Cisco Updated 300-110 Exam Questions and Answers by bentley

The hidden node problem is a classic RF design flaw that emerges when APs transmit at excessive power levels relative to the attenuation characteristics of the environment. In a brick-walled building, AP signals penetrate walls with significant attenuation. When an AP transmits at maximum power, its signal propagates far beyond the intended cell boundary and reaches client devices that may be physically near other APs but unable to detect the original transmitting AP due to wall attenuation between them. These clients can hear the distant AP ' s signal but cannot hear each other — making them hidden from one another. This leads to simultaneous transmissions, frame collisions at the AP receiver, and dramatic throughput degradation. The 802.11 CSMA/CA mechanism depends on all stations being able to sense the medium before transmitting; hidden nodes defeat this mechanism entirely. The WLSD curriculum consistently identifies excessive AP transmit power in high-attenuation environments as a primary cause of hidden node conditions. The solution is to reduce AP transmit power so that cell sizes remain appropriate for the physical environment. Reference: WLSD Study Guide — RF Design Fundamentals, Hidden Node Problem, Transmit Power and Cell Size Optimization.

For optimized roaming across multiple Wireless LAN Controllers (WLCs) with Cisco 8821 IP phones, two critical settings must be configured. First, configuring mobility groups between WLCs (Option A) allows for seamless inter-controller roaming by establishing mobility tunnels between controllers, enabling them to share client security context, preventing re-authentication when a phone roams from an AP on one WLC to an AP on another. Second, using Cisco Centralized Key Management (CCKM) for authentication (Option B) reduces the time required for re-authentication during roaming from a full 802.1X exchange to a single-message re-key process. CCKM stores the wireless security keys at the WLC level, enabling rapid key re-derivation during roaming without contacting the RADIUS server. AP groups (Option C) control SSID and VLAN assignments per AP cluster but have no impact on inter-controller roaming. AVC profiles (Options D and E) control application visibility and QoS marking — marking voice as best effort (Option E) would actually degrade rather than improve voice quality. Reference: WLSD Study Guide — VoWLAN Mobility Optimization, CCKM Configuration, Mobility Group Design for Multi-Controller Deployments.

The design requirements — optimized performance, interference avoidance, high-density support, and roaming capability — collectively point to a dual-band strategy using narrow channel widths. For 5 GHz operation (Option A), 20 MHz channels are the correct choice for high-density and campus-scale deployments. The 5 GHz band has significantly more non-overlapping channels compared to 2.4 GHz (up to 24 non-overlapping 20 MHz channels in UNII-1, UNII-2, and UNII-3), enabling a robust channel reuse plan with minimal co-channel interference and excellent roaming cell separation. Wider 5 GHz channels (Options C and E — 80 MHz and 40 MHz) would consume multiple channel blocks, dramatically reducing the number of available non-overlapping channels and increasing co-channel interference in dense deployments. For 2.4 GHz operation (Option B), 20 MHz channels are mandatory — there are only three non-overlapping 20 MHz channels (1, 6, 11) in the 2.4 GHz band. Using 40 MHz channels in 2.4 GHz (Option D) eliminates all non-overlapping channel separation, causing massive co-channel interference and is universally contraindicated in enterprise designs. Reference: WLSD Study Guide — Channel Planning, High-Density Design, Frequency Band Selection.

This question hinges on a fundamental network engineering constraint: the maximum transmission distance of copper Ethernet cabling. IEEE 802.3 standards specify a maximum segment length of 100 meters (328 feet) for all standard PoE and Ethernet over Category 5e, 6, or 6A UTP copper cabling. The parking lot light poles are approximately 200 meters from the closest wiring closet — more than double the maximum copper distance. This immediately eliminates Options A and D, which specify Category 6 UTP cabling: at 200 meters, UTP copper cannot reliably carry Ethernet at any supported speed, and PoE cannot be delivered over this distance regardless of standard. The correct solution is fiber optic connectivity between the wiring closet and the parking lot, combined with a local AC/DC power module at each pole location. Fiber optic cabling supports single-mode runs of kilometers and multi-mode runs of hundreds of meters at Gigabit speeds — easily spanning 200 meters. At the AP mounting location on the light pole, an AC/DC power module (powered from the pole ' s existing electrical supply) converts AC power to the DC power the AP requires. Option B (fiber with 802.3af) is incorrect because PoE cannot be delivered over fiber — 802.3af requires copper cabling for simultaneous power and data delivery. Reference: WLSD Study Guide — Outdoor AP Deployment, Fiber vs. Copper Distance Limitations, Outdoor Power Solutions.