Frame Relay Packet Switching Technology

ISDN - Telephone, keyboard, cable and bandwidth
ISDN - Telephone, keyboard, cable and bandwidth. Stuart Hunter / Getty Images

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 the underlying infrastructure for Integrated Services Digital Network (ISDN) services sold to business customers.

How Frame Relay Works

Frame Relay supports multiplexing of traffic from multiple connections over a shared physical link using special-purpose hardware components including frame routers, bridges, and switches that package data into individual Frame Relay messages. Each connection utilizes a ten (10) bit Data Link Connection Identifier (DLCI) for unique channel addressing. Two connection types exist:

  • Permanent Virtual Circuits (PVC) - for persistent connections intended to be maintained for long periods of time even if no data is actively being transferred
  • Switched Virtual Circuits (SVC) - for temporary connections that last only for the duration of a single session

Frame Relay achieves better performance than X.25 at a lower cost primarily not performing any error correction (that is instead offloaded to other components of the network), greatly reducing network latency. It also supports variable-length packet sizes for more efficient utilization of network bandwidth.

Frame Relay operates over fiber optic or ISDN lines and can support different higher level network protocols including Internet Protocol (IP).

Performance of Frame Relay

Frame Relay supports the data rates of standard T1 and T3 lines - 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 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 stage conditions (and can be exceeded when the underlying physical link has enough spare capacity to suppor tit). Frame Relay does not restrict maximum performance to that of the CIR but also allows burst traffic, where the connection can temporarily (typically for up to 2 seconds) exceed its CIR.

Issues with Frame Relay

Frame Relay traditionally provided a cost-effective way for telecommunications companies to transmit data over long distances. This technology has decreased in popularity as companies are gradually migrating their deployments to other Internet Protocol (IP) based solutions.

Years ago, many viewed Asynchronous Transfer Mode (ATM) and Frame Relay as direct competitors. ATM technology differs substantially from Frame Relay, however - using fixed length rather than variable length packets and requiring more expensive hardware to operate.

Frame Relay ultimately faced much stronger competition from MPLS - Multi-Protocol Label Switching.

MPLS techniques have become widely used on Internet routers to efficiently enable Virtual Private Network (VPN) solutions that previously would have required Frame Relay or similar solutions.