Cisco QoS FAQ: QoS Tools and Architectures Q1. List four classification and marking tools, including the full names and popular acronyms. Answer: Committed access rate (CAR), policy-based routing (PBR), class-based marking (CB marking), dial peers, network-based application recognition (NBAR), QoS policy propagation with BGP (QPPB). Q2. List four queuing tools, including the … [Read more...]
Cisco QoS FAQ: Link-Efficiency Tools
Cisco QoS FAQ: Link-Efficiency Tools Q1. Describe what is compressed, and what is not compressed, when using payload compression. Be as specific as possible regarding headers and data. Answer: Payload compression does not compress the data-link header and trailer, but it does compress all the headers and data between the two. Specifically, the IP, TCP, UDP, RTP headers as … [Read more...]
Cisco QoS FAQ: Congestion Avoidance Through Drop Policies
Cisco QoS FAQ: Congestion Avoidance Through Drop Policies Q1. Describe the function of the congestion window in TCP, and how it is changed as a result of packet loss. Answer: The TCP congestion window, or CWND, is one of two windowing mechanisms that limit TCP senders. CWND can be split in half as a result of packet loss, slowing the sending rate. CWND can also be slammed … [Read more...]
Cisco QoS FAQ: Quality of Service Overview
Cisco QoS FAQ: Quality of Service Overview Q1. List the four traffic characteristics that QoS tools can affect. Answer: Bandwidth, delay, jitter, and loss. Q2. Describe some of the characteristics of voice traffic when no QoS is applied in a network. Answer: Voice is hard to understand; voice breaks up, sounds choppy; calls are disconnected; large delays make it difficult … [Read more...]
Cisco QoS FAQ: Traffic Policing and Shaping
Cisco QoS FAQ: Traffic Policing and Shaping Q1. Explain the points during the process of a single router receiving and forwarding traffic at which shaping and policing can be enabled on a router. Answer: Shaping can be enabled for packets exiting an interface, subinterface, or individual VC. Policing can be performed both on packets entering an interface or exiting an … [Read more...]
Cisco QoS FAQ: Congestion Management
Cisco QoS FAQ: Congestion Management 1. Describe the benefits of having a single FIFO output queue. Answer: The most basic benefit of queuing is to provide a means to hold a packet while the interface is busy. Without at least a single FIFO queue, routers would have to discard packets if the outgoing interface were busy. Q2. Explain the effects of changing a single FIFO … [Read more...]
Cisco QoS FAQ: LAN QoS
Cisco QoS FAQ: LAN QoS Q1. What is instantaneous buffer overrun? Answer: Instantaneous buffer overrun occurs when a switch port TX queue fills for an instant causing packet loss, which can adversely affect real-time applications. In a VoIP conversation, for example, 40 ms of congestion causes an audible clip in the conversation. Q2. What is meant by the term … [Read more...]
Cisco QoS FAQ: Classification and Marking
Cisco QoS FAQ: Classification and Marking Q1. Describe the difference between classification and marking. Answer: Classification processes packet headers, or possibly other information, to differentiate between multiple packets. Marking changes a field inside the frame or packet header. Q2. Describe, in general, how a queuing feature could take advantage of the work … [Read more...]
Cisco QoS FAQ: Management Tools and QoS Design
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 … [Read more...]
Cisco QoS FAQ: Call Admission Control and QoS Signaling
Cisco QoS FAQ: Call Admission Control and QoS Signaling Q1. Why is CAC needed in an environment where LLQ has been properly implemented? Figure: Legacy VoIP Network with CAC Answer: LLQ provides classification, marking, and prioritization of voice packets, but does not differentiate between voice streams. The priority queue can become overburdened with a larger … [Read more...]