CCNP Voice FAQ: Wireless LAN QoS Implementation

CCNP Voice FAQ: Wireless LAN QoS Implementation

Q1. Select the correct statement about wireless LANs.
A. WLANs are mostly implemented as extensions to wired LANS.
B. WLANs are occasionally implemented as overlays to wired LANs.
C. WLANs are sometimes implemented as substitutes for wired LANs.
D. All of the above.

Answer: D

Q2. Which statement is true about 802.11 wireless media access control?
A. It uses CSMA/CD.
B. It uses token passing.
C. It uses CSMA/CA.
D. All of the above.

Answer: C

Q3. Distributed coordinated function (DCF) performs collision avoidance using which of these?
A. Radio frequency (RF) carrier sense
B. Interframe spacing (IFS)
C. Random back-off/contention windows (CW)
D. All of the above

Answer: D

Q4. IEEE provides QoS extensions to wireless LANs by which of the following drafts/standards?
A. 802.11g
B. 802.11e
C. 802.11d
D. 802.11a

Answer: B

Q5. Select the item that is not a real-time function performed by the access point in the Split-MAC architecture.
A. Key management
B. Beacon generation
C. Probe transmission
D. Encryption/decryption

Answer: A

Q6. Which of the following shows the correct mapping of 802.11e priority levels to WMM access categories?
A. Voice(Platinum)=6/7, Video(Gold)=4/5, Best-Effort(Silver)=1/2, Background(Bronze)=0/3

B. Voice(Platinum)=6/7, Video(Gold)=4/5, Best-Effort(Silver)=3/2, Background(Bronze)=0/1

C. Voice(Platinum)=6/7, Video(Gold)=4/5, Best-Effort(Silver)=0/3, Background(Bronze)=1/2

D. None of the above

Answer: C

Q7. Select the correct statement about how wireless LAN controller copies/maps QoS fields in the Split-MAC architecture.
A. Wireless LAN controller copies the IP DSCP field (inner) to the DSCP field (outer) of the LWAPP data unit.

B. Wireless LAN controller maps the IP DSCP field (inner) to the 802.1p field (outer) of the LWAPP data unit.

C. Wireless LAN controller maps the DSCP field from the LWAPP data unit to the 802.1p field on the 802.1Q frame.

D. All of the above.

Answer: D

Q8. Which priority (802.1p) value is used/reserved for LWAPP control messages?
A. 6
B. 7
C. 0
D. 1

Answer: B

Q9. Which of the following is not a parameter set in the Edit QoS Profile page of the Web User Interface for Wireless LAN Controller, as a part of Per-User Bandwidth Contract?
A. Average voice rate
B. Average data rate
C. Burst data rate
D. Burst real-time rate

Answer: A

Q10. On the WLANs > Edit page of the web user interface of the wireless LAN controller, what does it mean if the general WMM or 802.11e policy for the interaction between the wireless client and the access point is set to Required?
A. This setting means that WMM or 802.11e QoS requests are ignored.

B. This setting means that QoS is offered to WMM or 802.11e-capable clients.

C. This setting means that all clients must be WMM/802.11e compliant to use this WLAN ID.

D. None of the above is correct.

Answer: C

Q11. How does distributed coordinated function (DCF) accomplish collision avoidance?

Answer: DCF uses radio frequency (RF) carrier sense, inter-frame spacing (IFS), and random backoff/contention windows (CW) to accomplish collision avoidance.

Q12. What is the standard (or draft name) for the wireless QoS of IEEE?

Answer: IEEE defines 802.11e as the first wireless standard, adding QoS features to the existing IEEE 802.11b and IEEE 802.11a (and other) wireless standards.

Q13. What is the Wi-Fi Alliance specification for wireless QoS?

Answer: While 802.11e was in the standardization process, Wi-Fi Alliance released a wireless QoS specification called Wi-Fi Multimedia (WMM) for the interim period.

Q14. Describe the relationship between 802.11e priorities and WMM access categories.

Answer: WMM reduces the eight priority levels of 802.11e to four access categories: Platinum, Gold, Silver, and Bronze. Platinum (voice) maps to priority 6/7, Gold (video) maps to priority 5/6, Silver (best-effort) maps to priority 0/3, and Bronze (background) maps to priority 1/2.

Q15. What contention mechanism does 802.11e use to provide prioritized RF access?

Answer: 802.11e (and its subset WMM) provides Enhanced Distributed Coordination Function (EDCF) by using different contention window (CW)/back-off timer values for different priorities (access categories).

Q16. Describe the Split-MAC architecture.

Answer: To address the centralized RF management needs of the Enterprises, Cisco designed a centralized lightweight access point wireless architecture with Split-MAC architecture as its core. Split-MAC architecture divides the 802.11 data and management protocols and access point capabilities between a lightweight access point (LWAP) and a centralized WLAN controller. The real-time MAC functions, including handshake with wireless clients, MAC layer encryption, and beacon handling, are assigned to the LWAP. The non-real-time functions, including frame translation and bridging, plus user mobility, security, QoS, and RF management, are assigned to the wireless LAN controller.

Q17. List at least three of the real-time MAC functions that are assigned to the LWAP in the SplitMAC architecture.

Answer: The real-time MAC functions that are assigned to the LWAP in the Split-MAC architecture include beacon generation, probe transmission and response, power management, 802.11e/ WMM scheduling and queuing, MAC layer data encryption/decryption, control frame/ message processing, and packet buffering.

Q18. List at least three of the non-real-time MAC functions that are assigned to the wireless LAN controller in the Split-MAC architecture.

Answer: The non-real-time MAC functions that are assigned to the wireless LAN controller in the Split-MAC architecture include association/disassociation, 802.11e/WMM resource reservation, 802.1x EAP, key management, authentication, fragmentation, and bridging between Ethernet and wireless LAN.

Q19. Which protocol is used between the wireless LAN controller and the lightweight access point in the Split-MAC architecture?

Answer: Lightweight Access Point Protocol (LWAPP) is used between the wireless LAN (WLAN) controller and the lightweight access point (LWAP) in the Split-MAC architecture. In the Cisco centralized lightweight access point wireless architecture (with Split-MAC architecture as its core), the WLAN controller ensures that traffic traversing between it and the LWAP maintains its QoS information. The WLAN data coming from the wireless clients to the LWAP is tunneled to the WLAN controller using LWAPP. In the opposite direction, the traffic coming from the wired LAN to the WLAN controller is also tunneled to the LWAP using LWAPP. You can set up the LWAPP tunnel over a Layer 2 or a Layer 3 network. In Layer 2 mode, the LWAPP data unit is in an Ethernet frame. Furthermore, the WLAN controller and the access point must be in the same broadcast domain and IP subnet. In Layer 3 mode, however, the 3 LWAPP data unit is in a UDP/IP frame. Moreover, the WLAN controller and access point can be in the same or different broadcast domains and IP subnets.

Q20. From which page of the web user interface of the wireless LAN controller can you examine and modify QoS profiles?

Answer: The Controller option from the web user interface menu bar provides access to many pages,including the QoS Profiles page. On the QoS Profiles page, you can view the names and descriptions of the QoS profiles, and you can edit each of the profiles by clicking on the Edit button.

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