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QoS Flashcards

1
Q

What happens when traffic volume exceeds available bandwidth?

A

Packets queued in memory until resources become available to transmit

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2
Q

QoS mechanisms enable:

A

Higher-priority IP traffic flows (e.g., voice, video) to be forwarded immediately

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3
Q

what are the 3 QoS mechanisms?

A

classification and marking, policing and shaping, congestion management and avoidance

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4
Q

What are the sources of network congestion problems?

A

latency (delay), jitter (delay variation), packet loss

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5
Q

what is packet delay?

A

the time it takes a packet to travel across a network from source to destination

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6
Q

what is processing delay?

A

The time it takes to accept a packet, examine it, and forward it to the output interface.

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7
Q

what is serialization delay?

A

The time it takes to place the bits of a packet from the NIC onto the media (Copper, Fiber, Wireless).

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8
Q

what is propagation delay?

A

The time it takes to place the bits of a packet from the NIC onto the media (Copper, Fiber, Wireless).

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9
Q

what is jitter?

A

the variation in the delay of received packets

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10
Q

voice traffic is susceptible to what problem?

A

packet loss

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11
Q

what protocol does voice traffic use?

A

RTP – real time protocol

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12
Q

what type of traffic has no tolerance for packet loss, and is insensitive to delays and drops

A

data (web)

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13
Q

what type of traffic is sensitive to delays and drops, but can tolerate latency and jitter?

A

voice

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14
Q

what type of traffic is unpredictable, less resilient to loss than voice, but can tolerate latency and jitter?

A

video

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15
Q

what are 4 common congestion queuing algorithms?

A
  • first in first out — FIFO
  • weighted fair queuing — WFQ
  • class based weighted fair queuing — CBWFQ
  • low latency queuing — LLQ
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16
Q

which queuing algorithm…
- works on a first come first served basis,
- has no packet priority,
- is the fastest

A

FIFO

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17
Q

which queuing algorithm…
- uses automated scheduling,
- does not use classification,
- applies priorities (weights) to different traffic and classifies them into flows,
- interactive traffic is given higher priority,

A

WFQ

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18
Q

which queuing algorithm…
- extends WFQ functionality,
- provides support for user-defined traffic classes

A

CBWFQ

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19
Q

which queuing algorithm…
- provides strict priority queuing to CBWFQ,
- reduces jitter in voice traffic,
- bandwidth assigned to class determines packet order

A

LLQ

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20
Q

what are the 3 QoS models?

A
  • best effort model (no qos)
  • integrated services (intserv)
  • differentiated services (diffserv)
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21
Q

which qos model provides the highest guarantee of QoS but it is very resource-intensive and therefore, limited in scalability?

A

Intserv

22
Q

which qos model is less resource-intensive and most scalable (aside from best effort)?

A

Diffserv

23
Q

what type of tool is weighted random early detection (WRED)?

A

congestion avoidance tool

24
Q

what type of tools are CBWFQ and LLC?

A

congestion management tools

25
Q

what are the 3 categories of qos tools?

A

classification and marking, congestion avoidance, congestion management

26
Q

Which QoS mechanism identifies and categorizes traffic?

A

classification and marking

27
Q

which qos mechanism uses WRED?

A

congestion avoidance

28
Q

Which QoS mechanism could drop or re-mark incoming or outgoing traffic that goes beyond a desired traffic rate?

A

traffic policing

29
Q

Which QoS mechanism can buffer egress traffic rates that momentarily peak above the desired rate?

A

traffic shaping

30
Q

T/F — DiffServ is less resource intensive and more scalable.

A

true

31
Q

T/F — IntServ is more resource intensive and less scalable.

A

true

32
Q

T/F — CBWFQ provides strict priority queuing to LLQ.

A

false

33
Q

t/f — The CBWFQ and LLQ queuing algorithms are QoS congestion management tools.

A

true

34
Q

t/f — LLQ provides strict priority queuing to CBWFQ.

A

true

35
Q

t/f — WRED is a QoS congestion avoidance tool.

A

true

36
Q

Which queuing algorithm is effective for large links that have little delay and minimal congestion?

A

fifo

37
Q

Which queuing algorithm allows delay-sensitive data such as voice to be sent before packets in other queues?

A

LLQ

38
Q

On a layer 2 switch, which CoS value should be assigned to voice frames?

A

5 (101)

39
Q

On a layer 2 switch, which CoS value should be assigned to best effort frames?

A

0 (000)

40
Q

On a layer 2 switch, which CoS value should be assigned to video conferencing frames?

A

4 (100)

41
Q

On a layer 3 router, which DSCP Decimal value should be assigned to voice packets?

A

EF (101110)

42
Q

Which QoS model is also called “Hard QoS”?

A

intserv

43
Q

Which QoS model provides many different levels of quality?

A

diffserv

44
Q

Which is a QoS model that a network engineer would implement to ensure a source to destination quality of service standard for a specified data flow?

A

intserv

45
Q

Which QoS model provides per-request policy admission control?

A

intserv

46
Q

Which QoS model is also called “Soft QoS”?

A

diffserv

47
Q

what is queuing delay?

A

the variable amount of time a frame or packet waits before it is transmitted on the link

48
Q

Which option is used for marking 802.1Q frames?

A

class of service (CoS)

49
Q

Which option is used for marking Layer 3 packets?

A

differentiated service code points (DSCP)

50
Q

What two fields are available in IPv4 and IPv6 headers to mark packets for QoS?

A
  • type of service
  • traffic class
51
Q

What statement describes the Class of Service field?

A

it is a layer 2 field

advanced networking (7 decks)

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