Frame relay access device

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A frame relay access device (FRAD) is the doorway to the frame relay service; it allows non-frame relay equipment to connect to and communicate across, a frame relay network. There is enormous variation between FRADs in the market; you must read carefully to determine exactly what any particular piece of equipment actually does. The basic function remains the same whether the FRAD is a high-capacity router or a simple pass-through for another technology: the FRAD takes non-frame-relay traffic and encapsulates it inside a LAPF-Core frame, as shown on the visual.

FRADs are available from a variety of vendors and come in many flavors. Each vendor supports a different mix of non-frame-relay protocols including Synchronous Data Link Control (SDLC), X.25, Binary Synchronous Communications Protocol (BISYNC), TCP/IP, Group III fax, and even voice and video.

The protocol encapsulation procedure itself is the subject of other specifications. If the FRAD is handling only one type of traffic, the encapsulation is straightforward. If the FRAD is handling multiple different traffic types, the FRAD that will receive the various traffic types at the other end of the frame relay service must be able to determine what is actually in any given frame relay frame to operate on it correctly. While some vendors use proprietary encapsulation schemes, the IETF has published a specification for multiprotocol encapsulation in frame relay in RFC 2427, the basis for Frame Relay Forum Implementation Agreement, FRF.3.1.


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