Frame Relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Services Digital Network (ISDN) infrastructure, it may be used today in the context of many other network interfaces. It is also a protocol standard for LAN internetworking which provides a fast and efficient method of transmitting information from a user device to LAN bridges and routers.

            The designers of Frame Relay aimed to provide a telecommunication service for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame Relay puts data in variable-size units called "frames" and leaves any necessary error-correction (such as re-transmission of data) up to the end-points. This 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.

            Frame relay is based on the older X.25 packet-switching technology which 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." (thrown away). The end points are responsible for detecting and retransmitting dropped frames. (However, the incidence of error in digital networks is extraordinarily small relative to analog networks.)

                 Frame Relay works at the data link layer to reduce the overhead associated with the movement of data across the wide area. Because we refer to Frame Relay as a WAN technology, it is natural that the protocols will work with the improvements made in the network over the past decades. It relays 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.  

             When the Frame Relay specification was developed, the primary goal was to carry data over the WAN. To handle this form of wide area communications, the core protocols for Frame Relay were established using the revised version of the data link protocols. Instead of using the network layer protocols, Layer 3 was gleaned down to efficiently carry the traffic while performing the same function as the network layer. Moreover, the data link layer was also streamlined to offer less overhead and processing on a link−by−link basis because the circuits across the wide area are much more reliable and error−free (thanks to fiber optics).

            

Newer wireless services known as the General Packet Radio Services (GPRSs) are designed around the movement of IP datagrams (always−on Internet access) from a cell phone or personal digital assistant (PDA) to the public Internet or a VPN connection to an intranet. Regardless of the direction that the data is going to flow, the use of the IP services from the handset enables us to use the network ad hoc. When an IP is created, it is packaged in a radio message. Once this message gets to the base station, it is then encapsulated into a Frame Relay frame to be carried across the wireless carrier's network to a router.

References:

http://en.wikipedia.org/wiki/Frame_Relay

http://www.protocols.com/pbook/frame.htm

http://searchenterprisewan.techtarget.com/definition/frame-relay

Broadband Telecommunications Handbook (Regis J. Bates)