Top 10 WLAN Interview Questions and Answers

This page covers WLAN questionnaire set prepared by experienced specialists in the WLAN domain. These top 10 WLAN interview questions and answers help engineers seeking WLAN jobs to crack the interview easily. These questions are very useful as viva questions as well.

Question-1. What is the difference between WLAN and WiMAX?

Answer-1. WLAN is used as a wireless local area network for providing connectivity between WLAN-compliant devices. WiMAX is used as a wide area network for providing access between various wireless devices. WLAN standards are evolving, including 11a, 11b, 11g, 11n, 11ac, 11ad, and more. WiMAX follows IEEE standards viz. 16d and 16e. Both use the OFDM modulation scheme.

Question-2. Explain the WLAN physical layer frame as per 802.11a?

Answer-2. WLAN has physical layer frame formats that differ in 11a, 11b, 11g, 11n, and 11ac. They all have three generic fields: preamble, header, and data payload (PSDU). The preamble carries STF (short training field) and LTF (long training field) used for front-end synchronization. Front-end synchronization includes time offset estimation and correction, frequency offset estimation and correction, and channel estimation and equalization. The header carries two important parameters: rate and length. Rate specifies the modulation-code rate of the data payload part, and the length field specifies the length of the data payload in units of OFDM symbols.

Question-3. What is the difference between 802.11a, 11b, 11g, and 802.11n?

Answer-3. The difference between 11a, 11b, 11g, and 11n lies in terms of data rate, frequency of operation, distance coverage, and more.

Question-4. What are the messages exchanged between STA and AP in WLAN? Explain the function of each.

Answer-4. There are various messages exchanged between a Station (STA) and an Access Point (AP) in a WLAN network for various purposes, such as establishing a connection, data transfer, terminating the connection, and more. Access points are devices that help extend wired networks with wireless capabilities. The main WLAN MAC messages are listed below with their main functions.

• Association request: This is sent by STA to AP to obtain association after authentication is done.
• Association response: This message is sent by AP in response to the received association request.
• Probe request: It is used to find out AP in the WLAN network.
• Probe response: It contains station (STA) parameters as well as data rates.
• Beacon: It is used by AP to announce the start of a CF (Contention Free) period.
• Disassociation: Used to announce the break-up of an existing association between peers in a WLAN network.
• Authentication: These packets are used by STA to request authentication.
• De-Authentication: Used by an authenticated station to announce that the receiver no longer needs to be authenticated.
• RTS/CTS: Used for the initial handshake between WLAN peers.
• ACK: Indicates the receipt of transmitted data whether reached on the other side or not.
• CF end: It indicates the end of CFP (contention-free period).

Many interview questions are based on WLAN frame types. The figure below depicts a WLAN network.

Question-5. What is the change in WLAN-11ac with respect to previous versions of WLAN?

Answer-5. WLAN-11ac has been introduced after previous versions of WLAN, which include 802.11a, 11b, 11g, and 11n. An 80MHz channel bandwidth is added. The number of MIMO streams has been enhanced to eight. 256QAM has been added.

Question-6. What is DSSS and CCK modulation scheme?

Answer-6. Direct Sequence Spread Spectrum (DSSS) and Complementary Code Keying (CCK) are modulation schemes employed in WLAN devices compliant with IEEE 802.11b.

Question-7. How much is the distance and data rate supported in WLAN devices?

Answer-7. There are different distances and data rates available in WLAN devices based on the IEEE standard they are supporting.

Question-8. What is the difference between WiFi and Bluetooth?

Answer-8. WiFi falls under the WLAN category, while Bluetooth falls under the WPAN category. WLAN specifications are published under IEEE 802.11, and Bluetooth under IEEE 802.15 standards. Bluetooth is the standard for wireless personal area networks or WPANs. It allows high-speed transmission of data over very short distances.

Question-9. Explain OSI stack and differentiate with TCPIP protocol stack.

Answer-9. The OSI protocol stack is the generic stack developed to make it easy for different manufacturers’ devices to inter-operate without any interfacing issues. The TCP/IP stack is specifically designed for internet applications.

Question-10. What is the difference between ad-hoc and infrastructure mode in IEEE 802.11?

Answer-10. In ad-hoc mode, WLAN mobile and stationary terminals, referred to as STAs (stations), communicate directly. In the infrastructure mode, STAs communicate via an entity called an AP (Access Point). It is similar to mesh and star topologies used in other wireless networks. Infrastructure mode is used to connect with a wired network.