Build bigger bandwidth for your network backbone five ways

Build bigger bandwidth for your network backbone five ways

Cost, flexibility and security are factors managers consider when choosing a network technology

By J.B. Miles

Special to GCN

Bandwidth, like winning, may not be everything, but to an information services manager looking to buttress a network against the pressures of too much traffic, it can look like the only thing.

Many variables come into play when considering the right LAN or WAN backbone technology for your networks, not the least of which are high connection rates, security and flexible bandwidth management. But for most designers of multiprotocol, multiservice networking environments, the paramount factor is bandwidth.

The leading contenders among high-speed, high-bandwidth WAN backbone technologies are Fiber Distributed Data Interface, Synchronous Optical Network, frame relay, asynchronous transfer mode and Gigabit Ethernet. Here are some of the principal features of each technology, along with a view of the viability of each.


Fiber Distributed Data Interface backbones have performed very well historically, having arrived well before newer backbone technologies such as ATM and Gigabit Ethernet. FDDI builds 100-Mbps fiber-optic LAN backbones into a counter-rotating token-ring topology that can span up to 200 kilometers. (Twisted-pair copper wiring may also be used for short hops.) FDDI offers great redundancy and can handle up to 170,000 packets per second. FDDI backbones are also extremely fault-tolerant.

But FDDI's heyday appears to be over. FDDI's 100-Mbps throughput speed doesn't measure up to the gigabit speeds of Gigabit Ethernet, and, though stable, FDDI doesn't meet the multiservice networking requirements and quality of service that technologies such as 622-Mpbs ATM backbones provide.


Sonet is popular among telephone companies and common carriers that use it mainly to aggregate slower-speed T1 and T3 lines into high-speed fiber-optic backbones. The base rate of Sonet is 51.84 Mbps, but this rate can be multiplexed into the multiple gigabit range. Sonet comes in a frame format with two main areas for payload and overhead, and it has built-in intelligence for advanced network management.

Sonet supports standardized optical interfaces, so interconnectivity and basic interoperability among different manufacturers' equipment are assured. It allows the multiplexing and de-multiplexing of signals into both high- and low-speed packages, with significant cost savings to users, and it is well-designed for popular private-line services. Its built-in redundancy and self-healing capabilities, especially in the four-fiber bidirectional ring version, make it especially fault-tolerant.

Sonet was originally optimized for voice traffic, and this is still where its real strengths lie. Given the rapid growth of data networks, pundits were predicting as late as last fall that Sonet use would decline as buyers migrated to newer transport technologies.

But so far the market for Sonet has been resilient. As long as both voice and data networks continue to grow exponentially, the telecommunications industry will continue to support Sonet.

Dense wavelength division multiplexing technology, an optical successor to Sonet, is building a following among long-distance carriers, but Sonet will continue to be a viable alternative for enterprise WAN backbones.

Frame relay

Frame relay is a popular WAN packet-switching topology offering variable throughput speeds of up to 45 Mbps. It is offered by all the major phone service carriers, including Sprint Corp., which recently halved its government rates under its FTS 2000 bridge contract to the new FTS 2001 contract.

Information sent over frame relay WANs is divided into frames or packets that contain the address to which data is sent. Frame relay's underlying technology is efficient because it doesn't process data packets itself. It relies instead on powerful third- and fourth-generation network switches for processing the data packets.

Frame relay backbones have become popular as pipelines for remote IP services, and the flexible technology allows for processing other important network protocols such as Systems Network Architecture and TCP/IP.

Frame relay backbones are often referred to as clouds because they don't rely on single physical connections between endpoints. Instead they create logical paths, or virtual circuits, that can act as both switched virtual circuits and permanent virtual circuits.

Thus, from a user's standpoint, frame relay economically meets the requirements for both switched dial-up lines and dedicated lines.

Because frame relay can handle different frame sizes, it is well-suited to handle almost any traffic that passes over it. And because network switches and high-end PCs and workstations now take on many of the burdens of protocol processing, such as error detection and correction from the network itself, frame relay is a good fit for multiprotocol, multiservice networks.


Asynchronous transfer mode is a switched technology that provides connections via switches rather than shared buses. Information on ATM backbones is assembled into fixed-length, 53-byte cells broken into 5-byte headers and 48-byte data payloads. Its switched nature allows ATM to offer benefits such as dedicated bandwidth per connection, high aggregate bandwidth, well-defined connection procedures and flexible access speeds.

ATM is best known for its high reliability and quality of service for mission-critical applications. Because of its layered architecture, it easily handles multiple services such as voice, data and video. It works equally well over twisted-pair, coaxial or fiber-optic lines.

Compared with the 1-Gbps speed of Gigabit Ethernet backbones, the ATM backbone speed of 622 Mbps is relatively slow. And ATM's 25-Mbps speed to desktop PCs hasn't been well-received in the marketplace.

To handle Internet protocols successfully, ATM desktop PCs and servers require a specialized format called LAN emulation, a kind of virtual LAN that adds further complexity to ATM installations. Despite its many benefits, ATM can be complex and expensive, and implementation requires a lengthy learning curve for most Ethernet-aware network managers.

Gigabit Ethernet

Until Gigabit Ethernet came along, Ethernet and Fast Ethernet backbones couldn't compete with the speed, flexibility, quality of service and scalability of ATM. But Gigabit Ethernet backbones offer 1-Gbps speed and now can run over Category 5 copper, coaxial and fiber-optic lines.

And Gigabit Ethernet's standards are secure, meaning the technology is fully backward-compatible with legacy Ethernet hardware standards and backbones can be scaled back to 10-Mbps Ethernet and 100-Mbps Fast Ethernet speeds as required.

Ethernet network management schemes are already well-understood by most managers and users, so no lengthy learning curve is required to get a Gigabit Ethernet backbone up and running.

The prices of Gigabit Ethernet gear also are dropping rapidly. Prices for Gigabit Ethernet switches are expected to drop 50 percent, or from about $1,000 per port to $500 per port, over the next six months. Industry watchers note that Gigabit Ethernet offers the same high standards for quality of service and reliability as ATM for a lower cost per port.

Gigabit Ethernet appears likely to become the leading multiprotocol, multiservice backbone technology. Reinforcing this trend will be the emergence of 10-Gbps Ethernet systems for metropolitan area networks.

J.B. Miles of Pahoa, Hawaii, writes about communications and computers.

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