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220-1201 Practice Question: A technician is setting up a new VoIP phone system
A technician is setting up a new VoIP phone system. To ensure voice quality, they need to prioritize voice traffic over data traffic on the network. Which QoS configuration method should be implemented?
⚠ Common exam trap
A common misconception is that VLAN tagging alone provides QoS, but VLANs only segregate traffic; prioritization requires Layer 3 markings like DSCP or Layer 2 CoS values.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure DSCP markings on the VoIP traffic
DSCP (Differentiated Services Code Point) markings allow VoIP traffic to be classified and prioritized at Layer 3, ensuring low latency and jitter for voice packets. By marking VoIP packets with a specific DSCP value (e.g., EF for expedited forwarding), routers and switches can apply QoS policies to give voice traffic priority over data traffic. This is the standard method for QoS in VoIP deployments.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the VoIP phones to use a static IP address
Why it's wrong here
Setting VoIP phones to use a static IP address provides consistent network addressing for easier management and troubleshooting. However, assigning a static IP does not inherently instruct network devices to prioritize that specific traffic over other data. Quality of Service (QoS) mechanisms, such as DSCP or queuing policies, are required to differentiate and prioritize real-time VoIP traffic based on its performance requirements.
- ✓
Configure DSCP markings on the VoIP traffic
Why this is correct
Configuring Differentiated Services Code Point (DSCP) markings on VoIP traffic is the most effective method for ensuring voice quality. DSCP values, like Expedited Forwarding (EF), are written into the IP packet header, signaling to routers and switches along the network path that these packets require preferential treatment. This ensures low latency, minimal jitter, and reduced packet loss for real-time voice, which is crucial for a high-quality VoIP experience.
- ✗
Enable VLAN tagging on the switch ports
Why it's wrong here
Enabling VLAN tagging on switch ports logically segments network traffic into separate broadcast domains, enhancing security and network organization. While VLANs isolate traffic, they do not inherently provide a mechanism for prioritizing one VLAN's traffic over another's. To achieve prioritization within or across these segmented networks, additional QoS configurations, such as DSCP or Class of Service (CoS) markings, are still necessary.
- ✗
Use a crossover cable between the phone and switch
Why it's wrong here
A crossover cable is specifically designed to connect two similar network devices directly, such as two computers or two switches, by reversing the transmit and receive wire pairs. Modern network devices typically feature Auto-MDIX, which automatically detects and corrects cable types, making crossover cables largely obsolete for most connections. Crucially, the physical cabling type used has no bearing on how network devices prioritize traffic based on Quality of Service policies.
Go deeper
Related to this question
Learn chapter
Networking Hardware: Routers, Switches, APs
Key term
Session Initiation Protocol
Session Initiation Protocol (SIP) is a signaling protocol used to start, maintain, and end voice and video calls over IP networks.
Key term
Latency
Latency is the time delay between a request being sent over a network and the response being received, often measured in milliseconds.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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