Frame Relay is a well established technology, and is used heavily by enterprises that require relatively low bandwidth connections. The user is cautioned against using a Frame Relay service to carry real-time traffic, as they often have difficulty maintaining sufficiently tight jitter specifications, and will usually not guarantee jitter within the specifications required for good real-time transport.
Frame Relay services provide classes of service that can be used to prioritize one traffic type over another. These classes of service work well to insure interactive applications like Telnet or Citrix get precedence over email transfers and file backup. But they are not designed to provide the kind of priority that real-time traffic requires. Furthermore, because frame relay services often have multiple PVCs using the same physical connection, it is difficult to get true priority on a priority queue. The router serving multiple PVCs creates a virtual port for each PVC, each having a high priority and best effort queue. There is no communications, however, between these two virtual ports, even though they are using the same physical port. Hence high priority traffic sitting in a queue on one virtual port cannot override traffic in the best effort queue on the other virtual port. This means true priority queuing is not happening, and leads to intermittent voice and video quality problems.