Upon completing this chapter, you will be able to
Describe basic classification and marking design principles
Describe basic policing and remarking design principles
Explain queuing design principles
Explain basic dropping design principles
Explain what are per-hop behavior queue design principles
Explain the role of RFC 4594 recommendation
List and describe QoS strategy models
Describe the 4-class QoS strategy model
Describe the 8-class QoS strategy model
Describe the 12-class QoS strategy model
Now that we have covered the various tools for enabling quality of service (QoS) in the network, it is possible to create a QoS strategy that best meets an organization’s requirements. This chapter presents 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.
Quality of service is critical to ensuring application performance consistency and optimized end-user experiences. As discussed in Chapter 15, “QoS Overview,” the fundamental purpose of QoS is to manage contention for network resources while addressing applications that require differentiated levels of service. Prior to developing a QoS strategy, you must perform the proper discovery to identify current and future applications and application characteristics within the environment. This information, coupled with an understanding of the end-to-end network design and traffic patterns, will drive the QoS design strategy model that is most appropriate for the business. Following are some common questions that you need to answer:
What traffic needs to be classified and marked?
Is it possible to leverage a 4-class, 8-class, or 12-class QoS strategy model from end to end?
Will traffic-marking characteristics stay in place as data traverses the infrastructure?
What traffic needs to be prioritized?
What traffic requires bandwidth reservations?
What traffic needs to be policed?
Is shaping required at the WAN edge or at other places within the infrastructure such as the Data Center Interconnect (DCI)?
How can congestion management and congestion avoidance techniques be leveraged to optimize TCP traffic?