Acknowledgments

My uncle Eulie used to work in the meat market in the small town I grew up in. I loved hot dogs but he'd never let me see how they made them He always told me that if I liked them, then I really didn't want to know how they were made This book has taken a while to complete, with several distractions from all directions. The path we all took to complete this book was a little messy like making hot dogs, I'm sure and two individuals in particular made this book possible in spite of the...

Automatic Alternate Routing

Prior to CallManager version 3.3, if a call was blocked due to insufficient location bandwidth, the caller would receive a reorder tone and manually have to redial the called party through the PSTN. Automated alternate routing (AAR), introduced in CallManager version 3.3, provides a mechanism to reroute calls through the PSTN or another network WAN link by using an alternate number when Cisco CallManager blocks a call because of insufficient location bandwidth. With automated alternate routing,...

Bandwidth per Codec

Both LLQ and RSVP see the Layer 3 IP packet. Layer 2 encapsulations (FR, MLPPP, and so on) are added after queuing, so the bandwidth allocated by both LLQ and RSVP for a call is based on the Layer 3 bandwidth of the packets. This number is slightly different from the actual bandwidth used on the interface after Layer 2 headers and trailers have been incorporated. RSVP bandwidth reserved for a call also excludes both cRTP and VAD. Table 8-21 summarizes the bandwidth RSVP allocates for calls...

Book Features

The core chapters of this book have several features that help you make the best use of your time Do I Know This Already Quizes Each chapter begins with a quiz that helps you determine the amount of time you need to spend studying that chapter. If you follow the directions at the beginning of the chapter, the Do I Know This Already quiz directs you to study all or particular parts of the chapter. Foundation Topics These are the core sections of each chapter. They explain the protocols,...

Book Organization

This book contains 10 core chapters with titles that are comparable to the major headings listed in the DQOS exam topics. For DQOS exam candidates, you can simply dive into Chapter 1 and read through Chapter 10. For those of you taking the QOS exam, the end of this introduction has some tips on what to focus on in Chapters 1 through 10. You will also want to read Appendix B, which covers the topics on the QOS exam but not covered on the DQOS exam. Chapters 1 and 2 cover most of the core...

CAC Mechanisms

When a call is placed in a circuit-switched network, a single 64-kbps circuit (DS0) is reserved on each PSTN trunk that the call must traverse to reach the called party and establish the voice conversation. This 64-kbps circuit remains established, without interruption from other voice channels, for the life of the conversation. As voice traffic converges on packet-switched networks, the uninterrupted channel of the circuit-switched network is no longer available. Due to the bursty nature of...

Calculation of Resources

After the regions have been defined and all devices have been configured to reside in the desired location, you can begin to allocate the desired bandwidth between the locations to use for CAC. This allocated bandwidth does not reflect the actual bandwidth required to establish voice conversations instead, the allocated bandwidth is a means for CallManager to provide CAC. CAC is achieved by defining a maximum amount of bandwidth per location to use and then subtract a given amount, dependent...

Call Admission Control Overview

Call admission control (CAC) mechanisms extend the capabilities of other quality of service (QoS) methods to ensure that voice traffic across the network link does not suffer latency, jitter, or packet loss that can be introduced by the addition of other voice traffic. CAC achieves this task by determining whether the required network resources are available to provide suitable QoS for a new call, before the new call is placed. Simply put, CAC protects voice conversations from other voice...

Call Rerouting Alternatives

If a call has been rejected by a CAC mechanism due to insufficient network resources, there needs to be some alternate route in place to establish the call. In the absence of an alternate route, the caller will hear a reorder tone. The reorder tone is called a fast-busy tone in North America, and is known as overflow tone or equipment busy in other parts of the world. This tone is often intercepted by Public Switched Telephone Network (PSTN) switches or PBXs with an announcement such as All...

CAR Marking Summary

CAR is another tool that examines packet header information to classify and mark packets. CAR provides fewer options for classification and marking than does CB marking, but CAR is considered to be DiffServ compliant because it can classify DSCP using an ACL and mark the DSCP field directly. CAR, along with CB marking and PBR, makes classification decisions based on the contents of packet headers and marks QoS fields based on those classifications. Dial peers provide very different...

CAR Without Be

Just like most descriptions of policing logic, this book uses token buckets to describe CAR logic. In this discussion, one bucket is called Bucket1, and the other is ingeniously called Bucket2. Bucket1 begins with Bc worth of tokens in it, and Bucket2 begins with Be worth of tokens in it. Of course, only Bucket1 is used when Be 0, but both Bucket1 and Bucket2 are used when Be is greater than 0. In some explanations found in other documents, you might hear Bucket1 referred to as the Bc bucket,...

CB Marking show Commands

CB marking provides only one show command that provides statistical information show policy-map interface. The statistics do provide some good insight to the packet volumes being marked by CB marking. The next sample configuration includes a new configuration and several variations of the show policy-map command. The same network is used for the next example as was used in the other CB marking examples, but with different marking criteria. In this case, traffic is generated so that the show...

CB Marking Summary

Class-based marking provides the most functional general classification and marking tool in IOS, as of IOS 12.2 mainline. Class-based marking provides the largest number of fields for classifying packets, and the largest number of fields that can be marked. It uses MQC for configuration, separating the classification details from the QoS action. Refer to Table 3-17, in the Foundation Summary section of this chapter, for a complete list of classification and marking fields used by CB marking.

