CLCOR Media And Qos Practice Test 2 — 15 Questions

Question 1

A collaboration engineer is deploying a new branch office with a Cisco Catalyst switch and a Cisco IOS router. The engineer wants to ensure that voice traffic is prioritized over data traffic during periods of congestion. The router's WAN interface is experiencing congestion, and the engineer has configured a low-latency queue (LLQ) for voice. However, voice quality is still poor. Which additional QoS mechanism should be configured on the router to prevent data traffic from starving the voice queue?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Configure class-based weighted fair queueing (CBWFQ) for data classes and ensure the priority queue is properly defined.. The correct answer is to configure CBWFQ for data classes and ensure the priority queue is properly defined. In a congested WAN, LLQ gives strict priority to voice, but without proper bandwidth guarantees for other classes, the priority queue may be starved if the policer is absent or misconfigured. CBWFQ ensures that each class gets its guaranteed bandwidth, and the priority queue is serviced first. This combination maintains voice quality while preventing data starvation.

Answer

Configure Weighted Random Early Detection (WRED) on the voice class.

Answer

Configure Low Latency Queueing (LLQ) with a strict priority and no policer.

Answer

Configure a priority queue with a policer to limit voice bandwidth.

Question 2

A collaboration engineer is deploying a new branch office with a Cisco Catalyst switch and a Cisco IOS router. The engineer wants to ensure that voice traffic is prioritized over data traffic during periods of congestion. The router's WAN interface is experiencing congestion, and the engineer has configured a low-latency queue (LLQ) for voice. However, voice quality is still poor. Which additional QoS mechanism should be configured on the router to prevent data traffic from starving the voice queue?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

TCP 7001 for both signaling and multiplexed media traversal. The Expressway traversal zone carries signaling and media between the internal Expressway-C and the external Expressway-E over the Assent protocol on TCP 7001. Because both call signaling and media are multiplexed on that single TCP connection, the DMZ firewall only needs a narrow rule permitting TCP 7001, which is exactly the predictable and easily managed transport the scenario requires.

Answer

TCP 443 for signaling and UDP 8443 for media traversal

Answer

UDP 5060 for signaling and a wide UDP port range for media

Answer

TCP 5061 for signaling and UDP 3478 for media traversal

Question 3

A collaboration engineer is configuring a Cisco IOS XE WAN edge router to support a site with both voice and video endpoints. The carrier provides a 50-Mbps WAN circuit and has agreed to honor DSCP markings. The engineer must ensure that during congestion, video conferencing traffic receives at least 20% of the link bandwidth while still allowing for burst up to 15 Mbps. Which QoS mechanism best meets these requirements?

Accepted Answer

Class-Based Weighted Fair Queueing (CBWFQ) with a bandwidth guarantee of 10000 kbps and a shape average of 15000 kbps with burst up to 15000 kbps. The correct answer combines a bandwidth guarantee to ensure a minimum of 20% of the link (10 Mbps) and a shaper to cap the maximum rate at 15 Mbps while allowing bursts. This provides the required minimum bandwidth and allows the video traffic to use additional bandwidth up to 15 Mbps when available, without starving other classes. CBWFQ without shaping would not allow bursting above the guaranteed rate, and LLQ would not provide a minimum guarantee.

Answer

Low Latency Queueing (LLQ) with a priority level of 10000 kbps for video

Answer

Class-Based Weighted Fair Queueing (CBWFQ) with a bandwidth guarantee of 10000 kbps and a burst size of 15000 bytes

Answer

Class-Based Weighted Fair Queueing (CBWFQ) with a bandwidth guarantee of 10000 kbps and a shape average of 15000 kbps

Question 4

A network engineer is deploying a new branch office with a Cisco IOS XE router. The WAN provider does not honor DSCP markings, so the engineer must re-mark all inbound traffic at the WAN edge. The provider offers a single class of service and marks all traffic with DSCP 0. The engineer needs to ensure that voice signaling (SCCP) is marked as CS3 and voice media (RTP) is marked as EF. Which QoS configuration on the router achieves this?

