Network Uptime

A: Most protocol analyzers define 'Utilization Percentage' as a percentage of the total use of bandwidth for a link based on a sampling period. Using Ethernet as an example, we know there are only two utilization values in Ethernet; zero percent, and one-hundred percent. Ethernet is either used, or it's not used.

A single chart showing two points alternating between 0 and 100 wouldn't be very helpful, so most utilization measurements are constructed by acquiring a large number of utilization samples over time to provide a more normalized perspective of utilization.

The 'pipe' is the maximum bandwidth available on the link that is physically connected to the analyzer. If the connected link is 100 megabits, then the utilization percentage is based on that theoretical maximum of 100 million bits per second. If you're plugged into a WAN link, the 'pipe' may only be 64,000 kilobits and the utilization percentage will be based on this slower bandwidth. Network analyzers don't have a way to determine switch backplane bandwidth capacities, or the number of ports that might be mirrored to a single port (at least, not yet). The utilization percentage is always based on the maximum bandwidth capacity of the port that's physically connected to the analyzer.

Q: "So what does it mean when the business managers want to see a study of overall network utilization? How can I get utilization information of every switched port in my network? Does it makes sense to gather utilization information in this fashion?"

In most cases, it's impractical (and very tedious!) to gather any type of statistical information on EVERY port on a switched network. Of course, this information is usually available, but most networks have so many switched ports that reporting on every available connection would be difficult to accomplish. For those of us from the 'old school,' we have to become more comfortable with the fact that it's no longer possible to view every bit of data from every device on the network. There's too much data and it's all going too fast!

Most people aren't concerned about every port on the network, and instead they analyze only the most IMPORTANT ports. The business side of the organization knows that there are certain servers, stations, switches, routers, or other devices that are critical to accomplishing the goals of the organization. It's these critical stations and network connections that need to be monitored.

It's not enough to have a technical diagram of the network, the network team should also be aware of the important applications running on the network and the flow of data that occurs within these applications. Without both the map and the route, there's no way to keep track of the race!