Fast Ethernet can support much longer distances than Gigabit Ethernet over multimode fiber, but it will take more fiber pairs to construct a high-speed backbone using Fast Ethernet with aggregation than with a single gigabit link. The major advantages to Fast Ethernet are cost, fault tolerance and distance. One Fast Ethernet connection can be up to 2 kilometers in length over multimode fiber. Using two or more links bonded together gives you increased bandwidth and fault tolerance. Switched Fast Ethernet connections will cost about $600 per port over fiber, as opposed to $1,500 per port for Gigabit Ethernet.

(As seen in "Fast Ethernet Distance Restrictions," page 92, for a summary of distance limitations for campus backbone wiring using Fast Ethernet.)

Beyond the Backbone Choosing a future topology as you move out from the core of the network is less of a science. If your core network is collapsed into a single building, you likely will have to budget your fibers from the core network to the rest of the campus. If your core is distributed across multiple buildings, you may have more options toward the network's edge.

In the case of a collapsed backbone in a single building, Gigabit Ethernet toward the edge of the network should leave you in good shape for several years. Running a multigigabit core with Gigabit Ethernet to each building provides lots of bandwidth for future multimedia-intensive applications, and makes it simple to set up a consolidated server farm. Likewise, when you assess your edge-network capacity, Gigabit Ethernet to each building gives you more flexibility as users' needs change, since it lets you deploy additional gigabit links later.

If distance between buildings limits your options, then load-sharing Fast Ethernet may be a more suitable choice; the multiple links offer failover capabilities that are absent from a single Gigabit Ethernet link. If you are moving from a dual-attached FDDI ring, the necessary infrastructure most likely will be in place to support this type of network.

Links from the network's core to the intermediate distribution points are often the first to experience high traffic loads. Monitor these links closely and be sure your fiber infrastructure provides for increasing traffic on them. We recommend extra fiber to these locations and suggest you purchase switches that can support multiple Fast Ethernet trunks and/or offer upgrades to Gigabit Ethernet. If you see point-to-point video in your organization's future, bandwidth to these distribution points will be critical.

On the Edge The first choice you'll have to make for the edge of your network is whether to use a few high-density switches or many lower-density "pizza boxes." If you choose the former, you will get more redundant features and have fewer boxes to manage. However, you'll pay two to three times the price per port of lower-density switches, and you may end up not using the densities that a chassis-based system offers. And within a building, allowable distances between your distribution point and your end stations get even shorter--not more than 100 meters for Fast Ethernet connections over Category 5 wiring.

If you choose the pizza-box solution--fixed-configuration devices with high-speed uplinks--you will end up with more infrastructure to manage, but you'll solve many of the distance problems associated with high-speed networks. With Fast Ethernet, if your cable links are longer than 100 meters you may be forced to insert intermediate switches between the wiring closet and the end user.