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34 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What are the basic components of a VoIP network?
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IP phones, gatekeepers, gateways, Multipoint Control Units, call agents, application servers, and videoconference stations
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These are basic components that you see in most VoIP deployments.
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Which of the VoIP components provides Call Admission Control (CAC), bandwidth control, and management and address translation?
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Gatekeeper
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A gatekeeper is typically used on VoIP networks that are medium to large in size. This is because many of the gatekeeper functions can be done on a normal router (acting as a voice gateway) with the correct software. A dedicated gatekeeper should be used in larger deployments, as additional knowledge of the whole network is required.
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Which of the VoIP components provides translation between VoIP and non-VoIP networks?
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Gateways
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Gateways are needed on almost all VoIP network deployments because some part of the network requires connection to a non-VoIP device. A typical location for a gateway would be between the VoIP network and a PBX or between the VoIP network and the PSTN.
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Which of the VoIP components provides real-time connectivity for participants in multiple locations to attend the same videoconference?
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Multipoint Control Unit (MCU)
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The MCU is a central component that is required if conferencing is required on the network.
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Which of the VoIP components provides call control for IP phones, CAC, bandwidth control, and management, and address resolution in MGCP VoIP networks?
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Call agent
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In MGCP VoIP networks, the call agent is a central device that is used to perform call control, CAC, bandwidth control, and management and address resolution. A call agent is very similar to a gatekeeper in other VoIP protocols (H.323).
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Which transport layer protocol is typically used for voice packets?
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UDP
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Because voice is very sensitive to delay and jitter, it is unimportant for it to utilize the connection-oriented behavior of TCP; a missed packet will not have time to be resent. Typically, it is acceptable for some small amount of loss on a VoIP call.
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What is the maximum recommended one-way delay for a good quality VoIP call?
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150 ms
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It is recommended that the one-way delay for a VoIP call stay below 150 ms. A call will, of course, work if the delay is over this limit, but the quality could be impaired.
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What is the recommended maximum packet loss on a VoIP call?
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1%
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It is recommended that the voice packet loss stay below 1% in order to retain a high-quality call.
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What is the typical traffic profile of a VoIP call?
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Steady low-bandwidth traffic
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Typically, a VoIP call requires a small amount of bandwidth (per call) but requires this bandwidth to stay consistent over the length of the call.
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What is the typical traffic profile for a video call?
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Bursty high-bandwidth traffic
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A video call is different from a VoIP call in that it does not typically require a steady amount of bandwidth. This is because the video codecs typically work by only relaying the difference in the video frames and not every frame. This means that the more movement in a video call, the more bandwidth it requires.
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What feature is used to control the bandwidth, delay, jitter, and packet loss requirements of a VoIP or video call?
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Quality of Service (QoS)
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Quality of Service is used in order to ensure that the higher-priority traffic is ensured priority assess through the network, to reduce delay, jitter, and packet loss.
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What feature allows a voice network to overlay a data network?
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Auxiliary VLAN (voice VLAN)
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The auxiliary VLAN feature allows a separate voice VLAN to be used from the data VLAN.
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What protocol is used to assign a voice VLAN to a Cisco IP phone?
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Cisco Discovery Protocol (CDP)
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CDP is used to assign the voice VLAN to each Cisco IP phone.
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Which Cisco IOS command is used to configure the voice VLAN of a switchport?
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switch(config-if)#switchport voice vlan vlan-id
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This command sets the voice VLAN that is assigned to a specific switchport.
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Which Cisco IOS command is used to trust all incoming CoS values coming in a specific switchport?
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switch(config-if)#mls qos trust cos
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This command is used to automatically trust the CoS values that have been assigned to the incoming frames.
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Which Cisco IOS command is used to trust all incoming CoS values coming in a specific switchport, but only if an IP phone is connected?
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switch(config-if)#mls qos trust device cisco-phone
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This command uses CDP to identify an IP phone on the switchport. If a phone is detected, the port uses QoS values based on the previously configured mls qos trust cos|ip-precedence|dscp command. If a phone is not detected, only default settings will be used.