CB Policing with Be

CB policing uses a simpler algorithm than CAR when a Be value has been configured. CB policing categorizes packets into three groups conform, exceed, and violate. By using three categories, a very simple and very useful algorithm can be used. Just like with CAR, to understand how CB policing works is to understand how the buckets are filled and drained. CB policing continues to replenish Bucket1 when a packet arrives. If Bucket1 is full, the extra, or spilled tokens, replenish Bucket2. If...

CB Policing Without Be

Bucket1 is the only token bucket used when Be 0 Bucket1 holds the tokens granted based on the configured committed burst. Bucket2 is used when Be is greater than (> ) 0, holding the tokens granted by Be. Unlike CAR, CB policing replenishes tokens in Bucket1 in response to policing a packet, as opposed to every Tc seconds. Every time a packet is policed, CB policing puts some tokens back into Bucket1. The number of tokens placed into Bucket1 is calculated...

Changes to the DQOS Exam Topics

Most likely, Cisco will announce changes, or Cisco will change the exam topics and maybe even announce a new DQOS 9E0-601 exam with a new exam number. There is even precedent for Cisco changing the entire question database for an exam without telling the public in order to defeat those who would copy questions from the exam and distribute them. Regardless, the exam will change one day, and you will want to know about the changes if you have not passed the...

QoS Overview

QoS affects the characteristics of network traffic. To understand the QoS concepts and configurations discussed in other chapters, you must know what can be manipulated namely, bandwidth, delay, jitter, and packet loss. Also, different types of traffic have different needs for bandwidth, delay, jitter and loss. Chapter 1 defines QoS terms explains the concepts relating to bandwidth, delay, jitter, and packet loss and identifies the traffic characteristcs of data, voice, and video traffic.

LAN QoS

The DQOS exam, at the time this book was published, covered some very basic concepts about QoS on LAN switches, but no configuration. This chapter covers LAN switch QoS concepts, and configuration. Why Well, successful voice implementation requires good QoS implementation, even in the campus. Also, when the exam does change one day, it may cover more details of campus QoS. We included this chapter in anticipation of the exam change and because we want this book to serve as a comprehensive...

QoS Tools and Architectures

Cisco provides a large number of QoS tools inside the router IOS. Two of the biggest challenges when preparing for either exam is remembering all the of tools and keeping track of which tools provide what features. Chapter 2 begins by listing and describing the classes of tools, and then also listing the tools themselves. The remaining chapters delve into more depth on each particular class of tool. QoS tools typically either follow one of two QoS architectural philosophies. The two...

Congestion Avoidance Through Drop Policies

Interestingly, statistics show that the biggest reason that packets are lost in networks is because a queue fills, leaving no room to hold another packet, forcing the device to discard the packet. Congestion Avoidance tools monitor queue depths, discarding some packets before the queue fills. The early discards cause the computers that sent the dropped packets to slow down the rate of sending packets, abating the congestison. As usual, this chapter covers the concepts and then the configuration...

Call Admission Control and QoS Signaling

To support voice and video traffic, you need many of the tools covered in the earlier chapters. However, even with those, a network that allows too many voice or video connections can make all the the voice and video traffic degrade to the point of being unusable. Call admission control (CAC) tools allow the network administrator to control the volume of voice and video connections. This chapter covers 10 CAC tools for voice along with configurations, and comparisons of the features of the...

Cisco Call Manager Resource Based CAC

The term locations refers to a CAC feature in a Cisco CallManager centralized call-processing environment. Because a centralized call-processing model is deployed in a hub-and-spoke fashion without the use of a terminating gateway at each spoke, an IP telephony CAC mechanism must be used to protect the desired number of voice conversations. Locations are designed to work in this nondistributed environment. Figure 8-20 shows a typical CallManager centralized call-processing model.

Cisco Qualified Specialist CQS Program

For any networker in any networking job, it helps to have knowledge and skills. Networkers can benefit from having proof' that they know a set of technologies. Having the right certification on your resume can help you land a job, both at another firm and inside the same company. For those networkers who work with customers and clients, having the right credentials, in the form of certifications, can help convince the salesperson to convince the customer to hire your company for the consulting...

Classification

Almost every QoS tool uses classification to some degree. To put one packet into a different queue than another packet, the IOS must somehow differentiate between the two packets. To perform header compression on Real Time Protocol (RTP) packets, but not on other packets, the IOS must determine which packets have RTP headers. To shape data traffic going into a Frame Relay network, so that the voice traffic gets enough bandwidth, the IOS must differentiate between Voice over IP (VoIP) and data...

Classification and Marking

QoS classification tools categorize packets by examining the contents of the frame, cell, and packet headers whereas marking tools allow the QoS tool to change the packet headers for easier classification. Many QoS tools rely on a classification function to determine to which traffic the tool applies. To place voice and data traffic in separate queues, for example, you must use some form of classification to differentiate the two types of traffic and place the identified traffic in the proper...

