What does the device do to WAN insertion frames prior to transmission?
When transmitting frames that have been placed in the WAN insertion FIFO, the device manages the basic frame-delineation functions and allows others to be programmed by the user. HDLC start/stop flags are automatically inserted by the device if in HDLC mode. GPF payload length and cHEC values are inserted by the device when in GFP mode. Encapsulation CRC values, GFP type headers, GFP extension headers, VLAN tags, or other frame modifications must be performed by the user software prior to placement in the WAN insertion FIFO. For example, consider inserting a WAN frame with cHDLC encapsulation. The user software must insert the cHDLC 4-byte Address, Control, and Protocol header bytes prior to the beginning of the Ethernet frame, and write the resulting data into the WAN insertion FIFO. The cHDLC example given below has a brief description of the entire packet and the data that should be written to WAN Insertion FIFO.
