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CCNP Core > Chap 14 - QOS (part 3) > Flashcards

Chap 14 - QOS (part 3) Flashcards

1
Q

What are the 4 AF classes?

A

AF1, AF2, AF3, AF4

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2
Q

Assured Forwarding which AF class has priority - AF1 or AF4

A

Neither, all AF classes are treated independently and should be placed in separate queues.

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3
Q

In Assured Forwarding how many Drop Priorities are there?

A

3 three drop probabilities: low, medium, and high.

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4
Q

What 5 adjectives can be used to describe what EF builds?

A

The EF PHB can be used to build

  • Low-loss
  • Low-latency
  • Low-jitter
  • Assured bandwidth
  • End-to-end service
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5
Q

What is the scavenger class, and what 3 types of traffic should fall into this category?

A
  • Provides less than best-effort services. It is for apps that:
    • have little or no contribution to the business objectives
    • are typically entertainment-related applications
    • are usually heavily rate limited or blocked entirely
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6
Q

What is the Class Selector marking for scavenger class?

A

CS1

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7
Q

When a PC is attached to a VOIP phone what does the phone do by default if the PC has marked its traffic?

A

By default it will clear the markings before sending it to the network

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8
Q

What CoS and DSCP markings does an IP Phone apply to its own voice traffic?

A

IP phones by default mark voice traffic with a CoS value of 5 and a DSCP value of 46 (EF),

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9
Q

Where are optimal trust boundaries?

A

At the IP phone or at the switch.

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10
Q

What are the 4 levels of QOS that a wireless controller can apply to wireless traffic?

A
  • Platinum
  • Gold
  • Silver
  • Bronze
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11
Q

When a wireless LAN is created what is the default QOS level?

A

Silver

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12
Q

On a wireless controller which QOS level should be assigned to phones?

A

Platinum

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13
Q

What are 2 traffic-conditioning mechanisms?

A
  • Traffic Policers
  • Shaping
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14
Q

What do Traffic Policers and Shapers do?

A

They classify traffic and enforce other QOS mechanisms such as rate-limiting

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15
Q

What do Policers do?

A

Drop or re-mark incoming or outgoing traffic that goes beyond a desired traffic rate.

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16
Q

What do Shapers do?

A

Buffer and delay egress traffic rates that momentarily peak above the desired rate until the egress traffic rate drops below the defined traffic rate.

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17
Q

What does a Shaper do if the egress traffic is below the desired rate?

A

Traffic is sent immediately

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18
Q

For incoming traffic where are Policers optimally placed?

A

At the edge of the network

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19
Q

For outgoing traffic where are Policers optimally placed?

A

At the edge of the network on core-facing interfaces

20
Q

Where are Shapers optimally placed?

A

Shapers are used for egress traffic and typically deployed by enterprise networks on service provider (SP)–facing interfaces.

21
Q

When is shaping useful?

A

Shaping is useful in cases where SPs:

  • are policing incoming traffic
  • have a maximum traffic rate SLA, which, if violated, could incur monetary penalties.
22
Q

What 2 actions can a Policer take ?

A
  • Drop the traffic
  • Re-mark the traffic with a lower priority
23
Q

If a Policer is marking down traffic what other steps should be taken?

A

Congestion-avoidance mechanisms, such as DSCP-based Weighted RED should be configured throughout the network to drop AFx3 more aggressively than AFx2 and drop AFx2 more aggressively than AFx1.

24
Q

What is Committed Information Rate (CIR)?

A

The policed traffic rate, in bits per second (bps), defined in the traffic contract.

25
Q

What is Committed Time Interval (Tc), and what is it measured as?

A

The time interval, in milliseconds (ms), over which the committed burst (Bc) is sent.

26
Q

What is Committed Burst (Bc), how is it measured, and what is it also known as?

A
  • The maximum amount of traffic that can be sent within a Tc.
  • Measured in bytes
  • aka the maximum size of the CIR token bucket
27
Q

What is a Token?

A

A single token represents 1 byte or 8 bits.

