frame relay

Frame relay is an affordable way to transmit switched-packet data within LANs and WANs.

Frame relay is a packet-switching telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between endpoints in wide area networks (WANs). The service, once widely available and implemented, is in the process of being discontinued by major Internet service providers. Sprint ended its frame relay service in 2007, while Verizon said it plans to phase out the service in 2015. AT&T stopped offering frame relay in 2012 but said it would support existing customers until 2016.

Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the endpoints, which speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service provider figures out the route each frame travels to its destination and can charge based on usage. Switched virtual circuits (SVC), by contrast, are temporary connections that are destroyed after a specific data transfer is completed.

An enterprise can select a level of service quality, prioritizing some frames and making others less important. A number of service providers, including AT&T, offer frame relay, and it's available on fractional T-1 or full T-carrier system carriers. Frame relay complements and provides a mid-range service between ISDN, which offers bandwidth at 128 Kbps, and Asynchronous Transfer Mode (ATM), which operates in somewhat similar fashion to frame relay but at speeds of 155.520 Mbps or 622.080 Mbps.

Devices

In order for a frame relay WAN to transmit data, data terminal equipment (DTE) and data circuit-terminating equipment (DCE) are required. DTEs are typically located on the customer's premises and can encompass terminals, routers, bridges and personal computers. DCEs are managed by the carriers and provide switching and associated services.

Frame relay is based on the older X.25 packet-switching technology that was designed for transmitting analog data such as voice conversations. Unlike X.25, which was designed for analog signals, frame relay is a fast packet technology, which means that the protocol does not attempt to correct errors. When an error is detected in a frame, it is simply dropped (that is, thrown away). The end points are responsible for detecting and retransmitting dropped frames (though the incidence of error in digital networks is extraordinarily small relative to analog networks).

Frame relay is often used to connect LANs with major backbones as well as on public wide area networks and also in private network environments with leased T-1 lines. It requires a dedicated connection during the transmission period and is not ideal for voice or video, which require a steady flow of transmissions. Frame relay transmits packets at the data link layer of the Open Systems Interconnection (OSI) model rather than at the network layer. A frame can incorporate packets from different protocols such as Ethernet and X.25. It is variable in size and can be as large as a thousand bytes or more. 

This was first published in March 2015

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