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Which Cisco IOS command is used to display configured voice parameters on an interface?
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switch#show interfaces interface-id switchport
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This command displays the configured voice parameters on an interface including the voice VLAN.
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Which Cisco IOS command is used to display the configured QoS parameters on an interface?
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switch#show mls qos interface interface-id
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This command displays the configured QoS parameters on a specific interface (or switchport).
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What is the recommended oversubscription ratio to be used on access-to-distribution links?
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20 to 1
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It is recommended that the links from the Access layer to the Distribution layer be oversubscribed at 20 to 1. In situations where this oversubscription is implemented, QoS may be required to give higher priority to delay-sensitive and critical traffic.
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What is the recommended oversubscription ratio to be used on distribution-to-core links?
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4 to 1
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It is recommended that the links from the Distribution layer to the Core layer be oversubscribed at 4 to 1. In situations where this oversubscription is implemented, QoS may be required to give higher priority to delay-sensitive and critical traffic.
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What is the field in the 802.1Q header that is used to mark QoS?
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Priority (PRI) field, 802.1p field, or CoS field
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The Priority (PRI) field is a 3-bit field that is part of the tag provided by 802.1Q. It was defined in the 802.1p standard as an extension of 802.1q. It is also known as the class of service (CoS) field.
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What are the available values that can be used in the CoS field?
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0 through 7
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The class of service (CoS) field is a 3-bit field that is able to hold values from 0 through 7. The lower values represent lower priority.
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What is the field in the IP header that is used to mark priority?
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Type of Service (ToS)
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The ToS field is included in the IP header to mark the priority of the IP traffic.
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What are the two different ways the ToS field in the IP header can be used?
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IP Precedence and Diffserv CodePoint (DSCP)
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There are two main techniques for using the ToS field. In the original standard, IP precedence (3 bits) was defined. Since then, an additional standard, DSCP, has been put forward that uses the same field but in a different way, as defined by RFC 2474. DSCP values are 6 bits.
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Of the eight bits available in the ToS byte, which are used to specify the DSCP value?
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The six most-significant bits
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The first six bits of the ToS field are used to specify the DSCP value.
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Of the eight bits available in the ToS byte, which are used to specify flow control?
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The two least-significant bits
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The last two bits of the ToS field are used to specify flow control.
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Which of the six DSCP bits are used for class selection?
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The three most-significant bits
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These three bits are used to correlate to CoS or IP precedence field values.
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Which of the six DSCP bits are used for drop precedence?
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The three least-significant bits
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These three bits are used to signify the drop precedence of the traffic.
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What is the purpose of a classification trust boundary?
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A trust boundary is used to specify the interfaces on which incoming classification markings are to be trusted.
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Trust boundaries are used in networks so that every device does not have to perform traffic classification. When trust boundaries are established, QoS automatically trusts the markings of the traffic incoming on the trusted interfaces.
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What are the two common methods of providing power over Ethernet?
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Cisco inline power and IEEE 802.3af
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Cisco inline power was introduced before the standard was finalized, but is still used in many networks. The IEEE 802.3af standard is supported on both Cisco equipment and other vendor’s equipment.
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What is the maximum amount of power that is supported over Cisco inline power and 802.3af?
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15.4 watts
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Both Cisco inline power and 802.3af provide up to 15.4 watts per port.
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What is the maximum amount of power that is proposed in the 802.3at draft?
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30 watts
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Because some of the newer equipment requires a higher amount of power than is currently supplied in the 802.3af standard, the 802.3at standard increases the maximum amount of power.
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Which Cisco IOS command is used to enable PoE on a switchport and automatically adjust the power supplied based on the discovery request?
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switch(config-if)#power inline auto
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This command is used to enable PoE on a specific switchport.
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Which Cisco IOS command is used to display the PoE configuration?
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switch#show inline power
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This command displays the current PoE configuration on the device.
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