28
Q

What 3 actions can a traffic conditioning mechanism take if there aren’t enough tokens in the bucket?

A
  • Drop the traffic
  • Remark the traffic
  • Buffer the traffic
29
Q

Why is the Bc value recommended to be larger than or equal to the largest possible packet?

A

Otherwise, there will never be enough tokens in the token bucket for larger packets, and they will always exceed the defined rate.

30
Q

For a single-bucket algorithm what happens to the accumulating tokens if the Bucket is filled to capacity?

A

They are dropped.

31
Q

In a single token bucket algorithm what does conforming traffic mean?

A

When there are enough tokens in the bucket to send the traffic onto the network.

32
Q

What is the recommended range for interpacket delay for non-VOIP traffic?

A

8 msec to 125 msec

33
Q

What is the recommended range for interpacket delay for voice traffic?

A

8 msec to 10 msec

34
Q

What are 3 different policing algorithms?

A
  • Single-rate two-color marker/policer
  • Single-rate three-color marker/policer (srTCM)
  • Two-rate three-color marker/policer (trTCM)
35
Q

How many buckets does the Single-rate Two-color Marker/Policer have, what are the 2 colors, and what is done with packets?

A
  • Single token bucket
  • Traffic either Conforms to or Exceeds CIR
  • Dropping or Marking Down can be done in either state
36
Q

For Marker/Policers what are the 2 options for rate and 3 options for color?

A
  • Single rate means a single CIR
  • Two-rate means a CIR and a Peak Information Rate (PIR)
  • Three Color means green for conforming traffic, yellow for exceeding but transmitted and red is exceeding and dropped
37
Q

For the srTCM how is traffic classified, and what action can be taken?

A
  • Two token buckets
  • Traffic classified as conforming, exceeding, or violating the CIR
  • Dropping or marking down can be done in each of the 3 states
38
Q

For the Single-rate Three-color Marker/Policer (srTCM) where does the second bucket get its tokens and what are they used for?

A

During slow traffic times excess tokens drop to the second bucket and can be used for temporary bursts that exceed CIR

39
Q

In the Single-rate Three-color Marker/Policer (srTCM) what is the variable assigned to the tokens in the second bucket and what value is assigned to them?

A
  • Te
  • The number of tokens in the Be bucket
40
Q

What are the three colors and what do they mean?

A
  • Conforming or Green, traffic under the Bc
  • Exceed or Yellow, over Bc but under Be, can be dropped or marked down
  • Violate or Red, usually dropped but optionally could be marked down
41
Q

In the Single-rate Three-color Marker/Policer (srTCM) why do the exceeding and violating rates vary?

A

Because they rely on random tokens spilling over from the Bc bucket into the Be.

42
Q

What are 3 advantages of the Single-rate Three-color Marker/Policer (srTCM)?

A
  • Fewer TCP retransmissions
  • More efficient for bandwidth utilization
  • Perfect policer for the AF classes AFx1, AFx2, and AFx3
43
Q

On a wireless network what are the DSCP values and 802.1P values for each of the 4 levels of QOS?

A
  • Platinum - DSCP 46 (EF) (44) and cs5
  • Gold - DSCP AF41 (34) and cs4
  • Silver - DSCP 0 and cs0
  • Bronze - DSCP AF11 (10) and cs1
44
Q

Formula to calculate Tc

A

Tc = (Bc / CIR ) × 1000.

45
Q

Formula to calculate Bc

A

Bc = (Tc / 1000) x CIR

46
Q

What is the srTCM?

of buckets:
Name of buckets:
6 variables:
Recommended for:

A
  • # of buckets: 2
  • Name of buckets: Bc bucket, Be bucket
  • 6 variables
    • CIR - the policed rate
    • ​Bc - max size of the CIR token bucket in bytes
    • Be - Excess burst size, max size of the excess token bucket in bytes
    • Tc - number of tokens in the Bc bucket
    • Te - number of tokens in the Be bucket
    • B - incoming packet length in bits
  • Recommended for AF classes: AFx1, AFx2, and AFx3

CCNP Core (46 decks)

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