User's Manual

Networking
Configuring the Quality of Service
Cisco ISA500 Series Integrated Security Appliance Administrator Guide 143
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STEP 1 Click Networking -> QoS -> WAN QoS -> Queue Settings.
The Queue Settings window opens.
STEP 2 Specify the way of determining how traffic in queues is handled for each WAN
port.
• SP: Set the order in which queues are serviced, traffic scheduling for the
selected queue and all higher queues is based strictly on the queue priority,
starting with Q1 (the highest priority queue) and going to the next lower
queue when each queue is complete.
• WRR: Enter the WRR weight, in percentage, assigned to the queues that you
want to use. Traffic scheduling for the selected queue is based on WRR.
• LLQ: Applies SP mode to Q1 and WRR mode to Q2 to Q6. Q1 has the highest
priority and is always processed to completion before the lower priority
queues. If you choose LLQ, enter the amount of bandwidth assigned to Q1,
and enter the WRR weights for other queues that you want to use.
• Random Early Detection: Check the box to enable the Random Early
Detection (RED) mechanism. RED is a congestion avoidance mechanism that
takes advantage of TCP's congestion control mechanism. By randomly
dropping packets prior to periods of high congestion, RED tells the packet
source to decrease its transmission rate. Assuming the packet source is
using TCP, it will decrease its transmission rate until all the packets reach
their destination, indicating that the congestion is cleared.
SP Egress traffic from the highest-priority queue (Q1) is transmitted
first. Traffic from the lower queues is processed only after the
highest queue has been transmitted, thus providing the highest
level of priority of traffic to the highest numbered queue.
WRR Distributes the bandwidth between the classes using the
weighted round robin scheme. The weights decide how fast each
queue can send packets. In WRR mode the number of packets
sent from the queue is proportional to the weight of the queue.
The higher the weight, the more frames are sent.
LLQ Integrates the SP and WRR queues to provide strict priority
queuing (PQ) to Class-Based Weighted Fair Queuing (CBWFQ).
LLQ allows delay-sensitive data (such as voice) to be given
preferential treatment over other traffic by letting the data to be
dequeued and sent first.