CLCOR Media And Qos — 30 Questions

Question 1

Which command allows an administrator to view the current status of registered media resources, such as transcoders, on a Cisco IOS gateway?

Accepted Answer

show sccp. The `show sccp` command on a Cisco IOS gateway displays the status of SCCP (Skinny Client Control Protocol) clients, which includes registered media resources such as transcoders, conference bridges, and MTPs. These resources register with the gateway's SCCP application, and the output lists their state (e.g., active, idle) and capabilities. This is the correct command to verify that transcoders are registered and available for use.

Answer

show dial-peer voice

Answer

show media resources

Answer

show voice gateway status

Question 2

In a Cisco Collaboration environment, what is the purpose of the 'Media Termination Point' (MTP) in relation to call signaling?

Accepted Answer

To provide DTMF interworking between endpoints.. The Media Termination Point (MTP) in Cisco Collaboration is specifically designed to provide DTMF interworking between endpoints that use different DTMF transport methods (e.g., inband vs. out-of-band). It can also be used for supplementary services like call hold, but its primary purpose in the context of call signaling is to ensure DTMF digits are correctly relayed. Unlike transcoders, MTPs do not change the codec; they only manipulate the media stream for DTMF and other signaling events.

Answer

To limit the bandwidth consumed by a call.

Answer

To provide codec transcoding services.

Answer

To cache video streams for faster playback.

Question 3

You are configuring a Media Resource Group List (MRGL) in CUCM to allow for transcoding. A call is placed between two endpoints where one supports G.711 and the other only supports G.729. If the MRGL contains a Transcoder, what must be configured to ensure the call succeeds?

Accepted Answer

Configure a Transcoder profile on the IOS gateway and assign it to the device pool's MRGL.. To make a G.711-to-G.729 call succeed, you must configure a transcoder on the IOS gateway and associate it with the device pool's Media Resource Group List so CUCM can allocate it for the call. The transcoder performs the actual codec conversion between the two endpoints. Simply enabling a service parameter or setting a region codec does not provision the hardware resource.

Answer

Set the Region codec to 'G.711 to G.729' explicitly.

Answer

Enable 'Allow Transcoding' in the Service Parameters.

Answer

Configure the IOS gateway as a Media Termination Point (MTP) only.

Question 4

You are configuring a Cisco IOS router to perform QoS marking for voice traffic originating from a local PBX. You need to ensure that the voice traffic is marked as DSCP EF. Which configuration command correctly applies this in a policy-map?

Accepted Answer

set dscp 46. The 'set dscp ef' command within a policy-map class is the correct method for modifying the DSCP value of a matching traffic class.

Answer

set ip dscp ef

Answer

mark dscp 46

Answer

set dscp voice

Question 5

You are troubleshooting a scenario where video quality is degrading during periods of high data utilization. You identify that video traffic is being dropped in the network. What is the most likely cause if you are using CBWFQ?

Accepted Answer

Video is not being correctly classified into the priority queue. In CBWFQ, video traffic is placed into a class-based queue, not the priority queue (LLQ). If video is not correctly classified into the priority queue (or a dedicated low-latency queue), it competes with other traffic and can be dropped during congestion. CBWFQ provides fair queuing among classes but does not guarantee low latency unless LLQ is configured. The most likely cause is misclassification or absence of a priority queue for video.

Answer

The voice traffic is taking up all bandwidth

Answer

The router's CPU is overloaded

Answer

The interface is configured for full-duplex

Question 6

You are configuring a Cisco gateway to handle voice traffic. You need to ensure that the gateway trusts DSCP markings from the incoming IP phone. Which command is used on the interface?

Accepted Answer

qos trust dscp. The 'qos trust dscp' command on the interface configures the switch to trust the DSCP values received from the connected device.

Answer

priority trust dscp

Answer

trust dscp

Answer

mls qos trust dscp

Question 7

Which parameter in the CUCM 'Service Parameters' section controls the default region bandwidth for audio calls?

Accepted Answer

Region configuration. CUCM doesn't use a single service parameter for this; instead, it uses the Region configuration to define bandwidth between locations.

Answer

Audio Bandwidth Parameter

Answer

Maximum Audio Bitrate

Answer

System-wide QoS policy

Question 8

When configuring a policy-map for voice traffic, which command is used to assign a specific bandwidth guarantee to a class?

Accepted Answer

bandwidth [kbps]. The command 'bandwidth [kbps]' is used in a policy-map class to assign a specific bandwidth guarantee to that class. It reserves a minimum amount of bandwidth for the class, ensuring that voice traffic gets the required capacity. This is a standard QoS configuration in Cisco IOS.

Answer

rate-limit [kbps]

Answer

guarantee [kbps]

Answer

priority bandwidth

Question 9

Which TWO of the following are key components of the Cisco QoS model for Voice?

