Low Latency Queuing
Encyclopedia
Low Latency Queuing 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.
(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 turns 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.
Cisco Systems
Cisco Systems, Inc. is an American multinational corporation headquartered in San Jose, California, United States, that designs and sells consumer electronics, networking, voice, and communications technology and services. Cisco has more than 70,000 employees and annual revenue of US$...
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.
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 jitterJitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...
(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 turns 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 ServiceClass of service-Class of service :As related to network technology, CoS is a 3-bit field within an Ethernet frame header when using 802.1Q tagging. The field specifies a priority value of between 0 and 7 inclusive that can be used by quality of service disciplines to differentiate traffic.While CoS operates only...
- Quality of ServiceQuality of serviceThe quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
- QPPBQPPBQoS Policy Propagation via BGP , is a mechanism that allows propagation of quality of service policy and classification by the sending party based on access lists, community lists and autonomous system paths in the Border Gateway Protocol , thus helping to classify based on destination instead of...
- Streaming mediaStreaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
- Traffic shapingTraffic shapingTraffic shaping is the control of computer network traffic in order to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds of packets that meet certain criteria...