Aggressive traffic can fill interface queues and starve more fragile flows such as voice, video, and interactive traffic. The results can be devastating for delay-sensitive traffic types, making it difficult to meet the service-level requirements that these applications require. There are many congestion management techniques available on Cisco platforms that can provide you with an effective means to manage software queues and to allocate the required bandwidth to specific applications when congestion exists. Upon completing this learning content, you will be able to: • Describe the functions of hardware and software queuing and various commonly used queuing algorithms. • Configure Weighted Fair Queuing (WFQ) to manage congestion. • Configure Class-Based Weighted Fair Queuing (CBWFQ) and low latency queuing (LLQ) to manage congestion. • Describe campus-based techniques to manage congestion.

Congestion is a normal occurrence in networks. Whether congestion occurs as a result of a lack of buffer space, network aggregation points, or a low-speed wide-area link, many congestion management techniques exist to ensure that specific applications and traffic classes are given their share of available bandwidth when congestion occurs. When congestion occurs, some traffic is delayed or even dropped at the expense of other traffic. When drops occur, different problems may arise that can exacerbate the congestion, such as retransmissions and TCP global synchronization in TCP/IP networks. Network administrators can use congestion avoidance mechanisms to reduce the negative effects of congestion by penalizing the most aggressive traffic streams as software queues begin to fill.

Different forms of connectivity within a network can have significantly different costs for an organization. Because WAN bandwidth is relatively expensive, many organizations would like to limit the amount of traffic that specific applications can send. This is especially true when enterprise networks use internet connections for connectivity to remote sites and the extranet. Downloading nonbusiness-critical images, music, and movie files can significantly reduce the amount of bandwidth that is available for mission-critical applications. Traffic policing and traffic shaping are two quality of service (QoS) techniques that can limit the amount of bandwidth that a specific application, user, or class of traffic can use on a link. Upon completing this course, you will be able to: • Explain how traffic policing and traffic shaping can be used to rate-limit traffic. • Configure class-based policing to rate-limit traffic. • Describe the implementation options that are available for traffic policing in the campus. • Configure class-based shaping to rate-limit traffic. • Given a Frame Relay WAN link, configure class-based shaping to rate-limit traffic. • Given a Frame Relay WAN link, configure the Frame Relay Voice-Adaptive Traffic Shaping and Fragmentation feature to improve the performance of voice transport.

In a network that consists of a large WAN covering many sites, the monthly recurring cost of even the smallest link upgrade can be too high. In some cases, the only option for low-bandwidth remote sites is to upgrade their wide-area circuit. In other cases, a set of quality of service (QoS) techniques can be used to improve the efficiency of these low-speed WAN links, which, in this context, typically refer to links with speeds less than or equal to 768 kb/s. Header compression and payload compression mechanisms reduce the sizes of packets, reducing delay and increasing available bandwidth on a link. Other QoS link efficiency techniques, such as link fragmentation and interleaving (LFI), allow fragile traffic types, such as voice and interactive traffic, to be sent either ahead or interleaved with larger, more aggressive flows. These techniques decrease latency and assist in meeting the service-level requirements of delay-sensitive traffic types such as voice.