Frame relay is a data-link layer, digital packet-switching network protocol technology designed to connect local area networks (LANs) and transfer data across wide area networks (WANs). Frame relay shares some of the same underlying technology as X.25 and achieved some popularity in the United States as part of the infrastructure for integrated services digital network (ISDN) systems sold to business customers.
While frame relay has mostly fallen out of favor, it still exists on some legacy systems and is also used in parts of the world that have been slower to upgrade.
How Frame Relay Works
Frame relay supports multiplexing of traffic from multiple connections over a shared physical link. It uses hardware components, including frame routers, bridges, and switches, to package data into individual frame-relay messages. Each connection uses a 10-bit data-link connection identifier (DLCI) for unique channel addressing.
There are two connection types. Permanent virtual circuits (PVC) is for persistent connections that must be maintained for long periods, even if no data is actively transferred. Switched virtual circuits (SVC) is for temporary connections that last only for a single session.
Frame relay achieves better performance than X.25 at a lower cost by not performing error correction. Error correction is offloaded to other components of the network to reduce network latency. It also supports variable-length packet sizes for more efficient use of network bandwidth.
Frame relay operates over fiber-optic or ISDN lines and supports different higher-level network protocols, including internet protocol (IP).
Frame Relay Performance
Frame relay supports the data rates of standard T1 and T3 lines, which is 1.544 Mbps and 45 Mbps, respectively, with individual connections down to 56 Kbps. It also supports fiber connections up to 2.4 Gbps.
Each connection can be configured with a committed information rate (CIR) that the protocol maintains by default. CIR refers to a minimum data rate that the connection should expect to receive under steady conditions (and can be exceeded when the underlying physical link has enough spare capacity to support it).
Frame relay doesn't restrict maximum performance to that of the CIR. It allows burst traffic, during which the connection can exceed its CIR temporarily (typically for up to two seconds).
Issues With Frame Relay
Frame relay provided a cost-effective way for telecommunications companies to transmit data over long distances. This technology decreased in popularity as companies migrated their deployments to other IP-based solutions.
Many viewed asynchronous transfer mode (ATM) and frame relay as direct competitors. ATM technology differs substantially from frame relay. ATM uses fixed-length rather than variable-length packets and requires more expensive hardware to operate.
Frame relay faced stronger competition from MPLS (multi-protocol label switching). MPLS techniques are now widely used on internet routers to enable virtual private network (VPN) solutions that would have required frame relay or similar solutions previously.