Classification and Marking Concepts

Most QoS tools classify traffic, which allows for each class of traffic to receive a different level of treatment from other traffic classes. You can use this method to prioritize one type of traffic over another. Classification and marking tools play a large role in this solution. Instead of giving queuing preference, or dropping a packet, or shaping, or policing, or fragmenting, and so on, classification and marking tools change some bits in the packet header. Other QoS tools throughout the...

Classification and Marking Concepts Questions

1 Describe the difference between classification and marking. 2 Describe, in general, how a queuing feature could take advantage of the work performed by a classification and marking feature. 3 Which of the following QoS marking fields are carried inside an 802.1Q header QoS, CoS, DE, ToS byte, User Priority, ToS bits, CLP, Precedence, QoS Group, DSCP, MPLS Experimental, or DS 4 Which of the following QoS marking fields are carried inside an IP header QoS, CoS, DE, ToS byte, User Priority, ToS...

Classification and Marking Design Choices

Classification and marking tools provide many options, but sometimes sorting out the best way to use the tools can be difficult. Classification and marking tools can classify based on a large number of frame and packet header fields. They can also mark a number of fields, the most notable being the IP Precedence and DSCP fields. You can use the classification and marking tools on all routers in the network, on many LAN switches, and even on IP Phones and host computers. This brief section...

Codec Delay

The time required to process an incoming analog signal and convert it to the correct digital equivalent A feature called look-ahead With the first component of codec delay, which is true for all codecs, the IP Phone or gateway must process the incoming analog voice signal and encode the digital equivalent based on the codec in use. For instance, G.729 processes 10 ms of analog voice at a time. That processing does take time in fact, the actual conversion into G.729 CS-ACELP (Conjugate...

Comparing Queuing Options Questions

13 Which of the following queuing tools allows for WRED inside a single queue First-In, First-Out Queuing (FIFO) Priority Queuing (PQ) Custom Queuing (CQ) Weighted Fair Queuing (WFQ) Class-Based WFQ (CBWFQ) Low Latency Queuing (LLQ) and IP RTP Priority. 14 Which of the following queuing tools can always service a particular queue first, even when other queues have packets waiting First-In, First-Out Queuing (FIFO) Priority Queuing (PQ) Custom Queuing (CQ) Weighted Fair Queuing (WFQ) Class-Based...

Comparing Queuing Tool Options

31 Which of the following queuing tools allows for WRED inside a single queue First-In, First-Out Queuing (FIFO) Priority Queuing (PQ) Custom Queuing (CQ) Weighted Fair Queuing (WFQ) Class-Based WFQ (CBWFQ) Low Latency Queuing (LLQ) and IP RTP Priority. 32 Which of the following queuing tools can always service a particular queue first, even when other queues have packets waiting First-In, First-Out Queuing (FIFO) Priority Queuing (PQ) Custom Queuing (CQ) Weighted Fair Queuing (WFQ) Class-Based...

Compression

Compression takes a packet, or packet header, and compresses the data so that it uses fewer bits. Therefore, a 1500-byte packet, compressed to 750 bytes, takes half as much serialization time as does an uncompressed 1500-byte packet. Compression reduces serialization delay, because the number of bits used to send a packet is decreased. However, delay may also be increased because of the processing time required to compress and decompress the packets. Chapter 7 covers the pros and cons of each...

Compression Questions

1 Describe what is compressed, and what is not compressed, when using payload compression. Be as specific as possible regarding headers and data. 2 Describe what is compressed, and what is not compressed, when using TCP header compression. Be as specific as possible regarding headers and data. 3 Describe what is compressed, and what is not compressed, when using RTP header compression. Be as specific as possible regarding headers and data. 4 List the three point-to-point payload compression...

Conceptual Questions

1 Describe the benefits of having a single FIFO output queue. 2 Explain the effects of changing a single FIFO queue's length to twice its original value. Include comments about how the change affects bandwidth, delay, jitter, and loss. 3 Explain the purpose of a TX Ring and TX Queue in a Cisco router. 4 Explain how a long TX Ring might affect the behavior of a queuing tool. 5 Describe the command output that identifies the length of the TX Ring or TX Queue, and whether the length was...

Congestion Avoidance

When networks become congested, output queues begin to fill. When new packets need to be added to a full queue, the packet is dropped a process called tail drop. Tail drop happens in most networks every day but to what effect Packet loss degrades voice and video flows significantly for data flows, packet loss causes higher-layer retransmissions for TCP-based applications, which probably increases network congestion. Two solutions to the tail-drop problem exist. One solution is to lengthen...

Congestion Management

Most people understand the basic concepts of queuing, because most of us experience queuing every day. We wait in line to pay for groceries, we wait for a bank teller, we wait to get into a ride at an amusement park, and so on. So, most of the queuing concepts inside this chapter are intuitive. Cisco uses the term congestion management to refer to queuing systems in their products. Queuing concepts in real life are quite similar to queuing in routers and switches. This chapter begins with a...

Congestion Avoidance Concepts and Random Early Detection RED

Congestion-avoidance tools rely on the behavior of TCP to reduce congestion. A large percentage of Internet traffic consists of TCP traffic, and TCP senders reduce the rate at which they send packets after packet loss. By purposefully discarding a percentage of packets, congestion-avoidance tools cause some TCP connections to slow down, which reduces congestion. This section begins with a discussion of User Datagram Protocol (UDP) and TCP behavior when packets are lost. By understanding TCP...

