The answer is to add a police command under the VOICE class to limit voice traffic to 5% and shape the priority queue. This reduces jitter because, without explicit policing, the priority percent 10 command allows the priority queue to consume up to 10% of link bandwidth, even though actual voice traffic is only 5%. During peak hours, microbursts from other traffic can cause the priority queue to be serviced erratically, introducing delay variation—this is the core reason voice jitter occurs: priority queue without police. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of DiffServ QoS and the critical difference between priority percent and explicit policing; a common trap is assuming that low average utilization (40%) means no congestion, but jitter stems from microbursts, not sustained load. Remember the tip: “Police the priority to match the voice rate—otherwise, the queue becomes a jitter generator.”
350-501 Automation and Quality of Service Practice Question
This 350-501 practice question tests your understanding of automation and quality of service. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service provider has deployed a new MPLS L3VPN service for a customer with multiple sites. The customer reports intermittent voice quality issues during peak hours. The provider uses a DiffServ QoS model with MPLS EXP markings. The PE routers apply the following policy on the customer-facing interfaces:
policy-map CUSTOMER-OUT
class VOICE
priority percent 10
set mpls experimental topmost 5
class VIDEO
bandwidth remaining percent 30
set mpls experimental topmost 4
class DATA
bandwidth remaining percent 70
set mpls experimental topmost 0
The core network has a simple policy that maps EXP 5 to PQ, EXP 4 to a low-latency queue, and EXP 0 to best effort. The provider monitors the network and finds that the PE-CE interfaces are not congested (average utilization is 40%), but the voice packets are experiencing jitter. The customer's voice traffic is about 5% of the link capacity. Which action is most likely to reduce the jitter?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a police command under the VOICE class to limit voice traffic to 5% and shape the priority queue.
The voice traffic is only 5% of link capacity, but the priority percent 10 command allows up to 10% of the link to be treated as priority. During peak hours, if other traffic (e.g., video or data) bursts and exceeds the remaining bandwidth, the priority queue can still be policed implicitly by the scheduler, but jitter arises because the priority queue is not rate-limited. Adding a police command under the VOICE class to limit voice to 5% and shaping the priority queue ensures that voice traffic does not exceed its actual rate, preventing microbursts that cause jitter in the priority queue.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Add a police command under the VOICE class to limit voice traffic to 5% and shape the priority queue.
Why this is correct
Policing and shaping the priority queue prevents bursts and reduces jitter.
Clue confirmation
The clue words "best", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure the core routers to map EXP 5 to a low latency queue instead of PQ.
Why it's wrong here
Low latency queue is for video; voice should remain in PQ; the issue is at the PE-CE, not core.
✗
Increase the priority percent to 20 for voice traffic.
Why it's wrong here
Increasing priority does not solve jitter; it might allow voice to consume more bandwidth but does not shape it.
✗
Change the set mpls experimental topmost to set ip dscp ef for voice.
Why it's wrong here
DSCP marking is not used in the MPLS core; it does not help jitter.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply increasing priority percentage or changing marking will solve jitter, when the real issue is the lack of explicit policing on the priority queue to match the actual traffic rate.
Detailed technical explanation
How to think about this question
In Cisco IOS, the priority command under a class in a policy-map implicitly polices the traffic to the configured bandwidth percentage, but only if a police command is not explicitly configured. Without explicit policing, the priority queue can experience tail drops or jitter if microbursts exceed the configured percentage, because the scheduler still enforces a rate limit. Shaping the priority queue with a police command ensures that voice traffic is rate-limited to its actual bandwidth (e.g., 5%), preventing oversubscription and reducing jitter even during peak hours.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Automation and Quality of Service — This question tests Automation and Quality of Service — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add a police command under the VOICE class to limit voice traffic to 5% and shape the priority queue. — The voice traffic is only 5% of link capacity, but the priority percent 10 command allows up to 10% of the link to be treated as priority. During peak hours, if other traffic (e.g., video or data) bursts and exceeds the remaining bandwidth, the priority queue can still be policed implicitly by the scheduler, but jitter arises because the priority queue is not rate-limited. Adding a police command under the VOICE class to limit voice to 5% and shaping the priority queue ensures that voice traffic does not exceed its actual rate, preventing microbursts that cause jitter in the priority queue.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best", "most likely". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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