A user runs the Cisco Unified Wireless IP Phone 7921 with an AP that runs autonomous Cisco IOS Software.
How does the 7921 decide whether to associate to an AP to avoid over congestion?
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A. B. C. D.B.
The Cisco Unified Wireless IP Phone 7921 is a VoIP phone that operates on wireless networks. In order to avoid over congestion on the wireless network, the phone needs to make decisions about which access point (AP) to associate with. The 7921 phone monitors the QBSS (Quality of Service Basic Service Set) information element to evaluate contention and channel utilization and make association decisions.
The QBSS information element contains various parameters that can be used by the phone to evaluate network congestion and channel utilization. The available options to evaluate QBSS information elements are:
A. The 7921 monitors the QBSS information element, which includes the Min and Max contention window fields, and uses the information to evaluate contention and channel utilization. The contention window defines the range of time a device waits before attempting to transmit data after detecting that the wireless medium is idle. The Min and Max contention window fields provide information on the minimum and maximum time ranges within which the device can select a random backoff time for transmission. By evaluating the Min and Max contention window fields, the phone can estimate the level of congestion and channel utilization in the wireless network.
B. The 7921 monitors the QBSS information element, which includes channel load information in the beacon and probe response frames. The beacon frames are periodically transmitted by the AP to advertise its presence and provide information about the network, such as SSID, supported data rates, and channel information. The probe response frames are sent by the AP in response to probe requests from wireless clients. The QBSS information element in the beacon and probe response frames contains channel load information that can be used by the 7921 phone to evaluate network congestion and channel utilization.
C. The 7921 monitors the QBSS information element, which includes EDCF (Enhanced Distributed Coordination Function) such as queuing on the radio egress port, and uses the information to evaluate AP load and make an association decision. EDCF is a QoS mechanism used to provide differentiated service to different types of traffic. It uses a queuing mechanism on the radio egress port of the AP to prioritize traffic. By monitoring the EDCF parameters in the QBSS information element, the phone can evaluate the AP load and make an association decision.
D. The 7921 monitors the QBSS information element, which includes radio access categories and the Min and Max contention window fields, to evaluate AP load. Radio access categories (RAC) are defined by the IEEE 802.11 standard and are used to differentiate between different types of traffic based on QoS requirements. The Min and Max contention window fields provide information on the range of time the device waits before attempting to transmit data. By monitoring the RAC and Min/Max contention window fields in the QBSS information element, the phone can evaluate the AP load and make an association decision.
In summary, the Cisco Unified Wireless IP Phone 7921 uses QBSS information element parameters to evaluate network congestion and channel utilization, AP load, and make association decisions. The available options to evaluate QBSS information elements are A, B, C, and D, depending on the specific parameters monitored by the phone.