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56.
VOIP is being implemented on the Company network. In a properly designed network, what is the
maximum amount of time a voice package should spend crossing a network?
- A.90 milliseconds
- B.120 milliseconds
- C.150 milliseconds
- D.240 milliseconds
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
| Delay is the time it takes for VoIP packets to travel between two endpoints and you should design networks to minimize this delay. However, because of the speed of network links and the processing power of intermediate devices, some delay is expected. The human ear normally accepts up to about 150 milliseconds (ms) of delay without noticing problems (the ITU standard recommends no more than 150 ms of one-way delay). |
57.
Jitter is causing problems with the VOIP application in the Company network. What causes
network jitter?
- A.Variable queue delays
- B.Packet drops
- C.Transmitting too many small packets
- D.Compression
- E.If a Cisco IP phone is attached, the switch trusts the CoS.
- F.None of the other alternatives apply.
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
| Delay variation or jitter is the difference in the delay times of consecutive packets. A jitter buffer is often used to smooth out arrival times, but there are instantaneous and total limits on buffering ability. Any type of buffering used to reduce jitter directly increases total network delay. In general, traffic requiring low latency also requires a minimum variation in latency. |
58.
You need to configure a new Cisco router to be installed in the Company VOIP network. Which
three interface commands will configure the switch port to support a connected Cisco phone and
to trust the CoS values received on the port if CDP discovers that a Cisco phone is attached?
(Select three)
- A.switchport voice vlan vlan-id
- B.mls qos trust device cisco-phone
- C.switchport priority extend cos_value
- D.mls qos trust cos
- E.mls qos trust override cos
- Answer & Explanation
- Report
Answer : [A, B, D]
Explanation :
Explanation :
1. To configure the IP Phone uplink, just configure the switch port where it connects. The switch
instructs the phone to follow the mode that is selected. In addition, the switch port does not need
any special trunking configuration commands if a trunk is wanted. If an 802.1Q trunk is needed, a
special-case trunk is negotiated by Dynamic Trunking Protocol (DTP) and CDP. Use the following
interface configuration command to select the voice VLAN mode that will be used:
Switch( config-if)# switchport voice vlan { vlan-id | dot1p | untagged | none}
2. mls qos trust [ cos ] : Configure the port trust state.
By default, the port is not trusted. All traffic is sent through one egress queue. Use the cos
keyword to classify ingress packets with the packet CoS values. The egress queue assigned to
the packet is based on the packet CoS value
3. mls qos trust device cisco-phone : Configure the Cisco IP Phone as a trusted device on the
interface.
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59.
You have been tasked with setting a trust boundary on the Company network. What is the basic
function of this trust boundary?
- A.Trust boundaries are points in the network where Layer 2 CoS markings are converted to Layer 3 DSCP or IP precedence markings.
- B.Trust boundaries are a point in the network where QoS functionality begins and ends.
- C.Trust boundaries determine whether certain types of traffic can pass.
- D.Trust boundaries are a point in the network where decisions about CoS markings on incoming packets are made.
- E.None of the other alternatives apply
- Answer & Explanation
- Report
Answer : [D]
Explanation :
Explanation :
| The perimeter formed by switches that do not trust incoming QoS is called the trust boundary. Usually, the trust boundary exists at the farthest reaches of the enterprise network (access-layer switches and WAN or ISP demarcation points). When the trust boundary has been identified and the switches there are configured with untrusted ports, everything else inside the perimeter can be configured to blindly trust incoming QoS values since the COS/QOS markings are then under the control of the network administrator, and not the end user. |
60.
The voice VLAN feature has been enabled on a new Company Catalyst switch port. What is the
effect of this?
- A.The CoS is trusted for 802.1P or 802.1Q tagged traffic
- B.PortFast is disabled on the port.
- C.Port Security is automatically enabled on a voice VLAN port.
- D.Untagged traffic is sent according to the default CoS priority of the port
- E.None of the other alternatives apply
- Answer & Explanation
- Report
Answer : [D]
Explanation :
Explanation :
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Default Voice VLAN Configuration: The voice VLAN feature is disabled by default. When the voice VLAN feature is enabled, all untagged traffic is sent according to the default CoS priority of the port. The CoS value is not trusted for 802.1P or 802.1Q tagged traffic. |
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