Congestion Avoidance Tools

This book covers three congestion-avoidance tools. One of the tools was never implemented in IOS (Random Early Detection, or RED) but because the other two features are based on RED concepts, Chapter 6, Congestion Avoidance Through Drop Policies, covers the basics of RED as well. All Congestion-avoidance tools consider the queue depth the number of packets in a queue when deciding whether to drop a packet. Some tools weigh the likelihood of dropping a packet based on the IP precedence or IP...

Considering the Effects of Packetization and Codec Delay

You need to consider packetization delay and codec delay together, because they do overlap. For instance, packetization delay consumes 20 ms while waiting on 20 ms of voice to occur. But what else happens in the first 20 ms Consider Table 1-18, with a timeline of what happens, beginning with the first uttered sound in the voice call. Table 1-18 Typical Packetization and Codec Delay Timeline G.729 Table 1-18 Typical Packetization and Codec Delay Timeline G.729 Begin collecting voice samples for...

Contents at a Glance

Chapter 2 QoS Tools and Architectures 83 Chapter 3 Classification and Marking 155 Chapter 4 Congestion Management 233 Chapter 5 Traffic Policing and Shaping 319 Chapter 6 Congestion Avoidance Through Drop Policies 425 Chapter 7 Link-Efficiency Tools 479 Chapter 8 Call Admission Control and QoS Signaling 541 Chapter 9 Management Tools and QoS Design 657 Appendix A Answers to the Do I Know This Already Quizzes and Q& A Sections 763 Appendix B Topics on the CCIP QoS Exam 831 Index 883

Data Bandwidth Considerations

Unlike voice, which consumes a constant amount of bandwidth, and unlike video, which consumes a range of bandwidth, data bandwidth requirements range wildly. Some applications might literally need less than 1 kbps, whereas others would take literally as much bandwidth as they can get. The bigger question with data bandwidth revolves around OSI Layer 8 the business layer. For instance, how much bandwidth should web traffic get Well, in many shops, web traffic consumes 80 percent of the network...

Data Delay Considerations

Unlike voice and video, the perceived quality of the data application does not degrade quickly when delay increases by mere hundreds of milliseconds. In fact, relative to voice and interactive video, data applications tolerate delay very well. Also unlike voice and video, data applications tend to have round-trip delay requirements. Two factors affect the delay requirements of a data application, as summarized in Table 1-27. Table 1-27 Factors to Consider for Data Delay Two factors affect the...

Data Jitter Considerations

Just like for delay, data application tolerate jitter much more so than voice and video. Interactive applications are much less tolerant ofjitter. I learned networking at a large SNA network inside IBM, and the adage when adjusting routes and QoS (built-in to SNA from the early days, but that's another story ) was that it was okay to have longer response times, as long as the response times were consistent. Human nature for some reason made consistency more important than net response time to...

Data Loss Considerations

Unlike voice and video, data does not always suffer when packets are lost. For most applications, the application needs to get all the data if the lost packets are re-sent, however, no real damage occurs. Some applications do not even care whether a packet is lost. For perspective, consider applications to fall into one of three categories those that use UDP and the applications perform error recovery, those that use UDP and the applications do not perform error recovery, and applications that...

Data Traffic Characteristics

This book, as well as the exams about which this book prepares you, assumes you have a fairly high level of knowledge about data traffic before using this book. In fact, the QoS and DQOS courses assume that you have been to the ICND and BSCI courses at least, and hopefully the BCMSN and CVOICE courses. In fact, when DQOS first came out, the expectation was that students should be CCNPs before attending the course. QoS has always been important, but QoS has become vitally important with the...

Dedications

Wendell Odom Mike Zanotto, or Mike Z as he's known throughout California and the world, has had a significant impact on my personal involvement with this book. Mike let me start our company's efforts to teach DQOS classes back in 2001 even when it didn't look like the class would be that popular just because it might turn into more. Well, it turned out to be a great move for Skyline Computer, and for me. Mike's willingness to take chances like that has had a lot to do with Skyline's success...

Differentiated Services Questions

5 Define the DiffServ term DSCP, including what the acronym stands for. 6 Define the DiffServ term PHB, including what the acronym stands for. 7 Compare and contrast the terms shaper, meter, and dropper, according to DiffServ specifications. Suggest typical points in the network where each is used. 8 Compare and contrast the contents of the IP ToS byte before and after the advent of DiffServ.

Diff Serv Per Hop Behaviors

Other than the general QoS strategies described in this chapter, DiffServ really provides two additional key features the DSCP field, and some good suggestions on how to use the DSCP field. In fact, two of the DiffServ RFCs, 2597 and 2598, are devoted to describing a set of DSCP values, and some suggested PHBs that should be associated with each DSCP value. IP defined a type of service (ToS) byte in RFC 791, which came out in September 1981. The IP protocol creators intended the ToS byte to be...

Diff Serv Specifications and Terminology

DiffServ is defined by the RFCs listed in Table 2-11. Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers Contains the details of the 6-bit DSCP field in IP header. An Architecture for Differentiated Service This is the core DiffServ conceptual document. Defines a set of 12 DSCP values and a convention for their use. Table 2-11 DiffServ RFCs (Continued) Table 2-11 DiffServ RFCs (Continued) Defines a single DSCP value as a convention for use as a low-latency...

