Everybody wants more bandwidth. If you ask your staff if you should install an extra three OC-3s, they'll say yes. When applications become bogged down, one of the first responses is always, "Buy a bigger pipe."
But do you actually need more bandwidth? If you have a 128-Kbps ISDN circuit and want to run 100 simultaneous VoIP sessions at 8 Kbps, you definitely do. No QoS (Quality of Service) device in the world can compensate for that much traffic.
However, if you have enough WAN bandwidth to run your mission-critical applications, and other applications can be pushed aside, you are faced with two options: Get more WAN bandwidth or use a traffic shaper. The decision can come down to ROI (return on investment).
On the surface, calculating ROI is a simple matter: Determine how much additional bandwidth mission-critical applications need. Take the price of that bandwidth per month and divide by the cost of a traffic shaper. That tells you how long until you'll see a return. But there are other considerations:
• If you buy more bandwidth, noncritical traffic will also increase--if the throughput is there, users will suck it up. This can mean a constant cat-and-mouse game.
• Factor management time into the equation. To do traffic shaping, an administrator must keep watch on the traffic and spend time developing and seeking approval for a policy defining which traffic gets priority. When your bandwidth is plentiful and rarely saturated, you won't need to worry. But as bandwidth gets tight, the amount of time spent watching traffic and making decisions increases.
• Be prepared for decreased productivity. A multi-megabyte e-mail attachment could very well cause your e-mail server to swamp a slow WAN for minutes. Users might not be able to access resources they need, and that downtime equates to a monetary loss.
Also consider whether you can do QoS with existing equipment. Many firewall and router vendors, for example, offer bandwidth-control capabilities for their devices for free or a modest upgrade cost. Radware and Cisco routers have this feature, Nortel provides shaping on its Contivity VPN concentrator, and Check Point firewalls have the company's Floodgate bandwidth manager. These devices may be good enough for your environment, making a separate standalone QoS device unnecessary. But again, dig a bit deeper: Bandwidth shaping costs CPU time, so the device's performance may degrade. Also, the granularity of control, such as regulating individual connections, may not be up to the level of a standalone device.
Maybe a compromise is in order: Some QoS-device vendors sell monitor-only solutions that let you graph the dominant protocols; you can then use your existing infrastructure devices for shaping. This is a reasonable solution: If your existing devices have the shaping features and performance to work with your traffic, you're ahead of the game. Worst case, you upgrade the monitor-only product to a full-fledged traffic shaper.
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