, according to Kihm Schroeder, vice president of network planning, is taking advantage of its relatively new network to utilize the latest optical networking technologies to build three major network rings around the U.S.
For larger customers with permanent connectivity, Schroeder hopes to configure the network using Corvis technology that lets them utilize bandwidth as they need it, ramping up for special occasions and paying only for amounts they actually use.
This capacity-on-demand service, pioneered by Williams Communications in concert with Sycamore Networks, represents the wave of the future for many backbone providers as they work to drive new services into the marketplace.
It's a long cry from typing in "log-in," and given the explosive evolution of Internet-based services, it won't be the last application that sends engineers back to their white boards to concoct new network schemes.
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