Chapter 10

"Do I Know This Already" Quiz

1.	Which of the following traffic types provides a consistent packet exchange? Interactive video Voice media Voice signaling Mission-critical data
Answer:	B
2.	Which of the following factors influence the bandwidth requirements of a VoIP call? Layer 3 routing protocol Layer 2 media type Codec selection Speech samples per packet
Answer:	B, C, D
3.	The International Telecommunications Union (ITU) G.114 specification states that the one-way delay of a voice packet should not exceed how many milliseconds (ms)? 100 150 200 250
Answer:	B
4.	How much bandwidth should be provisioned for a 384-kbps interactive video stream? 384 kbpsThe average rate of the stream 460.8 kbpsThe average rate of the stream + 20% 768 kbpsThe average rate of the stream * 2 192 kbpsThe size of H.264 compressed video
Answer:	B
5.	How sensitive is mission-critical data to jitter? (Link: Data Traffic) Low Low to moderate Moderate to high High
Answer:	B
6.	A converged network should be designed for less than what percentage of packet loss in the class that supports real-time applications? .5 1 1.5 5
Answer:	B
7.	A converged network should be designed for less than how many milliseconds of jitter in the class that supports real-time applications? 10 20 30 40
Answer:	C
8.	Where should traffic be classified? In the core As close to the source as possible As close to the destination as possible On the WAN router
Answer:	B
9.	What is the recommended differentiated services code point (DSCP) value for scavenger traffic? 0 CS0 CS1 AF13
Answer:	C
10.	What is the recommended DSCP class for bulk data applications? AF1x AF2x AF3x EF
Answer:	A
11.	What are the preferred methods of queuing on Cisco routers? PQ and CBWFQ PQ and CQ LLQ and CBWFQ LLQ and CQ
Answer:	C
12.	When using LFI, what is the recommended serialization delay of a voice packet? 510 ms 1015 ms 1520 ms 2025 ms
Answer:	B
13.	Where does WRED perform the most effectively? When applied to the LLQ When applied to a CBWFQ that services UDP applications When applied to a CBWFQ that services TCP applications When applied to a CBWFQ that services both UDP and TCP applications
Answer:	C
14.	What QoS mechanism should never be used in the core of the campus LAN? Classification and marking Congestion management Congestion avoidance
Answer:	A
15.	If the service provider manages the CE router, what inbound policy is required on the PE router? Classification and marking Congestion management Policing All of the above None of the above
Answer:	E

Q&A

1.	What is end-to-end QoS?
Answer:	End-to-end QoS is a means of offering the same treatment to a packet on each node it traverses.
2.	What do service providers use to contractually guarantee specific delay, jitter, and packet loss to their customers?
Answer:	A service-level agreement (SLA)
3.	When would an SLA be offered on a per PVC basis?
Answer:	When the physical interface services multiple customers.
4.	In a Cisco IP Telephony environment, which codec is best suited for the LAN?
Answer:	G.711
5.	In a Cisco IP Telephony environment, which codec is best suited for the WAN?
Answer:	G.729
6.	By default, how many milliseconds of speech are placed into every packet in a voice media stream?
Answer:	20 ms
7.	How much bandwidth is required to transport a G.729 VoIP call @ 50 packets per second over a Frame Relay circuit? Assume that cRTP and VAD are not enabled.
Answer:	28 kbps
8.	Enabling cRTP can reduce the overhead of the IP/UDP/RTP header from 40 bytes to how many bytes?
Answer:	2 or 4
9.	Cisco DSPs have the capability to compensate for how many milliseconds of lost speech?
Answer:	30 ms
10.	A Cisco IP Phone can compensate for how much jitter?
Answer:	2050 ms
11.	Data applications should be separated into no more than how many distinct classes?
Answer:	Four or five
12.	In a converged network supporting voice, interactive video, streaming video, mission-critical data, transactional data, and best-effort traffic, which class or classes should use the low latency queue?
Answer:	Voice and interactive video
13.	What tool is recommended to discover applications on your network?
Answer:	NBAR
14.	What DSCP value do Cisco IP Phones currently mark voice media traffic with?
Answer:	EF
15.	What CoS value do Cisco IP Phones currently mark voice media traffic with?
Answer:	5
16.	What DSCP value do Cisco IP Phones currently mark voice signaling traffic with?
Answer:	AF31
17.	What CoS value do Cisco IP Phones currently mark voice media signaling with?
Answer:	3
18.	What is the recommended CoS value for IP routing protocols?
Answer:	6
19.	What is the recommended DSCP value for IP routing protocols?
Answer:	CS6
20.	What is the recommended DSCP class for transactional applications?
Answer:	The AF2x class
21.	Which type of queue should voice signaling traffic use in an enterprise network?
Answer:	CBWFQ
22.	Which command is used to allocate 100 percent of the link to MQC?
Answer:	max-reserved-bandwidth 100
23.	What value should the Tc be configured for on a Frame Relay circuit that will transport voice media traffic?
Answer:	10 ms
24.	What is needed in a campus LAN before QoS is implemented?
Answer:	A hierarchical and redundant campus design
25.	Where in the campus LAN is policing typically configured?
Answer:	The access and distribution layers
26.	What is the recommended CoS value for IP routing protocols?
Answer:	CoS value of 6
27.	What QoS mechanism should never be implemented in the core of the campus LAN?
Answer:	Classification and marking
28.	If Cisco IP Phones have the capability to mark voice media and voice signaling traffic, why is it necessary to use access lists to classify these types of traffic?
Answer:	Cisco Softphone and certain CTI applications might not have the capability to mark this traffic, yet they have the same QoS requirements.
29.	When is a CoS-to-DSCP map used?
Answer:	When a switch receives a trusted frame with a CoS value, it will assign a DSCP value to the packet based upon this map.
30.	When should the CoS-to-DSCP map be modified?
Answer:	When the CoS value does not match the desired DSCP value by default. For example, a received packet with a CoS value of 5 will be marked with a DSCP value of decimal 40, which is not the same as DSCP EF (decimal 46). The CoS-to-DSCP map must be modified to map a CoS value of 5 to a DSCP value of EF (decimal 46).
31.	Which two queuing methods should be used in the service provider's backbone network?
Answer:	LLQ/CBWFQ and MDRR