Foundation Summary 679
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 should help solidify some key facts. For any of you doing your final prep before the exam, these tables and figures are a convenient way to review the day before the exam.
QPM needs to be able to communicate with the routers and switches, as well as learn about what devices are in the network. Figure 9-6 outlines the overall location and functions between the QPM server and the rest of the network.
Figure 9-6 QPM Server and Communication with Other Devices
Network Devices
Telnet |
COPS |
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SNMP |
Cisco Works 2000 |
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QPM |
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Inventory |
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LDAP Directory |
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680 Chapter 9: Management Tools and QoS Design
Table 9-10 lists some of the types of SAA probes supported in IOS 12.2.
Table 9-10 Types of SAA Probes
Type of Probe |
Function |
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ICMP echo |
Measures availability between a router and any other devices by sending ICMP |
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echos (pings) |
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IP Path echo |
Measures hop-by-hop response time by pinging each successive device in the route |
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to the true destination of the probe. |
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TCP connection |
Measures the time required to establish a TCP connection to a specified TCP port on |
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a specified IP host. |
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UDP echo |
Measures the round-trip time to send a packet to a specified UDP port number on a |
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specified IP host |
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UDP jitter |
Measures jitter, one-way delay, and packet loss in each direction |
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FTP |
Measures time required to retrieve (FTP get) a specified file from a specified FTP |
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server |
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HTTP |
Tests the time taken to do DNS lookup to find a web server, TCP connection |
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establishment time to the server, or the time required to download an object from |
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the server |
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DNS |
Measures the round-trip time between sending a DNS request and receiving a |
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response |
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DLSw |
Measures DLSw round-trip times, including DLSw stack delays, between a source |
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and destination, without requiring an SAA agent on the destination host |
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To meet the requirement to gather larger amounts of network performance information, SMS includes several components. Figure 9-7 shows the components, with an explanation of each component following the figure.
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Foundation Summary 683 |
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Table 9-12 One-Way Delay Budget Guidelines for Voice |
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One Way Delay (ms) |
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Description |
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0–150 |
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ITU G.114 recommended acceptable range |
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0–200 |
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Cisco’s recommended acceptable range |
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150–400 |
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ITU G.114’s recommended range for degraded service |
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400+ |
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ITU G.114’s range of unacceptable delay in all cases |
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Table 9-13 Delay Components, Variable and Fixed |
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Delay |
Fixed or |
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Component |
Variable |
Comments |
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Codec |
Fixed |
Varies slightly based on codec and processing |
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load; considered fixed in course books (and |
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probably on exams). Typically around 10 ms. |
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Packetization |
Fixed |
Some codecs require a 30-ms payload, but |
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packetization delay does not vary for a single |
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codec. Typically 20 ms, including when using |
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G.711 and G.729. |
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Propagation |
Variable |
Varies based on length of circuit. About |
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5ms/100 km. |
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Queuing |
Variable |
This is the most controllable delay component for |
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packet voice. |
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Serialization |
Fixed |
It is fixed for voice packets, because all voice |
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packets are of equal length. It is variable based on |
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packet size for all packets. The delay is based on |
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the clock speed of the WAN circuit. |
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Network |
Variable |
Least controllable variable component. Latency is |
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potentially higher in a packet-switched network |
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than in a leased line. |
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De-jitter buffer (initial playout delay) |
Variable |
This component is variable because it can be |
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configured for a different value. However, that |
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value, once configured, remains fixed for all calls |
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until another value is configured. In other words, |
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the initial playout delay does not dynamically |
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vary. |
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