Frame relay is a computer networking structure that allows for a quick and efficient way to transmit frames from one device to another. These frames, or packets of data, are usually sent between local area networks (LANs) within a wide area network (WAN). The way the frames are sent is like a relay — data is passed from one router or node to another from where it's then sent to another node or router. It's a relatively inexpensive technology though alternative structures like virtual private networks (VPNs) or multiprotocol label switching (MPLS) are often preferred.
Boasting rich High-Level Data Link Control (HDLC) capabilities, frame relay provides basic call setup along with variable length packet routing and delivering. What it does not provide is correction and end-to-end recovery of data. These functions must be available in the applications that use the protocol to transport information.
Frame relay protocol is modeled after packet-switched technologies much like x.25, which provides end stations with a way to dynamically share network medium and bandwidth. There are essentially two flavors of this protocol. One is based on Q.922 LAPF, the standard and most widely used deployment. The other conforms to LMI specifications and is used less frequently. While frame relay does not ensure data integrity or discard packets to prevent network congestion, it is still able to deliver data at a high degree of reliability.
Frame relay networks transmit frames to their destination by way of virtual circuits. There are two types of virtual circuits — permanent virtual circuits (PVCs) or switched virtual circuits (SVCs). SVCs are set up on a call-by-call basis. Clearly designated by a data link connection identifier (DLCI), virtual circuits provide two-way communication paths from one terminal device to another.
In a frame relay network, a number of virtual circuits can be used to send multiple messages at once all along a single, physical circuit. This capability often reduces the amount of network equipment required. It also reduces costs, while still providing secure, private, IP-based networks.
Frame relay makes a viable alternative for data transmission. Even though it cannot guarantee data integrity, most of the protocols it supports are integrated with their own set of error-correction mechanisms. Because of this, frames are able to travel at exceptional speed and arrive at their destination with minimal delay. This factor gives it many of the same qualities as a direct leased line connection, only at a considerably cheaper price.