IP is dynamic and connectionless, that is, users can be linked to any other user as the need arises. Although this characteristic gives IP one of its inherent advantages, it also has its downside. ISPs engineer their networks according to historical usage trends, but anticipating needs and predicting the future is not quite as reliable as knowing how much bandwidth is needed between two points in the network. In addition, with IP VPNs, every transmission is accorded the same level of service. While users can build the network with higher speed access ports, traffic can still encounter congestion once it is in the Internet.
Frame relay is a well known technology.
Many traffic engineering issues have been addressed over time with carrier and equipment vendor experience as well as the tight integration with ATM technology. As users of the Internet know, performance is not predictable on the current infrastructure. There are many applications that require predictability, such as voice and video. Although there are initiatives underway to provide a level of predictability on the Internet, it may be some time before it is truly a guarantee. Frame relay VPNs today offer a more reliable and predictable solution when the customer's network environment is multi-protocol, particularly if it includes SNA traffic.