Caught between traffic in the fast lanes –

President Dwight Eisenhower had a favorite saying: "People who walk in the middle of the road get hit by cars going both ways." He probably wasn't thinking of networks, but his words came to mind after a recent speaking engagement.

During my presentation, I mentioned that my employer, West Virginia University, intended to run a hybrid network consisting of both ATM and Gigabit Ethernet. My comments raised more than a few eyebrows.

The ATM folks rushed to tell me that Gigabit Ethernet is questionable when it comes to quality of service. I agreed; Ethernet QoS is in a state of disarray.

The Gigabit Ethernet crowd quickly pointed out that ATM is expensive, complex, and difficult to implement. I had to admit that, yes, that is also true.

But I have some words of wisdom for both camps: "Use a technology where it makes sense." Let's take the ATM/Gigabit Ethernet debate as an example.

In addition to QoS concerns, Gigabit Ethernet has scalability limitations. ATM scales from OC-3 to OC-48 and up; GbE runs at 1 gigabit per second -- no more, no less. If you don't need 1 Gbps you're overpaying for equipment and bandwidth; if you need more, you're plumb out of luck. With ATM you get what you want in terms of bandwidth and pay only for what you need.

On the other hand, ATM is complex and difficult to implement. It also can be expensive -- particularly to the desktop.

So why not adopt this approach? Where you have high bandwidth needs -- as in a data center or server farm -- and QoS isn't an issue, use Gigabit Ethernet. For the sections of your network that support video or voice services, ATM may be a better candidate. The backbone itself might be a good place to deploy ATM, since that's a crucial area where you need end-to-end QoS.

The good news is that you can easily interface the two transports using Gigabit Ethernet routers with ATM ports or ATM switches with Gigabit Ethernet interfaces.

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