Bandwidth Blowout Begets Breakdowns

April 1, 2005
Besides ensuring that networks are correctly constructed, end-users must understand traffic usage on them. “You have to be very careful.

To avoid a situation similar to blowing a fuse on an electrical network, you need to start looking at where you plug into the network,” cautions Mark Fondl, president and chief executive officer of Network Vision Inc. (, Newburyport, Mass.

Ethernet on the factory floor presents a common network- traffic-management problem now, he says. It arises from the technology’s deployment. One approach is to use the existing manufacturing information technology (IT) structure and layer devices on it. With this method, distributed local-area networks may also be used. “Network traffic can be separated on the wire. That’s typically called a converged network, where all devices are connected to the same physical structure,” Fondl explains. This may create bandwidth problems.

The other deployment approach is with a segmented network, on which only factory-floor devices are connected. Typically, end-users will deploy routers to connect the factory-floor networks to the corporate networks, says Fondl. The router provides isolation and bridging. “The router keeps unnecessary broadcast traffic on the factory floor from interfering with the corporate network,” he says. Likewise, the router acts as a firewall and keeps unnecessary broadcast traffic on corporate networks from interfering with factory-floor networks.

Subscription overload

A key part of this segmented-network arrangement is the use of multicast traffic, also known as publish/subscribe. Under this protocol, a device publishes data to which any other device on the network may subscribe. But while multicast allows many devices instant access to information, it also creates unpredictable network-traffic-control patterns. “If you subscribe to a particular device, the switches open up the channels and then start streaming the data. The device starts sending data that could be spread across the entire network, causing intermittent traffic congestion,” says Fondl.

Another network traffic-management problem comes from someone plugging a laptop into the network and activating a file transfer. That person may not knowingly create a traffic jam, but nonetheless, it can happen. “That may interrupt data feeds into supervisory control and data acquisition (SCADA) systems or others, overloading the bandwidth,” Fondl says.

What Network Vision and Tulsa, Okla.-based SolarWinds.Net ( both address with their respective network-management technologies is the monitoring of networks’ health. One way is to pinpoint where overloads occur, even at individual personal computers.

Even so, there are things that network managers should do to facilitate smooth traffic flow, believes Doug Rogers, vice president of operations at SolarWinds.Net. First, ensure that all passwords and community strings—the latter is what routers and switches call passwords—are not the manufacturers’ defaults or things like the title of the latest hit movie, Rogers says. Have something that is unique to your company and more than eight characters long. Change them frequently, too.

Also, if you use monitoring software, choose a solution that monitors and notifies in real time, Rogers advises. Installed monitoring software should be non-intrusive, have negligible impact on bandwidth and analyze network performance. The software should also be intuitive and user friendly.

C. Kenna Amos, [email protected], is an Automation World Contributing Editor.