Frame relay
Frame relay, also found written as frame-relay, is an efficient data transmission technique used to send digital information quickly and cheaply to one or many destinations from one or many end-points. Commonly implemented for voice and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line to a frame relay node. The frame relay network handles the transmission over a frequently-changing path that is transparent to all end-users.
Initial proposals for Frame Relay were presented to the Consultative Committee on International Telephone and Telegraph (CCITT) in 1984. Lack of interoperability and standardisation, prevented any significant, Frame Relay deployment until 1990 when Cisco, Digital Equipment Corporation (DEC), Northern Telecom, and StrataCom formed a consortium to focus on its development. They produced a protocol that provided additional capabilities for complex inter networking environments. These Frame Relay extensions are referred to as the Local Management Interface (LMI).
Frame relay developed as a stripped-down version of the X.25 protocol, releasing itself of the error-correcting burden most commonly associated with X.25. When an error is detected, the packet is simply dropped. Frame relay uses the concept of shared-access and relies on a technique refered to as best-effort, whereby error-correction is practically non-existant and reliable data delivery is practically unguaranteed. It is an industry-standard encapsulation utilizing the strenghts of high-speed, packet-switched technology able to service multiple virtual circuits and protocols between connected devices, such as two routers.
As a WAN protocol, frame relay is most commonly implemented at Layer 2 (data link layer) of the OSI model. Two types of circuits exist: permanent virtual circuits (PVCs) which are used to form logical end-to-end links mapped over a physical network, and switched virtual circuits (SVCs). The latter analogous to the circuit-switching concepts of the public-switched telephone network (or PSTN), the global phone network we are are most familiar with today. While SVCs exist and are part of the frame relay specification, they are rarely applied to real-world scenarios. SVCs are most often considered harder to configure and maintain and are generally avoided without appropriate justification.
Datalink Connection Identifiers or DLCIs are locally significant numeric values that represent each end-point. Multiple PVCs can be mapped to the same physical end-points (a process known as applying a subinterface). Frame relay is often provisioned with a Committed Information Rate (CIR) and a burstable component sometimes known as the Extended Information Rate (EIR).
Frame relay was designed to make more efficient use of existing physical resources, which allow for the overprovisioning of data services by telecommunications companies (telco) to their customers, as most clients were unlikely to be utilizing a data service 100 percent of the time. In more recent years, frame relay has acquired a bad reputation in some markets because of excessive bandwidth overbooking by these telcos.
Frame relay is/was often sold by telcos to businesses looking for a cheaper alternative to dedicated lines; its use in different geographic areas depended greatly on governmental and telecommunication companies policies. Some of the early companies to make frame relay products were StrataCom (later acquired by Cisco Systems) and Cascade Communications (later acquired by Ascend Communications and then Lucent Technologies).
At 2005 Frame relay is slowly being displaced by ATM and native IP-based protocols. And with the advent of the VPN and other dedicated broadband services such as cable modem and DSL, the end may be in sight for frame relay protocol and encapsulation.
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Categories: Network protocols