Home » SWITCH 642-813 Q&As » Section 4 - Prepare Infrastructure » 642-813 Q&A – Prepare infrastructure to support advanced services (66-70)

642-813 Q&A – Prepare infrastructure to support advanced services (66-70)

Section4 – Prepare infrastructure to support advanced services

QUESTION NO: 66
Jitter is causing problems with the VOIP application in the Pass4sure network. What causes network jitter?
A. Variable queue delays
B. Packet drops
C. Transmitting too many small packets
D. Compression
Answer: A

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.
Note: Jitter in Packet Voice Networks:
Jitter is defined as a variation in the delay of received packets. At the sending side, packets are sent in a continuous stream with the packets being spaced evenly apart. Due to network congestion, improper queuing, or configuration errors, this steady stream can become lumpy, or the delay between each packet can vary instead of remaining constant.

QUESTION NO: 67
VOIP is being implemented on the Pass4sure 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: C
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).

QUESTION NO: 68
The Cisco AutoQoS feature is being used throughout the Pass4sure VOIP network. Which three statements about this feature are true? (Select three)
A. The “mls qos” global configuration command must be entered before configuring AutoQoS.
B. CEF must be enabled.
C. The “no auto qos voip” command is used to disable Cisco AutoQos and revoke all configurations generated by Cisco AutoQos.
D. CDP must be enabled.
E. SNMP must be enabled.
Answer: BCD
Explanation:
All of these answers can be found from the Cisco Auto QOS FAQ document found in the reference link.
Portions of this document state:
Q. Does CEF need to be enabled for Cisco AutoQoS on routers?
A. Yes. Cisco AutoQoS uses Network Based Application Recognition (nBAR) to identify various applications and traffic types; CEF is a prerequisite for NBAR.
Q. What are the minimum requirements for enabling Cisco AutoQoS on routers and switches?
A. Minimum requirements to enable Cisco AutoQoS for VoIP traffic on supported platforms for WAN interfaces:
-Configure an IP address on the interface or a sub-interface.
-Configure “bandwidth” under any participating interfaces or sub-interfaces. For ATM PVC, configure “vbr-nrt” under the PVC.
Minimum requirements to enable Cisco AutoQoS for VoIP traffic on supported LAN interfaces for switch platforms:
-CDP must be enabled
Q. How do I disable Cisco AutoQoS? What configurations are deleted from router CLI when Cisco AutoQoS is disabled?
A. Issue a “no auto qos voip” command under the interface or VC to disable Cisco AutoQoS. All configurations generated by Cisco AutoQoS that have not been modified by the user will be deleted when it is disabled on a particular interface.

QUESTION NO: 69
Refer to the exhibit. Which three statements are true about the voice VLAN configuration of the Catalyst switch? (Choose three.)
69
A. The packet priority received from a device that is connected to the phone will be unmodified.
B. The packet priority received from a device that is connected to the phone will be overridden.
C. Incoming CoS values in packets from the connected phone will be left unmodified.
D. Packets without aCoS value that is set by the phone will be set to a value of 5.
E. Incoming CoS values in packets from the connected phone will be reset to a value of 5.
F. Packets without aCoS value that is set by the phone will be set to the default CoS value.
Answer: A,C,F
Explanation:
Traffic sent from the telephone to the switch is typically marked with a tag that uses the 802.1Q header. The header contains the VLAN information and the CoS 3-bit field, which determines the priority of the packet. For most Cisco IP Phone configurations, the traffic sent from the telephone to the switch is trusted to ensure that voice traffic is properly prioritized over other types of traffic in the network. By using the mls qos trust cos interface configuration command, you can configure the switch port to which the telephone is connected to trust the CoS labels of all traffic received on that port.
You can connect a PC or other data device to a Cisco7960 IP Phone port. The PC can generate packets with an assigned CoS value. You can configure the switch to trust the priority of frames arriving on the IP phone port from connected devices. The “switchport priority extend trust” command is used to set the IP phone access port to trust the priority received from the PC or the attached device.

QUESTION NO: 70
What happens when this device is connected to the LAN, with a default configuration?
A. The access point will attempt to download an encryption key from the nearest wireless server.
B. The access point makes several attempts to get an IP address from the DHCP server. If the access point does not receive an address, it assigns itself the IP address 10.0.0.1 for 5 minutes.
C. The access point will attempt to connect to the nearest wireless server using LEAP authentication.
D. The access point requests an IP address from the DHCP server. If the access point does not receive an address, it continues to send requests indefinitely.
Answer: D
Explanation:
When you connect a 350, 1130AG, 1200, or 1240AG series access point with a default configuration to your LAN, the access point requests an IP address from your DHCP server and, if it does not receive an address, continues to send requests indefinitely.
When you connect an 1100 series access point with a default configuration to your LAN, the 1100 series access point makes several attempts to get an IP address from the DHCP server. If it does not receive an address, it assigns itself the IP address 10.0.0.1 for five minutes. During this five minute window, you can browse to the default IP address and configure a static address. If after five minutes the access point is not reconfigured, it discards the 10.0.0.1 address and reverts to requesting an address from the DHCP server. If it does not receive an address, it sends requests indefinitely. If you miss the five-minute window for browsing to the access point at 10.0.0.1, you can power-cycle the access point to repeat the process.

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