Asynchronous Transfer Mode (ATM) protocol allows high-end users to exchange data across an established and mature broadband network. Built to service customers with very high performance and security expectations, the ATM protocol has met these expectations for a number of years. Despite the maturity of the technology, new technological developments have identified a number of disadvantages in the ATM protocol.
Service providers built ATM networks using a layered technology; the layers of that support ATM service include the physical layer of transmission media, the ATM layer of cell traffic and the adaptation layer that regulates data passing across the network. According to Technology For All, these three layers combine to form a network in which four different models of ATM service allow customers to choose from a selection of service plans. Because of the complexity of the network and the numerous devices required to drive the service, though, ATM network connections carry a high price tag. In addition to the high monthly bills, the network equipment required for ATM service also represents a significant customer expense. As of January 2010, an ATM Network Interface Card (NIC) from computer manufacturer Dell cost £266.4; in comparison, an Ethernet adaptor from the same company cost just £25.90.
Quality of Service
Asynchronous Transfer Mode data connections employ complex but somewhat outdated methods of controlling quality of service (QoS), according to a report presented to the University of Washington. While the technology does employ services across its topmost layer that examine available bandwidth and shape network traffic to fit into the available envelope, as reported by networking hardware manufacturer Cisco, it does not support the more advanced Forward and Backward Explicit Congestion Notification (FECN and BECN) available in Frame Relay or the automatic rerouting found in modern Internet Protocol (IP) networks. In addition, ATM networks may allow data customers to send bursts of traffic that exceed their designated bandwidth allocation, but the network may simply discard data cells in excess of the bandwidth cap; as a result of such discards, customers may experience slow data transfers or choppy Voice Over IP (VOIP) telephone connections.
Due in part to the expense of maintaining an ATM network, a number of service providers have reduced their support for the technology and redirected their sales efforts to newer, faster and less-expensive protocols. According to the report presented to the University of Washington, service providers had already considerably reduced the role of ATM in their backbone networks by the year 2000, and ATM directly to desktop users had nearly ceased to exist by the end of the 20th century. The report pointed out that ATM services will likely coexist with the less expensive and more reliable IP networks for some time, but that service providers will ultimately discontinue the service altogether. The elimination of ATM from service provider offerings could present a significant challenge to commercial broadband data customers, especially to those who have made heavy financial investments in the technology.