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Implementing IP quality of service, step 2

Step two of three on implementing IP quality of service on Cisco networks.

Step 2: Classifying traffic based on the requirements identified

The definition of traffic classes does not need to be general; it must include the traffic (application) types that were observed during the network audit step. You can classify tens or even hundreds of traffic variations into very few classes. The defined traffic classes must be in line with business objectives. The traffic or application types within the same class must have common requirements

IP quality of service

IP quality of service is becoming increasingly important as customers add bandwidth-intensive services and applications to their networks. Value-added resellers (VARs) and systems integrators who can troubleshoot and improve sub-optimal performance in a converged network environment have marketable skills. This excerpt from CCNP ONT Official Exam Certification Guide defines quality of service and the three steps to implementing it.

Voice traffic has specific requirements, and it is almost always in its own class. With Cisco LLQ, VoIP is assigned to a single class, and that class uses a strict priority queue (a priority queue with strict maximum bandwidth) on the egress interface of each router. Many case studies have shown the merits of using some or all of the following traffic classes within an enterprise network:

  • Voice (VoIP) class -- Voice traffic has specific bandwidth requirements, and its delay and drops must be eliminated or at least minimized. Therefore, this class is the highest priority class but has limited bandwidth. VoIP packet loss should remain below 1% and the goal for its end-to-end delay must be 150 ms.

  • Mission-critical traffic class -- Critical business applications are put in one or two classes. You must identify the bandwidth requirements for them.

  • Signaling traffic class -- Signaling traffic, voice call setup and teardown for example, is often put in a separate class. This class has limited bandwidth expectations.

  • Transactional applications traffic class -- These applications, if present, include interactive, database and similar services that need special attention. You must also identify the bandwidth requirements for them. Enterprise Resource Planning (ERP) applications such as Peoplesoft and SAP are examples of these types of applications.

  • Best-effort traffic class -- All the undefined traffic types are considered best effort and receive the remainder of bandwidth on an interface.

  • Scavenger traffic class -- This class of applications will be assigned into one class and be given limited bandwidth. This class is considered inferior to the best-effort traffic class. Peer-to- peer file sharing applications are put in this class.


    Go to Step 3: Defining policies for each traffic class



    Reproduced from the book CCNP ONT Official Exam Certification Guide Copyright [2007], Cisco Systems, Inc. Reproduced by permission of Pearson Education, Inc., 800 East 96th Street, Indianapolis, IN 46240. Written permission from Pearson Education, Inc. is required for all.

  • and business requirements. The exceptions to this rule are the applications that have not been identified or scavenger-class traffic.

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