65Configuring the data bufferOverviewData bufferThe Switch Series provides the data buffer to buffer packets to be sent out ports to avoid packet loss whenbursty traffic causes congestion.The switch controls how a port uses the data buffer by allocating the cell resource and packet resource(called "buffer resources").• The cell resource is the physical storage space in cells for the data buffer. The cell resource allocatedto a port indicates the maximum buffer space that the port can occupy in the buffer.• The packet resource is the logical buffering space in packets. A packet is counted as one regardlessof its length. A packet in the packet resource uses a certain amount of cell resources in the cellresource, depending on its length. The packet resource allocated to a port indicates the maximumnumber of packets that the port can store in the buffer.Set independently, the packet resource and the cell resource work simultaneously to regulate databuffering. A packet can be buffered only when both resources are adequate.Data buffer allocationCell resource allocationThe cell resource is divided into a shared resource and a dedicated resource. You can manually set thepercentage of the shared resource to the total buffer, and the remaining buffer becomes the dedicatedresource automatically.On an S5120-EI switch, the cell resource is allocated as shown in Figure 21.Figure 21 Cell resource allocation on the S5120-EI switchThe dedicated resource is allocated following these rules:Queue 0Queue 1Queue 2Queue 3Queue 4Queue 5Queue 6Queue 7Shared bufferPort 1 Port 2 Port 3 ……Dedicatedbuffer
