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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.

RFC 4594 QoS Recommendation

RFC 4594 QoS provides guidelines for marking, queuing, and dropping principles for different types of traffic. Cisco has made a minor modification to its adoption of RFC 4594, namely the switching of Call-Signaling and Broadcast Video markings (to CS3 and CS5, respectively). A summary of Cisco’s implementation of RFC 4594 is presented in Figure 16-4.

Figure 16-4

Figure 16-4 QoS Marking—RFC 4594

RFC 4594 is the recommendation but not the standard; it resides in the category of draft proposal RFCs. It recommends guidelines on how to configure 14 traffic classes that are associated with 28 different code-point marking values. Note that some of the PHBs shown in Figure 16-4 include multiple DSCP-associated values. For example, the AF class for multimedia streaming can have AF31, AF32, and AF33 DSCP values. RFC 4594 includes information on which PHBs should be used for certain traffic types and also what queuing and dropping mechanism should be used for that same traffic class.

Some sample recommendations highlighted in Figure 16-4 include

  • Voice traffic should be marked to EF/DSCP 46.

  • Voice should be queued using strict-priority queuing.

  • Broadcast video traffic should be marked to CS5/DSCP 40.

  • Multimedia conferencing should be treated with an AF PHB, provisioned with a guaranteed-bandwidth queue.

RFC 4594 is not a final RFC standard and will more than likely continue to be developed considering that needs and trends for QoS application requirements change over the time.

8. QoS Strategy Models | Next Section Previous Section

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