1-7
Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring QoS
Configuring QoS
Determining the Queue and TX Ring Limits for a Standard Priority Queue
To determine the priority queue and TX ring limits, use the worksheets below.
shows how to calculate the priority queue size. 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 adjust the queue buffer size
according to the
“Configuring the Standard Priority Queue for an Interface” section on page 1-8
.
shows how to calculate the TX ring limit. This limit determines the maximum number of
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. This setting guarantees that the
hardware-based transmit ring imposes a limited amount of extra latency for a high-priority packet.
Table 1-1
Queue Limit Worksheet
Step 1
__________
Outbound
bandwidth
(Mbps or Kbps)
1
1.
For example, DSL might have an uplink speed of 768 Kbps. Check with your provider.
Mbps
x
125
=
__________
# of bytes/ms
Kbps
x
.125
=
__________
# of bytes/ms
Step 2
___________
# of bytes/ms
from Step 1
÷
__________
Average packet
size (bytes)
2
2.
Determine this value from a codec or sampling size. For example, for VoIP over VPN, you might use 160 bytes. We recommend 256
bytes if you do not know what size to use.
x
__________
Delay (ms)
3
3.
The delay depends on your application. For example, the recommended maximum delay for VoIP is 200 ms. We recommend 500 ms
if you do not know what delay to use.
=
__________
Queue limit
(# of packets)
Table 1-2
TX Ring Limit Worksheet
Step 1
__________
Outbound
bandwidth
(Mbps or Kbps)
1
1.
For example, DSL might have an uplink speed of 768 Kbps.Check with your provider.
Mbps
x
125
=
__________
# of bytes/ms
Kbps
x
0.125
=
__________
# of bytes/ms
Step 2
___________
# of bytes/ms
from Step 1
÷
__________
Maximum packet
size (bytes)
2
x
__________
Delay (ms)
3
=
__________
TX ring limit
(# of packets)
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......