5.1 Frame Relay Concepts    
  5.1.3 Frame Relay stack layered support  
Frame Relay functions by doing the following:
  • Takes data packets from a network layer protocol, such as IP or IPX
  • Encapsulates them as the data portion of a Frame Relay frame
  • Passes them to the physical layer for delivery on the wire

The physical layer is typically EIA/TIA-232, 449 or 530, V.35, or X.21. The Frame Relay frame is a sub-set of the HDLC frame type. Therefore it is delimited with flag fields. The 1-byte flag uses the bit pattern 01111110. If the Frame CheckSum (FCS) does not match the address and data fields at the receiving end, the frame is discarded without notification.