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  Make Room For Frame Relay By David Willis Forget the traditional wisdom regarding frame relay. New advances make it viable for larger networks running at higher speeds, with support for real-time services and delay sensitive applications. Powerful management stations put the customer in charge of the network. Get ready for the ultimate guide to frame relay services, including a guide to the providers, on page 76. 
On the realm of wide area networks, packets and cells reign supreme over physical circuits. By mixing the high performance of switches and fiber in the core with the agility of packet networking at the edge, broadband WANs are
reaching unprecedented speeds and flexibility. At the juncture between the edge and the network core lies frame relay, the most widely deployed WAN interface. Once believed to be an interim step toward either Switched Multimegabit Data Service (SMDS) or ATM, and seen as limited to moderate speeds and data-only applications, frame relay is bursting its boundaries and conquering larger networks and even real-time applications.
Public frame relay service has been hugely successful for several reasons: It reduces network access costs by consolidating virtual circuits onto physical-access circuits; a variety of inexpensive equipment options is available; long-haul circuits cost a fraction of their physical circuit equivalents; and pricing is not distance-sensitive. A carrier can make changes to virtual circuits within a few hours at most. In most implementations, data may burst as high as the access port speed. Expansion Plans To keep up with demand for wide-area services, carriers have changed t heir approach to network design. They've been able to "over-engineer" their networks, thanks to lower deployment costs--that is, they've raised fiber capacity and switch performance to levels well beyond current needs. Baseline utilization levels remain at a low th reshold (often about 40 percent), so networks aren't blindsided by sudden traffic spurts. Equipment vendors have leveraged frame relay's performance and attractive pricing by integrating new traffic types. Systems Network Architecture (SNA) traffic, which many network engineers originally thought to be too delay-sensitive, is now widely supported on customer equipment. Carriers have begun offering branded SNA-over-frame-relay services, taking advantage of customer desires to collapse expensive, redundant WANs. Voice-over-frame-relay transport is now viable for interoffice voice trunking and off-premises extensions. Carrier support is limited (only Intermedia Communications and Infonet Services Corp. offer it as a branded service), but most carriers admit they have customers using frame relay for voice service, both domestically and internationally. Voice-over-frame relay will likely follow the same path as SNA--namely, equipment support will increase customer demand and experimentation; the Frame Relay Forum will adopt an Implementation Agreement, assuring vendor interoperability (as of January 1997, this step was not yet complete for voice); finally, carriers will package a branded solution. Granted, frame relay falls short of providing quality of service (QOS) levels and doesn't have the bandwidth reservation techniques found in ATM. Only the most primitive form of priority exists in most carrier networks. Customer premises equipment (CPE) may mark frames as discard eligible (DE), as a method of assigning lower priority to a given stream--for example, by protocol, User Datagram Protocol (UDP) port, packet size or interface source. However, DE marking is rarely activated by the customer, and is most often performed by the carrier to indica te traffic sent above a contracted committed information rate (CIR). In any case, true quality of service for frame relay remains a distant goal, and in the short term, carriers are likely to implement a priority scheme comprising just a few levels.
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by Peter Morrissey Updated Februayr 7, 1997 |
