Cisco ASA 5505 Configuration Manual page 1065

Chapter 49 Configuring QoS
Configuring the Priority Queue
To create the priority queue, perform the following steps.
Detailed Steps
Step 1 Go to Configuration > Device Management > Advanced > Priority Queue, and click Add.
The Add Priority Queue dialog box displays.
Step 2 From the Interface drop-down list, choose the physical interface name on which you want to enable the
priority queue, or for the ASA 5505, the VLAN interface name.
Step 3 To change the size of the priority queues, in the Queue Limit field, enter the number of average, 256-byte
packets that the specified interface can transmit in a 500-ms interval.
A packet that stays more than 500 ms in a network node might trigger a timeout in the end-to-end
application. Such a packet can be discarded in each network node.
Because queues are not of infinite size, they can fill and overflow. When a queue is full, any additional
packets cannot get into the queue and are dropped (called tail drop). To avoid having the queue fill up,
you can use this option to increase the queue buffer size.
The upper limit of the range of values for this option is determined dynamically at run time. The key
determinants are the memory needed to support the queues and the memory available on the device.
The Queue Limit that you specify affects both the higher priority low-latency queue and the best effort
queue.
To specify the depth of the priority queues, in the Transmission Ring Limit field, enter the number of
Step 4
maximum 1550-byte packets that the specified interface can transmit in a 10-ms interval.
This setting guarantees that the hardware-based transmit ring imposes no more than 10-ms of extra
latency for a high-priority packet.
This option sets the maximum number of low-latency or normal priority packets allowed into the
Ethernet transmit driver before the driver pushes back to the queues on the interface to let them buffer
packets until the congestion clears.
The upper limit of the range of values is determined dynamically at run time. The key determinants are
the memory needed to support the queues and the memory available on the device.
The Transmission Ring Limit that you specify affects both the higher priority low-latency queue and the
best-effort queue.
Creating a Policy for Standard Priority Queueing and/or Policing
You can configure standard priority queueing and policing for different class maps within the same
policy map. See the
configurations.
To create a policy map, perform the following steps.
OL-20339-01
"How QoS Features Interact" section on page 49-4
Cisco ASA 5500 Series Configuration Guide using ASDM
Configuring QoS
for information about valid QoS
49-7