Network Troubleshooting Study Guide for the CompTIA Network+

Wireless Connectivity Issues

Wireless networks can create a host of potential problems, including numerous connectivity issues. Given a scenario, you must be able to identify and troubleshoot common wireless connectivity issues.

Specifications and Limitations

Like a wired network, a wireless network is affected by wireless specifications and limitations, such as the specifications associated with and supported by an access point (AP) and physical limitations of the transmitting wireless signal. Remember, wireless connections, like wired connections, are only as capable as the weakest link in the network.

Throughput

Wireless throughput, or data transfer rate, is a measurement of the actual amount of data that is transmitted over a wireless connection. Throughput is limited by the AP’s theoretical bandwidth (the maximum data transfer rate), the AP’s available bandwidth, and the strength of the AP signal.

Speed

Wireless speed refers to how quickly data can be transmitted over a wireless connection. Wireless connection speed is affected by the maximum speed the AP supports, the speed the connecting device supports, and the speed provided to the AP from the internet service provider (ISP).

Distance

Like a wired connection, signal strength is limited by distance. The wireless signal begins at the AP with the strongest signal strength and attenuates as the signal travels away from the transmitting AP.

Received Signal Strength Indication (RSSI)

Also known as the received signal strength indicator, RSSI is a method for measuring the strength or quality of a wireless signal received by a connecting device. RSSI is indicated by a negative number and is the amount of signal loss that occurs between the transmitting AP and the receiving device. The loss is expressed in negative decibels relative to milliwatts (dBm), with a lower number indicating greater signal loss. For instance, a loss of -90 dBm or lower is a very weak signal and may indicate no signal, whereas the closer to 0 dBM, the better the signal.

Effective Isotropic Radiated Power (EIRP)

EIRP is a measurement of the signal strength or signal power being transmitted from an emitting device such as a wireless AP. It is regulated by the federal government. EIRP levels can be adjusted on most wireless APs either manually or by using auto adjust.

Considerations

Wireless connectivity can be affected by multiple factors, including the transmitting antenna, the channel used, and the location of the APs, among others. Troubleshooting these common situations and considerations can provide useful information as to the cause of wireless connection problems.

Antennas

The antenna of a wireless AP is the portion of the AP that transmits the wireless signal to receiving devices. Antennas vary in type and transmitting power, which can cause interference between APs or weak spots where there is a lack of coverage in the wireless network.

Placement

Wireless connectivity is affected significantly by the placement of the transmitting device’s antenna. In general, a wireless AP should be placed in a central location to provide the largest coverage area. If multiple APs are used in the wireless network, tools such as a heat map can identify the most appropriate placement to provide optimal coverage. This is done to minimize interference between APs, from other electrical devices, or due to structural issues.

Type

There are two primary types of antennas: omni and directional. The signals of omni antennas spread out from the origination point in a circle, whereas the signals of directional antennas travel in a straight line. Each type of antenna provides a different signal range and direction of transmission. The appropriate type of antenna should be chosen to meet the needs of the wireless network.

Polarization

Antenna polarization refers to how the radio wave travels from the sending device, with most wireless antennas utilizing a linear polarization. Linear polarization of antennas is commonly either horizontal or vertical. Generally, the sending and receiving devices should have the same polarization for optimal signal strength and to reduce attenuation or degradation.

Channel Utilization

Wireless networks primarily use the 2.4 and 5 GHz bands for signal transmission, using multiple frequencies combined into a common channel to provide optimum transmission strength. When an overlap of channels occurs, either on a single AP or between two or more APs, noise or signal interference can occur.

AP Association Time

AP association time refers to the amount of time it takes for a receiving device to be granted access to an AP. Delays in association time can be caused by multiple factors, such as distance and the number of current connections on the AP, which can affect wireless connectivity.

Site Survey

A site survey to evaluate a wireless network can identify multiple potential causes of wireless connectivity issues. For example, site surveys can identify gaps in coverage or areas where the demand on a wireless AP exceeds its capabilities, leading to connectivity problems.

Common Issues

Due to the use of radio waves in wireless transmission devices, there are common issues that can cause connection problems between APs and receiving devices. These issues can result in a complete lack of signal, signal attenuation or degradation, and slow transmission speeds.

Interference

Interference in a radio signal can cause connection problems, including signal degradation, or it can even hamper the ability to connect at all. Interference is often caused due to signal bleed in which a competing signal is transmitted over the same frequency. Signal bleed is commonly caused by other wireless signals, such as Bluetooth signals, or other electronic devices, such as microwaves. Proper placement of APs is crucial in preventing or reducing interference.

Channel Overlap

Channel overlap is another common cause of signal interference. A channel is a smaller portion of a frequency band. For example, the 2.4 GHz frequency used by wireless access points is commonly divided into 11 channels, with channels 1, 6, and 11 never overlapping because of their distance from each other. Channel overlap commonly occurs in two ways, either through two wireless APs using the same band, such as the 2.4 GHz band, or by a single wireless AP using a channel that overlaps with other channels, such as channel 3.

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Antenna Cable Attenuation/Signal Loss

Antenna cable attenuation occurs when the physical cable connecting the device containing the wireless antenna exceeds optimal parameters, thereby creating signal degradation or even signal loss. For example, if a coax cable is used for the physical connection, signal degradation can occur if the length the signal must travel exceeds the distance the cable is able to properly transmit the signal.

Radio Frequency (RF) Attenuation/Signal Loss

RF attenuation or signal loss commonly occurs when the RF signal is unable to properly communicate with the receiving device, often due to the placement of the AP. For example, RF attenuation may be caused due to an AP that is placed too far from the receiving device to create a strong connection or if a physical structure such as a wall is impeding the signal.

Wrong Service Set Identifier (SSID)

Wireless APs use SSIDs to identify and connect to wireless frequencies. SSIDs can be either basic service set identifiers (BSSIDs), for a single AP, or extended service set identifiers (ESSIDs), which are part of a set of APs. If the receiving device is attempting to connect to the wrong SSID, a connection cannot be made.

Incorrect Passphrase

Most wireless AP SSIDs require a password or passphrase to establish a connection and authenticate to the wireless network. If the incorrect or wrong password is entered, access to the wireless network will be denied.

Encryption Protocol Mismatch

Wireless networks use encryption standards, such as Wi-Fi Protected Access 3 (WPA3), to secure wireless transmissions. If the receiving device is not set to the same encryption protocol as the wireless AP, the receiving device will not connect due to protocol mismatch.

Insufficient Wireless Coverage

Insufficient wireless coverage often results in signal attenuation or an inability to connect to a wireless AP. Insufficient wireless coverage can be caused by a lack of APs transmitting in a location or by an excess number of receiving devices connecting to a single AP, overwhelming the available bandwidth on the AP.

Captive Portal Issues

When one is required, a captive portal is a web page that is triggered when a receiving device attempts to connect to an SSID. Captive portals are common for public wireless APs, such as at a coffee shop. To connect to the wireless AP, the connecting device is routed through the captive portal. If the captive portal is not working properly or has functionality issues, the connecting device will be unable to connect to the SSID.

Client Disassociation Issues

Client disassociation occurs when a receiving device has difficulties maintaining connection and authentication to a wireless AP. Client disassociation can be caused by multiple factors, including signal loss, excessive distance from the AP, lack of available bandwidth on the connection, or interference.