Two of the four performed well enough to merit Tester's Choice awards. But figuring out what to look for in frame relay access gear remains somewhat of a mystery. Congestion control is especially important since frame relay networks offer only minimal safeguards against congestion. Customers can use bandwidth above the CIR as it's needed-provided the extra bandwidth is available. But if the network becomes congested, frame relay switches may respond by discarding frames.
Carriers guard against frame loss by overprovisioning their networks.
However, there's no guarantee that frame relay networks will always have ample capacity. As more users sign on for frame relay services, the chances grow that networks will suffer from some congestion. Frame relay switches can't force access devices to throttle back on frame transmissions, but they do alert those devices when congestion occurs. When traffic gets heavy, frame relay switches mark frames with FECN or BECN bits to notify access devices that the network is getting congested. It's then up to the access gear to react to those indicators.