Do I Know This Already Quiz

The purpose of the Do I Know This Already quiz is to help you decide whether you really need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now. The 12-question quiz, derived from the major sections in Foundation Topics section of this chapter, helps you determine how to spend your limited study time. Table 6-1 outlines the major topics discussed in this chapter and the Do I Know This Already quiz questions...

Do I Know This Already Quiz Questions

The purpose of the Do I Know This Already quiz is to help you decide whether you really need to read the entire chapter. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now. The 8-question quiz, derived from the major sections in Foundation Topics portion of the chapter, helps you determine how to spend your limited study time. Table 3-1 outlines the major topics discussed in this chapter and the Do I Know This Already quiz questions that...

FIFO Queuing

NOTE This section covers FIFO Queuing, which like TX Queues, is not currently covered on the DQOS 9E0-601 exam. This section does cover some useful information for all people interested in QoS. Therefore, for you DQOS exam takers, you might choose to just focus on the concepts about FIFO, and not worry about memorization or configuration. And as always, check the websites listed in the Introduction for any news about changes to the exams. The first reason that a router or switch needs output...

Foundation Summary

The Foundation Summary is a collection of tables and figures that provide a convenient review of many key concepts in this chapter. For those of you already comfortable with the topics in this chapter, this summary could help you recall a few details. For those of you who just read this chapter, this review will help solidify some key facts. For any of you doing your final prep before the exam, these tables and figures will be a convenient way to review the day before the exam. Table 1-29...

Foundation Topics

This chapter introduces the long list of QoS tools and two important QoS architectures differentiated services (DiffServ) and integrated services (IntServ). You can think of QoS implementation as building a house. To properly build a house, you certainly need (and use) a large variety of tools. An experienced builder might be able to use the tools to build a house without an architectural plan. With the architectural plans, however, an experienced house builder can build a better house...

Foundation Topics Payload and Header Compression

Compression involves mathematical algorithms that encode the original packet into a smaller string of bytes. After sending the smaller encoded string to the other end of a link, the compression algorithm on the other end of the link reverses the process, reverting the packet back to its original state. Over the years, many mathematicians and computer scientists have developed new compression algorithms that behave better or worse under particular conditions. For instance, each algorithm takes...

FRED Questions

9 Identify the most significant difference between FRED operation and WRED operation. 10 List the three categories of flows defined by FRED, and identify which category has its packets discarded most aggressively. 11 Taking as many defaults as possible, list the configuration commands needed to configure precedence-based FRED on interface S1 1. 12 Taking as many defaults as possible, list the configuration commands needed to configure DSCP-based FRED on interface S1 1.

Gatekeeper in Call Manager Networks

Of all the CAC mechanisms discussed in this chapter, gatekeeper zone bandwidth is the only method applicable to multi-site distributed CallManager clusters. In this scenario, the CallManager behaves like a VoIP gateway to the H.323 gatekeeper, as is shown in Figure 8-27. Figure 8-27 Gatekeeper in a CallManager Topology Figure 8-27 Gatekeeper in a CallManager Topology In this example, the CallManager in Zone 2 requests the WAN bandwidth to carry a voce conversation from the gatekeeper on behalf...

Gatekeeper Zone Bandwidth

The gatekeeper function is an IOS-based mechanism specific to H.323 networks. Different levels of Cisco IOS Software provide various, specific capabilities within this feature. In Cisco IOS Releases 12.1(5)T and 12.2, the gatekeeper function has the capability to limit the number of simultaneous calls across a WAN link similar to the CallManager location-based CAC discussed in the preceding section. By dividing the network into zones, a gatekeeper can control the allocation of calls in its...

Gateway Calculation of Resources

The calculation to reach the CAC decision is performed by the terminating gateway. Different gateway platforms may use different algorithms. The H.323 standard does not prescribe the calculation or the resources to include in the calculation. It merely specifies the RAI message format and the need for the gatekeeper to discontinue routing calls to the terminating gateway in the event that the gateway has insufficient available resources for the additional call, and the gateway will inform the...

Goals of This Book

Unquestionably, the primary goal for this book is to help you pass the DQOS certification exam. However, the means by which that goal is accomplished follows the Cisco Press Exam Certification Guide philosophy, which makes a statement about helping a reader pass the test through a deeper understanding of the material, as opposed to simply helping the reader memorize the answers to multiple-choice questions. To accomplish this goal, the book's main chapters cover all the topics on the DQOS exam,...

GOCS Flow Based QoS

A flow consists of all the packets about which the following are true All packets use the same transport layer protocol (for instance, UDP or TCP). All packets have the same source IP address. All packets have the same source port number. All packets have the same destination IP address. All packets have the same destination port number. The slightly different, but just as exact definition, is that a flow consists of the packets between two IP sockets. For instance, a web browser on a PC,...

Header Compression

Header compression algorithms take advantage of the fact that the headers are predictable. If you capture the frames sent across a link with a network analyzer, for instance, and look at IP packets from the same flow, you see that the IP headers do not change a lot, nor do the TCP headers, or UDP and RTP headers if RTP is used. Therefore, header compression can significantly reduce the size of the headers with a relatively small amount of computation. In fact, TCP header compression compresses...

