DEPARTMENT OF COMPUTER APPLICATIONSMOBILE COMPUTING (MC1633)
1. Define SAMA.
Spread Aloha Multiple Access is a combination of CDMA and TDMA. The
CDMA better suits for connection oriented services only and not for connection less
bursty data traffic because it requires to program both sender and receiver to access
different users with different codes.
2. Define CDMA.
Code Division Multiple Access systems use codes with certain
characteristics to separate different users. To enable access to the shared medium without
interference. The users use the same frequency and time to transmit data. The main
problem is to find good codes and to separate this signal from noise. The good code can
be found the following 2 characteristic
3..What are the several versions in CSMA?
There are several versions in CSMA, they are as follows
a) non-persistent CSMA
b) p-persistent CSMA
c) 1-persistent CSMA
4.What is meant by non-persistent CSMA?
In, non-persistent CSMA, stations sense the carrier and start sending immediately
if the medium is idle., if the medium is busy, the station pauses a random amount of time
before sensing the medium again and repeating this pattern.
5.What is meant by p-persistent CSMA?
In p-persistent CSMA system nodes also sense the medium, but only transmit with a
probability of p. With the station deferring to the next slot with the probability 1-p,
i.e. access is slotted in addition.
6. What is SDMA?
Space Division Multiple Access (SDMA) is used for allocating separated spaces to users
in wireless networks. The basis for the SDMA algorithm is formed by cells and
sectorized antennas which constitute the infrastructure implementing space division
7. What is FDD?
In FDMA, the base station and the mobile station establish a duplex channel. The two
directions, mobile station to base station and vice versa are separated using different
frequencies. This Scheme is called Frequency Division Duplex (FDD)
8. What are the 2 sub layers in DLC?
Logical Link Control(LLC)
Media Access Control(MAC)
9) What is EY-NMPA?
Elimination yield –Non Pre-emptive Multiple Access (EY-NMPA) is a
scheme which uses several phases to sense the medium. access the medium
and for contention resolution.. Priority schemes can also be included.
This is actually used in HIPERLAN1 specification.
10) What do you mean by Polling?
Polling is a strictly centralized scheme with one master and several
slave stations. The master can collect the list of stations during the
contention phase and can poll these slaves according to many schemes
like round robin, random access, reservation scheme etc.
11) What are the four types of handover available in GSM?
1.Intra cell Handover
2.Inter cell Intra BSC Handover
3.Inter BSC Intra MSC handover
4.Inter MSC Handover
12) What is TETRA?
TETRA (Terrestrial Trunked Radio) systems use different radio carrier frequencies, but
they assign a specific carrier frequencies for a short period of time according to demand.
TETRA’s are highly reliable and extremely cheap.
13) what are the categories of Mobile services?
· Bearer services
· Tele services
· Supplementary services
14) What are the services provided by supplementary services?
· User identification
· Call redirection
· Call forwarding
· Closed user groups
· Multiparty Communication
15) What are types of Handover?
Inter-cell ,intra- BSC handover
Inter-BSC, intra-MSC handover
Inter MSC handover
16.What is meant by GPRS?
The General Packet Radio Service provides packet mode transfer for applications
that exhibit traffic patterns such as frequent transmission of small volumes.
17) What are subsystems in GSM system?
· Radio subsystem(RSS)
· Network & Switching subsystem(NSS)
· Operation subsystem(OSS)
18) What are the information in SIM?
· card type, serial no, list of subscribed services
· Personal Identity Number(PIN)
· Pin Unlocking Key(PUK)
· An Authentication Key(KI)
19) Define Normal Burst?
The frame used for normal data transmission within a time slot is called Normal Burst.
20) What are the logical channels in GSM?
· Traffic channel(TCH)
· Control channel(CCH)
23) What is the function of Medium Access Control Layer?
The functions of Medium Access Control Layer is responsible for establishes,
maintains, and releases channels for higher layers by activating and deactivating physical
24) What is meant by GEO?
GEO means Geostationary or Geosynchronous earth orbit. GEO satellites have a
distance of almost 36000 km to the earth. Examples are almost all TV and radio
broadcast satellites, many weather satellites and satellites operating as backbone for the
25) what are the advantages of GEO?
Three GEO satellites are enough for a complete coverage of almost any spot on
earth, senders and receivers can use fixed antennas positions, no adjusting is needed.
Therefore GEO’s are ideal for T.V and radio broadcasting.
26)What is Handover?
The satellite is the base station in satellite communication systems and that
it self is moving. So, additional instance of handover are necessary due to the movement
of the satellite
1.Intra Satellite handover:
2.Inter Satellite handover.
4.Inter System handover.
27) What are the registers maintained by the gateway of satellite?
1.Home Location Register(HLR).
2.Visitor Location Register(VLR).
