19

The BNRY is updated each time a packet is removed. In that way, the BNRY always follow the CURR

around the ring (see figure 10). However, in situations in which the packet processing is slower than the

packet reception, the ring may be full. When the ring becomes full, all incoming packets are aborted so that

packets already in the ring would not be overwritten (see figure 11). New packets will start to arrive after

the BNRY is updated. The missed packet tally counter would keep track of all missed packets. This

situation is unlikely if enough memory is allocated for the receive buffer ring. If the BNRY is located

outside the buffering, the overwrite protection function will not be available. All incoming packets would

overwrite packets already on the ring, whether the packets on the ring have been processed or not.

Direction

of Rotation

Boundary Pointer

Current Page Register

n

(after the removal of packet)

1

2

3

Boundary Pointer

4

n-1

n-2

1st Packet

Remote DMA

Removes Packet

2nd Packet

New Packets

Arriving

Figure 10. Removing Packets from the Receive Buffer Ring

Direction

of Rotation

Boundary Pointer

1

2

3

4

n-1

n-2

1st Packet

Remote DMA

Removes Packet

2nd Packet

New Packets

Arriving

5

n

Reception Aborted

by NIC overflow

Figure 11. Receive Buffer Ring Overwrite Protection