Accepted Answer

Classification and Marking. Classification and Marking (A) is a foundational component of the Cisco QoS model for Voice because voice traffic must first be identified (e.g., via NBAR, ACLs, or DSCP/CoS matching) and tagged with the appropriate per-hop behavior such as EF (DSCP 46) so downstream devices can treat it with the required priority. Low Latency Queuing (B) is also a key component, as LLQ provides a strict-priority queue with a configured bandwidth guarantee (e.g., 'priority percent 30' or 'priority 512') that bounds jitter and latency for voice RTP streams while still allowing other classes to be serviced. Best effort queuing (C) is not part of the voice QoS model because it offers no differentiation or delay guarantees, which is unsuitable for voice. Strict Priority Queuing without bandwidth limits (D) is incorrect because an unbounded PQ queue can starve all other traffic; LLQ was specifically created to add a policed bandwidth cap to strict priority for voice. Weighted Random Early Detection (E) is a congestion-avoidance mechanism typically applied to TCP-based data classes, not a core component of the voice QoS model, since voice uses UDP and requires priority queuing rather than drop-based congestion avoidance.

Answer

Best effort queuing

Answer

Strict Priority Queuing (PQ) without bandwidth limits

Answer

Weighted Random Early Detection (WRED)

Question 10

Which TWO of the following are true regarding Cisco Unified Communications Manager (CUCM) Locations?

Accepted Answer

They manage both audio and video bandwidth. Locations manage bandwidth for both audio and video, and they operate independently of regions.

Answer

They are optional for all deployments

Answer

They are used to define codec preferences

Answer

They define the gatekeeper address

Question 11

Which TWO of the following are examples of call signaling protocols that require specific QoS treatment?

Accepted Answer

H.323. SIP and H.323 are the primary signaling protocols used in CUCM and require CS3 marking.

Answer

RTCP

Answer

RTP

Answer

SCCP

Question 12

A collaboration engineer is configuring a Cisco IOS XE router to mark voice and video traffic at the network edge. The router connects to a service provider that trusts DSCP markings. The engineer must ensure that voice bearer traffic is marked EF, call signaling is marked CS3, and video conferencing traffic is marked AF41. Which two configurations are required to accomplish this marking on the router? (Choose two.)

Accepted Answer

Create a class-map that matches voice bearer traffic using a match protocol or ACL, and then in a policy-map, set the DSCP value to ef for that class.. To mark voice bearer as EF, you need a class-map to identify the traffic and a policy-map to set the DSCP value. Applying the policy-map inbound on the edge router ensures packets are marked before entering the service provider network. The other options either use incorrect tools for marking or omit required traffic types. Thus, the two correct configurations are the ones that classify and mark voice bearer and apply the policy inbound.

Answer

Use the set ip dscp ef command in a route-map and apply it to the WAN interface outbound to mark voice traffic.

Answer

Configure a policy-map that sets DSCP to af41 for video traffic and cs3 for call signaling, and attach it to the ingress interface with service-policy input.

Answer

Configure the mls qos trust dscp command on the ingress interface to trust incoming DSCP markings from the IP phone.

Question 13

A network administrator is configuring a Cisco IOS router to support a SIP trunk to a Cisco Unified Communications Manager. The administrator wants to ensure that voice signaling traffic is marked with the correct DSCP value. Which DSCP value is recommended for call signaling traffic in a Cisco collaboration network?

Accepted Answer

CS3 (24). Call signaling traffic should be marked with CS3 (DSCP 24) to ensure it receives appropriate priority without competing with voice media. This is a Cisco best practice and is widely adopted in collaboration deployments. Signaling must be reliable but is not as delay-sensitive as voice media, so a lower DSCP than EF is used.

Answer

AF31 (26)

Answer

EF (46)

Answer

AF41 (34)

Question 14

A network engineer is deploying a new branch with a Cisco IOS XE router acting as the WAN edge. The service provider marks all traffic with DSCP 0 (Best Effort), so the engineer must remark voice RTP flows entering the LAN-side interface before they are queued on the WAN interface. The engineer wants to identify voice bearer traffic by its DSCP value rather than by ACL. Which class-map match statement accomplishes this on the ingress interface?

Accepted Answer

match ip dscp ef. A class-map that matches the EF DSCP value selects traffic the phones already mark as voice bearer, satisfying the requirement to classify by marking instead of ACL. This is the standard approach when the trust boundary is moved to a routed interface: the router recognizes the existing Layer 3 marking, then the policy-map can preserve, remark, or queue those packets appropriately toward the WAN.

Answer

match protocol rtp audio

Answer

match cos 5

Answer

match access-group name VOICE-ACL

Question 15

A collaboration engineer is troubleshooting poor voice quality on a Cisco IP Phone. The network uses a Cisco Catalyst switch with QoS enabled. The engineer suspects that the phone's voice traffic is not being marked correctly. Which command on the switch can verify the DSCP value of voice packets received from the phone?

Accepted Answer

show mls qos ip. To verify the DSCP value of voice packets received from a phone, the show mls qos ip command on a Cisco Catalyst switch provides a breakdown of packets by DSCP. This helps confirm that the phone is marking voice media as EF and that the switch is trusting or re-marking appropriately.

Answer

show interfaces

Answer

show policy-map interface

Answer

show mls qos interface

Question 16

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?

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 17

A collaboration engineer is deploying a Cisco Expressway pair for Mobile and Remote Access. Remote endpoints register through the Expressway-E in the DMZ, and media traverses the Expressway-C and Expressway-E. The engineer must ensure that the media path between the two Expressway servers uses a single, predictable transport and that firewalls can be configured with a narrow rule set. Which transport should be used for the traversal zone media between Expressway-C and Expressway-E?

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 18

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 19

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 20

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)