536 Chapter 7: Link-Efficiency Tools

Q&A

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 with this book. It includes a testing engine and more than 200 multiple-choice questions. You should use this CDROM nearer to the end of your preparation, for practice with the actual exam format. You can even customize the CD-ROM exam to include, or not include, the topics that are only on the CCIP QoS.

Compression Tools

1Describe what is compressed, and what is not compressed, when using payload compression. Be as specific as possible regarding headers and data.

2Describe what is compressed, and what is not compressed, when using TCP header compression. Be as specific as possible regarding headers and data.

3Describe what is compressed, and what is not compressed, when using RTP header compression. Be as specific as possible regarding headers and data.

4List the three point-to-point payload compression options available in IOS.

5Suppose a packet is sent across a network with no compression. Later, a packet of the exact same size and contents crosses the network, but payload compression is used on the one serial link in the network. Describe the difference in bandwidth and delay in the network between these two packets.

6List the three options for Frame Relay payload compression in IOS. Which of the three is not Cisco proprietary?

7Which payload compression tool in IOS supports Link Access Procedure, Balanced (LAPB), High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP) encapsulations?

8How much bandwidth should a G.729 call require over Frame Relay, and how much should be required with cRTP?

9When TCP header compression is used, what is the range of sizes of the part of the frame that can be compressed, and what is the range of sizes for this field of the frame after compression?

LFI Tools 537

10When RTP header compression is used, what is the range of sizes of the part of the frame that can be compressed, and what is the range of sizes for this field of the frame after compression?

11To configure Stacker payload compression on a point-to-point link, what command(s) is used, and in what configuration modes?

12To configure Stacker payload compression on a point-to-point Frame Relay subinterface, what command(s) is used, and in what configuration modes?

13To configure FRF.9 payload compression on a point-to-point Frame Relay subinterface, what command(s) is used, and in what configuration modes?

14What command lists compression statistics for payload compression on a point-to-point link?

15What command lists compression statistics for payload compression on a Frame Relay point-to-point subinterface?

16To configure TCP header compression on a point-to-point Frame Relay subinterface, what command(s) is used, and in what configuration modes?

17To configure RTP header compression on a point-to-point link, what command(s) is used, and in what configuration modes?

LFI Tools

18List the words represented by the abbreviation LFI.

19Describe the main motivation for LFI tools in relation to the support of data, voice, and video traffic.

20To achieve a 20-ms serialization delay on a 128-kbps link, how long can the fragments be?

21To achieve a 10-ms serialization delay on a 64-kbps link, how long can the fragments be?

22Suppose that a 1500-byte packet exits a 56-kbps serial interface, and LFI is not used. How long is the serialization delay?

23Which 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?

24Which queuing tools can you enable for shaping queues when using FRF.12? Which ones actually interleave the traffic?

25Explain the popularly stated scheduling logic, which is consistent with the Cisco QoS courses, that defines how FRF.12 determines which packets can be interleaved in front of fragments of other packets.

C H A P T E R 8

Call Admission Control and

QoS Signaling

Suppose that you and a passenger are inside a vehicle traveling on a northbound highway. The highway consists of four regular lanes and one high-occupancy-vehicle (HOV) lane. To gain entry into the HOV lane, your vehicle must contain two or more people. In this instance, the HOV lane represents a priority queue, whereas the remaining four lanes represent lower-priority queues. As traffic begins to build in the four regular lanes, you decide to merge into the HOV lane. Over the next few miles/kilometers, the HOV lane maintains a constant rate of speed while the four regular lanes begin to stall. You are now enjoying the benefits of a priority queue. As you continue traveling northbound, you notice more vehicles, meeting the requirements of two or more passengers, begin to merge into the HOV lane. Over the next few miles/kilometers, your speed decreases until the HOV is now stalled.

In this instance each vehicle in the HOV lane has met the criteria to be placed in the highpriority queue. The expectation is that the HOV lane will move quickly. Contrary to these expectations, as more vehicles enter the HOV lane the slower the lane becomes. How do you prevent this issue from arising?

This scenario illustrates the need to have some mechanism in place to limit the amount of traffic that can gain access into the priority queue, ensuring that a consistent flow of traffic can be maintained across a network link. This concept is called call admission control (CAC), which is the subject of this chapter.

NOTE For those of you studying for the CCIP QoS 642-641 exam, most of the contents of this chapter are not covered on that exam. The RSVP topics in this chapter are. So, you may want to choose to skip sections of this chapter, and just read the sections covering RSVP. As always, recheck Cisco’s posted exam topics to make sure nothing has changed!