Free Nokia Quality of Service Practice Questions

Sample Practice Questions

Try these 10 sample questions from the Nokia Quality of Service practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1A real-time monitoring interval expects 1,000 packets and records 20 lost packets. What is the packet loss fraction for the interval?

   1. A.2%Correct answer: A
   2. B.0.2%
   3. C.5%
   4. D.20%

   Explanation: RFC 4712 defines the metric as "the number of packets lost divided by the number of packets expected." The fraction is 20/1,000, or 2%.

   Reference: RFC 4712: Transport Mappings for Real-time Application Quality-of-Service Monitoring — Section 2.1.2, Packet Loss in Fraction (page 14)

2. 2How many bits are in an IP differentiated services codepoint (DSCP)?

   1. A.2 bits
   2. B.3 bits
   3. C.8 bits
   4. D.6 bitsCorrect answer: D

   Explanation: RFC 2474 states that "the DSCP field is six bits wide." The two remaining bits belong to the rest of the DS field, while three and eight refer to different field sizes.

   Reference: RFC 2474: Definition of the Differentiated Services Field — Section 3, DS Field Definition

3. 3In Nokia's policer token-bucket model, what do the tokens represent?

   1. A.Bits in the passing packets
   2. B.Packets passing through the policer
   3. C.Bytes of available queue buffer
   4. D.Bytes in the passing packetsCorrect answer: D

   Explanation: Nokia models the bucket using "tokens which represent the bytes in the packets passing through the policer." It is byte accounting for traffic, not bits, packet counts, or available queue buffers.

   Reference: SR OS Advanced Configuration Guide: Class Fair Hierarchical Policing for SAPs — Overview / Policers

4. 4Three queues have PIRs of 80, 50, and 30 Mb/s and share a parent scheduler capped at 120 Mb/s. What is the maximum aggregate rate permitted by the parent?

   1. A.120 Mb/sCorrect answer: A
   2. B.160 Mb/s
   3. C.80 Mb/s
   4. D.50 Mb/s

   Explanation: Nokia states "A scheduler can enforce a maximum rate of operation for all child policers, queues, and associated schedulers." The child PIRs total 160 Mb/s, but the parent limits their aggregate to 120 Mb/s.

   Reference: SR OS Quality of Service Guide: QoS policies — Hierarchical scheduler policies / Hierarchical virtual schedulers

5. 5In an SR OS network QoS policy, which internal attributes determine the egress marking?

   1. A.The forwarding class and enqueuing priority
   2. B.The forwarding class and profile stateCorrect answer: B
   3. C.The queue ID and packet's incoming DSCP
   4. D.The scheduling priority and configured queue PIR

   Explanation: The guide states "The egress of the network QoS policy also defines the marking based on the forwarding class and the profile state." It is not based on the queue's description.

   Reference: SR OS Quality of Service Guide: Network QoS policies — Network QoS policies overview

6. 6What is a purpose of service differentiation on a shared network?

   1. A.Apply a single treatment despite different application requirements
   2. B.Provide different treatments for applications with different requirementsCorrect answer: B
   3. C.Dedicate a separate physical network to each individual flow
   4. D.Maintain an individual reservation for every flow at every core node

   Explanation: RFC 2475 says service differentiation is desired to "accommodate heterogeneous application requirements and user expectations". DiffServ can differentiate aggregates on shared infrastructure without requiring separate physical networks or per-flow core state.

   Reference: RFC 2475: An Architecture for Differentiated Services — Section 1.1, Overview

7. 7Where are the DSCP bits used for SR OS IP egress reclassification found in an IPv6 packet?

   1. A.The IPv6 Traffic Class fieldCorrect answer: A
   2. B.The IPv6 Flow Label field
   3. C.The IPv6 Hop Limit field
   4. D.The IPv6 Next Header field

   Explanation: The Nokia network QoS guide identifies "the Traffic Class field from the IPv6 header" as the source of DSCP bits for reclassification. The flow label, hop limit and next header fields are different IPv6 header fields.

   Reference: SR OS Quality of Service Guide: Network QoS policies — Network egress / Egress packet reclassification based on IP precedence DSCP

8. 8In Nokia's policer bucket model, the burst threshold is 2,400 bytes and the current level is 2,000 bytes when a 900-byte packet arrives. What is the packet's result and new bucket level?

   1. A.Conforming; the new level is 2,900 bytesCorrect answer: A
   2. B.Nonconforming; the new level remains 2,000 bytes
   3. C.Conforming; the new level is capped at 2,400 bytes
   4. D.Conforming; the new level remains 2,000 bytes

   Explanation: Nokia states: "If tokens for a packet arrive in the bucket when the current burst level of tokens is below the maximum burst threshold then the packet is considered to be conforming and all of its tokens are accepted into the bucket." The level is 2,000, below 2,400, so the packet conforms and 900 tokens are added, giving 2,900.

   Reference: SR OS Advanced Configuration Guide: Class Fair Hierarchical Policing for SAPs — Overview / Policers

9. 9In an SR OS hierarchical scheduler policy, which relationship can be configured between virtual schedulers?

   1. A.A queue schedules its parent virtual scheduler
   2. B.A policer schedules its parent virtual scheduler
   3. C.A forwarding class schedules its parent virtual scheduler
   4. D.A superior scheduler schedules a child virtual schedulerCorrect answer: D

   Explanation: Nokia describes a hierarchy "where policers, queues, or other schedulers are scheduled by superior schedulers." A scheduler can therefore be a child of a superior scheduler.

   Reference: SR OS Quality of Service Guide: QoS policies — Hierarchical scheduler policies

10. 10What role does egress remarking serve in the Nokia QoS architecture?

    1. A.Reserve bandwidth at each downstream hop using signaling
    2. B.Classify packets into a local ingress forwarding class
    3. C.Convey treatment information for downstream handlingCorrect answer: C
    4. D.Measure the customer's service-level agreement at the boundary

    Explanation: Nokia states that "a remarking action can be taken to guarantee the next downstream device will properly handle the different types of traffic." Consistent downstream interpretation remains dependent on the actual network configuration.

    Reference: SR OS Advanced Configuration Guide: QoS Architecture and Basic Operation — QoS Components