Accepted Answer

A policy-map that matches on ACLs identifying SCCP and RTP, sets DSCP CS3 and EF respectively, and is applied inbound on the WAN interface. The correct configuration uses ACLs to identify voice signaling and media, sets the appropriate DSCP values, and applies the policy inbound on the WAN interface. This ensures that traffic from the provider, which is marked DSCP 0, is re-marked before being forwarded to the LAN. Matching on DSCP 0 would not differentiate traffic types, and applying the policy on the LAN interface or outbound would not re-mark inbound WAN traffic.

Answer

A policy-map that matches on DSCP 0 and sets all traffic to EF, applied outbound on the WAN interface

Answer

A policy-map that matches on IP precedence and sets DSCP CS3 for signaling and EF for media, applied inbound on the LAN interface

Answer

A policy-map that matches on NBAR for SCCP and RTP, sets DSCP CS3 and EF respectively, and is applied outbound on the LAN interface

Question 5

A network administrator is deploying QoS for a Cisco Collaboration solution across a WAN. The administrator needs to ensure that voice signaling traffic (SIP) is marked with the appropriate DSCP value. According to Cisco best practices, which DSCP value should be used for voice signaling?

Accepted Answer

CS3 (24). Cisco best practices dictate that voice signaling traffic, such as SIP and H.323, should be marked with DSCP CS3 (24). This marking ensures that signaling receives appropriate treatment in the QoS policy, typically placed in the AF31 class, which provides a guaranteed bandwidth and low drop probability. This is distinct from voice media, which uses EF (46). Using CS3 helps maintain call setup and teardown performance without competing with voice media for strict priority queuing.

Answer

EF (46)

Answer

CS4 (32)

Answer

AF41 (34)

Question 6

A collaboration engineer is troubleshooting poor voice quality on a Cisco Collaboration deployment. The engineer suspects that the QoS configuration on the WAN router is not correctly prioritizing voice traffic. Which two actions should the engineer take to verify that voice traffic is being marked and queued correctly? (Choose two.)

Accepted Answer

Capture traffic with an inline packet analyzer and inspect the DSCP field in the IP header of voice packets.. To verify QoS marking and queuing for voice traffic, the engineer should use show policy-map interface to see classification and marking statistics, and also capture packets to inspect DSCP values in the IP header. These two methods together confirm that voice traffic is marked correctly and is being placed in the appropriate queue. Other commands either do not show DSCP or are not valid for this purpose.

Answer

Check the output of show interface for queue drops and compare with voice call quality reports.

Answer

Run the show call active voice compact command to view the DSCP markings on active voice calls.

Answer

Use the debug policy-map command to see real-time classification and marking decisions.

Question 7

You are implementing a QoS policy on a WAN edge router. You have a requirement to prioritize video traffic. Which queueing mechanism is recommended by Cisco to minimize jitter and latency for video streams?

Accepted Answer

Low Latency Queuing (LLQ). Low Latency Queuing (LLQ) is the Cisco-recommended mechanism because it combines a strict priority queue for delay-sensitive traffic (voice/video) with CBWFQ for all other classes, ensuring voice gets absolute priority while preventing starvation of other traffic. This minimizes jitter and latency for real-time streams.

Answer

Weighted Fair Queuing (WFQ)

Answer

Priority Queuing (PQ) only

Answer

Random Early Detection (RED)

Question 8

A network administrator is troubleshooting one-way audio issues between a Cisco IP Phone and a Cisco TelePresence endpoint. The path traverses a router with a configured class-map. Which command would you use to verify the packet markings on the ingress interface?

Accepted Answer

show policy-map interface. The command `show policy-map interface` displays the actual packet markings and QoS statistics applied to an interface by a policy-map. Since the class-map is referenced within a policy-map, this command shows the number of packets matching each class and the marking actions (e.g., DSCP, CoS) that were applied. This is the only option that directly verifies the markings on the ingress interface.

Answer

show class-map configuration

Answer

show ip rtp statistics

Answer

show qos interface

Question 9

What is the default behavior for DSCP markings on traffic originating from a Cisco IP Phone that has not been configured with specific QoS policies?

Accepted Answer

Marked as DSCP 46 for voice and CS3 for signaling. Cisco IP Phones ship with a built-in QoS trust behavior: voice media (RTP) is marked DSCP 46 (EF) and call signaling (SCCP/SIP) is marked CS3 (DSCP 24) by default, even before any switch or CUCM QoS policy is applied. This allows the phone to self-mark its traffic so the upstream switch can trust it via 'mls qos trust device cisco-phone' or 'trust dscp'. The phone only re-marks if a CUCM softphone/phone security profile or a switch policy overrides it.

