10 WLAN interview questions and answers

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

Question-1. What is the difference between WLAN and WiMAX? Answer-1.WLAN is used as wireless local area network for providing connectivity between WLAN compliant devices. WiMAX is used as 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 uses OFDM modulation scheme. Read more.

Question-2. Explain the WLAN physical layer frame as per 802.11a? Answer-2.WLAN has physical layer frame formats different in 11a, 11b, 11g, 11n and 11ac. They all have three generic fields i.e. preamble, header and data payload (PSDU). 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. Header carries two important parameters rate and length. Rate specify modulation-code rate of the data payload part and length field specify length of data payload in units of OFDM symbol. Refer WLAN frame structure to know more about 11a,11b,11n,11ac frames and WLAN MAC layer protocol to know about various frames exchanged between STA and AP.

Question-3. What is the difference between 802.11a, 11b, 11g and 802.11n? Answer-3.The difference between the 11a, 11b, 11g and 11n lies in terms of data rate, frequency of operation, distance coverage and more. Refer difference between 11a,11b,11g,11n page to find out the same.

Question-4. What are the messages exchange between STA and AP in WLAN? Explain the function of each. Answer-4.There are various messages exchanged between Station (STA) and Access Point (AP) in a WLAN network for various purpose such as establishing connection, data transfer, terminate the connection and more. Access points are devices which help extend wired network with wireless capabilities. The main WLAN MAC messages are listed below with their main function. 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 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 break up of existing association between peers in a WLAN network. Authentication: These packets are used by STA to request authentication. De-Authentication: Used by authenticated station to announce that receiver is no longer need to be authenticated. RTS/CTS: Used for initial handshake between WLAN peers. ACK: indicates the receipt of transmitted data whether reached on other side or not. CF end: It indicates end of CFP (contention free period). Many interview questions are based on WLAN frame types. Figure below depicts 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 version of WLAN which include 802.11a, 11b, 11g and 11n. 80MHz channel bandwidth is added. Numbers of MIMO streams have been enhanced to eight. 256QAM has been added. Read more.

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 to IEEE 802.11b. Read more.

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. Refer interview question no.3.

Question-8. What is the difference between WiFi and Bluetooth? Answer-8. WiFi fall under WLAN category while Bluetooth fall under 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 WPAN. It allows high speed transmission of data over very short distances. Refer bluetooth and WLAN pages to know more about these technologies.

Question-9. Explain OSI stack and differentiate with TCPIP protocol stack. Answer-9. OSI protocol stack is the generic stack developed to make it easy for different manufacturers devices inter-operate without any interfacing issues. TCP IP stack is specifically designed for internet applications. Refer difference between OSI and TCPIP stack.

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 as STAs (stations) communicate directly. In the infrastructure mode STAs communicate via entity called as AP (Access Point). It is similar to mesh and star topologies used in other wireless networks. Infrastructure mode used to connect with wired network.

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