Wn Exam 01

Front 1

Describe two characteristics of an ad-hoc wireless network?

Back 1

Creates peer-to-peer arrangement among devices within range.

The nodes in ad-hoc network communicate over virtual paths.

Front 2

Describe advantages and disadvantages of an infrastructure WLAN over an ad-hoc wireless network.

Back 2

Advantages are Centralized security, Scalability and Better Operating Range.

Disadvantages are Increased costs of access points and other devices.

Front 3

Name the two ways in which infrastructure WLANs are configured.

Back 3

Whether an access point is connected back to a wired LAN or not.

Front 4

Give examples of a wireless PAN's cable replacement technologies.

Back 4

Bluetooth, Infrared, RFID

Front 5

5 properties of RF waves

Back 5

Amplitude

Frequency

Phase

Propogation Speed

Wavelength

Front 6

What is the frequency if the speed of light is 300 million meters per second and wavelength is 27.3 meters?

Back 6

Speed of light = Frequency*Wavelength

Frequency = Speed of light/Wavelength

Frequency = 300/27.3

Frequency = 11Mhz

Front 7

Briefly explain AM and FM modulations

Back 7

Amplitude Modulation (AM) varies amplitude (height) of the transmitted radio wave to match the waveform of the transmitted data signal.

Frequency Modulation (FM) adjusts the vibration rate or frequency of a signal.

Front 8

Name the basic forms of multiplexing used in communications.

Back 8

Frequency Division Multiplexing (FDM)

Code-Division Multiplexing (CDM)

Time-Division Multiplexing (TDM)

Wave-Division Multiplexing (WDM)

Front 9

Explain how one fibre-optic cable provides different channels on a TV?

Back 9

Cable TV uses broadband network to transmit multiple streams. Once the multiple RF signals reaches the home, a cable-ready TV or a set-top box assigns the signal streams to different channels on a TV.

Front 10

Explain how scatternets are formed and outline two drawbacks of scatternets

Back 10

Scatternet is a group of non synchronized piconets that connect through a common device that serves as a bridge between the piconets. Between 2-10 piconets form a scatternet.

Front 11

What are the main properties of the Bluetooth transmitter class?

Back 11

There are three RF transmitter classes: Class 1, Class 2 and Class 3.

Class 1 have a range of 100m and a transmit power of 1mw to 100mw.

Class 2 are the default transmitters for bluetooth products. Maximum range of 10m and a transmit power of 0.25mw to 2.5mw.

Class 3 are small and haven't enough range to be useful. Maximum range of 10cm and transmit power less than 1mw.

Front 12

What are five criteria that should be considered when deciding whether Bluetooth or IR is a better solution for a given WPAN.

Back 12

Bandwitdh

Range

Environment

Convenience

Interference

Number of devices

Cost

Front 13

Describe the different methods that can be used to form a Bluetooth piconet.

Back 13

A master device actively scans for slave devices and, when it detects one in its range, it can invite the device to join a piconet as a slave.

A master device can passively wait for a slave to contact it, and then invite the slave to join the piconet as a slave.

Front 14

Differentiate between a piconet and a scatternet.

Back 14

A Bluetooth network is called a piconet. A scatternet is made up of between two and ten piconets.

Front 15

What is the relationship between a base station and a mobile switching center?

Back 15

A mobile switching center coordinates communications between a base station and a telephone central office.

Front 16

How does the use of MIMO technology deal with the effects of multipath propagation?

Back 16

Multipath propagation occurs when portions of the electromagnetic wave reflect off objects and the ground, taking paths of different lengths between a sender and receiver. This results in the blurring of the received signal at the receiver.

Moving objects between the sender and receiver can cause multipath propagation to change over time.Some signals are delayed more than others and may overlap another signal arriving at the receiver, resulting in errors due to inter-symbol interference (ISI)

Front 17

What is the main way in which OFDM is so fundamentally different from FDM?

Back 17

All the subbands are used by one source at a given time. Therefore OFDM is a multi-carrier modulation scheme while FDM is a single carrier scheme.

Front 18

Which is better, a low frequency reuse factor or a high frequency reuse factor for cellular mobile communication?

Back 18

Generally a high reuse factor is better because the cells that use the same set of frequencies are farther apart (separated by more cells).

Front 19

With the aid of a diagram illustrate a cell pattern with a frequency-reuse factor of 3 and outline the principle of frequency reuse in mobile communication

Back 19

Frequency reuse implies that the same channels can be used by many cells as long as the cells are not adjacent to each other.

Front 20

Briefly explain the operation of roaming in mobile communication.

Back 20

Seamless roaming is used in mobile telephony. As the mobile phone moves between cells (antennae), it disconnects from the cell it is having and establishes a connection to the next cell in an overlapping manner, which prevents a loss of service connectivity.

Roaming helps ensure that a traveling wireless device (typically a cell phone) is kept connected to a network without breaking the connection.

It is a general term referring to the ability for a mobile customer to automatically make and receive voice calls, send and receive data, or access other services, including home data services, when travelling outside the geographical coverage area of the home network, by means of using a visited network.

Front 21

Explain tunneling

Back 21

Tunneling is a process in which an IP datagram is encapsulated with an outer IPheader so as to be transmitted across the Internet using the destination address and parameters of the outer header.

Front 22

List and briefly define the capabilities provided by Mobile IP.

Back 22

Discovery: A mobile node uses a discovery procedure to identify prospectivehome agents and foreign agents.

Registration: A mobile node uses an authenticated registration procedure to inform its home agent of its care-of address.

Tunneling: Tunneling is used to forward IP datagrams from a home address to a care-of address.

Front 23

Explain the distinction between a mobile user and a nomadic user.

Back 23

A mobile user is connected to one or more applications across the Internet suchthat the user's point of attachment changes dynamically, and that all connections are automatically maintained despite the change.

For a nomadic user, the user's Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back in.

Front 24

What are the purposes of the HLR and VLR is mobile networks? Which elements of mobile IP are similar to the HLR and VLR?

Back 24

The home network in GSM maintains a database called the home location register (HLR), which contains the permanent cell phone number and subscriber profile information about each of its subscribers.

The HLR also contains information about the current locations of these subscribers. The visited network maintains a database known as the visitor location register (VLR) that contains an entry for each mobile user that is currently in the portion of the network served by the VLR.

VLR entries thus come and go as mobile users enter and leave the network.The edge router in home network in mobile IP is similar to the HLR in GSM and the edge router in foreign network is similar to the VLR in GSM.