Refer to the exhibit. What is the overall type of queuing being used on the outgoing data for
interface Ethernet0/1?
A.
LLQ
B.
FIFO
C.
CBWFQ
D.
priority queuing
E.
weighted fair queuing
Explanation:
The above exhibit is an example of Class-Based Weighted Fair Queueing (CBWFQ).
After the weight for a packet is assigned, the packet is enqueued in the appropriate class queue.
CBWFQ uses the weights assigned to the queued packets to ensure that the class queue isserviced fairly.
Configuring a class policy—thus, configuring CBWFQ—entails these three processes:
Defining traffic classes to specify the classification policy (class maps). This process determines
how many types of packets are to be differentiated from one another.
Associating policies—that is, class characteristics—with each traffic class (policy maps). This
process entails configuration of policies to be applied to packets belonging to one of the classes
previously defined through a class map. For this process, you configure a policy map that specifies
the policy for each traffic class.
Attaching policies to interfaces (service policies). This process requires that you associate an
existing policy map, or service policy, with an interface to apply the particular set of policies for the
map to that interface.http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/cbwfq.html#wp17641
Low Latency Queuing (LLQ) is a feature developed by Cisco to bring 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
Low Latency Queueing Configuration Task List
To configure LLQ, perform the tasks described in the following sections. The task in the first
section is required; the tasks in the remaining sections are optional.
• Configuring LLQ (Required)
• Configuring the Bandwidth Limiting Factor (Optional)
• Verifying LLQ (Optional)
• Monitoring and Maintaining LLQ (Optional)
See the end of this chapter for the section “LLQ Configuration Examples.”
Configuring LLQ
To give priority to a class within a policy map, use the following command in policy-map class
configuration mode:
Configuring the Bandwidth Limiting Factor
To change the maximum reserved bandwidth allocated for CBWFQ, LLQ, and IP RTP Priority, use
the following command in interface configuration mode:
Verifying LLQ
To display the contents of the priority queue, such as queue depth and the first packet queued,
use the following command in EXEC mode:
The priority queue is the queue whose conversation ID is equal to the number of dynamic queuesplus 8. The packets in the priority queue have a weight of 0.
Monitoring and Maintaining LLQ
To tune your RTP bandwidth or decrease RTP traffic if the priority queue is experiencing drops,
use the following commands in EXEC mode, as needed:
LLQ
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair
Queueing (CBWFQ). Strict priority queueing allows delay-sensitive data such as voice to be
dequeued and sent first (before packets in other queues are dequeued), giving delay-sensitive
data preferential treatment over other traffic.
Without Low Latency Queueing, CBWFQ provides weighted fair queueing 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 that class. 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 when you configured it. 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 manifesting as jitter in the heard
conversation.
The Low Latency Queueing feature provides strict priority queueing for CBWFQ, reducing jitter in
voice conversations. Configured by the priority command, Low Latency Queueing enables use of a
single, strict priority queue within CBWFQ at the class level, allowing you to direct traffic belonging
to a class to the CBWFQ strict priority queue. To enqueue class traffic to the strict priority queue,
you configure the priority command for the class after you specify the named class within a policy
map. (Classes to which the priority command is applied are considered priority classes.) Within a
policy map, you can give one or more classes priority status.
When multiple classes within a single policy map are configured as priority classes, all traffic from
these classes is enqueued to the same, single, strict priority queue. One of the ways in which the
strict priority queueing used within CBWFQ differs from its use outside CBWFQ is
in the parameters it takes. Outside CBWFQ, by using the ip rtp priority command, you specify the
range of UDP ports whose voice traffic flows are to be given priority service. Using the priority
command, because you can configure the priority status for a class within CBWFQ, you are no
longer limited to a UDP port number to stipulate priority flows. Instead, all of the valid match
criteria used to specify traffic for a class now applies to priority traffic. These methods of specifying
traffic for a class include matching on access lists, protocols, and input interfaces. Moreover,
within an access list you can specify that traffic matches are allowed based on the
IP Differentiated Services Code Point (DSCP) value that is set using the first six bits of the Type ofService (ToS) byte in the IP header. Although it is possible to enqueue various types of real-time
traffic to the strict priority queue, we strongly recommend that you direct only voice traffic to it. This
recommendation is made because voice traffic is wellbehaved, whereas other types of real-time
traffic are not. Moreover, voice traffic requires that delay be
nonvariable in order to avoid jitter. Real-time traffic such as video could introduce variation in
delay, thereby thwarting the steadiness of delay required for successful voice traffic transmission.
Configuration Tasks See the following sections for configuration tasks for the Low Latency
Queueing feature. Each task in the list indicates if the task is optional or required.
Configuring Low Latency Queueing (Required)
Verifying Low Latency Queueing (Optional)
Configuring Low Latency Queueing
To give priority to a class within a policy map, use the following command in policy-map class
configuration mode:
Verifying Low Latency Queueing
To see the contents of the priority queue (such as queue depth and the first packet queued), use
the following command in EXEC mode:
The priority queue is the queue whose conversation ID is equal to the number of dynamic queues
plus 8. The packets in the priority queue have a weight of 0.http://www.cisco.com/en/US/docs/ios/12_0t/12_0t7/feature/guide/pqcbwfq.html#wp5329
http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/
qcfwfq_ps1835_TSD_Products_Configuration_Guide_Chapter.html#wp1001719