Answer

Marked as DSCP 34 (AF41)

Answer

Traffic is not marked until a policy-map is applied

Answer

Marked as DSCP 0 (Best Effort)

Question 10

You are configuring QoS for a Cisco Unified Communications Manager (CUCM) deployment. You need to ensure that audio media traffic between endpoints is marked correctly. Which DSCP value should be assigned to RTP audio traffic according to the Cisco SRND best practices?

Accepted Answer

DSCP 46 (EF). Cisco SRND best practices mark voice RTP media with DSCP EF (46), which maps to the Expedited Forwarding per-hop behavior defined in RFC 3246. EF provides low latency, low jitter, and low loss — exactly what voice media requires. Call signaling is marked CS3 (24), and video is typically AF41 (34), so EF is reserved for audio.

Answer

DSCP 34 (AF41)

Answer

DSCP 24 (CS3)

Answer

DSCP 0 (BE)

Question 11

Which DSCP value is recommended for Call Signaling traffic in a Cisco Unified Communications network?

Accepted Answer

CS3 (24). Cisco recommends DSCP CS3 (24) for call signaling traffic in a Unified Communications network, which includes SCCP, SIP, and H.323 signaling between endpoints and call control. CS3 provides a distinct per-hop behavior from voice bearer traffic, which uses EF (46). This separation lets QoS policies prioritize voice media above signaling while still protecting signaling from best-effort traffic.

Answer

AF31 (26)

Answer

EF (46)

Answer

AF41 (34)

Question 12

When using 'RSVP' for Call Admission Control (CAC), what happens if the available bandwidth on the path is less than the requested amount?

Accepted Answer

The call is blocked. With RSVP-based Call Admission Control, when a call's RSVP PATH/RESV signaling requests more bandwidth than is available on any link along the path, the router rejects the reservation and the call is blocked (denied). RSVP CAC is a deterministic admission control mechanism: if the requested bandwidth cannot be reserved, the call setup fails rather than proceeding with degraded quality. This ensures that admitted calls receive their guaranteed quality of service.

Answer

The call is placed but with a lower quality codec

Answer

The call is put on hold until bandwidth is available

Answer

The call proceeds, but marks the packets with Best Effort

Question 13

An administrator needs to enforce a bandwidth limit for video calls at a specific site in CUCM. Which configuration object should be used?

Accepted Answer

Location. In Cisco Unified CM, the Location object is the configuration element that enforces call admission control (CAC) by defining the maximum audio and video bandwidth available between locations. When a video call is placed, CUCM subtracts the call's bandwidth from the Location's video bandwidth pool, and if the limit is exceeded, the call is denied or rerouted. This makes Location the correct object for enforcing a per-site bandwidth limit for video calls.

Answer

Region

Answer

Partition

Answer

Device Pool

Question 14

In a multi-site deployment, you have a requirement to transcode between G.711 and G.729. If the transcoder resources are exhausted, what is the expected outcome for a new call requiring this conversion?

Accepted Answer

The call will be rejected. When transcoder resources are exhausted, Cisco Unified Communications Manager (CUCM) cannot allocate the necessary DSP resources to convert between G.711 and G.729 codecs. Without a transcoder, the two endpoints cannot negotiate a common codec, so the call is rejected with a cause code indicating resource unavailability (typically 'No Bandwidth' or 'Unavailable').

Answer

The call will use G.711 regardless

Answer

The call will proceed with no audio

Answer

The call will fall back to an MTP

Question 15

You are configuring a Cisco IOS router to perform traffic shaping for voice traffic. Why is traffic shaping often used in conjunction with queuing?

Accepted Answer

To prevent interface congestion by smoothing out traffic bursts. Traffic shaping is used with queuing to prevent interface congestion by smoothing out traffic bursts — it buffers excess traffic and releases it at a configured rate (e.g., the CIR), ensuring the interface does not exceed the contracted bandwidth. Queuing then schedules the shaped traffic according to class priorities, so shaping and queuing work together to manage congestion and protect voice quality.

Answer

To prioritize voice over data traffic

Answer

To reduce the CPU utilization of the router

Answer

To increase the total throughput of the interface