What to look for in an ATM testing tool.

In a perfect world, communications would be simple. Your network would be comprised of all new equipment, all parts of which would be 100% compatible with every other part. One source would install the entire network, train your staff, and monitor the network to ensure that it remained trouble-free.

Reality, however, is much more complex. Legacy systems are aging, new service options are announced every day, and your network users are demanding new features and options, preferably by noon tomorrow. Meanwhile, you are dealing with proprietary switching protocols, competing standards, staffing issues, and budgetary constraints. Communications now is anything but simple.

ATM is gaining ground in large network systems because it makes possible the high-quality voice, video, and data services your network users want. The reason for the growing interest in ATM is simple, but the task of provisioning, installing, and monitoring ATM networks to ensure quality of service is not.

To guarantee reliable ATM service, you must test thoroughly. There's no getting around it -- you'll need test equipment. There may be a single instrument perfect for your network test and analysis needs, but your ideal solution is probably different from your neighbor's. One size does not fit all.

Before you spend money on test equipment for ATM, it's worth taking the time to ask some questions. Do you need a portable test set, or will it be used in a central location? Does it need the flexibility to test other services, such as frame relay or ISDN?

Will you need to monitor quality of service (QoS) after installation? Do you need a global test solution for your networks worldwide? Should it be scalable to higher line rates and provide full physical layer testing as well? Do you need remote monitoring capabilities?

What and where you are planning to test will influence your decision. An upgradable multi-function instrument is the best choice for the central office, lab, mobile telephone switching office (MTSO), or manufacturing floor where you need to test the ATM backbone or its components.

Many ATM problems are caused not by the service itself but by faults on the underlying physical layer. As a result, an instrument intended for network setup and qualification should combine strong physical layer testing capabilities with ATM test features such as QoS analysis.

For protocol analysis, you need a very different set of features. This kind of escalated troubleshooting requires the computing power to capture, filter, and decode ATM cells at full bandwidth.

A protocol analyzer should test not only the physical layer and the various network elements, but also decode the WAN and encapsulated LAN traffic carried on the network. This type of instrument is ideal if you need to test hybrid networks, which may include frame relay, fast Ethernet, or ISDN, in addition to ATM.

But if you need something portable for provisioning and first level troubleshooting at multiple sites, a single-purpose battery-powered test set would be your choice. Specify a test set that offers in-service monitoring, support for QoS measurement, and thorough physical layer testing.

In the past, only multiple test sets could address environments with multiple physical interfacing requirements. Now, however, some vendors offer capabilities like DSI, DS3, and OC3c in a single test set. Make sure you get all the capabilities you need.

If your network testing requirements are global, your test set should handle not only U.S. rates such as DS1 and DS3, but also E1 and E3. The manufacturer of your tester should be able to supply not only your Akron office but your facilities in Amsterdam as well.

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