How Policing Works

The internal processing logic used by IOS when implementing CAR differs slightly from the logic used when implementing class-based (CB) policing. Regardless of the internal processes, each policing tool wants to classify a packet relative to whether it is within the traffic contract. Based on that classification, the packet can be allowed to pass, be dropped, or be re-marked with a different IP precedence or IP DSCP (differentiated services code point) value. Single and dual token-bucket models...

Info

Cisco provides a large number of quality of service (QoS) features inside Cisco IOS Software. When most of us think about QoS, we immediately think of the various queuing mechanisms, such as Weighted Fair Queuing, or Custom Queuing. QoS features include many more categories, however fragmentation and interleaving features, compression, policing and shaping, selective packet-drop features, and a few others. And inside each of these categories of different QoS tools, there are several competing...

Integrated Services Questions

9 Imagine an enterprise network, connected to an Internet service provider (ISP), that is connected to a second ISP, which is then connected to another enterprise network. The second ISP does not support IntServ directly. Discuss the two options that allow the other three networks to support IntServ for flows that pass through the nonsupporting ISP. 10 Compare and contrast DiffServ and IntServ in terms of using classes, flows, and scalability. 11 Describe the two options available to a router...

Integrated Services Resource Reservation Protocol

In Chapter 2, QoS Tools and Architectures, this book introduced the concepts of differentiated services (DiffServ) and integrated services (IntServ). Most of the rest of the chapters in this book cover QoS features that either use DiffServ, or behave similarly. This section covers some of the key concepts and configuration related to IntServ. The IntServ model, defined in RFC 1633, includes provisions for best-effort traffic, real-time traffic, and controlled-link sharing. Controlled-link...

Interpreting the DQOS Exam Topics

The exam topics, like most exam topics listed by Cisco for other exams, use action words that follow a quasi-standard called Bloom's Taxonomy of the Cognitive Domain. Bloom's taxonomy defines a standard for word usage for when educators create objectives for courses. Objectives written according to Bloom's Taxonomy define what the learner should be able to accomplish after taking the class. So, when you look at an exam topic, look for the action word. If you want to see a description of Bloom's...

Introduction

Computing in general, and networking in particular, must deal with the issues relating to constrained resources. For computers, operating systems must find a way to equitably distribute the CPU time and memory among the various programs running on the computer. When the need for memory exceeds the available memory, the CPU spends more time performing memory management, moving data from memory to permanent storage, typically on a hard disk. Of course, the computer may be low on CPU resources at...

Introduction to IOS QoS Tools

Ultimately, this book will help you pass one or two QoS exams (the CCIP QoS exam and the Cisco Channel Partner DQOS exam). Both exams cover a wide variety of types of QoS tools. This chapter lists the tools covered on the DQOS exam any tools only covered on the QOS exam are listed in Appendix B, Topics on the CCIP QoS Exam. Of particular note, neither exam covers the implementation details of these tools on LAN switches, so the configurations and features of QoS tools on LAN switches is not...

Introduction to IP Quality of Service

Describe the Integrated Services model. List the key benefits and drawbacks of the IntServ model. Describe the Differentiated Services model. List the key benefits of the DiffServ model compared to the IntServ model. Describe the interoperability between DSCP-based and IP Precedence-based devices in a network. Describe the building blocks of IP QoS mechanisms (classification, marking, metering, policing, shaping, dropping, forwarding, queuing). List the IP QoS...

IP Data Basics

With voice and video, signaling occurred first in order to create the voice or video call. Although it is not called signaling in the data world, something similar does occur for instance, when you open a web browser, and browse www.cisco.com, several things happen before the first parts of the web page appear. For our purposes for QoS, this book focuses on the actual payload flows the actual data rather than the data equivalent of signaling. Most applications use one of two TCP IP transport...

IP Destination Caching

Unlike AVBO, PSTN fallback does not require the static configuration of the IP destinations. The software keeps a cache of configurable size that tracks the most recently used IP destinations to which calls were attempted. If the IP destination of a new call attempt is found in the cache, the CAC decision for the call can be made immediately. If the entry does not appear in the cache, a new probe is started and the call setup is suspended until the probe response arrives. Therefore, an extra...

Jitter

Consecutive packets that experience different amounts of delay have experienced jitter. In a packet network, with variable delay components, jitter always occurs the question is whether the jitter impacts the application enough to degrade the service. Typically, data applications expect some jitter, and do not degrade. However, some traffic, such as digitized voice, requires that the packets be transmitted in a consistent, uniform manner (for instance, every 20 ms). The packets should also...

Link Efficiency

The category of link efficiency encompasses two real topics compression and fragmentation. Rather than treat these topics in two separate chapters, I have included them in one chapter (Chapter 7, Link-Efficiency Tools) to match the organization of the Cisco QoS courses (and the IOS documentation to some degree). Compression reduces bandwidth utilization by making packets smaller before transmission. Two general types of compression tools exist in IOS payload compression and header compression....

