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Cisco QoS FAQ: Management Tools and QoS Design

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Cisco QoS FAQ: Management Tools and QoS Design

Q1. What do the following acronyms stand for? IPM, QPM, SAA, QDM

Answer: Internetwork Performance Monitor, QoS Policy Manager, Service Assurance Agent, and QoS Device Manager.

Q2. What QoS Management tool is actually a component of the CiscoWorks2000 Routed WAN Management Solution?

Answer: IPM.

Q3. What QoS management tool is free?

Answer: QDM.

Q4. What QoS management tool(s) enables you to define QoS policies, after which it creates the appropriate configurations, and deploys the configurations to identified network devices?

Answer: QPM.

Q5. Which QoS management tool(s) includes as a primary feature the capability to graph realtime information about bit/byte/packet rates and packet loss?

Answer: QDM, IPM, and QPM.

Q6. Describe the two primary components of SMS and their general roles.

Answer: SMS includes the Service Level Manager, to which the user connects. The SMS Collection Managers (CMs) actually collect the statistics, which are then asynchronously fed back to the SLM.

Q7. What QoS management tool(s) generates packets, called probes, and measures various performance attributes, such as delay and jitter?

Answer: SAA.

Q8. What QoS management tool(s) includes as a primary function the capability to produce historical performance reports as compared to service-level agreements?

Answer: SMS.

Q9. What QoS management tool(s) includes as a primary function the capability to troubleshoot and isolate network-wide performance issues by viewing the individual components in a complete end-to-end path through the network?

Answer: IPM.

Q10. Does QDM or QPM support more devices?

Answer: QPM.

Q11. Among QPM, QDM, SMS, and IPM, which tool(s) originally had a limited capability to create real-time or historical graphs of performance?

Answer: QPM.

Q12. What QoS management tool(s) is embedded into a router?

Answer: QDM.

Q13. Which QoS management tools are available in CiscoWorks2000 bundles?

Answer: IPM and SMS.

Q14. List Step 1 in the QoS design process, and give a short summary of what the step includes.

Figure : Four Steps for QoS Design

cisco-qos-faq-management-tools-qos-design

Answer: Step 1 is to “determine customer priorities/QoS policy.” It includes discussions with appropriate personnel to determine what level of quality each type of traffic should get.

Q15. List Step 2 in the QoS design process, and give a short summary of what the step includes.

Answer: Step 2 is to “characterize the network.” It includes a network audit, which is used to plan any needed upgrades of bandwidth, and to determine all the details needed in order to successfully classify the traffic in that particular network.

Q16. List Step 3 in the QoS design process, and give a short summary of what the step includes.

Answer: Step 3 is to “implement policy.” It includes actual choices of QoS tools, and then the configuration of the tools.

Q17. List Step 4 in the QoS design process, and give a short summary of what the step includes.

Answer: Step 4 is to “monitor the network”. It includes using the QoS management tools to see historical trends, and the process of reviewing the reports versus policies to allow the four-step process to repeat, improving the quality of the QoS implementation over time.

Q18. What are the ITU G.114 and Cisco recommendations for maximum one-way delay for voice calls?

Answer: The ITU recommends 150 ms, with Cisco stating it can be as high as 200 ms.

Q19. What delay component represents the most controllable variable delay in a voice call?

Answer: Queuing delay.

Q20. How much bandwidth does a G.729 call require if ignoring the Layer 2 header/trailer? How much bandwidth does it require if using Frame Relay?

Answer: The call requires 24 kbps discounting the data-link framing; adding the Frame Relay headers and trailers, the call takes 26.4 kbps.

Q21. Summarize the Cisco recommendations for marked values for voice and video traffic.

Answer: Cisco suggests that voice payload be marked with DSCP EF, CoS 5, and/or precedence 5; video payload with DSCP AF41, CoS 4, and/or precedence 4; and voice and video signaling with DSCP AF31, CoS 3, and/or precedence 3.

Q22. Describe the Cisco recommendation for queuing voice and video traffic.

Answer: Cisco recommends using LLQ, placing the voice payload into the low-latency queue, and the video payload into a separate queue. If the IOS does not support LLQ, Cisco suggests enabling IP RTP Priority.

Q23. Summarize the Cisco recommendations for tuning shaping parameters when shaping must be enabled on VCs carrying voice.

Answer: Cisco suggests choosing configuration settings such that Bc is equal to CIR / 100, which will make Tc equal to 10 ms. Be is equal to zero to prevent bursting over the CIR. If adaptive shaping is used, Cisco suggests that the mincir be set equal to the CIR value with no adaptive shaping being used.