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102 Chapter 2: QoS Tools and Architectures

Table 2-8

Comparison of CAC Tools (Continued)








CAC Type

CAC Decision Is Based on Whether . . .






Local Voice Busy-Out


One or more local interfaces fail; if they all fail, no IP




connectivity would exist, so the trunk is placed in busy-




out state






Advanced Busy-Out


Probe measurements are better than a configured


Monitor (AVBO)


“impairment factor”; if value is higher, the entire trunk is




placed in busy-out






PSTN Fallback


Probe measurements are better than a configured




“impairment factor”; instead of busying-out the trunk,




calls are allowed or rejected on a call-by-call basis






Resource Availability


Terminating gateway’s calculation of available DSPs and


Indicator (RAI)


DS0s implies it has adequate number of resources or not






Gatekeeper Zone Band-


Gatekeeper believes that the bandwidth into the zones in


width (GK Zone


question has been oversubscribed or not










Resource Reservation


The RSVP reservation request flow can, both at call setup


Protocol (RSVP)


and ongoing throughout the call, reserve the needed




bandwidth on all RSVP-supporting links in the IP network





*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





QoS Device Manager (QDM)

Uses code that is stored in Flash memory, running inside each router;


user can use a web browser to manage QoS configuration and view


statistics for an individual router. The product is free.



QoS Policy Manager (QPM)

Application runs on Windows NT or Windows 2000, accessible by a


browser. Enables the engineer to manager QoS policies network


wide; QPM takes policies and creates QoS configurations, stages,


implements, and allows back-out of QoS configurations throughout


the network.





Introduction to IOS QoS Tools 103




Table 2-9

QoS Management Tools (Continued)











Service Assurance Agent

The feature formerly known as Response Time Reporter (RTR), SAA



is a feature of IOS. This feature can be configured to create, send,



respond to, and measure the performance of probe packets.



Measurement-based CAC mechanisms create SAA probes on routers;



the routers send and receive the probes; and then the routers tell SAA



the results.





Internetwork Performance

Formerly a separate product, this Cisco Works feature monitors net-


Monitor (IPM)

work performance in real time. It also provides an easy GUI interface



to configure SAA probes.





Service Management Solution

SMS is a feature of Cisco Works that provides performance statistics



similar to IPM, but with the intent to save historical data and to pro-



vide reporting about whether configured service level agreements



(SLAs) are being met. IPM is used for operating the network and



looking at current network statistics; SMS is used for historical



reporting, trending, and SLAs.





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.