Integrating Fast Ethernet Into Existing 10MB Ethernet Networks
Now that Fast Ethernet is here, the question becomes, "How do I start using it?" Integrating Fast Ethernet into existing networks need not be done all at once. Here are some aspects of 100Mbps implementation that should be considered.
Implement switching in high-traffic areas to concentrate the bottlenecks on the network. Since Fast Ethernet provides higher throughput of bits, it makes sense to figure out which network connections need the most relief. Which segments consistently attempt to pump the most bytes though? Which segments consistently demonstrate the highest average percent bandwidth usage according to your protocol analyzer?
Installing switches will help you figure out which network segments are moving the most information due to the effect switches have on your network. Installing switches is like moving from traffic lights to limited-access highways. The idea works extremely well in isolating cross-town traffic, e.g. peer-to-peer networking, but doesn't necessarily help when all of the traffic slows down at particular locations, e.g. an enterprise-wide server or the network Internet firewall. Because there are other ways of isolating network bottlenecks, implementing switches is primarily useful when installing Ethernet switches in preparation for 100Mbps Ethernet.
Installing switches also gives the added benefit of segmenting collision domains. In classic Ethernet, there can be up to four hubs or repeaters between any two stations, but in Fast Ethernet that number is only one or two. Installing switches in place of repeaters spares you from having to segment your network at a later point, allowing the cost of the transition to be spread over a longer period of time.
Once bottlenecks have been identified, upgrade those network connections to 100 Mbps. The primary difficulty in this step is verifying that the existing cabling
will be sufficient for Fast Ethernet. On UTP, the cable either needs to meet Category 5 specifications or have four pairs with proper twist maintained on
Category 3. If you're planning on using 100BASE-TX, your wiring closet will also need to be certified for a higher speed. There are many devices available, such
as wire pair scanners, which will make this job much easier.
Installing the initial Fast Ethernet connections is much easier if the switches installed earlier are Ethernet, capable of operating at either classic Ethernet speeds or Fast Ethernet speeds. If the switches installed were only 10Mbps switches, they can be used as "hand-me-downs," replacing hubs in segments where users require more bandwidth.
Gradually work the Fast Ethernet out into the rest of the network, as far out and down as desired. Note that the price of Ethernet cards is not substantially
higher than that of 10Mbps cards, so it may be a wise idea to plan ahead by installing Ethernet cards when installing new machines. If there comes a point in the
future when 100Mbps Ethernet needs to be implemented on that machine, all that will need to be changed is the connection on the other end. On the other hand,
upgrading a machine from a 10Mbps card to a 100Mbps card will require reconfiguring the user's machine, installing a new driver, etc. A short-term expenditure
can greatly offset the cost in man-hours and down-time later on.