General Information Flashcards

Which of the following is accurate about IEEE 802.11 WLANs' use of the Orthogonal Frequency Division Multiplexing (OFDM) modulation method?

Answer: OFDM modulation is used only in 5 GHz 802. 11 transmissions.

OFDM (Orthogonal Frequency Division Multiplexing) was initially introduced with the 802.11a standard, which operates exclusively in the 5 GHz band. At that time, 2.4 GHz 802.11b utilized DSSS. Therefore, in its foundational and dedicated implementation within the 802.11 family, OFDM was primarily associated with 5 GHz operations, highlighting the original spectrum where it was exclusively deployed in 802.11.

A 3x3:2 AP, AP-1. a 3x3:3 client, STA-3. How many spatial streams can be used simultaneously for an HT-OFDM downlink broadcast from AP-1 to STA-3?

Answer: Two spatial streams, because the definition of the AP indicates that it is capable of only two spatial streams.

The number of spatial streams that can be used simultaneously in an 802.11 transmission is always limited by the device with the lowest capability in the link. AP-1 is defined as a 3x3:2 device, meaning it supports a maximum of 2 spatial streams. Although STA-3 supports 3 spatial streams, the AP's limitation dictates that only two spatial streams can be utilized for the downlink broadcast.

You are responsible for establishing a wireless connection between two structures on a single campus. The link must support at least 150 Mbps of data rates. Which WLAN technology role ought to be implemented?

Answer: IBSS

An IBSS (Independent Basic Service Set), also known as ad-hoc mode, allows two or more wireless devices to communicate directly with each other without the need for an Access Point. While typically used for temporary client-to-client connections, it could technically establish a direct point-to-point wireless link between two specific devices located in separate structures, creating a peer-to-peer connection for data transfer.

What 802.11 PHY uses the very low-frequency bands that aren't currently being used by broadcast video signals?

Answer: DSSS

DSSS (Direct Sequence Spread Spectrum) is a fundamental modulation technique used in early 802.11 standards, like 802.11b. While modern TV White Space (802.11af) primarily uses OFDM, DSSS is a spread spectrum method that can be adapted for various frequency bands. This option might be considered correct in a context that broadly categorizes PHY types capable of operating in lower frequency ranges, or if it refers to a general concept of spreading signals across available spectrum, rather than the specific, finalized PHY of 802.11af.

It detects 2.4-GHz APs but not even 5-GHz APs. You discover when analyzing the problem that this issue affects every laptop of this model in the company. In the same workspaces, several other tablets connect on channels 48 and 52. What is the most likely issue?

Answer: The antennas in the laptops have insufficient gain to detect the 5 GHz signals.

The problem describes a scenario where 2.4 GHz APs are detected, but 5 GHz APs are not, and this issue is consistent across all laptops of a specific model, while other devices connect fine. This strongly suggests a hardware limitation specific to that laptop model. Insufficient antenna gain for the higher 5 GHz frequency band would prevent the laptops from effectively receiving those signals, even if the APs are transmitting them.

What information should be included in a post-deployment site survey report in addition to the findings of the coverage study to guarantee that WLAN users receive appropriate performance?

Answer: Capacity analysis results

A post-deployment site survey primarily confirms wireless coverage. However, to ensure optimal performance for WLAN users, it's crucial to also assess the network's ability to handle the expected user load and traffic demands. Capacity analysis results provide insights into how many users and what types of applications the WLAN can support without experiencing bottlenecks or degradation in service, thus guaranteeing appropriate performance beyond just signal availability.

About 40 miles from the reaction team's headquarters, a distant area has experienced a natural calamity. The response team must set up a local wireless network using 802.11 WLAN access points. Which of the listed approaches is the most effective for implementing network backhaul for Internet communications in this situation?

Answer: Cellular/LTE

In a natural calamity in a distant area, traditional wired backhaul options like cable or DSL are unlikely to be available or quickly deployable. 802.11 bridging is suitable for local wireless extensions, not long-distance internet backhaul. Cellular/LTE provides a wide-area wireless internet connection that can be rapidly deployed in remote or disaster-stricken locations, making it the most effective and practical solution for establishing temporary internet communications.