A DTE-DCE interface specification based on LAPD (Q.921), the Integrated Services Digital Network version of LAPB (X.25 data link layer). A common specification was produced by a consortium of StrataCom, Cisco, Digital, and Northern Telecom.
Frame Relay is the result of wide area networking requirements for speed; LAN-WAN and LAN-LAN internetworking; "bursty" data communications; multiplicity of protocols and protocol transparency. These requirements can be met with technology such as optical fibre lines, allowing higher speeds and fewer transmission errors; intelligent network end devices (personal computers, workstations, and servers); standardisation and adoption of ISDN protocols. Frame Relay could connect dedicated lines and X.25 to ATM, SMDS, BISDN and other "fast packet" technologies.
Frame Relay uses the same basic data link layer framing and Frame Check Sequence so current X.25 hardware still works. It adds addressing (a 10-bit Data Link Connection Identifier (DLCI)) and a few control bits but does not include retransmissions, link establishment, windows or error recovery. It has none of X.25's session layer but adds some simple interface management. Any network layer protocol can be used over the data link layer Frames.