Interview questions for Wireless Network Engineer

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. What is the wireless communication concept?

Wireless communication is the transfer of information between two or more points that are not connected by any physical medium. Wireless communications can be via Radio communication,Microwave communication, Light, Visible and Infrared communication.

3. What do you mean by frequency reuse?

Each cellular Base Station is allocated a group of radio channels to be used. These radio channels can be used by another base station which is at a suitable distance away from it.

4. 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.

5. 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.

6. What do you mean by Mobile Station Subsystem?

It includes mobile equipment which refers o a physical terminal such as a telephone which includes the radio trans-receiver signal processor and the Subscriber Identity Module

7. What do you mean by Base Station Subsystem?

It consists of one or more BTS and BSC. Each BTS is related to one cell which includes an antenna, a video trans-receiver, and a link to BSC. BSC controls multiple BTS units, manages the handoffs of the mobiles, and controls the paging.

8. What do you mean by Network and Switching Subsystem?

It controls handoffs between cells in different BSSs, authenticates users, validates and maintains their accounts. It is mainly supported by four databases like Home Location Register., Visitor Location Register, Authentication Center, and Equipment Identity Register.

9. What Are The Different Modes Of An Access Point (ap) Operation?

An AP can be performed by one of these modes of operation:
o Root Mode— This is the actual AP mode. It can associate wireless clients and bridge the traffic to the wired network when needed.
o Bridge Mode— AP acts as a bridge and can be used to connect wired networks at a distance.
o Repeater Mode— When the Ethernet port is disabled, the AP becomes a repeater and associates to a nearby root AP.
o Work Group Mode— A Workgroup Bridge (WGB) can provide a wireless infrastructure connection for Ethernet-enabled devices. Devices that do not have a wireless client adapter in order to connect to the wireless network can be connected to the WGB through the Ethernet port. The WGB associates to the root AP through the wireless interface.

10. Where Can I Download The Latest Firmware, Drivers, And Software For My Wireless Network?

Cisco AirNet equipment operates best when all components are loaded with the most current version of the software
Due to United States export compliance regulations, you must be registered on to download wireless software. Registration is free.

11. 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.

12. Can I Use My Wireless Device On An Aircraft?

Under current Federal Aviation Administration (FAA) rules, the use of wireless devices on an aircraft is permitted if the aircraft is parked at the gate and the door is open, and if usage is allowed in the airport. The device must not interfere with flight operation equipment such as navigation radar, communications, or emergency services.
The use of wireless devices on an aircraft with the door closed, whether it is sitting at the gate, taxiing, or in flight, is prohibited by the FAA and other Civil Aviation Agencies worldwide. Wireless devices used on the aircraft (when the door is open at the gate) must meet the requirements of the local country agency or have been granted a waiver by the agency or airport authority.
Wireless devices that are stored on the aircraft for use at the gate must meet certification requirements for the country that the local carrier is flagged for, and must be able to operate in the frequency band of the host country, unless a waiver is granted to the system user. It is the responsibility of the system installer to obtain all licenses and frequency or usage waivers.

13. What Antenna Should I Use For The Cisco Air Net 1010 Access Point?

This device has a built in antenna. You do not need to connect an antenna.
The Cisco AirNet Antenna Reference Guide has all the information about the different types of antennas and accessories that Cisco provides as a part of the Cisco WLAN solution.

14.  I Have An Access Point About 50 Feet Away From My Client. The Signal Is Very Weak And There Is Significant Interference In The Path (paper Storage). What Should I Do To Obtain Proper Coverage?

Install a high gain antenna for greater transmission and reception so that the signal at a longer distance can be picked up easily.

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