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CCNP Core > Chap 14 - QOS (part 1) > Flashcards

Chap 14 - QOS (part 1) Flashcards

1
Q

What are the 4 primary goals for implementing QOS?

A
  • Expediting delivery for real-time applications
  • Ensuring business continuance for business-critical applications
  • Providing fairness for non-business-critical applications when congestion occurs
  • Establishing a trust boundary across the network edge to either accept or reject traffic markings injected by endpoints
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2
Q

What are the 3 tools QOS uses to achieve it goals?

A
  • Classification and marking
  • Policing and Shaping
  • Congestion management and avoidance
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3
Q

What are the 3 leading causes of quality issues?

A
  • Lack of bandwidth
  • Latency and jitter
  • Packet loss
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4
Q

What are the 2 categories that network latency can be broken down into?

A
  • Fixed latency
  • Variable latency
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5
Q

What are the 3 Fixed latency causes?

A
  • Propogation delay
  • Serialization delay
  • Processing delay
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6
Q

What is the 1 Variable latency cause?

A

Delay variation

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7
Q

What is Propogation Delay?

A

Propagation delay is the time it takes for a packet to travel from the source to a destination at the speed of light over a medium such as fiber-optic cables or copper wires.

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8
Q

What is the Refractive Index and which is worse, higher or lower?

A
  • The ratio arrived at by the lack of vacuum conditions in a fiber-optic cable or a copper wire that slows down the speed of light
  • The larger this value is the slower light travels
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9
Q

What is the speed of light?

A

299 Million meters per second

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10
Q

What is the formula for calculating speed of light through a medium?

A
  • speed of light in a vacuum divided by the refractive index
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11
Q

What is the refractive index value of optical fiber?

A

1.5

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12
Q

What is the speed of light through a fiber cable with a refractive index of 1.5?

A

200,000,000 meters per second

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13
Q

What are 2 unknown variables to take into account when calculating average latency of a fiber circuit?

A
  • Fiber does not always take the shortest path to the destination
  • Components required for fiber optic cable (repeaters and amplifiers) may introduce additional delay
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14
Q

What is the ITU recommendation for the maximum amount of delay regardless of application type?

A

Should not exceed 400 ms

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15
Q

What is the ITU recommendation for real time traffic?

A

Should not exceed 150 ms

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16
Q

What is serialization delay?

A

the time it takes to place all the bits of a packet onto a link.

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17
Q

What is the formula for calculating serialization delay?

A

packet size in bits / line speed in bits per second

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18
Q

What is processing delay?

A

The fixed amount of time it takes for a networking device to take the packet from an input interface and place the packet onto the output queue of the output interface.

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19
Q

What 5 factors affect processing delay?

A
  • CPU speed
  • CPU Utilization
  • IP Packet switching mode (process switching, software CEF, hardware CEF)
  • Router architecture (centralized or distributed)
  • Configured features on both input and output interfaces
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20
Q

What is delay variation?

A

The difference in the latency between packets in a single flow, aka jitter

21
Q

What are 3 major factors that can help or hurt variable delay?

A
  • Queuing delay
  • Dejitter buffers
  • Variable packet sizes
22
Q

When causes jitter (Variable delay) ?

A

Caused by queueing delay experienced by packets during periods of network congestion.

23
Q

As it is being experienced what 3 things does Queuing Delay depend on?

A
  • The number and sizes of packets already in the queue
  • Link speed
  • Queuing mechanism.
24
Q

Where are de-jitter buffers typically located?

A

On voice and video endpoints

25
Q

What are de-jitter buffers?

A

Dynamic buffers on a voice or video endpoint that can mitigate jitter up to around 30 ms.

26
Q

What happens if a packet doesn’t arrive in a de-jitter buffer in the 30 ms window?

A

It gets dropped.

27
Q

What can be done to prevent jitter?

A

Use queuing mechanisms such as low-latency queueing (LLQ) that allow matching packets to be forwarded prior to any other low priority traffic during periods of network congestion.

28
Q

When does packet loss occur?

A

Usually as a result of congestion on an interface.

29
Q

What 4 things can be done to prevent Packet Loss?

A
  • Increase bandwidth
  • Implement QoS congestion-avoidance and congestion-management mechanism.
  • Implement traffic policing to drop low-priority packets and allow high-priority traffic through.
  • Implement traffic shaping to delay packets instead of dropping them
30
Q

Should Traffic Shaping be used on real-time applications?

A

No, because it relies on queuing that can cause jitter.

31
Q

What can be used to mitigate micro-bursts?

A

Use Microsecond or Low-burst shaping

32
Q

What are the 3 QOS Implementation Models?

A
  • Best effort
  • Integrated Services (IntServ)
  • Differentiated Services (DiffServ)
33
Q

What is IntServ?

A
  • Integrated Services
  • Applications signal the network to make a bandwidth reservation and to indicate that they require special QoS treatment.
34
Q

What is DiffServ short for and how does it work?

A
  • Differentiated Services
  • The network identifies classes that require special QoS treatment.
35
Q

What 2 things does IntServ do?

A
  • It uses Resource Reservation Protocol (RSVP) to reserve resources throughout a network for a specific application
  • Provides call admission control (CAC) to guarantee that no other IP traffic can use the reserved bandwidth.
36
Q

With IntServ what happens to bandwith that had been reserved but wasn’t used?

A

It is wasted

37
Q

What is the biggest drawback when using IntServ?

A

All nodes, including the endpoints running the applications, need to support, build, and maintain RSVP path state for every single flow.

38
Q

What was IntServ created for?

A

For real-time applications such as voice and video that require bandwidth, delay, and packet-loss guarantees to ensure both predictable and guaranteed service levels.

39
Q

What was DiffServ designed to do?

A

To address the limitations of the best-effort and IntServ models.

40
Q

Is DiffServ considered an end-to-end solution?

A

No, solution because end-to-end QoS guarantees cannot be enforced.

41
Q

What are 2 differences between DiffServ as compared to IntServ?

A
  • There is no need for a signaling protocol
  • DiffServ is more scalable because there is no RSVP flow state to maintain on every single node.
42
Q

What QOS model is the most popular and widely deployed?

A

DiffServ

43
Q

What is packet classification?

A

It is a QoS mechanism responsible for distinguishing between different traffic streams. It uses traffic descriptors to categorize an IP packet within a specific class.

44
Q

Where should packet classification be done?

A

At the network edge, as close to the source of the traffic as possible.

45
Q

What are the 7 traffic descriptors typically used for Classification?

A
  • Internal: QoS groups (locally significant to a router)
  • Layer 1: Physical interface, subinterface, or port
  • Layer 2: MAC address and 802.1Q/p Class of Service (CoS) bits
  • Layer 2.5: MPLS Experimental (EXP) bits
  • Layer 3: Differentiated Services Code Points (DSCP), IP Precedence (IPP), and source/destination IP address
  • Layer 4: TCP or UDP ports
  • Layer 7: Next Generation Network-Based Application Recognition (NBAR2)
46
Q

What are the 4 most frequently used Traffic Descriptors?

A

Layer 2, Layer 3, Layer 4, and Layer 7 traffic descriptors

47
Q

What is NBAR2, what does it do, what does it use to do it, and what does it include?

A
  • A deep packet inspection engine
  • That can classify and identify a wide variety of protocols and applications
  • It uses Layer 3 to Layer 7 data
  • This includes applications that dynamically assign TCP or UDP port numbers.
48
Q

What are NBAR2’s two modes of operation?

A
  • Protocol Discovery
  • Modular QOS CLI (MQC)

CCNP Core (46 decks)

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