Restrictions; Low-Latency Queueing - Cisco WS C4224V 8FXS - 200Mbps Ethernet Switch Software Configuration Manual

Low-Latency Queueing

Restrictions

Note
Low-Latency Queueing
Catalyst 4224 Access Gateway Switch Software Configuration Guide
10-14
DTS does not support the following:
Fast EtherChannel, Multilink PPP (MLP), Tunnel, VLANs, and dialer
•
interface
Any VIP below a VIP2-40
•
A VIP2-50 is strongly recommended when the aggregate line rate of the port
adapters on the VIP is greater than DS3. A VIP2-50 card is required for OC-3
rates.
The LLQ feature brings strict PQ to CBWFQ. Strict PQ allows delay-sensitive
data such as voice to be dequeued and sent before packets in other queues are
dequeued.
Without LLQ, CBWFQ provides WFQ based on defined classes with no strict
priority queue available for real-time traffic. CBWFQ allows you to define traffic
classes and then assign characteristics to these classes. For example, you can
designate the minimum bandwidth delivered to the class during congestion.
For CBWFQ, the weight for a packet belonging to a specific class is derived from
the bandwidth you assigned to the class at configuration. Therefore, the
bandwidth assigned to the packets of a class determines the order in which packets
are sent. All packets are serviced fairly based on weight; no class of packets may
be granted strict priority. This scheme poses problems for voice traffic that is
largely intolerant of delay, especially variation in delay. For voice traffic,
variations in delay introduce irregularities of transmission, such as jitter in the
heard conversation.
LLQ provides strict priority queueing for CBWFQ, reducing jitter in voice
conversations. Configured by the priority command, LLQ enables use of a single,
strict priority queue within CBWFQ at the class level. This allows you to direct
traffic belonging to a class to the CBWFQ strict priority queue. To enqueue class
traffic to the strict priority queue, specify the named class within a policy map and
then configure the priority command for the class. (Classes to which the priority
command is applied are considered priority classes.) Within a policy map, you
Chapter 10 Traffic Shaping
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