Home > Articles > QoS Design Principles and Best Practices

QoS Design Principles and Best Practices

Chapter Description

In this sample chapter from Designing for Cisco Network Service Architectures (ARCH) Foundation Learning Guide: CCDP ARCH 300-320, 4th Edition, the authors cover some best practice QoS design principles and QoS strategy models that are used to implement the numerous QoS tools we have at our disposal. Remember that usually, more than one solution fits the given QoS requirements, so simplifying the models leveraged can significantly accelerate and ensure proper QoS deployment.

Queuing Design Principles

The only way to provide QoS service guarantees to business-critical applications is to enable queuing to every node that has the potential for congestion. Queuing should be enabled regardless of whether congestion is occurring rarely or frequently. Although frequently deployed at the WAN edge, this principle must be applied not only to congested WAN links but also within the campus network. Speed mismatch, link aggregation, and link subscription ratios can create congestion in the network devices by filling up queuing buffers.

Because each distinctive application class requires unique QoS service requirements, it is recommended you provide a distinctive queue for each traffic class. One of the main justifications for leveraging distinctive queues is that each QoS service class can accept certain QoS-enabled behaviors such as bandwidth allocation and dropping ratios.

It is recommended you use a minimum of four standards-based queuing behaviors on all platforms and service provider links when deploying end-to-end QoS across the network infrastructure:

  • RFC 3246 Expedited Forwarding PHB (used for real-time traffic)

  • RFC 2597 Assured Forwarding PHB (used for guaranteed bandwidth queue)

  • RFC 2474 Default Forwarding PHB (default nonprioritized queue, best effort)

  • RFC 3662 Lower Effort Per-Domain Behavior (less than best-effort queue, bandwidth constrained)

5. Dropping Design Principles | Next Section Previous Section

There are currently no related articles. Please check back later.