The Certified Wireless Design Professional (CWDP-305)

The use of 80 MHz channel widths reduces the number of available non-overlapping channels in the 5 GHz band, increasing the likelihood of co-channel interference (CCI) and reducing frequency reuse. Although wider channels provide higher theoretical throughput, they are inappropriate in dense or high-concurrency environments due to overlap and contention.

According to CWDP-305, All-Wireless-Office (AWO) environments that rely entirely on WLAN for application delivery should be optimized for reliability and minimal interference. A channel plan using 20 MHz widths allows for better AP placement, isolation of frequencies, and greater spatial reuse, directly improving latency-sensitive application performance such as real-time communications or database access.

Changing the channel width to 20 MHz across the APs restores the integrity of the channel reuse plan and aligns with the original design, preventing interference that may degrade application performance.

Comprehensive and Detailed Explanation:

In 802.11b, the 1 Mbps data rate usesDirect Sequence Spread Spectrum (DSSS)with an 11-bit Barker code. Each bit of data is represented by an 11-chip sequence, resulting in a chip rate of:

1 Mbps × 11 chips/bit = 11 Mchips/s

However, thechip raterefers to the rate at which the chips (the smaller units of data in DSSS) are transmitted. For 802.11b, the chip rate is11 Mchips/sfor the 1 Mbps data rate.

CAPWAP and DTLS are the type of standards-based encryption used by office extension APs for the traffic tunnel. Office extension APs are wireless access points that can be deployed in remote locations and connect to a central wireless controller via a secure tunnel over the Internet. CAPWAP is the Control and Provisioning of Wireless Access Points protocol, which defines how the wireless controller and the office extension APs communicate and exchange control and data messages. DTLS is the Datagram Transport Layer Security protocol, which provides encryption and authentication for the CAPWAP tunnel. DTLS is based on TLS, but it uses UDP instead of TCP as the transport layer protocol, which makes it more suitable for real-time applications. DTLS protects the CAPWAP tunnel from eavesdropping, tampering, and replay attacks, and ensures the confidentiality and integrity of the wireless traffic. References: CWNP, CWDP Certified Wireless Design Professional Official Study Guide, Configure OEAP and RLAN on Catalyst 9800 WLC, Hardening Microsoft 365, Office 2021, Office 2019 and Office 2016

In the 5 GHz band, the number of available non-overlapping 40 MHz channels without DFS (Dynamic Frequency Selection) varies by regulatory domain. Typically, the UNII-1 and UNII-3 bands are available without DFS requirements.

Each 40 MHz channel requires two adjacent 20 MHz channels. Considering the available spectrum and avoiding DFS channels, you can typically configure three non-overlapping 40 MHz channels.

For long-range point-to-point bridge links, dish antennas are preferred due to their narrow beamwidth and high gain. An 11 dBi dish antenna focuses energy more efficiently in a single direction, which reduces the amount of Intentional Radiator (IR) power needed to meet link budget requirements.

From CWDP-305:

“Dish antennas provide high gain and a narrow beam, making them ideal for point-to-point bridge links over long distances. This minimizes interference and maximizes EIRP efficiency.”

— Reference: CWDP-305 Official Study and Reference Guide, Chapter on Infrastructure Design

Comprehensive and Detailed Explanation:

Latency is a critical metric when designing WLANs for VoIP (Voice over IP) applications. High latency can result in poor call quality, including delays and echoes. Industry standards recommend that one-way latency should not exceed 150 milliseconds to maintain acceptable voice quality. Therefore, during site surveys and network design, measuring and minimizing latency is essential to ensure a high-quality VoIP experience.

In public WLAN environments, security and privacy are paramount. To prevent clients from communicating directly with each other, many WLANs implement peer-to-peer blocking (also known as client isolation). This feature ensures that each client can communicate with the internet but not with other clients on the same network, thereby enhancing security.

The CWDP-305 Official Study and Reference Guide discusses this feature:

"Client isolation prevents wireless clients from communicating directly with each other, which is especially important in public or guest networks to protect user privacy and security."

Therefore, the inability to detect other devices on the subnet is likely due to peer-to-peer blocking being enabled on the WLAN infrastructure.

Orthogonal Frequency Division Multiple Access (OFDMA), introduced in 802.11ax, enhances efficiency by dividing a channel into smaller sub-channels called Resource Units (RUs). This allows multiple devices to transmit simultaneously within the same channel bandwidth, reducing latency and improving throughput. Unlike previous standards like 802.11n and 802.11ac, which primarily support single-user transmissions per channel, OFDMA's ability to handle multiple concurrent transmissions without relying on MU-MIMO leads to more efficient spectrum utilization and better performance in dense environments.

Comprehensive and Detailed Explanation:

Involving end-users in the final meeting ensures that the WLAN infrastructure meets their needs and expectations.Their feedback is crucial for validating the network's performance and usability, as they are the primary users who will interact with the system daily.