3.Satellite User Mapping Register(SUMR).
28)Advantages of MEO
Using Orbits around 10,000Km, the system only requires a dozen satellites
which is more than the GEO system, but much less than a LEO system. Further more
these satellites move slower relative to the earth’s rotation allowing a simpler system
Depending on the inclination a MEO can cover larger populations, thus requiring less
29) Applications of Satellite ?
Satellites can be used in the Following Areas
· Weather Forecasting
· Radio and TV broadcast Satellites
· Military Satellites
· Satellites for Navigation
30) What are the applications in satellites?
· Weather forecasting satellites
· Radio & TV broadcast satellites
· Military satellites
· Satellites for navigation
· Mobile communication
31) What are the advantages of LEO?
· Data rate is 2400 bit/s
· Packet delay is relatively low
· Smaller footprints of LEO allows frequency reuse
· Provide high elevations
32) Define the inclination angle and perigee.
The inclination angle is defined as the angle between the equatorial plane and the plane
described by the satellite orbit. An inclination angle of 0 degrees means that the satellite
is exactly above the equator. If the satellite does not have a circular orbit, the closest
point to the earth is called the perigee.
33) Define the elevation angle and footprint.
The elevation angle is defined as the angle between the centre of satellite beam and
the plane tangential to the earth’s surface. The foot-print can be defined as the area on earth
where the signals of the satellite can be received.
34) Define Header core.
Seven bytes field contains the sizes of the header and the body, the content type of the object. Depending on this header information, the receiver may decide if it has
enough resources(memory, cpu, power, display etc) available to decode and further process the object.
35) What is MSC?
Main Service Channel(MSC) carries all user data.
eg. audio, multimedia data.
36) What is FIC?
The Fast Information Channel(FIC) contains Fast Information Block(FIB) with
256bits each(16 bit checksum). An FIC carries all control information which is
required for interpreting the configuration and content of the MSC.
37) What are the different types of disk?
· A flat disks
· Skewed disks
· Multi disks
38) What are the goals of DVB?
The goal of DVB is to introduce digital TV broadcasting
using satellite transmission (DVB-5) cable technology (DVB-c)
and terrestrial transmission (DVB-7).
39) Name some of the formats supported by MOT?.
¨ Multimedia and Hypermedia information coding experts group(MHEG)
¨ Join photograph’ s experts group(JPEG)
¨ American standard code for information interchange(ASCII)
¨ Moving pictures expert group(MPEG)
¨ Hypertext markup language(HTML)
¨ Hypertext transfer protocol(HTTP)
¨ Graphics interchange format(GIF)
40) Give structure MOT object.
7bytes variable size variable size
Header core Header Extension Body
Header core : contain the size of the header and body and the content type of the object.
Header Extension : contains additional object handling data such as repetition distance to
support caching, segmentation information and priority of the data.
Body : contains arbitrary data to be transmitted.
41)What are different interleaving and repetition schemes applied by DAB to objects and
42) What are the advantages of DAB?
1.DAB can offer sound in CD like quality.
2.DAB can use single frequency network where all senders transmitting the same
radio program can operate at the same frequency.
3.DAB use VHF and UHF frequency bands.
4.DAB uses DQPSK modulation scheme.
5.DAB user COFDM and FEC.
6.DAB can transmit up to six stereo audio programmes with a data rate of
43) What is object repetition?
DAB can repeat objects several times. If an object A consists of four
segments(A1,A2,A3,A4) a single repetition pattern would be
44) What is EIT?
Event Information Table(EIT) contains status information about the current
transmission and some additional information for set-top boxes.
45) What are the service information sent by DVB?
Digital Video Broadcast Containers are basically MPEG-2 frames. DVB
sends service information. These information are,
1.Network information table(NIT).
2.Service Description Table(SDT).
3.Event Information Table(EIT).
4.Time and Date Table(TDT)
46) What are the advantages of DVB?
1.Data rates planned for users are 6-38mbit/s for the downlink and 33-100kbit/s for
2.Transmitted along with TV programmes and doesn’ t require additional lines or
hardware per customer.
3.Can be used in remote areas and developing countries where there is no high band
width wired network.
47) what is meant by beacon?
A beacon contains a timestamp and other management information used for
power management and roaming.
e.g., identification of the base station subsystem(BSS)
48) What is Active scanning?
Active scanning comprises sending a probe on each channel and waiting for
response. Beacon and Probe response contain the information necessary to join the new
49) What is Passive Scanning?
Passive Scanning Simply means listening into the medium to find other networks,
i.e. receiving the beacon of another network issued by the synchronization function
within an access point
50) what is the primary goal of IEE 802.11?
The primary goal of the standard was the specification of a simple, robust, WLAN
which offers time bounded and asynchronous services also it should be able to operate
with multiple physical layers.