Express lanes for LANs

Gigabit Ethernet ups network speed by a factor of 10, but it won't stop there--an even faster Ethernet is on the way.

Only a few years ago, the speed race in network connectivity was a battle between Ethernet's 10mbps transmission rate and Token-Ring's 16mbps. Even though the difference between the two was relatively small, Token-Ring's 60 percent edge justified its continuing (if nominal) presence in the network marketplace outside of IBM shops in the early 1990s. Change doesn't necessarily happen quickly in the networking world. Token-Ring and Ethernet standards took nearly the entire decade of the '80s to progress from their modest original speeds of 4mbps and 2mbps, respectively.

But in 1994, the IEEE finalised specifications for a Fast Ethernet, or 100BaseT, variation of the 802.3 Ethernet standard. By that time, the only competition remaining was among Ethernet variants. Its development has since become a leapfrog race: almost as soon as 100BaseT increased performance tenfold to 100mbps, research began into Gigabit Ethernet, or Gig-E, which offered another factor-of-10 jump. The Gigabit Ethernet (IEEE 802.3z) standard was formalised in June 1998, but an industry group is already developing a standard for 10 Gigabit Ethernet (see sidebar, "The Ethernet express").

On the following pages, we'll show you how Gigabit Ethernet might help improve your network's performance, describe the issues and costs associated with upgrading, and tell you about an even faster version of Ethernet that's on the way.

The Information Gatekeepers Inc. (IGI), a research firm, reports that sales of Gigabit Ethernet equipment exceeded US$2 billion in 1999, the first full year after the standard was adopted. However, at the end of 1999, the same group estimated that only an insignificant portion of this (less than 0.04 percent) was being invested in deployments of Gig-E to desktop computers. In fact, IGI indicated that Gig-E's predecessor, 100 Megabit Fast Ethernet, held only a 2 percent share of end-to-end networking at that time--fully five years after that standard was approved. Clearly, pervasive deployment of advanced Ethernet technologies lags significantly behind the development of the standards.

There are a number of reasons for Gig-E's slow acceptance. Early in the life of the standard, some network administrators expressed doubt that it could actually run over Category 5 copper cabling--though this capability has now been thoroughly proven. Also, costs were quite high at first, but in the past year, the gap between Fast Ethernet and Gigabit Ethernet has narrowed. Gig-E network interface cards (NICs) have dropped below $500, and switches are available for roughly $300 to $400 per port.

Perhaps the greatest problem facing Gigabit Ethernet is that it's sandwiched by its older and younger siblings. When the 802.3z standard was announced, most companies were still in the process of converting to Fast Ethernet or had barely even begun converting. Now, just as Gigabit Ethernet costs are dropping, the still speedier 10 Gigabit Ethernet standard is almost a reality. With the speed bar getting bumped up yet again, many network planners contemplating a move to Gig-E are not certain whether they should even bother with that step in the Ethernet chain.

Switched vs. looped
Unlike the upcoming 10 Gigabit Ethernet, 802.3z is not a dramatic departure from Fast Ethernet technology. The two are technically quite similar, with Gigabit Ethernet's transmission parameters tuned to a higher rate. One key difference is that Gigabit Ethernet is strictly deployed as switched--not looped--Ethernet. The original Ethernet structure is looped, where all the nodes on a physical subnet use a shared transmission medium. Of course, the effective bandwidth of a shared loop drops as more nodes are added.

Switched Ethernet, on the other hand, uses switched hubs that intelligently direct data frames between source and destination, rather than relying on subnetwide broadcast and packet collision detection methods. Switching reduces network congestion by establishing a virtual direct link between any two nodes and guarantees a specific level of throughput. Some hub vendors offer switched 10 Megabit Ethernet hubs and consider switching so powerful that even at 10mbps they may be more effective than Fast Ethernet.

As yet, Gigabit Ethernet has not been widely deployed on desktop computers. Few desktop applications demand the kind of bandwidth Gig-E offers. Unless you're working with an application such as CAD that may shuttle large amounts of data over a network, you're unlikely to detect a performance boost. But Gigabit Ethernet is gaining acceptance for network infrastructure use, playing niche roles of growing importance in several areas, including:

• Server backbones: Connecting high-traffic servers to each other using Gigabit Ethernet hubs is an ideal use because they maintain complete compatibility with other Ethernet technologies and can offer the same or greater increases in performance as installing multiple NICs.

• Storage area networks (SANs): Gigabit Ethernet can compete with optical fiber in providing fast links to shared drive arrays, with the dual advantages of being less costly and easier to work with. Its speed is suitable for this task, but it's prudent to note that SAN products are often so proprietary that they may not be compatible with some vendors' network hardware products.

• Wide area network (WAN) links: As with SANs, Gigabit Ethernet has cost and use advantages for WAN implementations, but technical restrictions limit its value for long distance networking. It can extend to only 330 feet on Cat 5 cable; that distance stretches to 900 feet using multimode fiber and 3.1 miles with single-mode fiber. As a result, Gigabit Ethernet can serve as a connector between buildings in a campus environment but isn't likely to be used to link buildings across town.

Every network planner likes to fantasise about technologies that offer features and costs that promise to remain stable for a while. In reality, networking standards such as Gigabit Ethernet are being developed at a more rapid rate than ever. Gigabit Ethernet is part of a growing line of succession, not a product that exists in a vacuum. Network planners must evaluate the entire line, including upcoming developments such as 10 Gigabit Ethernet, when determining physical upgrade strategies. With PCs and servers there's always a faster processor waiting in the wings to overtake the current speed champ.

Networking technologies are beginning to mirror that market, making it inevitable that no matter how rapidly you update your network, you're bound to lag behind the pacesetting technology at times. But with Fast Ethernet, Gig-E, and 10 Gigabit Ethernet, network designers have a good choice of technologies to address specific network performance issues.