Link Fragmentation and Interleave Questions

7 List the words represented by the abbreviation LFI. 8 To achieve a 20-ms serialization delay on a 128-kbps link, how long can the fragments be 9 What queuing tools can you enable directly on a serial interface when using multilink Point-to-Point Protocol with link fragmentation and interleaving (MLP LFI), as compared to when you are just using PPP 10 What command can you use to determine the fragment size used for MLP LFI What is the only parameter of the command 11 What command enables FRF...

Link Efficiency Tools

Most WAN links are leased from a service provider, with one of the variables affecting the pricing being the bandwidth on the link. For instance, the distance and the bandwidth, or clock rate, on the link affect leased lines. Frame Relay service providers base their prices in part based on the access rate of the access links into the Frame Relay network, and the committed information rate (CIR) of the various virtual circuits (VCs). If the offered load on the network consistently exceeds the...

Link Efficiency Tools Summary

Most link-efficiency tools have a very specific application that becomes obvious when you discover what each tool can and cannot do. Not all compression and LFI tools support every type of data link. Both compression and LFI tools may operate on a subset of the packets that exit an interface. For instance, TCP header compression just compresses IP packets that also have TCP headers. Frame Relay fragmentation only operates on a subset of the packets, based on which of two styles of fragmentation...

Location Based CAC Operation

The Cisco CallManager centralized call-processing model uses a hub-and-spoke topology. The host site, or hub, is the location of the primary Cisco CallManager controlling the network while the remote sites, containing IP endpoints registered to the primary CallManager, represent the spokes. The Cisco CallManager Administration web page can be used to create locations and assign IP endpoints, such as IP Phones, to these locations. After the locations have been created and devices have been...

Location Based CAC Summary

Table 8-15 evaluates location-based CAC against the CAC evaluation criteria described earlier in this chapter. Table 8-15 Location-Based CAC Evaluation Criteria (AAR was added in CallManager release 3.3.) End-to-end between originating and terminating location, although locations have no knowledge of the network topology in between

Locations and Regions

In Cisco CallManager, locations work in conjunction with regions to define how voice conversations are carried over a WAN link. Regions define the type of compression, such as G.711 or G.729, used on the link, and locations define the amount of available bandwidth allocated for that link. Figure 8-21 illustrates a CallManager centralized call-processing model with three remote sites. Each remote site has a location name that all IP endpoints in that location are associated with and a region...

Loss

The last QoS traffic characteristic is packet loss, or just loss. Routers lose drop discard packets for many reasons, most of which QoS tools can do nothing about. For instance, frames that fail the incoming frame check sequence (FCS) are discarded period. However, QoS tools can be used to minimize the impact of packets lost due to full queues. In most networks today, the number of packets lost due to bit errors is small, typically less than one in one billion (bit error rate BER of 10-9 or...

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

Marking

Marking involves setting some bits inside a data link or network layer header, with the goal of letting other devices' QoS tools classify based on the marked values. You can mark a wide variety of fields, and each has a particular purpose. Some fields are more widely used, and some are less widely used. Some marking options make sense for all devices on the LAN, whereas others only when using specific hardware platforms. Marking at the WAN is possible, too. The following sections list the...

Measurement Based Voice CAC

This section focuses on the following measurement-based CAC techniques Advanced Voice Busyout (AVBO) These are the first of two types of CAC mechanisms that add visibility into the network itself, in addition to providing local information on the originating gateway as discussed in the preceding sections. Before we discuss the actual features within this category, some background information on service assurance agent (SAA) probes is necessary, because this is the underlying technique used by...

Other Marking Fields

You can use single-bit fields in Frame Relay and ATM networks to mark a frame or cell for Layer 2 QoS. Unlike IP precedence, IP DSCP, and 802.1P ISL CoS, however, these two fields are not intended for general, flexible use. Each of these single-bit fields, when set, imply that the frame or cell is a better candidate to be dropped, as compared with frames or cells that do not have the bit set. In other words, you can mark the bit, but the only expected action by another QoS tool is for the tool...

Packet loss

Unfortunately, improving one QoS characteristic might degrade another. Bandwidth defines the capacity of the transmission media. Compression tools reduce the amount of bandwidth needed to send all packets, but the compression process adds some delay per packet and also consumes CPU cycles. Jitter is the variation in delay between consecutive packets, so it is sometimes called delay variation. A router can reduce jitter for some traffic, but that usually increases delay and jitter for other...

Packetization Delay

The IP Phone or voice gateway must collect 20 ms of voice before it can put 20 ms worth of voice payload into a packet. (The defaults for G.711 and G.729 on IP Phones and Cisco IOS Software gateways are to put 20 ms of voice into an RTP packet the value can be changed.) Therefore, for the sake of discussion in this book, we consistently consider packet delay always to be 20 ms in examples. That is, the speaker must talk for 20 ms before a packet containing 20 ms of voice can be created.

Payload Compression

Cisco IOS Software supplies three different options for point-to-point payload compression tools on serial links, namely Stacker, Microsoft Point-to-Point Compression (MPPC), and Predictor. Consider the following criteria when choosing between the payload compression options The types of data-link protocols supported The efficiency of the compression algorithm used Whether the device on the other end of the link supports the tool Of course, when two Cisco routers are used on each end,...

