QoS Flashcards by Kuba Adamczyk

What does VoIP stand for?

Voice over IP

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When the switchport voice vlan command is applied to an interface, which traffic will be tagged? Traffic from the PC or from the IP phone?

Traffic from the IP phone
(traffic from the PC will be untagged as usual for an access port)

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Configure the voice VLAN:
SW1(config-if)# […]

switchport voice vlan vlan-number

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What does PoE stand for?

Power over Ethernet

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PoE: What does PSE stand for?

Power Sourcing Equipment

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PoE: What does PD stand for?

Powered Device

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Electronic devices use [AC/DC] power.

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PoE: […] can be configured to prevent a PD from taking too much power.

Power policing

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QoS: […] refers to the overall capacity of a link.

Bandwidth

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[…] delivery means there is no guarantee that data is delivered or that it meets any QoS standard.

Best effort

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What Layer 2 header field can be used for QoS markings?

PCP / CoS

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QoS: […] is the percentage of packets that do not reach their destination.

Loss

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QoS: […] is the amount of time it takes traffic to go from source to destination.

Delay (=one-way delay)
(Two-way delay measures both ways)

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What is considered acceptable one-way delay for interactive audio traffic?

150 ms or less

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QoS: […] is the variation in one-way delay between packets sent by the same application.

Jitter

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What Layer 3 header field can be used for QoS markings?

DSCP

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QoS: What does RED stand for?

Random Early Detection

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What is considered acceptable jitter for interactive audio traffic?

30 ms or less

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What is considered acceptable loss for interactive audio traffic?

1% or less

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Tail drop is harmful because it can lead to […].

TCP global synchronization

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QoS: By default, queued messages will be forward in a […] manner.

FIFO

When packets are dropped due to a full queue, it is called […].

tail drop

CoS/PCP 5 = […]

voice traffic

QoS: What features drop random packets when traffic queues pass a certain threshold?

RED / WRED

QoS: What does WRED stand for?

Weighted Random Early Detection

CoS/PCP [...] = best effort

CoS/PCP 4 = [...]

video traffic

CoS/PCP [...] = critical applications

CoS/PCP 0 = [...]

best effort

CoS/PCP 3 = [...]

critical applications

CoS/PCP [...] = video traffic

CoS/PCP [...] = voice traffic

DF = DSCP [...]

DSCP: What does DF stand for?

default forwarding

[...] = DSCP 0

EF = DSCP [...]

[...] = DSCP 46

RFC 4594 recommends the [...] marking for high priority data traffic.

AF2x (AF21, AF22, AF23)

AF value to DSCP value

AFXY = DSCP 8*X + 2*Y

CS value to DSCP value

CS value * 8

RFC 4594 recommends the [...] marking for best effort traffic.

RFC 4594 recommends the [...] marking for voice traffic.

RFC 4594 recommends the [...] marking for interactive video traffic.

AF4x (AF41, AF42, AF43)

RFC 4594 recommends the [...] marking for streaming video traffic.

AF3x (AF31, AF32, AF33)

If an IP phone is connected to a switchport, the QoS trust boundary should be at the [...].

IP phone

What does CBWFQ stand for?

Class-Based Weighted Fair Queuing

What QoS scheduling algorithm uses a weighted round-robin scheduler while guaranteeing a minimum bandwidth to each queue?

CBWFQ

What does LLQ stand for?

Low Latency Queuing

LLQ designates one or more queues as [...] queues.

strict priority

[...] buffers traffic in a queue if the traffic rate goes over the configured rate.

Shaping

[...] drops traffic in a queue if the traffic rate goes over the configured rate.

Policing

IP phones mark their call signaling traffic as PCP/CoS [...].