Reducing The Number Of Data Link Frames

At present we have both DL_DATA and DL_ACK frames travelling in each direction.

The small DL_ACK frames consume much bandwidth, and increase the number of hardware interrupts that must be serviced by the operating system.

Instead, we use frame piggybacking:

• When the receiver gets a DL_DATA frame, it does not immediately send an DL_ACK frame.
• The receiver waits until it has its own outgoing DL_DATA frame, and piggybacks the pending DL_ACK in the outgoing header.
• If no DL_DATA frame becomes available in a short time, the receiver must send an DL_ACK frame, by itself.