Wireless network engineers are in extremely high demand, a trend that continues to escalate. 

To get one of these lucrative and specialized network engineer gigs, though, you first need to ace the job interview. You may possess all of the core credentials — from expertise in wireless equipment and WLAN design, to the ability to perform network technology wizardry with strong analytical and problem-solving skills. But if you aren’t prepared for the kinds of questions employers are likely to ask, you could miss a grand opportunity.

Ready to land the wireless network engineer job you want? Review and practice answering the seven essential wireless network engineer interview questions below. The Q&A is divided up into basic entry-level, mid-range and advanced questions.

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Warming up

Depending on the level of the wireless network engineer position you’re applying for, you may get lucky and start out with a few easier questions. These might include:

1. Explain the difference between IBSS, BSS and ESS. 
BSS stands for Basic Service Set — these are the stations that can communicate with each other at the physical layer (PHY) of the OSI model. Every BSS is identified with a BSSID, which is the MAC address of the WiFi chipset that runs on a Wireless Access Point (WAP) servicing the BSS.
IBSS, which stands for Independent BSS (IBSS), is a type of ad-hoc BSS that can’t connect to any other basic service set since it contains no access points. This means it cannot connect to any other basic service set.

ESS stands for Extended Service Set. An ESS contains several connected Basic Service Sets whose access points (APs) are connected by a distribution system.

2. Explain the difference between WLAN and WiMAX. 
WLAN stands for wireless local area network, and it provides connectivity between devices that are WLAN compliant. WLAN follows 802.11 standards set by the Institute of Electrical and Electronics Engineers (IEEE) including 11a, 11b, 11g, 11n, 11ac and 11ad.

WiMAX, on the other hand, is used as a wide area network for providing access between various wireless devices. WiMAX follows IEEE standards 16d and 16e.

Getting tougher

Hiring managers for a wireless network engineer position aren’t likely to let candidates for these coveted jobs off the hook that easily, though. Now that you’ve built confidence by practicing some “simple” wireless network engineer interview questions, see how you do on these more difficult ones:
3. Explain the DSSS and CCK modulation schemes. 

DSSS stands for Direct Sequence Spread Spectrum and CCK stands for Complementary Code Keying. Both of these are modulation schemes for WLAN devices, and they are compliant to IEEE 802.11b.

In DSSS systems, PN codes modulate information bits, and the whole system bandwidth is always available for all users.

CCK replaced the Barker code in wireless digital networks in 1999 because CCK uses bit sequences more efficiently and thus makes more efficient use of them. CCK has the ability to transfer more data per unit for a given signal bandwidth.

4. Explain how TCP/IP and OSI stack differ. 
The network models TCP/IP (Transmission Control Protocol/Internet Protocol) and OSI (Open Systems Interconnection) have different layers. TCP/IP is a four-layered standard designed for Internet applications while OSI for network protocol architecture is a seven-layered standard.
OSI is a generic stack developed to allow different devices to communicate without any interfacing issues, allowing for open access to protocols. In the TCP/IP model, the network access layer corresponds to the physical and data link layers in the OSI model.

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Advanced interview questions

If you’re applying for a senior-level position as a wireless network engineer, you’ll need to really bone up on some particularly challenging interview questions and answers. Try your hand at these:

5. Describe the basic guidelines for implementing CAPWAP. 
CAPWAP (Control and Provisioning of Wireless Access Points) is a standard networking protocol that allows central WLAN access control (AC) to manage a collection of wireless access points. To implement CAPWAP, you must first check your firewall configurations.

Verify whether the firewall configurations only allow traffic from access points that use Lightweight Access Point Protocol, or LWAPP. If so, then your first step is to adjust the firewall to allow traffic from access points that use CAPWAP.

Next, enable the CAPWAP UDP ports 5246 and 5247. Your goal is to prevent access points from being stranded by opening new protocol ports if access control lists (ACLs) are blocking the control path between access points and controller.

6. Explain how WLC works when considering packet transfer. 
A LWAPP packet encapsulates all 802.11 packets and sends them to the wireless LAN controller (WLC).

WLC acts based on the destination IP address. So for example:
•    If the destination is a wireless client, the packet gets encapsulated with the LWAPP before being decapsulated and then sent to the wireless client.
•    If the destination is on the network’s wired side, the LWAPP changes the 802.11 header to an Ethernet header and then sends the packet to the connected switch, and then to the wired client.
•    WLC removes the Ethernet header when a packet comes from the wired side, replacing it with a 802.11 header and encapsulating it with LWAPP. Ultimately it is decapsulated and sent to the wireless client.

7. In WLAN, what messages are exchanged between AP and STA and what are the functions of both? 
There are various messages exchanged between AP and Station in a WLAN network for different purposes such as establishing connection, data transfer terminating the connection and more. APs are devices that help give a wired network wireless functionality. These are a few WLAN MAC messages along with their primary function:
•    Association response. The AP sends this message in response to receiving an association request.
•    Association request. STA sends this message to AP after authentication in order to obtain association.
•    Authentication. STA requests authentication with this message.
•    De-authentication. An authenticated STA uses this message to announce that the receiver no longer needs authentication.
•    Probe request. In WLAN network, this message is sent to find out AP.

To ace wireless network engineer interview questions, you’ll need to invest time preparing for them. While you may be familiar with some or all of the topics discussed here from your experience as a wireless network engineer, you still need to be able to articulate your answers succinctly, through clear communication. 

More resources:
•    How to Get the Best IT Salary
•    The Best IT Interview Tips for Every Tech Pro

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