Configuring Data Buffers - HP 5920 Configuration Manual

Configuring data buffers

Data buffers temporarily store packets to avoid packet
The switch stores outgoing packets in the egress buffer when congestion occurs.
Figure 24 Data buffer structure
Egress buffer
A buffer uses the following types of resources:
• Cell resources—Store packets. The buffer uses cell resources based on packet sizes. Suppose a cell
resource provides 208 bytes. The buffer allocates one cell resource to a 128-byte packet and two
cell resources to a 300-byte packet.
Packet resources—Store packet pointers. A packet pointer indicates where the packet is located in
•
cell resources. The buffer uses one packet resource for each outgoing packet.
Each type of resources has a shared area and a fixed area.
Fixed area—Partitioned into queues, each of which is equally divided by all the interfaces on a
•
switch, as shown in
An interface first uses the relevant queues of the fixed area to store packets.
a.
When a queue is full, the interface uses the corresponding queue of the shared area.
b.
When the queue in the shared area is also full, the interface discards subsequent packets.
c.
The system allocates the shared area among queues as specified by the user. Even if a queue is not
full, other queues cannot preempt its space. Similarly, the share of a queue for an interface cannot
be preempted by other interfaces even if it is not full.
Shared area—Partitioned into queues, each of which is not equally divided by the interfaces, as
•
shown in
to user configuration and the number of packets actually sent. If a queue is not full, other queues can
preempt its space.
The system puts packets received on all interfaces into a queue in the order they arrive. When the
queue is full, subsequent packets are dropped.
Fixed area
Cell resources
Shared area
Fixed area
Packet resources
Shared area
Figure 25. When congestion occurs:
Figure 25. The system determines the actual shared-area space for each queue according
loss.Figure 24 shows the structure of egress buffers.
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