QoS

Question 1

What are the quality requirements for voice and video?

Answer 1

Latency <150ms
Jitter < 30ms
Loss < 1%

Question 2

What is delay in reference to QoS?

Answer 2

Latency

Question 3

What is jitter in reference to QoS?

Answer 3

Variation in Delay

Question 4

What is loss in reference to QoS?

Answer 4

Packet loss

Question 5

By default, whenever congestion is experienced on a router or switch, packets are sent out in a ____________ manner

Answer 5

First In First Out (FIFO)

Question 6

_____________ can be experienced whenever it is possible for packets to come in quicker than they can be sent out

Answer 6

Congestion

Question 7

When traffic is being processed as First In First Out and with no QoS in place what will the router do?

Answer 7

Buffer traffic and queue it up

Question 8

What are a couple of ways to mitigate congestion?

Answer 8

Add more bandwidth
Use QoS techniques

Question 9

QoS queuing can reduce what for particular traffic?

Answer 9

Latency, jitter and loss

Question 10

What are some of the markings for QoS?

Answer 10

COS (Class of Service)
DSCP (Differentiated Service Code Point)
ACLs
NBAR (Network Based Application Recognition)

Question 11

What Layer does COS (Class of Service) reside at?

Answer 11

Layer 2

Question 12

What layer does DSCP (Differentiated Service Code Point) reside at?

Answer 12

Layer 3

Question 13

What carries the COS QoS marking?

Answer 13

A 3 bit field in the Layer 2 802.1Q Frame Header

Question 14

What is the value range for the COS 3 bit field in the Layer 2 Frame Header?

Answer 14

0-7

Question 15

What COS values are reserved for network use like routing protocols?

Answer 15

6 and 7

Question 16

True or False: With COS, the higher the value the more important the traffic is

Answer 16

True

Question 17

With COS, what value do IP Phones mark their call signaling traffic as?

Answer 17

3

Question 18

With COS, what value do IP Phones mark their voice payload traffic as?

Answer 18

5

Question 19

What is used to carry DSCP QoS Marking?

Answer 19

The TOS (Type of Service) byte in the Layer 3 IP Header

Question 20

What is the value range with DSCP?

Answer 20

0-63

Question 21

What is the default DSCP value?

Answer 21

0

Question 22

What is the default COS value?

Answer 22

0 for best effort traffic

Question 23

How many bits are used with DSCP marking?

Answer 23

6

Question 24

With DSCP, IP Phones mark their call signaling with what value?

Answer 24

24 (CS3)

Question 25

With DSCP, what do IP Phones mark their voice payload with what value?

Answer 25

46 (EF)

Question 26

True or False: Only DSCP or COS can be in a packet but not both

Answer 26

False. Both DSCP and COS are in the packet. COS for Layer 2 and DSCP for Layer 3

Question 27

What does NBAR stand for?

Answer 27

Network Based Application Recognition

Question 28

What layers does NBAR inspect a packet up to?

Answer 28

3-7

Question 29

What are the 3 main sections of MQC (Modular QoS CLI)

Answer 29

Class Maps
Policy Maps
Service Policies

Question 30

____________ can be used to manage congestion on routers and switches

Answer 30

Queuing

Question 31

This type of queuing gives bandwidth guarantees to specified traffic type

Answer 31

CBWFQ (Class Based Weight Fair Queuing)

Question 32

This type of queuing is just CBWFQ but with a priority value

Answer 32

LLQ (Low Latency Queuing)

Question 33

___________ and ____________ can be used to control traffic rate

Answer 33

Traffic shaping and policing

Question 34

Traffic shaping _________ any excess traffic so the overall traffic stays within the desired rate limit

Answer 34

Buffers

Question 35

Traffic policing ___________ or re-marks excess traffic to enforce the specified rate limit

Answer 35

Drops

Question 36

This is another term for worm or junk traffic

Answer 36

Scavenger traffic

Question 37

What is the recommended value for DSCP scavenger traffic?

Answer 37

DSCP 8 (CS1)