PBR Marking Summary

PBR provides another classification and marking tool that examines packet header information to classify and mark packets. PBR is unique compared to the other tools in that it can classify based on information about the route that would be used for forwarding a packet. However, PBR has fewer options for matching header fields for classification as compared with the other tools. PBR can mark IP precedence, QoS group, as well as the ToS bits. Refer to Table 3-17, in the summary for this chapter,...

Policing but Not Discarding

Shapers queue excess packets, and policers discard excess packets. However, policers allow a sort of compromise, where the packets are not discarded, but they are marked so that if congestion occurs later, this particular packet is more likely to be discarded. Consider Figure 5-17, for instance, and the policing function on R1. Figure 5-17 Marking Down Packets with Policing Policing, Marking Down Excess Traffic Figure 5-17 Marking Down Packets with Policing Policing, Marking Down Excess Traffic...

Policing with CAR and CB Policer Questions

5 List the command, with the correct syntax, that sets a policed rate of 512 kbps, a Bc of 1 second's worth of traffic, and a Be of an additional 0.5 second's worth of traffic, when using CAR. Do not assume any defaults explicitly set the values in the command. You can choose any other settings needed for the command. 6 Which policing tools allow for three categories of actions to take 7 Explain the concept behind re-marking policed packets versus discarding the packets. 8 CB policing has been...

Priority Queuing

Priority Queuing's most distinctive feature is its scheduler. PQ schedules traffic such that the higher-priority queues always get serviced, with the side effect of starving the lower-priority queues. With a maximum of four queues, called High, Medium, Normal, and Low, the complete logic of the scheduler can be easily represented, as is shown in Figure 4-9. As seen in Figure 4-9, if the High queue always has a packet waiting, the scheduler will always take the packets in the High queue. If the...

Priority Queuing and Custom Queuing

7 Assume a queuing tool has been enabled on interface S0 0. Describe the circumstances under which the queuing tool would actually be used. 8 Explain the circumstances under which it would be useful to enable a queuing tool on a subinterface. 9 Describe the classification feature of Priority Queuing, including the list of items that can be examined for classification decisions. 10 Describe the classification feature of Custom Queuing, including the list of items that can be examined for...

PSTN Fallback Scalability

Examples 8-13 and 8-14 in the preceding section describe a simple network in which the remote site router acts as the terminating gateway for the voice conversation. The IP address of the remote site router and the network congestion values of the link between the remote and host router are held in the cache of the host site router. When the host site router receives the digits 12 followed by 2 additional digits, the host cache is consulted to determine whether the call can be successfully...

Qa

As mentioned in the Introduction, you have two choices for review questions. The questions that follow next give you a more difficult challenge than the exam itself by using an open-ended question format. By reviewing now with this more difficult question format, you can exercise your memory better, and prove your conceptual and factual knowledge of this chapter. You can find the answers to these questions in Appendix A. The second option for practice questions is to use the CD-ROM included...

QoS Exam Objectives

Describe policy-based routing and how it can be used to classify and mark IP packets. Configure the policy-based routing mechanism on Cisco routers. List other mechanisms that also support classification and marking capabilities (committed access rate, class-based marking). Describe the Modular QoS CLI (MQC) concept and its structure. Describe Modular QoS CLI classification options. Configure the Modular QoS CLI to perform classification. Describe network-based application recognition (NBAR)....

QoS Exam Topics

Describe how queuing works on Cisco routers Describe FIFO Queuing (FQ) and its benefits and drawbacks Describe Priority Queuing (PQ) including its benefits and drawbacks Describe Custom Queuing (CQ) including its benefits and drawbacks Describe Weighted Fair Queuing (WFQ) including its benefits and drawbacks Configure Weighted Fair Queuing (WFQ) on Cisco routers Describe IP RTP Prioritization Configure IP RTP Prioritization on Cisco routers Configure the Modular QoS CLI to perform service...

QoS Management Tools

Utilize QoS Device Manager to monitor performance, establish baselines and configure QoS policies. Utilize QoS Policy Manager to configure advanced QoS policies, scale policy deployment, upload verify roll-back policies, and deploy QoS policies by external time-based event-based scripts. Configure Cisco Service Assurance Agent to measure key SLA metrics and monitor network performance between local and remote devices. Monitor and troubleshoot network performance with IPM and SMS.

QoS Tools Questions

1 List four queuing tools, including the full names and popular acronyms. 2 List four link-efficiency tools, including the full names and popular acronyms. 3 Which of the following tools can be used for classification and marking CAR, CB marking, PQ, CB shaping, QDM, WFQ, WRED, FRTS, LLQ, GTS, RAI, FRF, RSVP, SAA, MLPPP LFI, AVBO, CQ, NBAR, QPM, CAR, FRED, QPPB, cRTP 4 Which of the following tools can be used for policing CAR, CB marking, PQ, CB shaping, QDM, WFQ, WRED, FRTS, LLQ, GTS, RAI,...

QoS Tools That Affect Jitter

Several QoS features can help with jitter issues. You'll find more detail about each of these tools in various chapters throughout this book. For now, however, knowing what each class of QoS tool accomplishes will help you sift through some of the details. The best QoS tool for jitter issues is . . . more bandwidth again More bandwidth helps bandwidth-related problems, and it also helps delay-related problems. If it helps to reduce delay, and because jitter is the variation of delay, jitter...