102 Chapter 2: QoS Tools and Architectures
Table 2-8 |
Comparison of CAC Tools (Continued) |
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Tool |
CAC Type |
CAC Decision Is Based on Whether . . . |
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Local Voice Busy-Out |
Local |
One or more local interfaces fail; if they all fail, no IP |
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(LVBO) |
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connectivity would exist, so the trunk is placed in busy- |
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out state |
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Advanced Busy-Out |
Measurement |
Probe measurements are better than a configured |
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Monitor (AVBO) |
based |
“impairment factor”; if value is higher, the entire trunk is |
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placed in busy-out |
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PSTN Fallback |
Measurement |
Probe measurements are better than a configured |
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based |
“impairment factor”; instead of busying-out the trunk, |
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calls are allowed or rejected on a call-by-call basis |
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Resource Availability |
Resource |
Terminating gateway’s calculation of available DSPs and |
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Indicator (RAI) |
based |
DS0s implies it has adequate number of resources or not |
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Gatekeeper Zone Band- |
Resource |
Gatekeeper believes that the bandwidth into the zones in |
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width (GK Zone |
based |
question has been oversubscribed or not |
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Bandwidth) |
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Resource Reservation |
Resource |
The RSVP reservation request flow can, both at call setup |
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Protocol (RSVP) |
based |
and ongoing throughout the call, reserve the needed |
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bandwidth on all RSVP-supporting links in the IP network |
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*Trunk conditioning acts like a measurement-based CAC tool in my opinion; the IOS documentation, and the DQOS course, list this CAC tool as a local CAC tool. Cisco QoS exam questions are not based on my opinion, so it is listed as a local CAC tool in this book!
Management Tools
Cisco provides several management tools, and features of management tools, that assist in managing the QoS policies and configuration in a network. Table 2-9 lists these tools and provides a short description of the functions of each tool.
Table 2-9 QoS Management Tools
Tool |
Features |
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QoS Device Manager (QDM) |
Uses code that is stored in Flash memory, running inside each router; |
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user can use a web browser to manage QoS configuration and view |
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statistics for an individual router. The product is free. |
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QoS Policy Manager (QPM) |
Application runs on Windows NT or Windows 2000, accessible by a |
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browser. Enables the engineer to manager QoS policies network |
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wide; QPM takes policies and creates QoS configurations, stages, |
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implements, and allows back-out of QoS configurations throughout |
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the network. |
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Introduction to IOS QoS Tools 103 |
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Table 2-9 |
QoS Management Tools (Continued) |
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Tool |
Features |
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Service Assurance Agent |
The feature formerly known as Response Time Reporter (RTR), SAA |
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(SAA) |
is a feature of IOS. This feature can be configured to create, send, |
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respond to, and measure the performance of probe packets. |
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Measurement-based CAC mechanisms create SAA probes on routers; |
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the routers send and receive the probes; and then the routers tell SAA |
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the results. |
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Internetwork Performance |
Formerly a separate product, this Cisco Works feature monitors net- |
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Monitor (IPM) |
work performance in real time. It also provides an easy GUI interface |
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to configure SAA probes. |
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Service Management Solution |
SMS is a feature of Cisco Works that provides performance statistics |
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(SMS) |
similar to IPM, but with the intent to save historical data and to pro- |
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vide reporting about whether configured service level agreements |
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(SLAs) are being met. IPM is used for operating the network and |
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looking at current network statistics; SMS is used for historical |
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reporting, trending, and SLAs. |
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Summary
If you do not work with QoS tools every day, and you are reading this book to pass one of Cisco’s QoS exams, you may be feeling overwhelmed after reading the first section of this chapter! However, do not be dismayed—the rest of the chapters in this book are devoted to a deeper description of the tools introduced here. You need to memorize a lot of facts for the exam—facts for which you can just refer to this book after you pass the exam—but each chapter purposefully includes the most important facts to memorize in tables, and these tables are included in the “Foundation Summary” section of each chapter.
Cisco has created a “QoS framework” that shows the various components of a network relating to QoS. The exam does cover the QoS framework, and each chapter reminds you about which parts of the framework are covered in that chapter. Figure 2-8 shows the Cisco QoS framework.
The bottom half of the figure shows five key categories of QoS tools, all of which are covered in Chapters 3 through 7 of this book. Chapter 8 covers CAC and QoS signaling; RSVP is mentioned as one of the signaling features in the upper part of the framework. Management tools, as covered in Chapter 9, are shown on the right side of the QoS framework. Not all parts of the QoS framework are covered on the Cisco QoS exams. The framework itself is covered on the exams, so make sure that you are familiar with the terms and the organization of this diagram.
The row of the framework that lists IntServ, DiffServ, MPLS, and Hybrid, refer to different QoS architectures. Two of these architectures are covered on the Cisco QoS exams—IntServ and DiffServ. Most of the rest of this chapter explains these two QoS architectures.