CWNP CWNA-109 Online Access

The least expensive solution available for increasing throughput for these users without implementing configuration options that are not recommended is to use a 40 MHz channel on the 5 GHz radio. This solution can double the channel bandwidth and increase the data rates for the 5 GHz capable 802.11ac clients. Using a 40 MHz channel on the 5 GHz radio is also less likely to cause co-channel interference or overlap with other channels than using a 40 MHz channel on the 2.4 GHz radio, which has only three non-overlapping channels. Using a 160 MHz channel on the 5 GHzradio may provide even higher throughput, but it may also consume too much of the available spectrum and cause more interference with other devices or networks. Installing a second AP in the coverage area may also improve the throughput, but it may require additional costs and configuration. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 216; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 206.

The channel that can be used for VHT transmissions according to the 802.11 specification is channel 144. VHT stands for Very High Throughput and is the PHY layer specification for 802.11ac devices. VHT transmissions can use channel bandwidths of 20 MHz, 40 MHz, 80 MHz, or 160 MHz in the 5 GHz band. Channel 144 is one of the channels in the 5 GHz band that can support VHT transmissions with any of these bandwidths. Channel 6, channel 1, and channel 11 are channels in the 2.4 GHz band that cannot support VHT transmissions, as they are only compatible with legacy (802.11b/g/n), HT (802.11n), or ERP (802.11g) transmissions with up to 20 MHz bandwidth. References: [CWNP Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 214; [CWNA: Certified Wireless Network Administrator Official Study Guide: ExamCWNA-109], page 204.

Return loss is a measure of how well the components of an RF system are matched in terms of their impedance. Impedance is the opposition to the flow of alternating current in a circuit, and it depends on the frequency, resistance, capacitance, and inductance of the components. When the impedance of the source, the transmission line, and the load are not equal, some of the power is reflected back to the source, causing a loss of forward power. This loss is expressed in decibels (dB) as return loss. The higher the return loss, the lower the reflection and the better the impedance matching. Conversely, the lower the return loss, the higher the reflection and the worse the impedance matching.

VSWR (Voltage Standing Wave Ratio) is another way of expressing the same concept. It is the ratio of the maximum voltage to the minimum voltage along a transmission line due to the interference of the incident and reflected waves. A VSWR of 1:1 means that there is no reflection and perfect impedance matching. A VSWR higher than 1:1 means that there is some reflection and impedance mismatch. The higher the VSWR, the higher the reflection and the lower the return loss.

Therefore, a significant impedance mismatch between components in an RF system will cause high reflection, high VSWR, and low return loss.

FT (Fast Transition) is an IEEE 802.11 standard method for fast roaming. FT is defined in the IEEE 802.11r amendment and is also known as Fast BSS Transition (FBT) or Fast Secure Roaming. FT is a feature that allows a client station to quickly switch from one AP to another within the same ESS (Extended Service Set) without having to re-authenticate and re-associate with each AP. This reduces the latency and packet loss that may occur during roaming, thus improving the user experience and maintaining the security of the connection. FT works by using pre-authentication and key caching mechanisms that allow the client station and the APs to exchange security information before the actual roaming occurs. This way, when the client station decides to roam to a new AP, it can use a fast reassociation request and response that contain only a few fields, instead of a full authentication and association exchange that require more time and data. References: 1, Chapter 9, page 367; 2, Section 6.3