QoS Flashcards by Bale S

What happens when traffic volume exceeds available bandwidth?

Packets queued in memory until resources become available to transmit

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QoS mechanisms enable:

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

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what are the 3 QoS mechanisms?

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

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What are the sources of network congestion problems?

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

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what is packet delay?

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

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what is processing delay?

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

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what is serialization delay?

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

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what is propagation delay?

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

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what is jitter?

the variation in the delay of received packets

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voice traffic is susceptible to what problem?

packet loss

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what protocol does voice traffic use?

RTP – real time protocol

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

data (web)

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

voice

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

video

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what are 4 common congestion queuing algorithms?

first in first out — FIFO
weighted fair queuing — WFQ
class based weighted fair queuing — CBWFQ
low latency queuing — LLQ

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

FIFO

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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,

WFQ

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

CBWFQ

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

LLQ

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what are the 3 QoS models?

best effort model (no qos)
integrated services (intserv)
differentiated services (diffserv)

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

Intserv

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

Diffserv

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

congestion avoidance tool

what type of tools are CBWFQ and LLC?

congestion management tools

what are the 3 categories of qos tools?

classification and marking, congestion avoidance, congestion management

Which QoS mechanism identifies and categorizes traffic?

classification and marking

which qos mechanism uses WRED?

congestion avoidance

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

traffic policing

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

traffic shaping

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

true

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

true

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

false

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

true

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

true

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

true

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

fifo

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

LLQ

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

5 (101)

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

0 (000)

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

4 (100)

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

EF (101110)

Which QoS model is also called "Hard QoS"?

intserv

Which QoS model provides many different levels of quality?

diffserv

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?

intserv

Which QoS model provides per-request policy admission control?

intserv

Which QoS model is also called "Soft QoS"?

diffserv

what is queuing delay?

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

Which option is used for marking 802.1Q frames?

class of service (CoS)

Which option is used for marking Layer 3 packets?

differentiated service code points (DSCP)

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

- type of service - traffic class

What statement describes the Class of Service field?

it is a layer 2 field