Low-latency queuing (LLQ) is a
network scheduling
A network scheduler, also called packet scheduler, queueing discipline (qdisc) or queueing algorithm, is an Arbiter (electronics), arbiter on a Node (networking), node in a packet switching communication network. It manages the sequence of netwo ...
feature developed by
Cisco
Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...
to bring strict
priority queuing
In computer science, a priority queue is an abstract data type , abstract data-type similar to a regular queue (abstract data type), queue or stack (abstract data type), stack data structure in which each element additionally has a ''priority'' a ...
(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
, Cisco IOS Software Releases 12.0 T
Development
Class-based weighted fair queuing (CB-WFQ) was initially released without the support of a priority queuing system, thus it could not guarantee the delay and jitter
In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significa ...
(delay variation) requirements of real-time, interactive voice and video conversations. Since for CBWFQ, the weight for a packet belonging to a specific class is derived from the bandwidth assigned to the class, which in turn determines the order in which packets are sent. All packets are serviced fairly based on weight and 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.
In order to address this, Cisco released LLQ to provide strict priority queuing for CBWFQ by enabling the use of a single, strict priority queue within CBWFQ at the class level. This allows for directing traffic belonging to a class to the CBWFQ strict priority queue. One or more classes priority status can be given within a policy map. 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.
See also
* Class of service
* Quality of service
*QPPB The QoS Policy Propagation via BGP, often abbreviated to QPPB, is a mechanism that allows propagation of quality of service (QoS) policy and classification by the sending party based on access lists, community lists, and autonomous system paths in ...
*Streaming media
Streaming media is multimedia that is delivered and consumed in a continuous manner from a source, with little or no intermediate storage in network elements. ''Streaming'' refers to the delivery method of content, rather than the content it ...
* Traffic shaping
References
Congestion Management Configuring CBWFQ and LLQ
External links
Cisco QoS – Low Latency Queuing
Telecommunications engineering
Network performance
Streaming
Teletraffic
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